Homemade hydrofoil?

[walleyehed]

Re: Homemade hydrofoil?

Airman, just yankin' yer chain........I'm an IA, and pilot as well. We just got sold our dash-10 Commander and bought a total reconditioned Citation 550......Little more fuel, but can cruise at 37-42,000 ft. Trues 358kts.<br />ANYWAY, there are alot of theories out there on "foil" shapes, and I have a problem saying the foil generates lift....yes, it is stream-lined, but most have the very T.E. angled sharply down- this, I believe is where the lift comes from at high speed...just my thought, but I feel the foil shape is just to lower drag.<br /> The low-end lift is the total surface of the foil under water when trimed in-"angle of attack" to you and I.<br /> I have enough power on my boat that planing is not a problem but I do find a higher motor heighth works better as an added bonus.<br /> I've learned alot on these forums, and have experimented with what I have now nick-named the "dhadley heighth dimension"........I'm very happy with my current set-up, and I will never be without a "foil" on any boat I own......<br />

 

[Jdeagro]

Re: Homemade hydrofoil?

Good conversations, and I am learning a lot.<br /><br />I find it interesting that pilots (walleyehed) would use a Hydrofoil on his boat but (I am assuming)wound not think of flying his plane without Flaps, and trim tabs. <br /><br />The man wants to run his boat on plane at slower speeds. The more variable surface he has available the better the results. The hydrofoil will provide some lift but due to size (total area in excess of the cavitation plate) and the angle of attack ( you can change the angle of the trim tabs but the hydrofoil is fixed) the amount of lift is far less than a properly sized set of tabs. <br /><br />The mans problem is that the boat is stern heavy, and once the bow starts to rise the problem gets worse. The boat is rotating in all directions on an axis, so balance and stability are crucial. <br /><br />The foil on this boat will most likely cause excessive lift at high speeds driving the bow down, and it is not adjustable. I know the motor can be trimmed up, but at some point the prop can not compensate for the foil, and why do you want to use prop energy for any other purpose but propelling?<br /><br />Lifting the boat with extra consentration of lift in the center on a V bottom boat can do nothing but create side to side stability issues, especially in turns.<br /><br />I would agree with Dhadley that raising the motor could or would help the boat when using a foil, but where does it say this in the direction. You pay $25 to $50 and it simply says drill four holes, bolt it on, and go for it. Raising the motor adds just a little extra to the complexity of the installation. <br /><br />It is still a good debate, and I believe worth every word. Keep it going, we will all learn!

 

[pburchett]

Re: Homemade hydrofoil?

Hey ZMOZ. Here is my experience and everyone will want to pay attention. I saw the same “hydrofoil” The Edge or the Cobra in a magazine. I thought that the price was way too high. So I set out to the metal shop and bought enough 3/8 inch aluminum to make 2 of them. Total cost of everything plus bending of the aluminum was $35.00. I gave the other one to my Dad who had attempted to make one out of 1/8 th inch aluminum, which folded up under the pressure of the boat. I mounted it under the cavitation plate for reduced stress on the outdrive. I have hit several things and all is still intact. I did have to cut a hole in it for the trim tab and sloped the leading edges some so it would look like an airplane wing. I then had the machine shop put a 15 degree lip on it which was turned down. A little work, but I had nothing else to do. They both work great. My boat is a 19 ft Sea ray Cuddy and had a time getting on plane until I put this on it.

 

[Jdeagro]

Re: Homemade hydrofoil?

Hopsdak;<br /><br />You have effectively increased the hull size by adding two fixed trim tabs and the largest hydrofoil I have ever seen. It also appears that you have drilled four or five holes on each side of the cavitation plate. This is in addition to the jack plate. You sure spent some serious time and money to get the performance you wanted. <br /><br />The trim tabs, even though they are fixed, are keeping your boat stable at speeds. Keep them on the boat.

 

[MajBach]

Re: Homemade hydrofoil?

