Count,MessageID,category,ShortTitle,Message,Date,UserName,MsgPswd,Phone,Email,ParentMsgId
"1","950336","2","Re; Re; Revolutionizing a watersport||950336","Good response, Tom. When you say " it's much better to specify the pressure distribution and then calculate the section shape that will produce it. Would you be suggesting to use Xfoil to do the calculation?","2005-12-20","Ray Vellinga","nopswd"," ","rvell@san.rr.com","949055"
"2","949055","2","Re; Re; Revolutionizing a watersport||949055","I don't think the radius+ogive middle is a very good way to go. That was the philosophy behind my Proa 1-series.
The sudden change in curvature at the junction between the ogive and radius caused a sharp pressure spike:
This, in turn, led to laminar separation, premature stall from the leading edge, and increased drag. Separation near the leading edge is especially bad for a hydrofoil, because it leads to ventilation and the sudden loss of three-quarers of the lift.
So, while ogive sections may be easy to construct, I'm not enamored with their hydrodynamics.
Today, it's much better to specify the pressure distribution and then calculate the section shape that will produce it. That way you can see what needs to be fixed in the hydrodynamics and go after it directly instead of shooting in the dark by modifying the geometry. ","2005-12-17","Tom Speer","nopswd"," "," ","946625"
"3","946625","2","Re; Re; Revolutionizing a watersport||946625","Tom Speer, any discussion of ogival hydrofoils sections is of interest to me. I have made and flown several such foils. They are easy to construct by welding a rolled piece of metal plate to a flat metal plate and then grinding to make the welds fair.
You have mentioned the idea of adding a radius to the leading edge of the ogival foil. This could be done by welding the forward edges of the top and bottom plates to a rounded section--a tube or a bar. Two questions: Do you have some guidelines on choosing a radius to the rounded leading edge? And, is the junction between the rounded edge and the top plate and the bottom plate a big problem? Would you think this to be a difficult transition?","2005-12-12","Ray Vellinga","nopswd"," ","rvell@san.rr.com","945783"
"4","945783","2","Re; Revolutionizing a watersport||945783","Yes, it's possible to design fore-aft symmetric foils that will work equally well in both directions. You basically have two possible approaches: sharp-edged, and rounded edges.
Examples of the sharp-edged foils are the ogival that have been used by may hydrofoil designers. They have the advantage of being simple to construct and have low drag within their design range of angles of attack. The problem with sharp leading edges is they only have a small range of angles of attack at which the flow is attached. Outside that range, they experience leading edge separation. This can lead to sudden ventilation - a charactersitic that has bedeviled many craft that use these sections. You can find section data for ogival sections published in the literature and in books like Hoern'er's "Fluid Dynamic Drag".
The round-edged approach promotes leading edge suction for low drag and does not necessarily suffer from leading edge stall. There will be a separated zone at the trailing edge which can cause some increased drag. Elliptical sections have been used for some stopped-rotor VTOL aircraft.
To the best of my knowledge, the only round-edged sections specifically designed for use as hydrofoils can be found at http://www.basiliscus.com/ProaSections/ProaIndex.html. XFOIL predicts the Proa-3 series sections have performance comparable to NACA 6-series sections.
","2005-12-10","Tom Speer","nopswd"," "," ","935018"
"5","942165","2","Foil works in forward or reverse direction||942165","You haven't said specifically which watersport you want to revolutionize, but I'm pretty sure I know. I won't say it outright here because you seem to be concerned with someone stealing your idea. I have had discussions with others wanting to do the same thing, and have evaluated some of the pitfalls. If you drop me a line at tothebin@adelphia.net, I'll send you my contact info and we can talk, I'm in Stuart Florida. I may not have the ultimate answer for you, but I think I can help.","2005-12-03","Scott Smith","nopswd"," ","boatswithwings@adelphia.net","941596"
"6","941596","2","Foil works in forward or reverse direction||941596","Nat,
I appreciate your response, but have no idea what you said. I'm not familiar with a "soft" foil. I have so many questions, I feel I'm just going to be more of a burden than anything on here. But again, I am willing to pay someone for their time. Also, maybe there is somewhere I can go for more info, I have tapped the internet for all its worth.
Thanks to all,
Derek","2005-12-02","Derek","nopswd"," ","Derekseaman@gmail.com","941408"
"7","941408","2","Foil works in forward or reverse direction||941408","I SUGGEST THAT YOU CONSIDER A SOFT FOIL OVER A RIGID SPAR FOR SAFETY. ALSO, IF PROPERLY DESIGNED IT COULD BE INHERENTLY STABLE. (THAT IS IT WOULD DEFORM TO REDUCE THE ANGLE OF ATTACK IF STALL APPROACHES.) NAT K","2005-12-02","NAT KOBITZ","nopswd"," ","kobitzn@ctc.com","940695"
"8","940695","2","Foil works in forward or reverse direction||940695","Thank you all for your help. Unfortunately, I am still unsure if the design I have in mind is possible. There are many variables that are not taken into consideration with hydrofoil boat designs that I have to think about. For example, instead of proplusion, this board will be towed, and the rider of the board will be able to manipulate the board in ways we could not with a boat. If there is anyone that would be willing to give me a little more in depth advice, possibly over the phone, or in person (I live in Orlando), I would be more than willing to pay for your time. I need to first determine whether it would be physically possible to do what I want, and then if it is, I would have to explain some of the problems that might arise that are not addressed with any other hydrofoil. If all goes well, I would like to make a few prototypes, and start a company that would revolutionize the fastest growing watersport.
Thanks for everyone's time,
Derek Seaman
407-739-1827","2005-12-01","Derek","nopswd"," ","derekseaman@gmail.com","938319"
"9","938319","2","Foil works in forward or reverse direction||938319","A complete copy of this 57 page report is in my hands. Today I offered it to Barney Black to be posted on the IHS site. If he accepts, you can download it from there soon.
I have used the Ogival sections with some success. They are useful because they can be built easily using sheet metal, a welder and a metal grinder.","2005-11-26","Ray Vellinga","nopswd"," "," ","935301"
"10","938089","2","Re; Hydro foil designs||938089","Go to a good technical library and take out a copy of "Theory of Wing Sections" by Ira Abbott and Von Doenhoff, by Dover Publications, Inc., NY c 1959.
All the airfoil sections described there will work as foils. The charts shown for lift and drag coefficients will be accurate for air or water. Just remember that water is 800 times more dense that air so the resulting speed, lift, drag, etc. will differ accordingly. ","2005-11-26","Ray Vellinga","nopswd"," "," ","935322"
"11","935334","2","Foil drag, size vs. angle of attack||935334","Ray, you seem to know what you are talking, about please look at my posting and see if you have any input.
Thanks
Dan Bush","2005-11-20","Dan Bush","nopswd"," ","lostboys81@bellsouth.net","918835"
"12","935322","2","Hydro foil designs||935322","I have a 1973 Carri Craft Catarmaran. Full displacement hulls. Lenght 57", beam 12'.If I did the calculations correctly theoritcal hull speed is close to 20 knots. I am not willing to repower or pay the fuel penalty for this speed. I should mention I have lived on /traveled in this boat for three years and the following speeds and fuel economies are from more than 1000 hours of travel,deterimined by gps. While in drydock two years ago I added three fins/stabilizers on each hull, 8" wide and 8' long. This solved the problem of excessive roll at anchor or docked. When I added these fins I expected to lose a knot or more due to extra drag. Much to my surprise and pleasure I actually picked up a knot in speed. Boat weighs approximately 38,000 lbs empty, has twin Isuzu 150 horse diesels, and the best speed I have gotten out of her to date has been a little over 12 knots at 2400 rpm slinging 20x20 four bladed nibrile props. I have solved an over heating problem and can now go to a continous 2700 rpm. Fuel effiency at 9 knots is(I am not a liar, normally I tell people three knots per gallon) 4 knots per gallon at approximately 50,000 lbs gross weight. Currently I am in dry dock and it occurred to me that by reshaping my stabilizers as hydro foils I could gain more speed. I need foil designs. It seems that the strenght of my stabilizers is sufficient to support the weight of the boat. Idiots ran STRAPS over the fins and lifted my boat with no damage.They moved it while I was not present from one place to another in the yard. The front fin is canted upwards three inches out of level which I suspect is the reason for my speed gain. I currently have helicopter foil designs which I may expand out to eight feet and install. It seems to me with the front fin pitched 3% higher then the middle and last foil like Burt Rutans designs the level of the boat should be limited by stalling of the front first. I am seriously contemplating adding trim control but before I do this I would like to add hydrofoils and play with it for six months.
I should add that I am a fully competent welder, actually "enjoy" fiberglass work, can wander around a machine shop and identify a tool or two. Feed back on hydro foil shapes would be greatly appreciated. This is not "pie-in the sky", I will be modifying my stabilizers in the next few weeks. Your help will be greatly appreciated and is worth a wild time out fishing, or traveling to some exoctic port to get into exoctic trouble.","2005-11-20","Dan Bush","nopswd"," ","lostboys81@bellsouth.net","2"
"13","935307","2","Foil works in forward or reverse direction||935307","I have a photocopy of a few pages of Report No. E-79-6 "WATER TUNNEL OBSERVATIONS ON THE FLOW PAST A PLANO-CONVEX HYDROFOIL", by R.B. Wade, February 1964, Division of Engineering and Applied Science, CALIFORNIA INSTITUTE OF TECHNOLOGY, Pasadena, California. On the cover page, it also says "Office of Naval Research Department of the Navy Contract Nonr-220(24)", and "D.J.Nigg" in handwriting. I forget where I got it, maybe from Donald Nigg himself. Is he still making foils?
Anyways, the paper gives lift & drag data for a foil with an "ogive" section. That means straight line on the bottom, circular arc on the top. The model used for testing is 0.19" thick, with a chord length of 2.77". At zero degrees angle of attack CL is 0.4 and CD is 0.013. This would be the same forward or reverse.
