Hydrofoil assisted catamarans.

I am absalutely amazed at the claims made by fitting a foil underneath a semi displacement cat.

As I have one I am extremely interested. My application for further information (and yes I would buy one) has fallen on deaf ears by Hysucat.

I am now searching for any information that would enable me to fabricate something myself.

So far it would appear that an attack angle of approx 2 degrees would be a good start.

The plan would be to buy 1x8x4 1 inch sheet of marine ply, cut it in half lengthways and glue together.

Epoxy this across the two hulls, centre to centre with an angle of 2 degrees , shape a foil design with 4 inch grinder and 16 grit disc , coat with fibre glass resin and matt.

If its a failure I can beach it and with a hammer and the ole grinder its gone.

If it works only half of what they say thats 20% increase in my speed with similar decrease in fuel consumption.

I an assuming that 2 foot x 10 foot foil area will be sufficient to lift 14 tons, actually much less Im not lifting it into full flight.

It will of course need an upright in the centre or maybe two.

According to the Hysucat web site (no pictures at all) a 44 foot semidisplacement with speed of 22+ is just right for hydrofoil assistance.

Oh by the way I was on the internet searching yesterday for 10 hours ,--theres not much out there for such incedible claims.

 

Ok I am also going to say that this claim of 40% increase in speed is impossible.

These hydrofoils retro-fitted claim an astonishing increase in speed without any further modifications or adjustments.

How can this be? The propeller just would not be able to push 40% faster,--wheres the extra pitch come from??

This would have meant that the prop had a 50% slip before the fitting of the foils.

This is hardly possible iether.

 

look at bladerunner in NZ
guys name is greg shine, used to work for me, build dozens foil cats, very clever, and will answer your phone call

http://www.bladerunnerboats.co.nz/Site/Welcome_to_Bladerunner_Boats.ashx

 

Did you know that foilers bank IN on turns? I,ve seen some of these cats on West Coast surf beaches and bars, pretty impressive

 

Hoppe's design comprises a main lifting foil mounted just forward of the CG and two smaller, cantilevered, 'balance' foils near the transom. I have seen the system work well on only very (VERY) lightly loaded cats operating in the fully planing speed regime. It is not a 'bolt and go' modification by any means..the foils are specifically designed to carry a certain weight with a particular hull form and the props are sized accordingly.

I have personally been involved in several foil-assisted projects with displacement or semi-dispacement cats and trimarans ( a couple of them quite large..over 300 tons displacement) and the results were ..to put it politely..disappointing. In at least two of those examples, the vessels in question were actually slower in top speed with the foils than when the foils were removed.

I'm only guessing here..but it could be the lack of response to your query has to do with Hysucat recognizing that your hull type may not be amenable to a foil-assist solution....they only 'get it right' on very few specific examples.

 

Bmcf-- what do you call lightly loaded?

I wish I could just find a decent picture of one. This seemingly shroud of secrecy is infact strengthening your comments about them not being as succesfull as they seem to want you to think.

I have read that they say no further modifications are necessary. That was involving the Prout 60 foot cat that supposedly had an increase of 29 to 43 knots by bolting this thing on.

I think that is a lie and is impossible without re-propping.

My Seawind Ventura 44 (Crowther design) may not be a suitable donar but wouldnt you agree that that is no excuse to ignore a potential customers e mail. Bit unprofesional--wouldnt you say?

I did look at Blade runners web site. To be honest I have nothing to say to him yet. I am at present trying to find or communicate with the people that make them.

Maybe I could have a word with him.

 

now I am completely puzzled, he does make them, lots of them, he can put you right on expected performance increases as I think he has done some cougar cats, what he found was they cruised at what was before the top end, fuel saving being the most advantageous plus
I dont understand, you say this is all clouded in secrecy, I give you the number of man who has made a success of the whole thing , for many years, and you say you have nothing to say? Can you enlighten or do you wish to go around in circles?

