Formula fins wearing out?

Out for a little tune-up racing with a couple of friends yesterday, and I noticed that the board felt a little differently on starboard tack than it did on port. I wrote it off to mis-adjusted harness lines. This morning when I examined the fin prior to wetsanding out a scratch at the tip, I noticed what looked like scratches at the root. I wondered how they might have gotten there. On closer examination, I discovered that they weren't scratches, but cracks where the skin was failing. The fin was in the early stages of breaking, and when I bent it under load, it deflected about 35% more on one side than on the other!!!! It's a relatively new 70 cm Curtis that came with the board, which was delivered in June. Granted, I sail a lot, but should a fin wear out that quickly? Worse news. I examined my older (one season old) Curtis 70 cm, and it too has delaminations at the root. Worse news yet, my sailing buddy (who has since switched to Deboichet) has cracks in the root of his Curtis 70 which came stock with his F175 last year. Should these fins be covered by warranty? Is anyone else having trouble with Formula fins?

Check your fins guys. Look for scratches and light spots about 3' to about 1/4 inch from the root. Nothing like a broken fin 3 miles downwind from home (except a broken mast or boom).

Frank Weston

Frank,

I check mine all the time and have not seen this. I did crack one trying some early little jumps with a Formula board

Yes, I have a similar problem (small cracks) w. my stock Curtis 58cm fin, which came w. my F155, and it's only about half year old! (and I am only 70kg's). I admit, I sail it sometimes in quite overpowered conditions (in 20's knots), but I think it should sustain this. I also have 65cm stock Curtis, but sailed it only several times. Now I regret I bought this extra fin from Curtis line. I too wander if I can claim the warranty w. those fins,

Lightening/cracking.scoring of the fin root can foretell fin breakage. Curtis fins are not alone in developing this look or problem. Except for some plastic fins, every fin I've ever owned has developed stress cracks in the root. Even the flexible glass wave fins get this condition over time. I've had exactly one fin break in this fashion, but I usually don't keep them long enough for that to happen a lot if it would.

Frank: Is your fin painted? Or skim coated in any way? Is this the stuff that's causing problems? Sounds worse than that, though. If it's really deflecting 1/3 more on one side than the other, trash the fin.

frank, I have exactly the same thing on my curtis 70 that i bought for use on my starboard 175. the fin had maybe 15 or 20 hours on it, as i was mostly using the stock 65. i am only 160 lbs, so i don't load my fins up so much. the stock 65 has probably ~200 hours on it, but it is fine. i think that jim k is looking into warranty possibilities.

jeff feehan

Stock Curtis that comes with the board. No paint. Believe me, there are cracks that are structural, not cosmetic. From just the few responses this morning, seems like this is a pervasive problem. I expect fins to fatigue and get soft, but not so much that damage is visible and apparent after only a few months of sailing and no abuse.

We'll see.....

Frank Weston

I have 3 other fins (MauiFin) used w. my small board. One of them is a G10-Carbon, 28cm, the other 2 are G10, 24&32cm. They've been used for 4 years, B&J, higher jumping, and even unintentional hitting of some objects. There are absolutely no signs of cracking in them. Right, these are much shorter ones, yet... I have no experience w. other long (58+) fins but only w. stock Curtis/Starboard. But, I would expect the longer fins from whatever the manufacturer to be more durable.

Hi Bill, it sounds like these materials behave a bit like reinforced concrete. Although it sounds like Franks fin has actually gone further based on its new found flexibility.

A reinforced concrete beam WILL crack on the tension side - even at small loads. This is normal behaviour, and the concrete microcracking is what allows the steel to take up the tension load.

I can see the parallels with fin materials - the resin does the same job as the concrete ie making the members shape, keeping the reinforcing in place and stopping it buckling, as well as taking the compression load. And the carbon etc does the same job as the steel by taking the tension load before it cracks the resin/comcrete too much.

The only difference is that resin would have a higher tension strength than concrete. Concrete's tension strength is almost nothing. I suppose this would mean that the resin would need a higher load to start to crack.

Or am I completely off base?

Cheers

Jeff, the load that goes into a FW fin is mind blowing. I can hardly believe it that they hold on for a single leg! A few months of regular use is enough to send a high aspect racing fin to its maker. I haven't read down the thread far enough to see Bill Kilne's response, so he may say I'm full of it.

I had the stock Curtis 54cm fin of my Starboard GO EVA (the original one) cracked after 1y of regular good usage. This fin has a yellow paint job on it which is clearly cracked on both sides of the base. Difficult to tell though if it is only the paint that has cracked or also the main structure (I might try to sand the paint off to check). Also difficult for me to tell if it influenced the behaviour of the fin, I honestly didn't notice (I didn't even know about it then).

I had asked back then both Bill and our local Starboard importer what this means, I received a rather vague answer that they had never seen such a fin breaking under normal conditions, no further details though. As I didn't want to test my luck, I didn't use this fin any further afterwards.

In the meantime I am using a Starboard F155, there the Curtis 58 stock fin is keeping up the pace till now after >1y of decent usage (although I mostly use a longer model since recently).

Strange that this thread is not receiving any (similar) input from non-Curtis users, or is Curtis the only fin used in big quantities???

Regards,

yes, the loads are probably very high, even in 'normal' use. but i suspect that a lot of damage is done in very short periods of extremely high load, like when much of the fin clears the water when the rider hits a piece of chop wrong while beating.

anyway like i said, mine had probably 15-20 hrs on it, and i only weigh 160lbs.

i don't think mine is as bad as frank's, i haven't noticed that it bends differently on either side. i do have the cracks that he described. i am afraid that the whole thing will break off.

jeff feehan