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repair fin cracked at the base

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direnc
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repair fin cracked at the base

Postby direnc » Thu Sep 13, 2012 11:58 am

Hi,

I bought a second hand Cabrinha 2011 raceboard a while ago. Yesterday, while installing the fins I noticed that one of the front fins has a crack where the fin enters the powerbox. How can I fix this? I am thinking of filling the crack with cyanoacrylate glue and covering the whole fin base with a thick layer of epoxy.

Thanks!
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P1060234c.jpg

Tone
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Re: repair fin cracked at the base

Postby Tone » Thu Sep 13, 2012 12:46 pm

get in contact with Cab, that fin looks like the epoxy hasn't soaked into the fin material, carbon kevlar by the looks of it.

if you start adding layers of material to the fin you will only make it very very slow.

look at new fins.

zfennell
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Re: repair fin cracked at the base

Postby zfennell » Thu Sep 13, 2012 5:17 pm

i can't really tell from the pic.
but if fibers are damaged at the base ( particularly longitudinal fibers)
you will not be able to restore any lost strength with glue (regardless of the flavor)

no surprise that fin stresss is highest at the base.

if you need to reinforce the damage, you will need to replace the fibers.
grind out the damage with enough overlap ( 1 in mininum) to transfer loads to remaining material.
relaminate with similar cloth and resin.
sand back to initial contour (unless you're smart enough to make a mold of the surface before you start.
-bill

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davesails7
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Re: repair fin cracked at the base

Postby davesails7 » Fri Sep 14, 2012 12:08 am

Looks like its just the outer coating. I'm pretty sure the fins are g10 with a thin carbon/kevlar veneer. It looks like just the coating that holds the veneer is peeling?

Is be surprised if the fin cracked since these are so short (compared to other fins). I've got the same fins and also have a set of Rista fins which are 50% longer. Seems like the Rista fins are thinner as well.

If there is damage to g10 how do you fix it? Can you see the fibers in g10?

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Re: repair fin cracked at the base

Postby Nico » Fri Sep 14, 2012 2:49 pm

I am afraid that fin has terminal cancer.
No way are you going to be able to fiux that properly.
From the scratches on the Cab logo I gather that fin has seen a bit of mileage, and it probably has had a bit of extra strain from touching bottom. If it is a back fin it more than likely is the reason why it started to fail there.
Without touching it will be impossible to cause this kind of damage, specially not with those cab fins as they are not very long.
Sorry for the bad news, find new fins.
nico

direnc
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Re: repair fin cracked at the base

Postby direnc » Fri Sep 14, 2012 10:57 pm

There are some broken fibers and it's possible to bend the fins a few degrees. This is a canted front fin. I coated both sides of the fin with a thick layer of CA glue. It's no longer possible to bend the fin, but I do not know if it will be able to withstand the stress while riding it. If this reinforcement fails, I'll try fixing it with epoxy and fiberglass cloth.

I am still learning to ride this board, and investing in new fins is not an option right now. Should this fin fail, would it be possible to use this quad fin board with only two fins? Not for racing, but light wind freeriding?

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Re: repair fin cracked at the base

Postby Nico » Mon Sep 17, 2012 3:36 pm

Thats how I use mine, with just the two back fins. A lot more fun and faster on a broad reach.
nico

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Re: repair fin cracked at the base

Postby chipmunk » Mon Sep 17, 2012 8:24 pm

Yep must agree with Nico it’s knackered the only thing you can do is re-pot it
But you will need to cut the old head off it will make it smaller but its better than scrapping it
http://kiteracing.com/Pot_a_Fin.html

direnc
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Re: repair fin cracked at the base

Postby direnc » Tue Sep 18, 2012 9:27 pm

Thank you guys. I am very pleased to learn that it can be used in a twin fin configuration. I'll use it as it is as long as it lasts, and then use only twin fins or just repot them.


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