Maybe someone with access to the whole report could get it posted on the IHS website. As a last resort, I could scan what I have, but it's incomplete. Not sure about the copyright issues here.","2005-11-20","Mac Stevens","nopswd"," ","stevensm@earthlink.net","935018"
"14","935301","2","Foil works in forward or reverse direction||935301","I have a photocopy of a few pages of Report No. E-79-6 "WATER TUNNEL OBSERVATIONS ON THE FLOW PAST A PLANO-CONVEX HYDROFOIL", by R.B. Wade, February 1964, Division of Engineering and Applied Science, CALIFORNIA INSTITUTE OF TECHNOLOGY, Pasadena, California. On the cover page, it also says "Office of Naval Research Department of the Navy Contract Nonr-220(24)", and "D.J.Nigg" in handwriting. I forget where I got it, maybe from Donald Nigg himself. Is he still making foils?
Anyways, the paper gives lift & drag data for a foil with an "ogive" section. That means straight line on the bottom, circular arc on the top. The model used for testing is 0.19" thick, with a chord length of 2.77". At zero degrees angle of attack CL is 0.4 and CD is 0.013. This would be the same forward or reverse.
Maybe someone with access to the whole report could get it posted on the IHS website. As a last resort, I could scan what I have, but it's incomplete. Not sure about the copyright issues here.","2005-11-20","Mac Stevens","nopswd"," ","stevensm@earthlink.net","935018"
"15","935018","2","Revolutionizing a watersport||935018","I think the use of foils may change the watersport I love. Unfortunately, I cannot seem to find the information I need to make a basic hypothesis on the design. Every hydrofoil I have seen is based upon moving in one direction (boats don't reverse at high speeds). Is it possible to have a hydrofoil design that allows movement in opposite directions and will perform well either way? If you could imagine a symmetrical jet propelled boat, so that it could go backwards or forwards either way. Any help would be appreciated.","2005-11-19","Derek","nopswd"," ","derekseaman@gmail.com","2"
"16","931880","2","Re; Assistance wanted - foil design||931880","Dear Bob,
Please give me a call or send me your phone number and email contact.
You can call me on (203) 313 4061.
My company, Hydrofoil Assisted Water Craft HAWC Technologies was recently formed.
We work to help people like you, and believe we will have a solution for you. We need to assess your vessel's basic information first in order to do a speed prediction based upon the vessel's length, displacement weight and power amongst some other info.
Looking forward to talking with you.
BR
Gerhard ","2005-11-14","Gerhard Kutt","nopswd"," ","caemarine@earthlink.net","926828"
"17","926832","2","Assistance wanted - Foil design||926832","We have a 24 meter commercial Catamaran with a cruising speed of approx. 25 knots with full load. We plan to retrofit the vessel with "aasisting" foils.
We are looking for an hydrofoil expert that can assist in the design and technical specification of "assisting" foils that will be placed between the hulls of the Cat. The goal is to reach a cruising speed of approx 27-28 knots and with a lower the fuel consumption than today. (if possible)!
Best regards, Bob Email: swedbob@hotmail.com","2005-11-05","Bob","swedbob"," ","swedbob@hotmail.com","2"
"18","926828","2","Assistance wanted - foil design||926828","We have a 24 meter commercial Catamaran with a cruising speed of approx. 25 knots with full load. We plan to retrofit the vessel with "aasisting" foils.
We are looking for an hydrofoil expert that can assist in the design and technical specification of "assisting" foils that will be placed between the hulls of the Cat. The goal is to be able to reach a cruising speed of approx 27-28 knots and lower the fuel consumption.
Best regards, Bob","2005-11-05","Bob","swedbob"," ","swedbob@hotmail.com","2"
"19","925912","2","Foil drag, size vs. angle of attack||925912","I appreciate the feedback, but it wasn't really what I was asking. I'm not trying to determine the optimum foil size or profile at this time. I am trying to find out at a fixed speed and weight, which has less drag, a larger foil at lower angle of attack, or a smaller foil at higher angle of attack. A perfectly trimmed hydrofoil boat (without active controls) will perform quite differently if the overall weight or weight distribution changes. I see three directions to attack this problem. One is to have foils sized and trimmed for optimum performance when the boat is lightest, then increase the angle of attack when the boat is heavy. The second is to size and trim the foils for the boat at its heaviest, then run the foils at a reduced angle of attack when the boat is lighter. The third is of course to size and trim the foils at a point halfway between the weights, and then re-trim accordingly as the weight changes. I'm trying to figure out which will have the least drag penalty when run at the most commonly used weight.","2005-11-04","Scott Smith","nopswd"," ","boatswithwings@adelphia.net","920315"
"20","920315","2","Foil drag, size vs. angle of attack||920315","Check your data. I believe it is in error.
NAT KOBITZ","2005-10-26","NAT KOBITZ","nopswd"," ","kobitzn@ctc.com","918835"
"21","918835","2","Foil drag, size vs. angle of attack||918835","Scott Smith: Look on page 522 and 523 of "Theory of Wing Sections" By Abbot & Doenhoff for the
best Lift over Drag ratio, L/D for the wing section NACA 63412. This section is in common use.
The best L/D is at about Coefficient of Lift = .4. This occures at -6 degrees Angle of Attack.
The Excel formula attached determines that the area should be 1.32 square feet.
If your cord were 4.75 inches, the span should be 40.1 inches.
","2005-10-24","Ray Vellinga","nopswd"," ","rvell7829@yahoo.com","917973"
"22","917973","2","Foil drag, size vs. angle of attack||917973","This is a rather simple question, and I hope there is a simple answer, but here goes: I am looking at the design of a foil wing that must support a fixed weight at a fixed speed, let's say 1000 pounds at 30 mph. Which has less drag, a larger foil at lower angle of attack, or a smaller foil at higher angle of attack? Other considerations such as stall angle are not important.","2005-10-22","Scott Smith","nopswd"," ","boatswithwings@adelphia.net","2"
"23","917248","2","Re; Stevenson SportFoiler Published||917248","This is indeed good news, as there have been many requests over the years for these plans. IHS should ask permission to reprint them in the next hydrofoil CD-ROM","2005-10-20","Barney C Black","poopdeck"," "," ","916786"
"24","916786","2","Stevenson SportFoiler Published||916786","Stevenson Projects produced a set of plans for the SportFoiler, a single person surface-piercing hydrofoil. Unfortunately, several years ago they abruptly discontinued the plans, although many of us have asked for them.
To my delight, Stevenson Products has published the plans (for free!!) online. The address is: http://www.stevproj.com/TheSportfoilPlans.pdf
I want to thank the people at Stevenson, as this project shows just how easy hydrofoils are to build. Don't dismiss these plans. ","2005-10-19","Barry Steele","nopswd"," "," ","2"
"25","908696","2","Re; Req for Technical Paper||908696","I don't have a copy of the paper; however you may be interested in the following excerpt from IHS archival correspondence taken from www.foils.org/students.htm, and you may want to try the email contact:
[18 Jan 01] We were sort of toying with the idea of using supercavitating foils. Do any of you know where I can get some good information on supercavitating foil sections, or the design of supercavitating hydrofoil vessels. I don't remember who asked, but I am pretty sure we are just doing our hull with FastShip and then doing analysis using NavCad. If you have a better suggestion (which can be handled at an undergraduate level) Id love to hear it as well. -- Earon S. Rein, MIDN USN (m015346@nadn.navy.mil)
Responses...
[18 Jan 01] Two suggested sources:
Altman, R., "The Design of Supercavitating Hydrofoil Wings," Technical Report 001-14, Hydronautics Inc., April 1968.
Martin, M., "The Stability Derivatives of A Hydrofoil Boat - Part II", Technical Report 001-10(II), Hydronautics Inc., January 1963.
[18 Jan 01] The best info I'm aware of on supcav foil sections is the Carderock work in the 1970s on the "TAP-2" series of base-vented supercavitating foils. The work may have been done by Young Shen but I'm not sure. -- Mark Bebar (bebar@foils.org)
","2005-10-06","Barney C Black","poopdeck"," "," ","904808"
"26","904808","2","Req for Technical Paper||904808","Where can I find this paper Altman, R., "The Design of Supercavitating Hydrofoil Wings," Technical Report 001-14, Hydronautics Inc., April 1968[. Can somebody email me the pdf version of this paper at the following mp_mathew@hotmail.com.","2005-10-01","M.P. Mathew","nopswd"," ","mp_mathew@hotmail.com","2"
"27","889045","2"," Supercavitating Foils||889045"," I have to design supercavitating hydrofoils for a hydrofoil vessel going upto a max speed of 70 knots. I was thinking of going for Tulin's sections. But I also know that the L/D charecteristics for this type of sections below 40 kts would be absymally poor. Am I correct? Can I use the public domain XFOIL(by Mark Drela) for getting the fully wetted Lift and Drag charecteristics for these sections for the non cavitating regime(upto 40 knots)or is XFOIL not suitable for sharp leading edge profiles.
My second question: Can I use base ventilated tulin section foils so that I can get supercavitating regime even at low speeds. How are supercavitating flows and base ventillated foils related. Can I use linearized Tulin's theory for base ventillated foils. Are base ventillated foils approaching sigma (cavitation no.) = 0 . How do i get the lift and drag coefficients for base vented foils otherwise. Any references will be highly appreciated. Thanx
","2005-09-06","MP Mathew","nopswd"," ","mpmathew73@yahoo.com","2"
"28","888679","2","Re; Question on fully submerged foils||888679","My Dynafoils use a fixed rear foil, fully submerged. The front foil is a simple mechanical system, fully submerged foil coupled to a surface follower. There are no other controls except steering and throttle. It can be a handfull to control at times, but only because it is short, with deep foils and lots of power. At moderate power levels and reasonbly calm seas it handles just fine, with no roll control aparatus or trimming of the foils needed. On smaller boats with less roll moment, steering works just fine to control roll issues.","2005-09-05","Scott Smith","nopswd"," ","boatswithwings@adelphia.net","872569"
"29","888667","2","Re; Cheap ready made hydrofoils?||888667","I have copies of the old Popular Science articles on how to make wooden foils cheaply, with a tablesaw. Would work very well for you. Drop me a line and I'll e-mail them to you, free.","2005-09-05","Scott Smith","nopswd"," ","boatswithwings@adelphia.net","2"
"30","884493","2","Re; Idea; Use Air to Bank Turns||884493","Grant,
Your proposal to use air feed to control the lift force on a hydrofoil is a sensible one. So sensible in fact, that it has been successfully implemented on both small and large hydrofoils!
