NotWal said...

I Elmoed another fin yesterday. That's the second this year. I'm moved once again to consider a folding fin system and to moan about the piss poor design of current fin systems.

Power Box is piss poor. Classic box is adaptable and nicely forgiving. Trim box is piss poor and happily obsolete. For strength and adaptability for folding Tuttle wins hands down.

How did the Head / Box style contribute to the breakage?
Unless the fin broke inside the box, which is pretty rare but can happen.

If it broke flush with the board then it is the fin construction not the Head / Box.

If the box ripped out of the board then it is the board construction.

Bearing in mind that fins are not really designed to hit things but when they do somethings gotta give, better the fin than the box I say!

I thought the whole point of those brass threaded dowel inserts (sorry don't know name) was to strip so the bolts pulled out? Obviously not.

I believe you could just make the threads in the brass fitting(s) weaker by running the right size drill through them to take some of the thread surface off. Obviously trial and error, so it would pay to have some spares before attempting this. Maybe you could modify the fin so you can thread some fishing line through the bolt hole and tie it to the fin, so when you lose the fin, it is still tied to somewhere on the board like a washer in the bolt hole. Just some thoughts.

I've given it some thought in the past, but as I haven't lost a fin yet (just a matter of time), I won't have a passion for finding a solution like you. Please post if you work something out.

nebbian said...

NotWal said...

Back of the head broke off. The bolt stayed there. Box is undamaged. In my previous one the cross bolt pulled through the head.

I've had the back of the head break off on a tuttle box fin as well. The front insert stripped, and the fin pivoted around on the rear bolt, mangling and breaking the carbon head.

If it was a powerbox system then the (single) bolt would have stripped and the fin fallen out. Much better imo, it's easier to replace a cross dowel than repair a fin head. Many thanks to Decrepit for helping me out that time.

The significant differences between the power and the tuttle are -
#1 The Tuttle has considerably more material supporting the cross bolt
#2 With a properly fitted Tuttle fin (snug fit) you can support it using the front bolt only. So you can have a strippable cross nut on the front bolt and fix a tether where the back bolt should be. The geometry of both power and tuttle allows the fin head to pivot out of the box if not constrained by a bolt.
The trouble with the Power system is -
#1 Because the cross nut has little to support it, it will pull through more easily. If you use a strippable cross nut it will have to fail with a relatively light tap. #2 There's nowhere to attach a tether. However I think you may be able to enlarge the bolt hole a tad and pass a tether through there.

Brick said...

This defininately qualifies as No;2

I lost a fin a few weeks ago at low speed when I hit some crap submerged. Fancy an F2 not having a tuttle box.....the fin tore above the brass threaded gizmo.
There is hardly any material above this so it ripped straight out .I guess it can be argued that at least the box did'nt get busted ,but fins that become unrecoverable get a bit expensive too when it was only just a bit more than a bump.

I was paddling in shallow murky Sydney Harbour in probably 40cm of water and missed or couldn't see whatever I hit with the fin. It threw me off. If I was sailing fast it probably would have taken the fin. So I believe if you are doing a good speed it would be easy to miss anything in the water. I just wonder how those formula guys go with those expensive 70cm fins. I'd hate to lose one.