Hydrofoil assited sailing cats

[Buildboats]

Planing hulled sailing cats are being developed that could be surpassing the conventional ideas of a displacement hulls soon, even in the world of multihulls. Monohulls are planing to catch-up to the multi's in most Ocean racing classes and using planing bottoms to do it. I think if the development of Yues Parlier's 60 ft cat ends up winning races... the idea of planing hulled multihulls will have to be looked at very differently and taken serious by prominent multihull designers. I have found great success on my proto-type, the speed that I achieve a plane 10kts even with very thin hulls, will make sailing such a vessel possible. I would enjoy good conversation on this concept of hull shape

I agree with you! Here is a solution I came up with to the high drag region of the speed range problem with stepped planing hulls-as applied to a trimaran. The basic concept needs to be tested on an RC boat (like Parliers was) and then taken further. I think it could work extraordinarily well thruout the speed range:
Rotatable Hull(ROH) Multifoiler - Boat Design Forums(under Sailboats)
Address:Rotatable Hull(ROH) Multifoiler

[Buildboats]

Yes I agree...the step is the problem with planing hulls and they also build planing hulls fairly wide to generate lift at lower end. I found that the foil replaces the wide hulls and then some. I think the step issue might be answered with lift strakes and roll overs to direct the water from the hull in directions that support the hull and are a bonus. I built my proto-type 4 yrs ago and used it for 1 yr without the foil. The hulls are very thin 16" wide with a nice clean entrance, but it was a dog and I was worried that the foil would not generate as much lift as I was hoping and all would be in vain. It took 20 mph to get on top of the water at max gross weight "not good". It went great at idle for trolling and passing the day around the harbour. She just cruised around with no effort like a displacement hull. I actually began to get impressed by how well it went from idle to 10 - 15 mph with a load. It wasn't even thinking of planing yet, it was clean, smooth, and quite. Then I added the foil and it was a different boat... she was on a plane at 10 mph fully loaded and would just cut through the tops of the wave like a wave piercer. I went out on the limb with the bridge deck as well, I built it very close to the water so there's a lot of compression in the tunnel. The boat rides on a bed of foam in the tunnel behind the c/g. This was out of the norm from any experience I have had with cats. We always looked for high bridge decks and thought they woold slam less. Well that's just wrong... I have found that there is no time for the wave to accelerate and hit the bridge deck. I remember hitting waves on our 60 ft spronk cat and you would think the rig was going to come down sometimes I also found bridge decks that have a step curve up to the deck cause a lot of slam and drag as well. If you carry the curve to the bow slowly there is now no wall to hit the wave. The added weight is nothing compared to the beating the bridge deck and rig takes. There is free lift in the tunnel just waiting to be used... compress it, reduce the slamming, profile of the boat, and the backwash coming up through the net and right back into the cockpit. Seems to always be the case with spray, it always find the cockpit. I built the foil out of oak and its been 3 yrs now... it its still going strong. I didn't even need trim tabs on it but they would be nice to balance with a load and people walking around... it's only 19 ft long. By adding lift strakes the wetted surface is reduced and you still have waterline for the reach. The first pic is before and after adding the foil from idel to full throttle

I thought you were talking about sailboats-my apologies! Your boat is very interesting. I've heard of a powerboat manufacturer(Hsucats?sp?) using a foil in combination with a catamaran configuration but don't know much about it.
Good Luck!

[Buildboats]

It is with a sailing cat or a power cat... I believe it might be best with a bit of both infact. I had a 60 ft cat and it went 18 kts with a 115hp outboard but dragged a ton of wave with her when power was on at over 10 kts, it was a displacement hull. Very clean displacment hull but is still carried that wave behind the boat with the engine on. This is what I'm talking about... we build big fast multihulls and put diesels in them and go 6 kts like a mono under power. that boat I posted was to have a sail rig on it at some point but I decided not to mess it up... she was so nice to use. It was really about the hull and at what speed I could make the boat get on a plane with the foil. That happens at 10 mph and that would be with or without sails as the boat doesn't know whats providing the push?

[Buildboats]

Hasucat does build foils and do a great job getting boats to go well. Hoppy has put much effort forward with the design.

[FranklinRatliff]

http://www.hydrofoil.com/gallery.htm

Very forward thinking hydrofoil concepts proposed by a Florida company.