The name most commonly applied to this method of hydrofoil stabilisation is "controlled ventilation". In this context, the term "ventilation" refers to air being drawn down to the foils. On the other hand "cavitation" refers to water changing state to 'steam' due to very low pressure as sometimes occurs on hydrofoils so isn't as accurate a description of what is happening.
My understanding is that this concept was first practically applied by the Swiss based company Supramar headed up by the hydrofoil pioneer Baron Hans von Schertel. Early experiments were carried out on a Supramar ST 3A fully submerged air-stabilised hydrofoil research craft. Later, various large passenger hydrofoils adopted the concept, in particular the Supramar PT 150 of which three were built. My understanding is that air stabilisation may have variously been used to assist with roll, pitch and heave stabilisation of hydrofoil.
Hans von Schertel wrote a number of technical papers on this concept at the time pointing out its advantages over conventional flapped hydrofoils. None the less, it never seems to have achieved widespread application. I don't know why.
You would be able to find out more details if you can gain access to early issues of Jane's Surface Skimmers or the journal "Hovering Craft and Hydrofoil" from the 60's.
In more recent years, there had been renewed interest in foil stabilisation using air feed. A research project in Australia had considered this approach for use in controlling lift on motion control foils (for catamarans and the like). In that case, the concept had been referred to as "lift dumping foils". I don't believe this progressed to any operational systems.
I was not aware of any Italian research / patents on this concept but would be interested to hear more about that.
Good luck with your own experimentation.
Martin","2005-08-28","Martin Grimm","nopswd"," ","seaflite@alphalink.com.au","883043"
"31","883043","2","Re; Idea; Use Air to Bank Turns||883043","I believe this type of foil control is called artificial cavitation. I am not sure what or how much effect it has on foils at different speeds. It may not be enough effect to control the boat. The Italian patent was for large fast ferries carrying a couple of hundred passengers. I don’t think it was ever used. I think that Boeing may have investigated this idea too. I believe they held a few patents for artificial cavitation in other forms as well. I was thinking it might have application in smaller recreational boats.
My first test will be to try to improve the turning ability of My Volga. A 90-meter turning radius is not exactly turning on a dime (with very little banking). My first trial will be to use some 1” rubber hose and a lot of duct tape. Two hoses (port and starboard) will run from the cockpit to the bow and down to the center two struts (of 4) on the front foil the hose will end right at the top of the foil. A valve at the cockpit controls the airflow. Massive amounts of duck tape should smooth out the bump the hose will make as it goes down the strut. The strut is not hollow; it is made of 1/4'” stainless steel. Any ideas?
","2005-08-25","Grant Calverley","nopswd"," ","grant@sanjuantimberframes.com","882728"
"32","882728","2","Re; Idea; Use Air to Bank Turns||882728","Revision #1 of Idea
On rethinking it seems air passages on from the struts to the foils should not be crossed from port to starboard and visa versa. On a boat unevenly loaded or running parallel to waves it would not right its self. It could even get dangerous as the heavy side of the boat would lose lift and sink even lower. The lower it sinks the greater the lift on the opposite side. Opps bit of a problem. It would be easier to make a foil without the cross over air tube feature anyway.
Another benefit to not having it cross over is after an operator initiated banked turn is complete the boat would right itself automatically. The lower (deeper) side would have more lift than the upper side creating a righting effect. The operator initiated banked turn air system would need to override or supply more air than the altitude control air system. The two systems would be somewhat fighting each other.
","2005-08-24","Grant Calverley","nopswd"," ","grant@sanjuantimberframes.com","882721"
"33","882721","2","Idea; Use Air to Bank Turns||882721","Hello,
I have been kicking around a simple idea for stabilizing fully submerged foils for a long time. I did a patent search a while back and found that an Italian had patented a very similar idea for fast hydrofoil ferries before I was born in 1963. It seems like a good Idea so I will attempt to describe it. Maybe some one else can use the idea and make it real. I am not an engineer but would be interested to have some feedback.
The system would have almost no moving parts. It would use hollow struts and foils. Air supplied to the tops of the foils to reduce lift would main mechanism for stability, banked turns and attitude control. Two separate sets of holes on the port and starboard sides of the foils (like holes on a flute) would be across the top in the low-pressure area.
Banked Turns. When a banked turn to the right is desired an air is supplied to the right side of the foil decreasing its lift creating a banked turn. The mechanism could be as simple as a two tubes and valves (for port and starboard turns) near the steering wheel. Open the valve just before starting your turn. Electronically a turn signal lever like on a car would work well and is already instinctive to use. I have a Volga 70 and may try a duck tape and plastic hose version of this banked turn concept next year. (when I get it running)
Altitude Control and Stability. The banked turns would require some mechanical input to initiate. Attitude control would be automatic and may require a separate set of holes from the banked turn set. The line of holes on the top surface of the starboard side of the foil would be connected through the hollow foil to a corresponding set of holes in the side of the strut on the port side of the boat. At slow speeds all of the holes in the strut would be below the surface. As the boat gains speed the strut raises out of the water and the first of a serious of holes is exposed to the air. The low pressure of the wing sucks the air down through the hole and reduces the lift slightly. As the boat speeds up more holes are exposed and the lift is reduced even more maintaining equilibrium in altitude. Having the air lines cross from port strut to starboard foil and vies versa would aid in banked turns.
There are a few problems /questions in my mind. 1) Is there enough suction on the top surface of the wing to suck the air down the tubes and blow out the water that would be there already? Would you need compressed air?.(the Italians used compressed air and some complicated sensors from what I remember) 2)The hole’s orifices would need to be sized and located very carefully. Not to big and not too little. 3) Would there be a big lag time as the water is pushed out of the struts and hollow foils. 4) At slower speeds water would circulate through the strut and foils holes, would this effect lift? 5) Would the boat right its self after completing a banked turn?
I would appreciate some feedback and may try some simple experiments on my Volga next year if it is warranted. What do you think, does it have merit or is it flawed? I never even took Physics in high school so go easy on me.
Grant Calverley
","2005-08-24","Grant Calverley","nopswd"," ","grant@sanjuantimberframes.com","2"
"34","872638","2","wsome Re; Re; Re; FOIL SHAPE AND AN||872638","Awsome answer. Thank you Tom.
I have already experienced much of what you have discussed. I actually started with a low angle, and found that the drag of the foils actually pulled the boat down. I compensated by doubleing the front angle, and that helped. I had already preset the rear foils at an angle of six degrees. So by end of testing on the first day, it came down to the fact that my jet pump could not supply enough thrust.
I have doubled the size of the pump, and have created a four bladed impeller. I also have an output reduction cone built to see if reducing the output diameter doesn't increase the speed of the output.
I have several things to try including two more motors.
I was hoping to get 12mph, and the first pump failed miserbley.
I don't think I will have any chances at the pond till next weekend
Thank you
","2005-08-06","Umi_Ryuzuki","nopswd"," ","umi_ryuzuki@hotmail.com","872597"
"35","872597","2","Re; Re; FOIL SHAPE AND ANGLE||872597","You have the basic idea, but I think you're missing a couple of things. You do get the area by assuming lift = weight and dividing by the dynamic pressure and design lift coefficient. But you have to use consistent units.
The factor F in your formula is the fluid density divided by 2. For water, the density is (using your English units) 1.939 slug/ft^3, so the Factor F should be 0.9695 for fresh water, or pretty close to 1.
The velocity has to be in ft/sec to be consistent, so I'll take the "12" in your calculations as being 12 ft/sec (same as 8.2 mph or 7.1 kt). The velocity has to be squared, which I'm not sure you did to come up with your final result.
So at a speed of 12 ft/sec and a lift coefficient of 0.5349, I get an area of 0.067 sq ft or 9.64 sq in for the required area. Since each of your wings have an area of 7.5 sq in, getting the 5 lb of lift from 6 of them is not a problem. The extra area will let you fly at half the design speed of 12 ft/sec.
However, while the average lift coefficient may be 0.5349, that doesn't mean the local lift coefficient will be the same over all parts of the wing. For your swept foils, the tips will be loaded more heavily than the root. This is due to the downwash in the wake of the hydrofoil and how it affects the conditions along the span.
And the angle of attack of the foils will not be 2.25 degrees as indicated by the two-dimensional section data. Those data are for a foil of infinite span, so it produces an infintessimal downwash. The shorter the span, the greater the downwash to produce the same lift, so the angle of attack has to be increased to offset the downwash. Your foils have an aspect ratio of 4, and at a lift coefficient of 0.5349, an additional 2.44 degrees of angle of attack will be needed because of the downwash. So the incidence of your foils will be more like 4.7 degrees than the 2.25 given by the section data for the same lift coefficient.
