Kiteforum.com

Hello to all. I am looking for feedback regarding snapped fins on race boards. I do not want to do brands or pimping just looking for some real opinions regarding race fins and their resistance. I bought a 2011 race board with factory fins around 40cm's long. Not long after, maybe 10-12 sessions one of the forward fins snapped off at the base. I was working on my leeward rail and crankin it when the board just lost stability and turned left, I fell off and turned the board over and saw the snapped fin. I contacted the distributor and as I hoped the fin was replaced without any issues, fantastic service and comitment. Here comes the dilema, while out the other day the replacement fin snaps again! it had survived more or less the same water time as the first fin. The board lives in my van in a flat secured position with the fins always on the board. They are impecable and have no bangs or scrapes and do not get subjected to any leaveraging. Why have they failed then? Have the manufacturers underestimated the radial force on a 40 cm lever? I must point out that the fins are made from a G10 composite and are heavier than you would imagine just looking at them. If you have held a large G10 fin you will know what I mean. Are they too rigid? or when inserting them into the tuttle enclosure do they reduce them too much in diameter? I hope to upgrade my board and with the price of the fins had considered keeping them to use on my new board, but now I am not so convinced. I imagine they should be bomb proof. I dont jump with my race board just an occasional pop to get over surf while getting out on the water. This should be acceptable use and not undermine the integrity of the fin, well within its working parameters I would have thought? How many fins have you guys snapped? How much abuse have you given fins and they are still intact? I have thought of aquiring a set of top branded fins but could not imagine my animic state if this happened to one of them! The other pain in the ass is that you loose the portion of fin that snapps off. In both cases the fins have snapped at the base in line with the board. If I could retain the broken off piece for evidence I think it would be easier to demonstrate material failure and not operator error.

Awaiting your feed back, many thanks.



WjM.......

Hi,

I have had composite fins snap on me due to the layup being badly done, but so far I have never had a G10 Fin fail at the base. Is it tear off and bend in a straight line at the base, or does it snap of completely and clean?

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Gunnar

From talking with people that do make fins, G10 is pretty much the only thing that will hold up at all. If you ever ride a softer fin, you will understand why it is G10. A flexy racefin makes the ride super unpredicatable..at high speeds that is pretty much the last thing you want.

When you had the board in your car, was it standing on the fins? or did you leave it upside down. Maybe the constant banging from the truck created a weakness in the stiff g10 material?

I've never had a problem with a G10 fin either.

I have seen some people take fins on and off between sessions and keep them protected in neoprene sleeves. I don't do this. But the only snapped fins I have seen were in very shallow water. I try to hop of the board before it gets to waist deep or less.

Thanks for the replies, the board lives face down on a shelf overhanging with the fins not coming in contact with anything. The board is rachet strapped to the roof and cushioned to prevent movment and damage, I am just short of wrapping it in cotton wool! I will take a couple of pictures of the two snapped fin bases, not that it will shed much light on the subject but it might give somebody who knows a better insight. I work with composites and I did see a high resin content on the first fin that snapped but knowing the physical properties of G10 I still cannot understand why they snapped. There was no warning before the fin snapped, when it did it just tore straight and cleanly off the board, no noise or anything the only tell tale is that the board goes all wobbly and you fall off! I have seen high speed wipe outs and boards cartwheeling across chop at speed landing side ways or back to front on the fins and no problem. I have always used large kites as the wind is marginal where I ride and I love the power of a big kite, I just hope I am not pushing the fins too hard! The competition guys must ride a hell of a lot harder than me and for a lot longer, or do they just change boards and fins more often?

I am off to remove the tuttle insert and take a few photos.....

Good winds to all....

WjM...........

High resin content could be the cause of a fin breaking. All the strength comes from the fibres, so the higher the fibre content (provided they are wetted out completely) the stronger the fin.
The resin by itself is brittle.

How are G10 fins made? I was under the impression that G10 is a compressed fiberglass material that comes in sheets, and the fins are CNC cut out of sheets of G10.

Hello again, I have taken some photos and removed the tuttle fin box insert to examine the newly broken fin and it is a lot more revealing than the first fin I broke. If you observe the photos closely the actual width of the fin body is almost double the size of the slot in the tuttle insert. The fin has been machined down 40-50% of its width to fit it into the tuttle box insert. The full width can be seen outlined around the G10 in the slot. The G10 has levered itself apart exactly where it enters the tuttle box insert. The wide body of the fin is machined down to accomodate the tuttle sleeve and where it is bonded in to the insert it has literally torn itself apart. The shoulder of the machined section when under load while riding is trying to lever itself out of the enclosure and because it is bonded in it simply snaps. It is really difficult to describe it, even when looking at the photos but with the actual piece in your hand the answer is very apparent. The distributor agrees with me and hopefully the manufacturers will also. The fact that they have reduced the thickness of the fin by such a large amount does not make sense. It would be more mechanically sound to enlarge the slot in the insert to accomodate the full width of the fin. I recon there is a 5-10º cant on the fin which means it looses even more width than if it was slotted straight into the tuttle insert. If the fin is replaced or not under guarantee remains to be seen, hopefully it will be. The problem for me is that I have two of these fins on my board and I know the exact same thing will happen again sooner than later. I doubt if they will modify the fin configuration for a 2011 board. I can only imagine that they will have to rethink the design and modify it to give the fin the longevity and restistance it should have on the 2012 and subsequent models.

Good winds to all.
I will post again when I get a resolution.

WjM.......

Thanks for the pictures.

That is some of the worst potting I have seen.

Only a small part of the fin thickness is actually potted in the plug.

When I repot fins I put as much of the fin in as possible into the tuttle box mold and then I pour the Epoxy around the fin. I would never sand off so much of the fin to pot it.

If you look at the plug in your pics you can see that the foil part of the fin is really not being supported by the plug.

I have only seen something like this on some Fanatic Windsurf fins years back. And those would also shear off exactly like that.


--
Gunnar

These break because the effective thickness of the fin for mechanical strength is like 3-5mm instead of 8mm or so.
Crap-ufacturing engineers the strength out of even G-10.
They are just saving money by using an undersized blank.
Proper G-10 fins are monolitihic, the base and fin are machined from one blank the size of the tuttle base.
An acceptable cost shaving alternative is to pot the full thickness blade into a tuttle cavity yielding a cheaper fin with similar bending strength to a monolithic one. This isn't a bad thing to do as it also allows tuning cant, toe and rake...