My last Clark Foam 6'2C and double foil fins

General Discussion
1

I have a Clark Foam 6’2 C and I been contemplating on weather or not to shape it. But today I finally decided to give it a go. I have shaped a few fishes and on all of them I have used regular glass-on fiberglass single foil keel style fins, with toe and cant. But this board (being the last Clark Foam blank I will ever shape) I wanted to put some nice double foil wooden keel fins on it. My question is, what are the positive’s and negative’s of double foil fins? And would it be better to set them parallel to the stringer with no cant or to toe them in and have cant? I really want this board to work great, so any help would be great

Thanks

SCOTT

2

Scott,

There are no negatives to double foiled fins. Your plan is quite sound. No toe-in, or cant, set parallel to the stringer is proper. Go for it.

3

Many a “Twin-Fin” came out of San Diego County with fins foiled both sides and no cant or tow-in. AND--------They worked. Mcding

4

I don’t know how you guys foil the double foiled keels.

But it is best to foil them less round at the inside, symetric foiled is not that good for side-fins.

Because your fins need lift to hold your board in turns. If you foils the inside like the outside than the lift to the centre equals the lift to the side what results in no lift. Foiling the inside is good for a streamlined inside but keep it flatter than the outside!

I don’t doubt that symetric foiled fins hold in turns but for the same lift the create more drag!

That is what I think about it.

5

Hans,

I’ve resisted, but just can’t let a misconception, such as you have, be the final post on this subject. Remember, engineers have proven in the past that a Bumble Bee can’t fly. Yet it does! Yours is a similar error. Now, that’s the good news, the bad news is that I’m not going to give you the answer. You need to put your thinking cap on and figure it out. Hint: How does an aircraft with symmetrical wing foils manage to fly? According to your concept it can’t. Yet it does! The same reason the aircraft is able to fly, is the reason the symmetricaly foiled fin works, in the application under discussion.

6

A guy named Lis has double foiled on his fish and quads.They have a reputation for working well…when a fish is banked into a turn ,just one side is in the water.Like a single fin pintail,with all that straight rail.

7

I agree that symetrically foiled fins work. Otherwise a singlefin would never work.

But I stay by my point that you create more drag for the same lift.

I thaught that a symetrical aircraft wing works because of the angle of attack.

So if I’m wrong, what can be, FCS is wrong too → http://www.surffcs.com/…s/foil_education.pdf<-.

And remember, I’ve never said that a symetric foiled fin does not work.

I don’t want to make you angry or say that you are wrong. I can really imagine that I am wrong but I stay with my theory until I know a better one.

8

AOA is the answer, as well as the single fin contact during a hard banked turn. Thank you for your courteous and thoughtful response. Lift on the fin is an over rated occurance. Don’t get too carried away with the theory. The real test is always in the water.