But more than that, the downwash will increase the drag substantially. You should allow for an additional drag coefficient of 0.0228 because of the lift-induced drag. This is 0.21 pound of additional thrust required. The induced drag goes down by the square of the span, so if you make your foils wider they will be much more efficient. But this runs into problems of strength and stiffness, so the span is always a compromise. The induced drag goes DOWN with speed (squared), so flying at too slow a speed can actually require more power than going fast.","2005-08-05","Tom Speer","nopswd"," ","me@tspeer.com","2"
"36","872572","2","Re; Cheap ready made hydrofoils?||872572","Take a look at http://www.fastacraft.com/moulded_foils.html","2005-08-05","Tom Speer","nopswd"," ","me@tspeer.com","2"
"37","872569","2","Re; Question on fully submerged foils||872569","It's not enough to balance lift against weight. You also have to balance the moments that want to turn the craft, tip it over, or pitch it. And the problem with balancing the lift is the lift is constantly changing as a function of speed, the attitude of the craft, and the disturbances from waves, gusts, thrust changes, etc. So when it does change, there has to be a means of returning it to its original value. If you hold a broom upside down on your hand, it's easy to compensate for the weight of the broom. But the moments are unstable so you can't maintain that balance without actively compensating for any change.
There're also the problems of regulating the flying height, maneuvering and accommodating different amounts of payload.
Lift at a constant speed and attitude does drop off as the foils get close to the surface. It's possible to use this effect to stabilize the craft if you are operating in flat water. But this also robs the fully submerged foil of much of its performance advantages.","2005-08-05","Tom Speer","nopswd"," ","me@tspeer.com","2"
"38","862463","2","Re; Cheap ready made hydrofoils?||862463","There were some articles published in the late 1950s - early 1960s in hobbyist magazines as to how to make wooden hydrofoils and add them to runabout-type boats. For example, Popular Science June 1960 has an article, "How I Fitted Oak Hydrofoils To My 14-Foot Runabout." Science and Mechanics Feb 1960 has a similar article, with foil design for boats up to 18 feet length. Take a look at the magazine descriptions on the IHS website in the Hobbyist section of this page: www.foils.org/popmags.htm.
You can buy copies of old magazines by searching for them on eBay and/or google.com. Sooner or later, just about everything shows up on eBay. Google will find you magazine sellers who sell directly. I have used the Canadian company "Smelly Old Books" http://members.ebay.com/aboutme/sobooks/(contact: John Muxlow jj.muxlow@ns.sympatico.ca) to obtain reasonably priced copies of articles back to the 1920s and earlier (S.O.B. has an almost complete collection of Mechanix Illustrated, Popular Mechanics, and Popular Science). It has been a while since I contacted them, so I hope the URL and email address are still good.","2005-07-18","Barney C Black","nopswd"," "," ","0"
"39","861182","2","Re; FOIL SHAPE AND ANGLE||861182","So No help or confirmation on the previous calculations?
","2005-07-15","Umi_Ryuzuki","nopswd"," ","umi_ryuzuki@hotmail.com","0"
"40","860748","2","Re; Question on fully submerged foils||860748","Maintaining a close enough balance between weight and lift without feedback control to allow a flight for more than a few seconds is currently not possible. Suggest you consider a mechanical feedback controller. The Rave, Hobie Trifoiler, and the height control on Talaria IV all use mechanical surface sensors with linkages to their foils to maintain a balance between lift and weight. ","2005-07-14","Harry Larsen","nopswd"," ","htdr.larsen@verizon.net","0"
"41","860689","2","Re; Question on fully submerged foils||860689","Thanks! That puts me very close to the goal.
Andy","2005-07-14","Andy","nopswd"," "," ","0"
"42","860646","2","Re; Question on fully submerged foils||860646","If you are using fully submerged foils for main lift, you can have a 25 to 35% lift stabilizing, surface piercing foils to supplant an autopilot. I do not know of any all fully submerged foil systems that are self stable.","2005-07-14","NAT KOBITZ","nopswd"," ","kobitzn@ctc.com","0"
"43","860356","2","Question on fully submerged foils||860356","I have read that fully submerged foils require flight control. My question is whether this is strictly necessary, or if I could design a submerged foil for a specific boat through experimentation that would be functional without flight control. The idea being to balance the lift against the weight of the boat.
Thanks,
Andy
","2005-07-13","Andy","nopswd"," "," ","0"
"44","856862","2","Cheap ready made hydrofoils?||856862","Forgive me for my ignorance- I'm only just starting to embark on a project to add hydrofoils to a 12' boat. I've been searcing for ready made aerofoil sections that could be used, and of course there are none specifically for hydrofoils-other than sailing ones, which are still expensive and probably unsuitable. When I searched under 'aluminium aerofoil section extrusions' I came up with extrusions intyended as sun blinds, see page 14 for an example :http://www.productselector.co.uk/docs/4/02274/external/COL02274.pdf
I realise the sections avaiable would not be the most efficient, but would using these extrusions provide a cheap and reasonably efficient way of getting foilborne?
Any comments?
Cheers, Roland
r.wilson@bath.ac.uk","2005-07-07","Roland Wilson","nopswd"," ","r.wilson@bath.ac.uk","0"
"45","855770","2","Re; Re; FOIL SHAPE AND ANGLE||855770","Let me see if I read all this correctly.
S = L / F U^2 Cl
S = 5lbs/ (2.09)(12©÷)(0.5349*) *assuming a 2.25¡æ angle of attack.
S = 5lbs/ 160.9835
S = 0.310591 sq ft
Therefore S = 44.725104 sq inches divide by 3 for each foil
Each wing needs an area of 14.908 sq inches
¡î14.908 = 3.861 square plate cut diagonally
Am I correct in assuming a six wings one on each side of the struts with
a root of 2.5"
trailing edge of 3.875"
tip length of 1.375"
Will fly a 5 lbs (2.268k) hydrofoil?
Would this include control surfaces, or would adding control surfaces to the existing area be preferred?
Thank you in advance.
Umi_Ryuzuki
Nyow
\
=^o^=
","2005-07-04","Umi_Ryuzuki","nopswd"," ","umi_ryuzuki@hotmail.com","0"
"46","830353","2","Re; Foil Design Help||830353","hi sam,
you might want to re-think the approach to what you are trying to achieve. a hydro foil solution for wake boards has been around for ages.
it's called the WEDGE and is a fold down foil under the stern of the boat that pulls the boat DOWN at speed to increase the wake.
http://www.glencraftmarina.com/Pages/malibu.html
cheers
boogie","2005-05-17","Boogie","nopswd"," "," ","0"
"47","824680","2","Foil Design Help||824680","Gday mate my name is sam doolan and I am an Industrial design student from
RMIT university Melbourne Australia. I am currently designing a foil, which
creates larger wakes for wakeborders by lifting the front of the boat and
transferring the weight to the back, to give it larger wakes. However I am
sure how the foils should be designed. Wether one at the front of the boat,
or coming off both sides or both. Would you be able to answer this question
for me.","2005-05-06","sam doolan","nopswd"," ","doolans@bigpond.net.au","0"
"48","824319","2","Re; Re; coordinated (banked) turns||824319","Could you send us a picture?","2005-05-06","Harry Larsen","nopswd"," ","htdr.larsen@verizon.net","0"
"49","823711","2","Re; Re; coordinated (banked) turns||823711","Thanks for your response and info. We call the boat "straightfastboat" as it's very fast in a straight line, 65mph+ and requires slowing and greater immersion of the rudder to turn with a bit of inboard banking. I'll try deepening the rudder as a first move and stay away from adjustable angle of attack in the foils. ","2005-05-05","Mike Turner","nopswd"," ","mike@turnermarinegroup.com","0"
"50","823598","2","Re; Re; coordinated (banked) turns||823598","Roll can be a complicated consequence of rudder deflection. Since the rudder is located below the center of mass, a port deflection of an aft-mounted rudder will result in a rolling moment to port.
It also produces a yawing moment, of course, and as the craft yaws to port, it picks up a sideslip (leeway) angle. If the foil system has positive roll stability - like a V foil configuration - the sideslip angle will also make the craft roll to port. Roll due to sideslip is likely to be the more powerful effect of the two. As the bank develops, the sideslip angle will be reduced.
But it takes some time for the craft to rotate enough to generate the sideslip. So there's lag between when you put in the input and when the rolling due to sideslip is experienced. The rolling moment due to the rudder deflection itself is prompt. The sideslip itself will reduce the force on the rudder, lessening the rolling moment from that source.
If the rudder is on a forward strut, then the craft will yaw in the opposite direction, the sideslip will be reversed, and the roll due to rudder deflection and the roll due to sideslip will be of opposite sign.
So the relationship between rudder and roll depends on the placement of the rudder, the stability of the craft, and the frequency of the input. The rolling due to rudder could be opposite in sign for different frequency ranges.
","2005-05-04","Tom Speer","nopswd"," ","me@tspeer.com","0"
"51","823592","2","Re; Re; coordinated (banked) turns||823592","Yes, typically. Like ailerons on an airplane wing.
But they could be done in many ways. You could change the incidence on a whole foil, positive for the port foil and negative for the starboard foil to get a positive rolling moment. You could articulate the outer panel of a hydrofoil. Flaps are an effective and easily mechanized way to go. But not the only way.
Aeronautical experience has shown that it's not a good idea to try to produce roll from a canard (forward wing), however. The resulting downwash has the opposite effect on the aft wing and can cancel or even reverse the intended rolling moment. The effects could be even more complicated by the way hydrfoil downwash is affected by the free surface.","2005-05-04","Tom Speer","nopswd"," ","me@tspeer.com","0"
"52","821847","2","Re; Re; coordinated (banked) turns||821847","When you dig up the info on this I'd love to se it. I have a Volga 70 that I'd like to convert the banking in turns to inboard rather than that disconcerting outboard feeling. My rudder depth will be increased soon and I'll report the result. It currently is as deep as the prop blade sweep. Anyone have anything to suggest? ","2005-05-02","Mike Turner","nopswd"," ","mike@turnermarinegroup.com","0"
"53","821718","2","Re; Re; coordinated (banked) turns||821718","You mention 'roll surfaces'... are those the main hydrofoil surfaces (or flaps on the main foil)?","2005-05-01","Wayne Johnson","nopswd"," ","tspwtj@yahoo.com","0"
"54","821713","2","Re; Re; coordinated (banked) turns||821713","The mechanical... I wanted to be sure that I was not missing a simple thing like 'roll is a consequence of rudder', or some other simple mechanical link.","2005-05-01","Wayne Johnson","nopswd"," ","tspwtj@yahoo.com","0"
"55","821318","2","Re; coordinated (banked) turns||821318","The definition of a coordinated turn is zero lateral acceleraion (along the Y axis). One way to achieve it is to use lateral acceleration feedback to a rudder. The rudder turns the craft about its Z axis to zero the leeway angle that results in the side force causing the acceleration.
