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Monofin repair (glass fibre)

Thread Status: Hello , There was no answer in this thread for more than 60 days.
It can take a long time to get an up-to-date response or contact with relevant users.

nenrandir

Well-Known Member
Sep 16, 2011
82
5
48
Some days ago I discovered that the blade on my monofin has broke. Any ideas on how to repair -- or will I have to resort to duct tape? ;)
 

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Don't know much about repairing monos in particular, but a modest amount about glass and stress.

You need to determine why it failed and how far the damage extends beyond the crack (it might be a lot). Looks like maybe the blade is Ving when you stroke it, with the stress concentrating in the center. Assuming that is the case (it might not be), figure out how many layers of glass in that area of the fin and get some similar thickness glass cloth and good quality epoxy. The manufacturer should be able to help with that. Then think about how to spread the stress. Very carefully sand down the area where it is damaged and an equal area beyond the damage Think an inch or so. Layer in cloth and epoxy, carefully squeezing down the composite to get the minimum resin content. When you have refilled the sanded area, extend the reinforcement at least another inch or two along the trailing edge of the blade. Build up the edge so that it will resist future bending to failure. Extend this layer up the center of the fin for the same reason.

What you are trying to do is add just enough stiffness to the smallest possible area of the fin so that the fin will not bend to failure in the future. You probably want to do this in stages, testing the fin as you add glass. Do too much and you will change the action of the fin, not necessarily for the better.

Finally, think about your technique. It may be that changing technique will reduce bending forces on the fin.

Good luck with it. You have a tricky job in front of you.

Connor
 
An additional thought.

It might not be a bad idea to try a band-aid, first. There are several post/threads in this forum that illustrate gluing a cover over the crack. Much easier if it works and if it doesn't, the necessary glass work is not greatly increased.

Connor
 
Thanks for this Connor. I contacted Leaderfins and they were, as always, fast to respond and they will send repair stuff. I'll see what I can work out following your instructions.

Technique may indeed be an issue, I'll have to look into that more closely. It looks to me like it is a stress issue rather than impact, some self-scrutiny (and filming!) may be in order.

I tried to search the forum for repair ideas but didn't come up with any threads. If your forum-fu is more developed than mine, feel free to link :)
 
You might want to ask Leaderfins for their advice. They have almost certainly seen this kind of thing before.

Connor
 
You might want to ask Leaderfins for their advice. They have almost certainly seen this kind of thing before.

Yep, did (above: "I contacted Leaderfins and they were, as always, fast to respond and they will send repair stuff"). I also asked for advice on how to repair. I'll see how this compares to your advice and try to make something of it. Reports will follow (if anyone's interested...)!
 
Hi,

If it broke because of V effect then it is to soft in the middle and it will cause problems in the future as well, even if you put over rubber, fiberglas, epoxy etc.
Only smart solution in my opinion is to cut it in the shape of dolphin tail fin as it should done as original design of the monofins.
If it is too hard after, sand it or cut the few layers off.
All the best.
 
Last edited:
Got a repair kit from Leadersfins, they suggested patching on some rubber. I'll try with this first, if it doesn't seem to work the dolphin cut sound interesting...
 
In my experience (25 years) this is what I would do.
let me know if you need any help.
 
I had this happen on a stereo fin. I purchased nice carbon fabric and wraped both sides with it and added a lot of pressure while cured. The crack in the is fixed, extra strong in the back, and didnt affect any of the fin stroke. I think it helped, if anything.
 
Update some time later: I repaired the fin with a rubber patch, only to see it break again a few uses later. I guess the rather extreme V-shape the blade gets when kicking stresses it too much. I've now done a dolphin cit which seems to work, but it has worsened the V-tendencies and reduced the blade area significantly...

Ergo, new fin.
 
Here it is, the dolphin cut hyperfin, in quite nice surroundings...
 

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How does it swim?

A v-bend isn't necessarily a bad thing. In fact, quite the opposite!
 
I'm sure it can do its job, in my case though it feels like an already flimsy fin got even flimsier. I've tried out other fins (eg Waterway glide) and they have delivered a different kind of performance that I think suits my style better.

But we'll see, I might be entirely wrong about it...
 
Try focusing less on strength and more on fluidity and technique in a pool.

That fin might surprise you!

I like my (fairly stiff) Starfins because it really snaps back when I put a good flex in it.

I would like a softer blade for relaxing, gentle, flowy dynamic... Instead of an athletic and purposeful one tho.

Enjoy it! Less knee bend and more core undulation.

What size is it... In case you don't like it? ;)
 
broken, repair
 

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Hi, well, a bit too late, that's true, but good that you brought it up anyway if someone else feels more handyman than I do ;)
 
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