Skid fin/bracket question

[daveracerdsh]

Somewhere I have read that in stock outboarding a skid fin bracket has to be attached to the back of the sponson by a minimum of 4 bolts. I can't find it in the rules....am I wrong on this? any help would be appreciated. Thanx

[jeff55v]

It's been a while since I've studied hydro stuff. But I think that's a PRO rule.
Add:
I found the rule.
(See attachment)

[daveracerdsh]

rule

Thanx jeff....we looked that up Sunday when building the new J boats. I sure could be wrong....but I think I have seen the 4 bolt rule. Maybe my memory is getting faulty in my old age...

[propfxrO84]

I always want several, usually more than 4 stainless bolts, holding mine on, But, that is for (D-mod and FEH though) What have you come up with to overcome the need for the bolts? Just curious? I may want to shed a little weight too!! thanks, BT

[pops67g]

Not a place to skimp....

I would think that in such an important place as a turn fin bracket that you would want to even exceed bare minimums with regard to mounting etc. I run D's but even a J can hurt you if something lets go in a turn.

[daveracerdsh]

Bracket

I agree pops...I also run D stock, and have 5 grade 8 bolts holding bracket onto back of sponson. People would be suprised at the amunt of force a skid fin is under while turning....I tried a slightly thinner fin 2 years ago and came back in from testing with the fin bent at a 40 degree angle from the force of the water....and you could not straighten this thing out in a vise. Just think about the force an Unlimited hydro puts on it's skid fin....amazing..

[daveracerdsh]

Skid fin

Sitting around tonight with not a lot to do...started watching some in boat videos from D stock hydro heats.....the amount of water one of these things puts out in the turn from the skid fin is stunning....watched a video of Darren turning hard and I would bet the skid fin spray was 40 feet in the air. Think of the forces involved with that.....

[pops67g]

Fin material

Since it's so easy to work with guys want to use aluminum for fins. The main problem is that the thickness that is required to keep it from bending creates extra drag. I use 1/8" chrome moly. It takes 4-5 hours to make a fin with this stuff because it's so tough but there is minimal drag and almost no chance you will ever bend it.

[modhydro]

Fins

Another alternative is to make them from carbon fiber. It is easy to make them tapered thinner towards the bottom where the bending stress approaches zero.

Steve

[DeanFHobart]

Carbon Fiber is Brittle

Carbon fiber is very brittle. Unless you know a lot about how to layup the carbon fiber woven cloth or uni-directional tape and know about it's strength properties I would stick with a metal fin.

I have seen carbon fiber fins break and cause accidents.

If you use steel, you can make it a little thinner. Any type of aluminum should be made from at least T6 hardness. 7075-T6 aluminum works well.