However, a tricky aspect of this with a hydrofoil is the center of mass of the craft is well above the foils, and the crew station is typically above that. So you have an issue with how you enter the turn. If the craft rolls about the hydrofoils, there will be a significant lateral acceleration of the center of mass, and a somewhat greater acceleration yet at the crew station. Acceleration feedback at that point would turn the rudder to point the craft to the outside of the turn. So you'd have the roll control and the yaw control fighting each other, and when the two get out of phase you could lose control.
Everything will be fine for slow gentle entries that don't develop much acceleration. But if you apply a frequency sweep to the wheel, sarting with a slow oscillation of the wheel and working up to faster and faster reversals, you will arrive at the point at which the motion becomes alarming. I had the chance to experience this when I rode on Harry Larsen's Talaria.
A better approach would be to rotate the craft about either the center of mass or the crew station. This requires that the hydrofoils describe a pendulum motion, swinging to the outside of the turn as the craft rolls and the g-loads increase - keeping the net hydrodynamic force aligned with center plane at all times. To get such a motion probably requires a means of generating direct side force on the foils, such as both a forward and aft rudder or a flap on a main strut in addition to the rudder. An interconnect between the roll surfaces and the side force flap(s) would generate the right linear acceleration of the foils in concert with the roll acceleration. The feedbacks would then deal with the left-over motion due to imperfect match in the interconnect, and the fact that the control deflections you want initially are not necessarily proportional to what you want in the steady state.
An alternative approach is to use model following. The commands from the helm go to a dynamic model that has the ideal chaaracteristics - rolling about the crew station, etc. The ideal model produces state, rate, and acceleration commands to a feedback regulator control law that makes the hydrofoil follow the ideal motion as closely as possible. The regulator would typically be designed using multivariable control theory (Linear Quadratic Gaussian, Pole Placement, or many others).
The ideal model can be simulated separately, independent of the configuration of the hydrofoil itself, assuming perfect model following. This lets you tune the characteristics in parallel with designing the rest of the system. For example, you might want the ideal model to descend a bit at the same time that it kicks the hydrofoils to the outside of the turn so that the foil tips don't broach because of the pendulum motion.
I recommend Thor Fossen's books and papers for more details.","2005-04-30","Tom Speer","nopswd"," ","me@tspeer.com","0"
"56","821034","2","Re; coordinated (banked) turns||821034","From a roll acceleration point of view a coordinated turn is no different than flying straight and level. Is your question related to the mechanical, sensor, electronic, or mathematical means of performing a coordinated turn? ","2005-04-30","Harry Larsen","nopswd"," ","htdr.larsen@verizon.net","0"
"57","819978","2","coordinated (banked) turns||819978","How do you get a fully submerged type hydrofoil to bank in a turn?
Are there any documents which explore the requirements of coordinated turning? ","2005-04-28","Wayne Johnson","nopswd"," ","tspwtj@yahoo.com","0"
"58","795120","2","Re; Foil pressure coefficient data||795120","I think your best bet would be to go to something like a Navier Stokes CFD code if you really want to characterize the flow well past stall.
You might be able to get some idea by going as far as you can with an integral boundary layer code like XFOIL. The idea is separation occurs in an adverse pressure gradient. So there must be a lower pressure ahead of the separated flow that is attached, and that might be predictable with a lesser method. My guess - and it's just a guess - is that even though you operate well past stall, the worst case as far as minimum pressure is concerned might be at or just past stall, and this could be computed with something like XFOIL.
If you application is operating near the surface, though, ventilation rather than cavitation is likely to be your real problem. They both end up with vapor on the suction side, but for completely different reasons. The separated flow will be a real bear when it comes to ventilation, because you are setting up all the necessary preconditions for ventilation. If you insist on the separation, you'll have to concentrate on keeping the air away from the separated regions.","2005-03-12","Tom Speer","nopswd"," ","me@tspeer.com","0"
"59","788896","2","Re: Foil pressure coefficient data||788896","Is stalling a separation of the boundary layer? Probably, the shapes with negative presure gradients will be usefull for your purpose to avoid cavitation. See my message No 7888876 and attached file.
","2005-03-01","Ihor Nesteruk","nopswd"," ","inesteruk@yahoo.com","0"
"60","788876","2","Hydrofoils without cavitation||788876","I am looking for people or organization wich are interested in futher investigation and wind tunnel tests of hydrofoils without cavitation. Please find the
details below and in the attached file.
Dr. Ihor Nesteruk
Institute of Hydromechanics
National Academy of Sciences of Ukraine
Kyiv
--------
Axisymmetric and plane shapes with negative pressure
gradients at a surface are calculated. It is shown
that the length of the pressure increase zone may be
very short. Some shapes of axisymmetric bodies tested
in a wind tunnel provide unseparated flow patterns.
Such shapes are both of theoretical and practical
interest, since the unseparated flow pattern gives an
opportunity to reduce the total drag of vehicles
moving in gas or liquid. Moreover presented shapes
probably provide no cavitation at arbitrary small
cavitation numbers (see theoretical and experimental
arguments in [1,2]). Tests in a water tunnel have to
be carried out to prove this fact. For the presented
2D profiles, there were no wind tunnel tests to
investigate their separation behavior at different
angles of attack. Such experiments could be carried
out in the wind tunnel of Kyiv Institute of
Hydromechanics. [1] Nesteruk I.: Can Shapes with
Negative Pressure Gradients Prevent Cavitation. 4th
ASME/JSME Joint Fluids Engineering Conference,
Honolulu, USA, July 2003: FEDSM2003-45323.[2]
Takahashi S., Washio S., Uemura K., Okazaki A.:
Experimental study on cavitation starting at and flow
characteristics close to the point of separation.
Fifth Symposium on Cavitation: No. Cav03-OS-3-003, 2003.
","2005-03-01","Ihor Nesteruk","nopswd"," ","inesteruk@yahoo.com","0"
"61","787296","2","Foil pressure coefficient data||787296","Could anyone tell me how I could get hold of minimum pressure coefficient data for aerofoils operating at and beyond the stall (ideally up to twice the stalling incidence)? I am designing a lifting device for a marine application which is heavily stalled for much of its operating life, and must not cavitate.
Many Thanks
Chris Huxley-Reynard
chris_huxley_reynard@hotmail.co.uk","2005-02-25","Chris Huxley-Reynard","nopswd"," ","chris_huxley_reynard@hotmail.co.uk","0"
"62","779156","2","Lift formula||779156","Konstatin Matveev's lift formula is encoded in Excel on this web site:
http://mysite.verizon.net/res6pe7p/
","2005-02-10","Harry Larsen","nopswd"," "," ","0"
"63","776265","2","Calculating Lift||776265","Sorry but I'm not too good at math. Can somebody please give me a simple equation that will allow me to calculate approximate lifting force in kg (what the hell is a newton anyhow ?) at a given area (sq meter) speed (kph) and angle of attack (I want to experiment with variable angles to load or unload a vessel). Now I know that aspect ratio, foil thickness, diehedral etc etc all play a part but I just want approximate values please. ","2005-02-05","Andy","nopswd"," ","formula@bigpond.net.au","0"
"64","764798","2","Re: FOIL SHAPE AND ANGLE||764798","It's achievable. You'll probably need a foil with a chord of about 750mm. At the speeds you're talking about, just about any decent airfoil section would work. The incidence of the foil needs to be set with its zero lift lne about 5 - 7 degrees above the trim attitude of the boat. If you build it so you can bend the trailing edge up or down, that will allow you to fine tune the lift.","2005-01-15","Tom Speer","nopswd"," ","me@tspeer.com","0"
"65","759759","2","Re: Foil Surfing||759759","there is no foil surfing allowed anymore.
You must shape your own board out of koa and paddle it - no more tow in's mish","2005-01-05","big wave surfer","nopswd"," ","bigwavesurfer","0"
"66","756659","2","Foil shape and size||756659","Many thanks for your reply to my request for info on foil design,
being an absolute bunny in this area everything Ican learn is a huge benefit.
Iam hoping to achive a slightly 'better'shape than a circle cord, I have a copy of the shape of a Speer H005 foil and am aiming at that shape if it will improve lift on the cord.
I note that the C/L increases somewhat at higher angles of attack is there some reason for not using 6,8 or 10 degree angles of attack?
Is there a minimium depth that the foil should be below the surface when travelling at speed, being a catamaran we dont draw much but I can extend the foil down by using longer end plates if required.
Once again many thanks for your time, I'll keep you posted with the results when they occur.
Regards John","2004-12-28","JOHN PAYNE","nopswd"," ","gateopen@xtra.co.nz","0"
"67","756181","2","Re: FOIL SHAPE AND ANGLE||756181","John,
I see that the table I provided you is unreadable. It may help if you know that the first line and the first column is Angle of attack = -4.00, second column is Coefficient of lift = .0065, third column is Coefficient of drag = .0309, forth column is Coefficient of Moment = -0.1053, and the fifth column is lift over drag ratio = .210. Hopefully, with this you can read the table.
