Hydrofoil assited sailing cats

Thanks Buildboats. Was there a particular foil series that you used?

Any idea on how much add'l drag you're getting from the foil at slow, nonplaning speeds (say 5 kts)?

 

I'm have no idea as to the series... I couldn't find answers to questions when I took this on, so I just build it and attached it. i spent a bit of time on the http://www.foils.org/ to get a basic idea on how to shape the foil. It was a huge difference as you can see from this pic. The top pic is top speed without the foil, she was a dog really and was hard to get on a plane since I made the hulls thin to test a ratio that would be used on a sailing cat "Thin to win ratio". Truthfully... I don't think there is any more drag than a dagger board would produce. If you were building a sailing boat, I would do as I plan to and that would be to have a the daggerboard go through the middle of the foil so you only need one board and the foil would be no more drag than a having 2 daggerboards. Other words it's not really worth worrying about. I have a hard time slowing my boat down to the 3 kts needed to down rig for fishing. I'll will say it make the boats more stable at slow speeds as well as banking into turns when going faster... something cats don't do well"turn". Or maybe they do it to well if you know what I mean. I have found that it is better to have round edges on the hull than shape ones. I'll go into this more in the next post

 

go to this post to see the difference

Guess you can't up load a pic twice...

http://www.boatdesign.net/forums/showthread.php?t=10731

 

if you go back to the fist page on this post you can see the difference coming out of the hole with and without the foil... the boat just stands up with the foil and fly out of the hole. How small a boat are you building or have built?

 

12 ft long - a dinghy for use off of the 'mothership'. Small outboard - 5 hp. Seems that small boats would benefit from foils even more than large - they're more subject to rough rides and they are more weight constrained. Would like to keep the whole shebang (with outboard) under 135 lbs. Seems like your design would be scalable for that kind of purpose too.

Why did you angle the foil instead of running it straight athwartships?

Cool project!

 

You have to angle it 2 degrees or it will not work...no more no less. The foil lifts the hull till it encounters cavitation at the surface. My boat goes so fast now 50 mph that the foil will get on top of the water and skip at times. I'm reaching a speed where the hull is beginning to be out of the water where the foil is attached. As you can see from this pic the other pic shows the foil pushing the water down while it lifts the bow right up and out of the water.

 

Sorry - my question wasn't clear. The foil has a 'corner' at the midpoint, like a delta wing. Why not just straight across?

 

Also, it looks like your hulls extend back aft of your transom - does that help with the trim when coming out of the hole? Any issues with steering?

 

yes you would build it straight... I did it for the c/g shift.

 

No issues at all i did it for getting on the boat... there steps.

 

You have any drawings of your sciff or pics if you've started building?

 

I would guess that your foil is going to be very small and if you want to save wieght make it out of carbon and high density foam. for ease of construction you might consider doing the end caps in wood so its easy to add the mounting hardware. I'd like to see your choice of hull shape? also you can add a bit of kevlar to the leading edge to stop any groves from forming if you catch any junk that might be floating in your path and get rapped around the leading edge which really doesn't slow you down if that happens but can cause chaff in the leading edge material if it not designed for abrasive encounters

 

next boats hull shape

this is the shape I have decided to build the next hull with... notice the soft edges instead of the sharpe eges of the proto-type. This change make for a softer ride and more forgiving turns. The other hull makes very shape course changes and when coming off the top of a wave, it could be quite aggressive in the change and catch the driver off guard. This is caused by the very sharpe edges in the other hull shape. It is very helpful to have the rollovers on the bottom to push water down instead of out from the hull. This is free lift and acts to stabilize the ride as well. Also works like a automatic trim tab when in ruffer water.

 

"Hydrofoil assited sailing cats"

So Why are you talkinmg about your fosil fuel powered boats????

start another thread if you have something interesting to say

 

pardon me

We are discussing foils on any hull and I started this thread if you have anything to contribute then please do. You don't need to confine our discussion on foils. foils on sail boats are the same as power boats. Do have something to add or are you just being silly.