 

First, let me say that this a bit awkward of a subject for me to discuss in detail the 'pros and cons' and 'hows and whys' because I've been directly involved with Hoppe's foils on some projects and 'other's' foils on other projects and have to maintain client confidentiality in all cases. I am not at liberty to say, specifically, 'this one worked' and 'that one didn't', and why. Sorry about that.

There are indeed a lot of successful applications of Hysucat foil-assisted cats that are out there running around. The hulls are typically assymmetic and fully planing to start with (thus lightly loaded and/or high-powered) ..'Cougar-like' hulls if you will.

The cases where the addition of foils have not produced good (or any) beneficial results are almost always heavily-laden, and often way over design displacement. Despite numerous attempts, I have yet to see where the foils produce a significant improvement in overall hull L/D for a displacement catamaran or a planing cat that is significantly overweight.

If you overlay two drag curves for any hull, with and without lifting foils, there is a critical 'crossover' point where the foil lift (and reduction of hull wetted area and total drag) becomes less than the bare hull drag. For too many vessels, this crossover point is not within reach, with existing power installation, or only just barely so. Thus you have the added drag of the foils in the lower speed regime and little/no benefit achieved at higher speeds.

As for the prop question..if a vessel is truly amenable to large reductions in drag above the cross-over point by the addition of lifting foils, then of course the props will have to be pitched to take advantage of that.

 

I posted two seperate answers to two different people in one post-- sorry.

I have sent an e mail to Bladerunner. I have recieved an e mail from some one of a different address-- could be him.

I was accusing Hysucat of secrecy.

Yes he does make them--cats, not Hysucat hydrofoils or does he.

I shall discuss it with him --

 

I did some digging and found some old data (that nobody can trace.. )that illustrates what I was talking about above. In this example, the cat was 140 metric tons displacement and with symmetric displacement hulls, waterjet propelled. The vessel in question was very light for its size. In this example, you can see that the total drag is worse over the much of the entire operating range with lifting foils attached, but there is a top speed improvement of consequence. Note also the very attractive--but, in this example, only moderately obtainable--'break point' in the drag of the vessel with the foils. A 'little more' installed power/thrust and this example would have really shined. In other cases, that 'break even' point in drag lies above the thrust limit curve and not below it.



Edit: The above graph was from detailed analysis/prediction using some pretty good tools. But as is so often the case, reality was a little different. The craft actually achieved 38 knots..or about 3 knots better than bare hull expectations..while the prediction was for 5 knots of improvement from the foils. Subsequent vessels in the series were delivered without foils; the cost of the foil system was not justified by a 3-knot speed increase in this case.

 

Right absalutely understood, and this is what I want to avoid.

I do not have an e mail from Bladerunner yet, or at least in a recognisable way. I am however talking to a guy from NZ.

He contacted me through the forum.

Bmcf Do you have any Idea at all how much a hydro foil costs.

I found an interesting site where a guy was using old helecopter rotors. he said usually the rotors will not be replaced with out the old ones being returned. However the rotors are not wanted, they just dont want them to have old ones that could be used in any way.

Apparantly as shipping was expensive, the manufacturer said saw the boss off the end and post that. we will then ship you a new one.

Consiquently old rotors are available, as much as 2 feet in width and 15 feet or more long.

What I could not find on the web was a picture of a catamaran hydrofoil, Oh plenty of pictures of boats zooming about but nothing of a hydrofoil itself.

Its like that yellowfin drive plenty of graphs and hype and distant pictures.

 

Probably trying to stop someone like you from copying them Jack!

 

That could be,--it'lle also stop me from buying them too.

Doubt if I could make a Yellowfin.

 

aww - don't sell yourself short!

 

How much does a hydrofoil cost?...er..what size foil, what size boat, how much lift, hull material? The foils under our trimaran (43' aluminum hull) cost about 16K$..they are billet aluminum foils, CNC machined.

The helo rotor idea sounds interesting..wonder what the foil section shape is?

-Bill