[tamkvaitis]

I was thinking about using foil on a multihull. My idea was to use ruder hydrofoil and design small step in the back third of the boat. Then the boat would start foiling, the area behind the step would lift out of the water, leaving only 2/3 of the surface in the water. From the information I have read in this forum. you the boat should start planing. because the Froude number would change dramaticly (smaller L and the same speed). This is just a concept idea.

[Chris Ostlind]

Have you seen this boat from Corsair? It has been designed by Morrelli-Melvin NA in SoCal.

http://www.corsairmarine.com/0FoilerIndex.htm

Chris

[Buildboats]

The Corsair foil work was by Hysucat I believe... the bow on the inside of the tunnel are very interesting on that boat as well. Have a look at the pics of the foil and you can see the section behind the bow is cut out, this makes for a good floatation up front.

[Buildboats]

Cool stuff on the hydrofoil.com site... they seem to work well on RC boats. I have seen the big foil attack boats that US Navy lent the DEA to chase drug runners back in the 80s from the FL Keys. I had one pass me at night once off Caysail keys in the straights of Fl it was a quite the speedster. I have seen video's of these boat going in ruff water and think the lifting action of hydrofoils lifting the hull out of the water might require a bit to much attention to use on a daily basis. Like when you need to sleep at night with auto pilot or have inexperienced crew driving while you catch a bit of shut eye. I have a friend that is making changes to hydroptere/ There adding more mast height and new floats to the boat. She has been very successful to date and is still performing well. This method seems to work well if flying over the water is your objective. I personally like to be in the water and just reduce the wetted surface, while keeping the waterline length for the big water. We chose to put a 35 ft accommodation in a 60 ft hull. we get to make thin hulls with lots of waterline and use lifting strakes that run the length of the hull instead if cutting the hull in half with a step. I think the step approach requires to much speed to become active and when it's not active there is a lot of drag.
It is most interesting to see a planing hull on a big catamaran This cat will be one to contend with on the race course against the 60ft Tri's he's going up against in France. There all very fast boats it will be intersting to see where this design challenge will lead to if he begins to beat them. There is a video on this page its the middle one you can see the hull in ruff water (looks great to me)

Yves Parlier's cat when up against the 60' tri's has done terribly-mainly because of the high drag region between 8 and 20 knots according to him. That performance gap is what sparked my idea(post #2).
Here is some technical info on the Chapman project that you might find interesting:
The Predicted and Measured Performance of a 16' Hydrofoil Catamaran
http://homepages.rya-online.net/ejcc...rtPaperWeb.htm

[Deering]

I'm interested in adding foil assist to a small outboard catamaran dinghy but am looking for some experienced guidance:

1. one foil centered or two towards the ends? Better balance with two, but will forward foil cause too much turbulance for the aft one?

2. Foil profile selection? Speed of around 12-20 kts. Foil length of about 15 inches. Want maximum lift, but want minimal drag at paddling/rowing speed. Assuming an angled (trimmed up) foil will cause too much drag. Trying to avoid complexity of retractable foils.

3. Maybe one fixed foil and one fin-foil on outboard cavitation plate? Where to locate the fixed foil in that arrangement?

Any suggestions or good references appreciated.

[Buildboats]

Glad to hear... good idea to add a foil, it will make a huge difference in the boat. I would recommend 1 foil as the boat is small and yes add a foil to the motor cav plate. You should have that anyhow makes for better attitude control on any boat and there cheap. I located my foil Just in front of the c/g and added 2 degrees of angle from the plane of the bottom of the hull. This is how the foil pushes on the bottom and is it is always pushing the hull up even if you pitchpull off the top of a wave... the foil is still pushing on the hull towards the surface. I built my foil out of Oak 1x2x6 and glass then cut it to make a V and glassed the halves together and placed a strut in the middle. Pretty basic really cost me 100 bucks in wood, epoxy, and glass. I found the c/g with the trailer and built a plate to bolt the foil to. I also added lock nuts to the inside of the foil so I could bolt it to through the aluminum plate. I had the 1/4 plate pre drilled with few extra holes so I could move the foil forward and aft while keeping the 2 degrees of angle in the process. this way I make changes in location, I didn't have to make any got it right the first time out just a lucky guess. I was looking for slow speed performance so I made my foil 13" deep and 1" think for lots of lift, It worked.

[Buildboats]

Sam Bradfield build a few hobies with foils that worked quite well. Then he built Elfo and then Scat not sure how well she did haven't herd much since her launching in the Keys. Then theres Volantis