","2004-12-27","Ray Vellinga","nopswd"," ","rvell@san.rr.com","0"
"68","756177","2","Re: FOIL SHAPE AND ANGLE||756177","Hello, John,
Here is a little cook-book on designing hydrofoil wings. As a welder, you may find the "ogival" AKA
Plano-convex shape easiest to fabricate out of aluminum, steel or stainless steel. The wing is created
by twice cutting a pipe lengthwise to form a vault-shaped piece. On the bottom inside weld a flat plate.
Use a grinder to make your welds fair. Fill in the pits with Bondo. Make everything smooth.
You may choose to round off the leading edge to avoid slicing marine life as you fly by.
The trailing edge should be sharp, but not so sharp as to be hazardous.
You then have a wing, the top of which is a segment of a circle with the underside flat.
For starters, make the thickness to cord ratio 10%.
You need to estimate the area needed, so get out your calculator. The formula is:
S = L / F U^2 Cl
S = Surface area in Square feet
L = Lift (this is the total weight of your boat, crew, etc., in Pounds)
/ = "divided by"
F = Factor to adjust for water density, unit measurements, etc. Use the number F = 2.09
U^2 = Velocity in MPH multipied by itself (squared)
Cl = Coefficient of lift. See the table provided below for Cl. You should cruise at a high L / D or say 2.25degrees.
Take off will be at a higher Cl & lower speed. You must make some assumptions based on experience.
I hope you didn't sleep through math class.
Contact me if you have problems: rvell@san.rr.com
Ray Vellinga
Water Tunnel Observations on the Flow Past a Plano-Convex Hydrofoil By R B Wade Feb 1964
Caifornia Institute of Technology
Graph the Characteristics of Hydrofoil in Non-cavitationg Flow, Table, Page 51
v = 31.32 ft/sec = 21.35 M/H
Re = 0.75 X 10^6
Angle Coefficient Coefficient Coefficient L / D
of of Lift of Drag of Moment ratio
Attack
Series 1 Series 2 Series 3
-4.00 0.0065 0.0309 -0.1053 0.210
-3.50 0.0487 0.0262 -0.0932 1.859
-3.00 0.0995 0.0223 -0.0782 4.462
-2.75 0.1247 0.0201 -0.0723 6.204
-2.50 0.1481 0.0190 -0.0665 7.795
-2.25 0.1721 0.0178 -0.0564 9.669
-2.00 0.1921 0.0164 -0.0476 11.713
-1.75 0.2140 0.0152 -0.0400 14.079
-1.50 0.2420 0.0149 -0.0375 16.242
-1.25 0.2636 0.0146 -0.0313 18.055
-1.00 0.2778 0.0136 -0.0244 20.426
-0.75 0.3106 0.0137 -0.0192 22.672
-0.50 0.3295 0.0131 -0.0140 25.153
-0.25 0.3583 0.0133 -0.0089 26.940
0.00 0.3714 0.0129 -0.0026 28.791
0.25 0.4023 0.0122 0.0016 32.975
0.50 0.4261 0.0119 0.0089 35.807
0.75 0.4478 0.0126 0.0148 35.540
1.00 0.4539 0.0138 0.0197 32.891
1.25 0.4490 0.0141 0.0245 31.844
1.50 0.4644 0.0152 0.0303 30.553
1.75 0.4781 0.0164 0.0356 29.152
2.00 0.5031 0.0164 0.0408 30.677
2.25 0.5349 0.0167 0.0474 32.030
2.50 0.5443 0.0172 0.0540 31.645
2.75 0.5725 0.0185 0.0593 30.946
3.00 0.5797 0.0184 0.0647 31.505
3.50 0.6360 0.0217 0.0775 29.309
4.00 0.6751 0.0245 0.0896 27.555
5.00 0.7732 0.0338 0.1151 22.876
6.00 0.8352 0.0447 0.1391 18.685
8.00 0.9873 0.0735 0.1858 13.433
10.00 1.0919 0.1182 0.2044 9.238
","2004-12-27","Ray Vellinga","nopswd"," ","rvell@san.rr.com","0"
"69","754783","2","Re: Foil Surfing||754783","I believe you need to really think about your design expectations. In the application you are considering, manueverablilty and stability are inherently opposite. If the board is stable, such as with surface peircing foils, you won't have the manueverability of a board such as the ones based on an "Air Chair" or "Sky Ski". You are going to eventually have to decide where to make the trade-off.","2004-12-22","Scott Smith","nopswd"," ","ssmith@veinrxinc.com","0"
"70","753679","2","FOIL SHAPE AND ANGLE||753679","I HAVE A 10 TON STEEL CATAMARAN HOUSE BOAT WITH 2 X 90 HP OUTBOARDS
THAT SUFFERS FROM A HUGE BOW WAVE COMING OVER THE FORE DECK AT SPEED
MAX SPEED BEING ABOUT 12 KNOTS DUE TO HALF A TON OF WATER ON THE BOW.
I WOULD LIKE TO ADD A FOIL BETWEEN THE HULLS AT THE BOW TO LIFT IT ABOVE THE BOW WAVE SITUATION. CAN YOU SUGGEST A FOIL SHAPE OR SITE THAT A SIMPLE PERSON CAN UNDERSTAND TO FIND A SHAPE WITH CLEAR INSTRUCTIONS AS TO WIDTH AND THICKNESS OF FOILS AND AN ESTIMATED LIFT IN LBS/SQ IN ON THE FOIL. I HAVE A 1200MM GAP BETWEEN THE HULLS AND FIGURE THAT I NEED ABOUT 2-3000 LBS LIFT IS THIS ACHIVEABLE, THE FOIL CAN BE AS LONG AS REQD AS THE BOAT IS 12M LONG.IM VERY HANDY WITH THE MIG WELDER IN THE GARAGE BUT CANNOT TRANSLATE THE INFO ON FOIL DESIGN SITES INTO A SIMPLE WELDABLE SHAPE THAT MAY WORK, ANY HELP WOULD BE APPRECIATED
JOHN","2004-12-19","JOHN PAYNE","nopswd"," ","gateopen@xtra.co.nz","0"
"71","743418","2","Re: Foil Surfing||743418","For your wakeboard, if you want an alternative to the inverted "T" fully submerged hydrofoil designs used on hydrofoil surfboards and sailboards today, you could consider using an arrangement of surface piercing foils... these would be self-stabilizing. Back in 1978, an individual named Michael Shannon of Birmingham MI sent a letter to Dave Keiper, who was offering foils kits for Hobie Cats. He stated that he and his partner James Coulter had successfully adapted parts from Keiper's foil kit to a windsurfer and planned to make a production run. In connection with this correspondence, Keiper sketched and annotated his own first thoughts on how he would do the design. Unfortunately, Keiper is deceased, and the return address on Shannon's letter no longer exists, according to the USPS database. So I don't know if this hydrofoil windsurfer ever went into production or not. Anyway, I put a copy of Keiper's notes and the Shannon letter up on the web at http://www.exigent.info/DAK-Windsurf.pdf. So take a look. It was common practice for the pioneering hydrofoil designers starting with Alexander Graham Bell to try out their hull/foil prototypes by towing them, so this is similar to a wakeboard being towed by motorboat, only the towed board is the end product rather than an interim test piece. Hopefully this info is of some help. Maybe someone else who checks the IHS BBS will know something of Shannon and Coulter. As to sources of foils and struts, that is another subject, but there are some: mostly in connection with human-powered vehicles, but also a company that makes them for adding to Moth class sailboats.","2004-11-24","Barney C Black","poopdeck"," ","barney@alum.mit.edu","0"
"72","742586","2","Re: Foil Surfing||742586","Hi Mitch,
In a first time, I think the better solution is a very simple inverted T foil on the rear (about under the rear foot) and a surface traking "patin" on the front. The rear foil must be about 0.1 square meter area.
For the front "canard" there are several solutions :
The more simple is a planing surface but you can try too somes V surface piercing foils.
Gérard","2004-11-23","Gérard Delerm","nopswd"," ","gerard.delerm@free.fr","0"
"73","742553","2","Foil Surfing||742553","I am interested in alternate designs for foil boarding waves. Currently many surfers are using a foil like the water ski chair type with a stand up board similar to a snow board. It seems to me that there might be a more stable and/or manuverable design like some of the boat foils I have seen. The speeds are 15-30 mph and generally the weight of a surfer(180lbs). Manuverability and stability is a must. Can you make some suggestions as to designers that might help me or direct me as to how to decide on a design and type of foil for surf? ","2004-11-23","Mitch Haynie","surfer"," ","haynie240@msn.com","0"
"74","730516","2","Re: Advanced Educational Pages||730516","Hi Barry,
If you try to do any Educational Pages project I can try to translate in French (in IHS there is “International” )
I am not a professional translator but I think I can make good translations if I can have “chat” with the author.
Gerard
","2004-10-30","Gerard Delerm","nopswd"," ","gerard.delerm@free.fr","0"
"75","730318","2","Re: Advanced Educational Pages||730318","An excellent suggestion. The closest the site has come is grouping correspondence by topic in the archives. Main page for accessing the master archives is http://www.foils.org/posted.htm.
There is also the barest start of an FAQ page at http://www.foils.org/faq.htm. However, no significant work was ever done on this.
As it states on the main page, the content of the IHS site reflects the interests of the members and visitors to the site who are willing to provide content. The site is very simple in design, no frames or anything, but rather sprawling. It is quite possible for someone with a particular interest or with a particular project in mind to assume responsibility for a page or pages on the site, whether the page currently exists or not, as an assistant to the webmaster. Revision and creation of pages is fairly simple with any WYSIWYG webpage creation program. File upload is easy with any FTP program such as CuteFTP. So if you were willing to undertake the project you suggest, even if it is over a considerable period of time, that is welcome, I believe, and fairly easily arranged.","2004-10-29","Barney C Black","poopdeck"," ","barney@alum.mit.edu","0"
"76","730307","2","Advanced Educational Pages||730307","I found Tom Speer's discussion on foil stability facinating. I've not see this information explained so clearly before. Similarly, I've read explanations on calculating foil sizes from Tom and others which made it understandable for someone who hasn't been in the industry for 30 years. I've seen so many of the questions I've asked years ago posted again and again.