NautiJohn:<br />Your posts in this forum have been persuasive enough for me to investigate purshasing a pair of your tabs. But enough plugs already! Fins cost substantially less and I have rarely seen a post from anyone that states they do no good. I too have a Dol-Fin and think it is fabulous and like Walleye, will never run a boat without one; (unless I try your product and it works even better).<br /><br />I didn't want to open up the can of worms but walleye just did. I don't believe these fins add lift like an airplane wing (perhaps they do when the motor is trimmed in and the bow rises during acceleration). The other real benefit is while on the plane. The larger area of the fin allows the motor to find a more vertical path through the water than it would without it. A boat at speed riding the surface of the water is almost sure to have a slightly bow high attitude. This is because the outboard is trimmed in the opposite direction (it is not parallel with the transom or slightly inward as during acceleration from a stop), thereby 'twisting' the stern down and the bow up.<br />Because gravity tries to pull the bow down and the outboard tries to push it up the two opposing forces must find a point of equalibrium. (when they get jostled out of equalibrium, you get porpoising). The end result of this is an outboard that is not perdendicular to the water surface but rather pointing down slightly and thereby pushing the water somewhat towards the surface; not ideal since this thrust in not parallel to the direction of travel. You can see this by the 'hump' of water that comes to the surface just behind the wake of the outboard. An extreme case would be a rooster tail. The 'hydrofoil' reduces this waste of thrust by adding more surface area to the outboard to react with the passing water, forcing the outboard DOWN a little further until it is closer to parallel with the direction of travel. The end result is bow - and thereby more of the entire hull - that reamins out of water at speed. However, this is offset by the fact that more of the outboard is under water thereby increasing drag and reducing speed. Most posts we have seen from owners with fins state that they lose a little top end with the addition of one of these foils. However, as someone has stated here time and time again, the foil allows you to raise the 'X-dimession', i.e., lift the outboard further out of water. I think the primary reason it allows one to do this is because it reduces the chance of ventilation by protecting the prop from the surface. The end result of adding the foil (as it pertains to planing speeds) is a hull that sits higher out of the water, thrust that is more directional to the travel of the boat and an outboard with reduced drag because it sits higher out of the water. This effect cannot be achieved by smart tabs simply by their design.<br />This science of what is happening here is totally different to what is happening at slow speeds. At slower speeds, with the motor trimmed in, the water meets the foil on is underside and obviously pushes the entire unit up.I think this is basically what smart tabs do too. ALthough one thing they can do a foil cannot is dampen the ride in chop as they are constantly adjusting in response to the forces acting on the stern.<br /><br />But enough science already! I look forward to the day when I tinker around with these smart tabs. Curious to see how the two will behave when both are mounted on the same boat.

 

[Hopsdak]

Re: Homemade hydrofoil?

nautiJohn,<br />The trim tabs are now fixed in the up position. They are only used as steps now and don't even touch the water on plane. My boat has a jack plate and a tunnel so the foil captures the water that comes out of the tunnel and i can jack the motor up to the point that the whole foil is just about out of the water. It did lower my top end a bit but the added lift it provides will keep the hull flat on the hole shot. Just about every tunnel hull flats boat on the Texas coast has some sort of cavitaion plate, compression plate, foil, or the like. It's a must have for any tunnel hull.<br />And you can adjust the amount of lift by triming the motor. I'm not sure how this design would work on a v-hull without a tunnel but in my app it made a huge difference.

 

[Jdeagro]

Re: Homemade hydrofoil?

MajBach;<br /><br />Thanks for the attention, it is appreciated. Please do not run Smart Tabs and any hydrofoil at the same time. At high speeds the lift from both will cause a bow down attitude, slower speed and worse, bow steering. Do your tests independantly. I agree with everything you have said regarding the porpoising issue, what goes up must come down. This ossilation creates slower speeds and less efficiency for at least two reasons; one, the prop is changing the angle of attack, and two, when the bow comes down the re-entry goes below the mean running possition creating a brake. The best senario is to keep the boat running as clean as possible. This will result in better prop bite and less "braking". Whatever devise accomplishes this, will increase the efficiency and of course comfort. Our advantage is that we can control the amount of lift (it is adjsutable), and tune the system to the boat, in minutes. Results are documented by editorial magazine tests in USA and at least six other countries.

 

[Jdeagro]

Re: Homemade hydrofoil?

Hopdak;<br /><br />I am sure that it made a huge difference, but even though the plates are up, they will provide side to side stability when the boat leans or rocks a little. They also provide lift when you accelerate. Move them all the way up and see for yourself. I think you will be surprised. The loss in top end is a result of the extra and increasing lift you get from the foil. Trimming the motor will help, but it gets to a point when the prop angle offsets the lift from the foil at the sacrifice of propulsion efficiency. Result, a loss of speed. <br /><br />We have had a number of flats boats, with and without foils come to us for better performance, and get it. <br /><br />Now that you have done all of the work to get your boat the way you want it, I would leave it alone.

 

[mattttt25]

Re: Homemade hydrofoil?

thanks for the lessons fellas, really learned a lot. but i may have missed something- i understand the whole lift theory, but where does the supposed stability come from? if my semi-vee hull is now out of the water more, won't i be less stable? i get up plenty quick, so will a foil really do anything? better run it chop, but how?<br /><br />thanks-

 

[catfish1]

Re: Homemade hydrofoil?

in response to: NautiJohn:<br />Your posts in this forum have been persuasive enough for me to investigate purshasing a pair of your tabs. But enough plugs already!<br /><br />majbach, i'm not seeing nautijohn pushing smart tabs on anyone! in fact, many repies of his say nothing about tabs. my point is, if someone has a planeing problem, whats wrong with giving facts and offering solutions? the tabs offer advantages that a foil cant offer, and they are not as expensive as one may think! my opinion is a foil is just a low cost way to get the boat on plane quicker, but it has nothing to offer in the order of handling or top end speed. fyi: i am one of the guys that is using a foil, and i'm not at all impressed with it!

 

[frankdel]

Re: Homemade hydrofoil?

