Just had a sail today and had a fin fail on me. 
Snapped off flush with the deck. Didn't hit anything that I remember and hadn't done a lot of miles on the fin. It was a G10. Just seems odd as has been a good fin until then, well looked after and haven't hit anything or run aground with it. I have other G10 fins that have taken much more abuse than this and still going strong. This one snapped off mid run in the middle of the river,square run powered up with I guess a far bit of load on it. 38cm fin on a 107ltr board and 6.5m sail
Have any other people had fins fail in this way.
yes it does happen, I've had a couple shear of near the base, usually due to a fault in the fin that gives way eventually.
if you retrieved the fin you can rebox it, depending on how wide you want the base, the further you go back with the angle the wider the base will be
Select to expand quotekeef said..
if you retrieved the fin you can rebox it, depending on how wide you want the base, the further you go back with the angle the wider the base will be
Unless those US navy divers recovering those bombs up here come across two fins (think "bird's claw") that I've snapped off sailing, then there's not much chance of me reboxing them 
Toby if you can, post a couple of close up photo's of the material break section you still have. Couple of our failure analysis gurus keen to have a look at what may have beeen the initiation point to the break. Dont rub back or rough up the breakage surface, photo as if if you can.
Yes it happens, and if you are lucky enough to have your front foot wedged in the footstrap whilst performing a Cirque du Solei routine you too can have the delight of damaging knee bits and eight weeks off sailing 
That's one of the reasons I don't like fins with a rear cut away at the base, may save a few spin outs but it's just asking for trouble.
All the load is at the base, that's where the fin should be strongest.
Saying that good G10 should have no trouble handling ordinary sailing loads, there must have been something wrong in the layup
Thanks Toby, thats got them a bit stumped. Other than those black marks on the leading edge, which may have been inclusions in the materal. This will start a stress riser and be the initiation point.
The material showing, looks to one lad to be not fully saturated with product?? Liquid bonding material looks to be short on volume at build point???
A bit hard to tell from the photo, don't forget there's probably a lot of fractured fibres on the surface, this could easily look like unwetted cloth. It would be nice to now run a sander over it to clean off all the broken stuff, that will give a better appreciation of resin content. My initial thought was the cloth doesn't look very parallel as you'd expect from g10, but that could also be the effect of broken fibres.
And I'm not sure about it starting from the leading edge, that edge is above the base, the trailing edge is at the base, I have a feeling it may have started from there. After all that's a lot weaker than the leading edge.
What sort of rake did the fin have?
I think with a raked fin the load is further back due to the twisting vector?
Hi Decrepit.
Yeah not sure either.
Had a look at the break line after Minerals' post and the black on the leading edge is some dirt particles I think.
The fin was an upright slalom fin. Not sure of the exact rake angle and have been unable to find the details online from the company website but they do state that the g10 used is a high quality product, but I guess you can't see the quality of the lay up when you have sheets delivered ready to mill.
Have a few other fins by the same manufacturer and not experienced any issues with these, plus the fact that it is not unheard of for this to happen, as told by others, am happy to stick with them as they are a great product and perform wonderfully.
theres a lot of solid white stuff in the middle ,could be bog, or my guess is not enough resin in the glass, theres also air bubbles, I thought g10 was layers of glass layed up and the pressed with massive pressure to release excess resin,
there for there wouldn't be any bubbles
Keef, I don't think you can tell that from the plan view, look at the profile, it's all broken bits of fibreglass. As I suggested earlier, that needs to be cleaned off before the lay up is clearly visible.
Three fins broke like that under me. All three were "black" fins, and always the same conditions. Going up wind in mefium winds. A lot of lateral pressure.
Since then I only use G10. So far so good.