Is there any way that somehow this explanation might be incorporated in an Advanced Educational page on the site? Perhaps as a continuation of the existing educational pages? I've gotten some great explanations from Tom, Mark Daskovsky, William O'Neill and Harry Larson.
I don't know if you have a hit counter on your basic educational pages, but I know I've been there many times and they have been very very valuable. I don't know how I could help, but I'd be happy to try.
Topics might be:
What shape foils? Typical NACA numbers (other better foils), what they mean and where to find the plots. The choices for submerged vs surface piercing vs strut foils.
How Big? Calculations on lift vs speed... or just a table. Wing loading.
Stability? Tom's stability discusson, formatted would be great.
Takeoff speed vs flying speed, relationship between these and parameters in determining them.
Estimating power requirements or max speed foilborne...
Add to the glossary words and terms which are used a lot on the discussions: freude numbers, sea states ... similar things which took a while to pull together.","2004-10-29","Barry Steele","nopswd"," ","barry_steele@yahoo.com","0"
"77","729123","2","Re: Foil Spacing||729123","Sumi raises an interesting point. PLAINVIEW never lost directional stability. One of the closest we probably came was when one of the main foil incidence angle control systems experienced a structural failure while foilborne. The result was that the foil with the failed system went to full-leading-edge-down. In response to the ship beginning to drop, the control system called for full foil-leading-edge-up. This resulted in one forward foil full leading edge up and the other forward foil full leading edge down while foilborne. The helmsman chopped the throttle immediately. The ship rolled and the hull hit the water at foilborne speed at an angle of 18 degrees. After impacting the water, the ship continued to roll to 32 degrees before coming to a stop. No one was hurt and there was no damage to the ship. We continued back to port hullborne.","2004-10-27","Phil Yarnall","poopdeck"," ","YarnallP@nswccd.navy.mil","0"
"78","729122","2","Re: Foil Spacing||729122","John, By conventional configuration, I refer to the airplane configuration. On PLAINVIEW, we showed the model test results done at the Michigan tank showing the loss of directional control to each of the skippers assigned. One could argue that the carriage helped the ship roll over, but it would still be quite a ride. I know of no instance where we actually encountered this situation since the crew was attuned to the possibilities.","2004-10-27","S. Arima","poopdeck"," ","sumi@foils.org","0"
"79","729121","2","Re: Foil Spacing||729121","Hi Sumi, By "Conventional" configuration, do you mean "airplane" configuration where the aft foil is lightly loaded, as was in the case of Plainview? I understand there was an incident where the stern tried to replace the bow in the foilborne mode, if you know what I mean.
","2004-10-27","John Meyer","poopdeck"," ","editor@foils.org","0"
"80","729120","2","Re: Foil Spacing||729120","I would like to add a word of caution to Tom's extensive and informative dissertation. The location of the struts on the hull, especially in the conventional configuration, one needs to look at the sea state and hull contact with the sea. In a quartering sea, where the bow of the ship could make contact with the wave could produce side loads that could easily overcome the ability of the aft strut to maintain directional control. Stability needs to be looked at in more than just the foilborne situation.","2004-10-27","S. Arima","poopdeck"," ","sumi@foils.org","0"
"81","729119","2","Re: Foil Spacing||729119","Phil, You may also recall that during detail design and construction of PLAINVIEW, it became apparent that the initial location of one of the diesel generators was too far forward and that the aft foil would have been too lightly loaded and subject to broaching, so the generator was moved aft by at least one frame space.","2004-10-27","Mark Bebar","poopdeck"," ","mbebar@csc.com","0"
"82","729118","2","Re: Foil Spacing||729118","On PLAINVIEW, the concern was not so much the space between the forward and aft foil, but rather the amount of lift capacity in the forward and aft foils. 90% of the lift capacity was in the forward foils and 10% of the lift capacity in the aft foil. Knowing the precise longitudinal center of gravity became a high concern. Ultimately, there was scale at the ramp to the ship. The weight and location of each new piece of equipment and gear was recorded when it came onboard and the LCG calculated. There was volume in the aft portion of the hull which was unusable for payload due to the requirement to maintain 90% of the load on the forward foils.","2004-10-27","Phil Yarnall","poopdeck"," ","YarnallP@nswccd.navy.mil","0"
"83","729117","2"," Stability Has Been Investigated||729117"," Yes, stability has been extensively investigated. The Hydronautics handbook on IHS's AMV CD#1 has a whole chapter devoted to trim and a whole chapter devoted to longitudinal stability. You can also find papers on hydrofoil stability on the NACA technical reports server (http://naca.larc.nasa.gov/).
There are also performance aspects to hydrofoil spacing. Constantin Matveev used to have a page on his web site that showed how the rear foil should be located in the rising part of the transverse wave generated by the forward foil. This leads to a foil spacing based on the design Froude number.
With regard to "stability", the foil spacing is just one of many important factors. I'd say there are really four areas to consider in addition to wave drag, all of which are affected by foil placement and spacing. The first is trim - the ability achieve an equilibrium where all the forces and moments balance (sum up to zero). For best performance, the least drag is obtained by the "airplane" configuration, with a large foil taking nearly all of the weight of the craft and a lightly loaded (quite possibly negatively loaded) stern foil for stability and trim. This means the main foil must be placed in the vicinity of the center of gravity, which for most boats is a little aft of midships. This only leaves half the length for foil spacing. If you look at the Carl hydrofoil, you'll see that the hull has a slender tail to put the stern foil farther aft while keeping the weight near the main foils.
Then there's stability itself. Stability has to do with whether the craft returns to a condition of equilibrium after having been disturbed from an initial equilibrium. So stability presupposes trim - it's meaningless otherwise. Stability is usually further broken down into static stability, which is the instantaneous tendency to return to trim after a disturbance, and dynamic stability which deals with whether or not the motion damps out over time. The pitch damping goes by the square of the distance between the foils and the center of gravity. So there's a definite connection between stability and foil spacing there. Heave damping is usually quite high by the nature of hydrofoils, so if the pitch heave coupling is stable, the dynamic heave stability will probably be stable.
The static stability in the longitudinal axis depends on how the moments change for a disturbance in pitch angle at constant depth, and how the moments change with depth at a constant pitch attitude. A bow-up change in pitch must generate a bow-down change in the pitching moment. As a practical matter, this requires that the forward foil be more heavily loaded - it must carry more of the boat's weight per unit area than the aft foil. So as you change the foil spacing and placement relative to the center of gravity, you have to change the area of the foils. An increase in height (decrease in depth) must also generate a bow-down pitching moment to have stable pitch-heave coupling. This is why you see inverted T foils used so extensively for the aft foil and either surface piercing foils or flapped foils forward. Again, the spacing and placement of the foils is very important, taking into account their heave stiffness.
Yaw damping also improves with the square of the distance between the foils and the center of gravity. So there's another effect of foil spacing. Roll damping goes by the square of the foil span, so it's not very affected by longitudinal spacing, although it's heavily influenced by the lateral spacing of the foils.
The next issue to consider is controllability. Control power is needed to achieve the desired trim state. Especially with surface piercing foils, there will be an optimum flying height for best performance, and the pitch attitude must be trimmed so as to achieve it. Control power is needed for stabilization if you are actively augmenting the craft's stability, as is universally done for fully submerged foil systems. Control is also needed for maneuvering. Finally, control power may be needed for achieving the desired ride quality, as in using direct lift to counter the effects of waves. If you have a system with high static stability, you need to have more control power for trim. If you have a system that is unstable, you need more control power than a neutrally stable craft.
Once again, hydrofoil spacing comes into account because it provides the moment arm for a given change in force at the foil. If you want to generate a direct force at the center of gravity, this will require more or less control from other foils to cancel out the moments if the foil is located away from the center of gravity. If you want to generate a moment but the foil is close to the c.g., it's like mounting a door knob near the hingeline of a door - pushing or pulling on the knob will not rotate the door. So you have to consider the foil placement with regard to what controls you intend to associate with it.
Finally, there's the issue of ride quality. In the longitudinal plane, the hydrofoil can either platform the waves, flying at a constant elevation with respect to the earth; or it can contour the waves, flying at a constant distance above the water surface and following the wave shape. If you're platforming, foil spacing may not be that important. Platforming requires a lot of direct lift control power, though, and the size of the wave you can platform at a given speed may be more limited by the control power than the flying height. But if you're contouring, then the craft will be maneuvering much more aggressively in pitch, and the foil spacing issues above come into play. No hydrofoil on the ocean does exclusively one or the other. Wave heights greater than the flying height have to be contoured. And the short wavelengths have to be platformed.
In the lateral-directional axes, ride quality may dictate how the vessel rolls into and out of a turn, if it rolls at all. Hydrofoils have their center of mass well above the foils. If they do a skidding turn in a upright attitude, there's an overturning moment toward the outside of the turn that has to be resisted. If they bank into the turn, then they have to roll first, then yaw as they carve the turn, and finally roll out. The rolling in and out of the turn causes lateral accelerations at the crew station that can be very disconcerting. The craft may actually have to apply direct side force to the foils while rolling so as to put the center of rotation near the center of gravity instead of at the foils. So there has to be a coordinated combination of rolling moment, yawing moment, side force, and lift to obtain acceptable lateral ride quality in maneuvers. Foil spacing would be a part of that equation, along with many other factors.
For example, an aft rudder will tend to produce side force to the outside of the turn, whereas a forward rudder would produce side force to the inside of the turn. It might be necessary to apply opposite forward rudder for a rapid change in aft rudder to generate the necessary side force while rolling, then wash out the forward rudder to allow the turn to develop. Depending on how sophisticated the control system is, the foil spacing may be important to tuning the interrelationship between the various forces and moments.