We've all stuck you arm out a car window while driving down the highway. A little rotation up and your arm gos up, twist it down and your arm gos down. Its the plaining surface of your of your hand not any lift design that gives this movement. Compare this to a foil, an air planes flaps,(I said flaps not the wing) and any lifting device on your cavitaion plate.<br /> On a boat all we want is lift and we get that by trimming in. Now add a foil and we get more surface to create lift. Thats works fine but now were on plane and want to lift the bow so we trim up. Thats works but remember what happens to your your hand when you tilt it down out the window. Well same is going on with your foil, its pointing down and its pushing the stern down. Its at this point a foil has undesirable effects. The best setup to have is hydraulic trim tabs and no foil. There not for everyone but on bigger boats and V-hulls there a must. <br /> Imagine your V-hull on dry land sitting on its keel. You need something to balance it right?<br /> When on plane you also need something to balance it and a trim tab will do the job. They'll also get you on plane and once on plane you trim them up. Now you have a lower unit to trim up that is unfettered and trims tabs that work independent of themselves and the lower units trim. Makes for higher efficiency and stability. Opps back to the point yes a flat homemade foil will work, The bends are to add rigidity and not some magical lift.<br /> Remember the hand out the window.

 

[MajBach]

Re: Homemade hydrofoil?

Well guys, we're beating this one to death, but overall it's been worth it; a lot of good input so far and we've managed to have keep it civil despite the varying points of view - kudos.<br /><br />catfish - I made those comments in jest,perhaps that wasn't obvious. No, John is not pushing his product on anyone but one can ascertain quite confidently from this thread and others, that he markets this product, not just uses it like so many others who express opinions pertaining to 'hydrofoils'. I just wanted him to know that.<br /><br />frankdel: I would agree with everything you stated above it it weren't for my personal experience. Even by my description, it would seem that a fin would slow a boat down at speed. however, I ran a stingray on an old 14' narrow tin with a 18hp on the back and it increased my speed from 17 mph to 21 mph. Although this was measured by a paddlewheel which might be affected by the stern position in the water.<br />On my current boat - a 17' tin that's 4-5 times as heavy and with a 90 on the back - the Dol-fin I'm running makes absolutely no difference in top end. i've checked it on more than one occassion during the same outing and used a GPS for speed. I was surprised too. The dol-fin drastically improves hole shot with heavy loads but also improves higher speed turning as it eliminates ventialtion.<br />Guess it's different on each boat.<br />I am anxious to try these smart tabs though for their dampening qualities and abilty to keep the boat level when weight is not centred. My 17' aluminum is wide and very rear heavy and, depending on the boat loading and wave Hz, somedays I can't even run on the plane in 1/2 foots waves without a ridiculous amount of pounding.

 

[Jdeagro]

Re: Homemade hydrofoil?

MajBach;<br /><br />I will be in Toronto at the Sheraton Centre Hotel for a Marine Distributor show (Kimpex is the distributor) from Sat. afternoon to tues. evening. Just in case you are a dealer or near by. E-mail John@Nauticusinc.com

 

[MajBach]

Re: Homemade hydrofoil?

Excellent! I don't know if i'll be around then though. Thinking about doing some musky fishin' up at the Moon. I will be dropping by the boat show at Ontario place mid-afternoon Friday. I will be coming in by boat too so if you see me....<br /><br />Two-tone brown Sylvan with a 90 Honda.<br /><br />Is this distributor show open to the public?<br /><br />Maybe I'll drop in Monday or Tuesday.

 

[Jdeagro]

Re: Homemade hydrofoil?

MajBach<br /><br />The show is not open to the public but if you ask for me ( John ) at the Nauticus boothI am sure they will let you come in. It may be interesting to you to see all of the other marine products as well. These displays will be represented by each manufacturer.

 

[Reel Appeal]

Re: Homemade hydrofoil?

Now thats a hydrofoil! <br />

 

[MajBach]

Re: Homemade hydrofoil?

How'd you get a picture of my weekender?

 

[vidar]

Re: Homemade hydrofoil?

if im going to drill holes in my hull and spend $$ i prefer electric/hydraulic trimplanes.....about 350$us here in norway... and then i can trim my boat as i please..and if sidewind or high load on one side i can level the boat by using them independently...that you cant do w springloaded tabs... or smarttabs..... but they are handy for very small/light hulls.... keep em running!

 

[Jdeagro]

Re: Homemade hydrofoil?

wo-max<br /><br />10 to 22 feet is our range, and i would be the first person to recommend helm controled trim tabs for larger boats or ones with high profiles, or Deep V narrow boats that lean excessively. If you are experienced at using them (helm controled tabs) you there are some advantages. If you arn't and have a fast light boat, missuse can be a problem.

 

[ZEE]

Re: Homemade hydrofoil?

Wow! Did this subject work up a sweat in a bunch of people or not? I can't argue the aero or fluid dynamics, but I can tell you that any transom heavy boat will perform better with any help, be it tabs or a foil. And, from personal experiments with several boat/motor combinations, the position of the motors cavitation plate relative to the bottom of the hull is critical. Many motors are mounted low and performance suffers. I don't know if it is an industru standard, but I believe that the cavitation plate must be on the same horizontal plane as the keel - that's what works for my past and present outfits. Add in adjustable trim tabs, and you got it all!