In most papers on hydrofoil stability, you will find equations that have a number of parameters called stability derivatives. They will describe how each derivative affects the craft's stability and trim. But what you'll find very difficult is coming up with good numbers for the stability derivatives to represent a given design. Getting those numbers is why companies spend so much money on testing and engineering analysis.
I hope this has given you the pointer you need. I think the Hydronautics handbook, "Hydrodynamics of Hydrofoil Craft", is the most comprehensive source on the subject. If you can find them, there are two Hydronautics companion volumes, "The Stability Derivatives of a Hydrofoil Boat, Part I (and Part II)" that deal with estimating the numbers you need to actually calcuate the stability of a given configuration.
","2004-10-27","Tom Speer","poopdeck"," ","me@tspeer.com","0"
"84","729116","2","Foil Spacing||729116","Does anyone know of anything that has been published on the fore-and-aft spacing between the main foils and the stabilizer as related principally to pitch stability? I have searched the IHS CD-ROMs (lists of titles and abstracts of those that were at all promising), and have looked through my own file of hydrofoil material (mostly of Grumman origin), and have found nothing. Has this ever been investigated? Or has the spacing of the foils which falls out from the proportions of the hull always provided sufficient pitch stability, and the question has never come up? I want only to be pointed in the right direction; not to have any research done.
Is this question worth answering? I don't know.
","2004-10-27","Joe Koelbel","nopswd"," ","JOEKOELBEL@aol.com","0"
"85","729115","2","Re: HYDROFOIL PONTOON||729115","Hi Ed. This same question has been asked of IHS several times over the years. Correspondence on the subject is archived on the IHS site at www.foils.org/motofoil.htm. I have yet to see a report or photo of a hydrofoil pontoon boat project completed and working. You should review this information. In particular, Charlie Pieroth's recollection of his work at Dynamic Development, Inc. should be of interest.","2004-10-27","Barney C Black","poopdeck"," ","barney@alum.mit.edu","0"
"86","725016","2","Re: HYDROFOIL PONTOON||725016","To review the photos as described above go to http://www.totalrisk.com/diveboat.zip and copy Ed
","2004-10-18","Ed DeMoss","11030h"," ","eldemoss@totalrisk.com","0"
"87","725012","2","Re: HYDROFOIL PONTOON||725012","To review the photos as described above go to http://www.totalrisk.com/diveboat.zip and copy Ed
","2004-10-18","Ed DeMoss","11030h"," ","eldemoss@totalrisk.com","0"
"88","724962","2","HYDROFOIL PONTOON||724962"," This is my first attempt to acquire information about putting a hydrofoil system under a pontoon boat. We have a 28 Ft. tritoon pontoon boat that has been built by our volunteer rescue dive group. The photos will best describe what it looks like. It is powered by a new Mercruiser Bravo 5.7 I/O with a ProCharger. It has 400 HP and runs right at 40 mph (via gps). It weights right at 6000 lbs. with dive tanks, equipment, and fuel. Planes very quickly.
There is a hydraulic lift on the front that extends 1 1/2 ft into the water on the front end that will lift well over 1500 lbs. The lift is for raising injured persons out of the water and for divers to get out quickly.
I weld aluminum as a hobby and have built and designed the entire system. We have an idea on how to do it but we need some advice and maybe some calculations. WE cover a very large lake and think this would be faster to respond to a accident. We have cad drawings on what exists.
2 questions am I asking the right group and is their anyone that can help? Thanks Ed DeMoss ","2004-10-18","Ed DeMoss","nopswd"," ","eldemoss@totalrisk.com","0"
"89","716776","2","Power Boat Foil Design||716776","I am doing some research and feasibility studies on developing surface piercing hydrofoils for a power boat in the 24-30 foot range. I have read up a little on the Talaria as well as pulled the patent documentation on one of the kits they made for the boats back in the seventies. I have a couple of basic questions for the group here. First, when calculating the lifting force of a surface piercing foil is the lifting force of the foil roughly equal to that of a fully submerged foil of the same width as the part of the foil that is under water? Also what NACA foil profiles do people reccommend? The 16-510 design Tom Lang used? I tried plotting this shape out using one of the foil programs and the foil bottom was concave. Is this right or did I mess something up? Thanks for all the help in advance. I'm sorry if some of this is a little simplistic!","2004-09-30","Jim Harrington","nopswd"," ","jharrin1@msn.com","0"
"90","716553","2","Hydrofoil kitesurfer||716553","Has anyone seen a kitesurfer hydrofoil made of glass/kevlar/carbon fiber instead of the usual and heavy steel?
I am interested in building my own but steel is ruled out due to weight.
Thxs
Rod","2004-09-30","Rod","rodrigo"," ","rod.vr@teleline.es","0"
"91","716442","2","Re: Looking for Scott Smith||716442","Look no farther, you've found him again! I can still be reached at ssmith@syntheon.com. Missed you Diane. Sorry Tori and Todd, been under the weather and out of touch for a few months, but I'm coming back around. For any Dynafoil enthusiasts out there, I'm cleaning out the extra projects and thinking about selling a pair of mine (4 is just too many). I'll post it here when I get my act together again. By the way, if any of you have a Honda PWC and wondered what would happen if you ignored the warning label and engaged the reversing lever while under way, here is the video. It is almost 3 meg, so if IHS decides not to post it, e-mail me and I'll send it to you.","2004-09-30","Scott Smith","nopswd"," ","ssmith@syntheon.com","0"
"92","715374","2","Check the Dynafoil area||715374","Hi Diane,
Check out the Dynafoil threads that he and I were posting on. Here's one address that's listed: ssmith@syntheon.com
I'm not sure if it's good though, and I had the same fatal crash a few weeks ago and lost his other address too.
Todd","2004-09-28","Todd Miller","nopswd"," ","austinado16@cs.com","0"
"93","714505","2","Looking for Scott Smith||714505","I am looking for Scott Smith from Florida. My computer crashed a few months ago and I lost his e-mail address. ","2004-09-26","Diane Bell","nopswd"," ","outlawbettybel@hotmail.com","0"
"94","701771","2","Re: foilboard design||701771","Sam,
The choice of aluminium or carbon fibre on a foam core would be a decision you need to make based on what you are most comfortable working with. Either material should in principle be strong enough for this purpose (provided your carbon skins used over the foam core are thick enough). One of the tricky bits for either construction material would be to work out how you would connect the foil to its support strut. I assume you are working on using an inverted "T" shape foil and strut? If you are able to weld aluminium or can get someone to do that for you after you make the parts, that may prove to give the best connection at the junction of the T. For carbon fibre, making a sufficiently strong junction will take a bit more design and construction effort so that it does not simply fail at that point when you do more harsh manoeuvres with the board. ","2004-08-30","Martin Grimm","nopswd"," ","seaflite@alphalink.com.au","0"
"95","697278","2","Re; foilboard design||697278","I suggest you take a look at Rich Miller´s article on hydrofoil sailboards. Go to: http://www.exigent.info/miller.pdf. You can also contact him directly for advice. I do not believe that he monitors this BBS.","2004-08-20","Barney C Black","poopdeck"," ","bcblack@erols.com","0"
"96","693486","2","foilboard design||693486","I am a kitesurfer and wakeboarder from England. I amm thinking of making a foil to go on the bottom of a board I have made. It would be for use at speeds of up to 20knts. I weigh about 13st, and my board is about 125cm long. I wouls be very keen to get some advice on foil design and building. Although I had been planning to make the foil from foam and carbon, I know that most production foils are aluminium. Why is this, and which is better to use. I have very little experience of hydrodynamics, but am keenm to learn. Many thanks, S.","2004-08-12","Sambo","nopswd"," ","sam.evans@students.pms.ac.uk","0"
"97","692405","2","Re; Re; Attitude control system||692405","Walt,
1. The text book "Theory of Wing Sections" by I.H Abbott & A.E. von Doenhoff provides geometry definition of various NACA profiles.
2. NACA foil sections are appropriate for underwater use. The main difference between air and water is the density of the fluid, that is easy to account for, see elsewhere on our website for information. Another issue is cavitation. This may not be a problem if your application is for relatively slow towing speeds.
3. The center of lift of foil sections is typically a quarter of the chord chord length aft of the leading edge. It remains at a relatively constant position for small variations in angle of attack.
4. Another package you could consider using is Wing Analysis Plus by Hanley Innovations (http://www.hanleyinnovations.com). This would help with answering many of the above issues.","2004-08-10","Martin Grimm","nopswd"," ","seaflite@alphalink.com.au","0"
"98","688064","2","Re; Re; Attitude control system||688064","Tom, thanks for the link. I'll take a look.","2004-08-01","Walt Allensworth","nopswd"," ","walt@aharinc.com","0"
"99","687887","2","Re; Attitude control system||687887","http://raphael.mit.edu/xfoil/","2004-08-01","Tom Speer","nopswd"," ","me@tspeer.com","0"
"100","685359","2","Attitude control system||685359","Hi! I'm building an underwater attitude control system that is to keep a towed device nearly horizontal. This system will include two movable underwater foils of modest size and force (under 100lb). The angle of attack of the foils will be controlled by weights. Is there a program I can use to generate [X,Y] pairs of points that describe common hydrofoil cross-sections? Are NACA foil sections appropriate for underwater use? Also... knowing the exact center of lift of the foil section is a critical aspect of the design. Are there programs that identify the center of lift of common foil sections?
Thanks in advance!","2004-07-27","Walt Allensworth","nopswd"," ","walt@aharinc.com","0"
Re; Re; How foils lift
Terry, I agree completely. I would just like to know what proportion is due to deflection downwards by the underside compared with suction from the upper side, especially at takeoff.
regds, Ian
[Date/Time=05-26-2003 - 11:11 PM]
Name:Ian Ward
ianward@ozemail.com.au,
[Msgid=441938]
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