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Cracked blade - can this be fixed?

Thread Status: Hello , There was no answer in this thread for more than 60 days.
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oferdegi

Process Oriented
Sep 29, 2005
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Well, shit happens:

Down at the pool, I lay all my stuff in a nice pile at the poolside & went in for warmup. Some time later, I grabbed my mono & had a great training session. Then, at home, as I rinse down my stuff, I notice a 4 cm lengthwise crack in the trailing edge, about 1/3 of the way width-wise. It's not just a crack or a scratch, the blade is actually broken through! :waterwork :waterwork :waterwork

I'm very careful with my turns, etc. and take really good care of my gear - the only possible cause I can think of is that someone just stepped right on the blade, over the uneven tiles of the poolside, and sheared the edge.

Now I wonder:

Can I keep using my mono, or the crack will just extend & split the whole blade through?

Can something like this be fixed, & how?

Is there anything I can do short term to stop the damage from extending - maybe drill a round hole at the crack's end?

If this can't be fixed, maybe it would be a good idea to widen the crack into some kind of small rounded "bay", and make another identical "bay" on the other side, for symmetry. This would prevent the crack from extending, but weaken the blade's trailing edge in general, & probably make some unpredictable hydrodynamic changes.

I'd really appreciate any opinion & advice.
Thanks,
Ofer

BTW, it's a WW model 2, middle distance - a fibergalss fin, pretty hard. It seems like it's pre-tensed in some way, because it has a complex curve to it, & different flexibilities in up/down bending. the break actually spoils the curve already - I just can't make it sit back in place & have it's nice old curve...:(
 
Well, I took my poor mono to work & took some pictures of the damage.
Here they are:

IMG_6962.JPG IMG_6965.JPGIMG_6968.JPG
 
Since the stresses on this part of the blade are low, I think that a simple patch with the thinnest cloth (model boat stuff) and epoxy would work. Maybe on both sides. The main thing is probably to make sure that the crack doesn't spread.
Aloha
Bill
 
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Appart from a patch on both sides, one needs to drill a hole at the end of the crack to lead the forces arround and prevent further tearing.

I've a crack in a fin like that, patched it, and it still works great.

Perhabs show and report your result, for future monofinners who may face a similar problem.

Kars
 
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Thanks Kars & Bill, and special thanks to DeepThought that PM'd me some good advice, too!

I took the mono to my finswimming coach, Alex, and he showed me a quick and efficient fix for the problem:

First, I drilled a nice round 4mm hole at the end of the crack, to disperse the tensions & stop the crack from developing. Then I just slapped a strip of duct tape (strong adhesive tape made of fabric) on both sides, to keep them together. I've been shown a fin fixed like this several years back, and still doing well, with a change of tape now and then. Alex said that patching the crack with fiber may create a stronger area, leading to a break at another point. I'm pretty sure it could be patched nicely, but that needs some very fine workmanship, and very thin fiber, like you suggested, Bill. Anyway, I'll try it out tomorrow, and see what it's worth. When I'll get my second mono, some time in the future, maybe I'll be able to spare this one for a few days & round up the patience to do a more permanent fix, or find some professional to do it for me.

Thanks again,
:) Ofer
 
I don't know if there are a lot of atoumotive body shops in your part of the world, but most body men are pretty good at fixing things with fibreglass. so that may be some thing to look into. Or if there are some boat builder there around you, they use a lot of fibreglass in their work also.
 
Last edited:
Good info Ofer. When I drilled fiberboard, it had a copper coating and seemed brittle. Did you use a glass drill or do anything special?
Aloha
Bill
 
Hello. I was looking for something to read tonight and i found your thread. Let me tell you what I have done to my monofin when it went into something pretty like yours.

I was thinking about drilling a whole, putting some fiberglass on it, but in the end my dad came with a wonderful idea, maybe it will not sound that good, I was not sure about it, and in the end it went ok.

We've cut the whole piece of the fin, like 1'5mcm on the blade, the crack on mine was like one cm long, my monofin feel great even though it is a little bit shorter than before.

Maybe it can work on yours too... give it a thought!!!
 
Well, Bill, the material on my mono seemed quite soft, actually. I just put some masking tape on bote sides to hold the top layer from snagging, and used a new set of drills. Went from 1 mm up to 3.5 or 4, and used the fastest speed on my drill. It came out just fine. If the mono works well, I'll take the time & put a bit of epoxy on the exposed edges, so that the water will not seep in through them - I'm not sure this is significant for monos, but that's what I would do on a boat.

Hi giovapnea. The crack on my fin was about 4-5 cm long. I think cutting that much off would have altered it to the worse - it's quite a hard mono even now, and that would have made it even more rigid. I thought of cutting two symmetrical rounded "bays" in the trailing edge, taking off the cracked area and another one on the opposite side for symmetry. But that's an extreme measure, I hope to get along without it.

good idea, hardhat - I'll look into it. I also thought about model builders, that can do really delicate work with thin material.

Thanks, and great diving to all,
:) Ofer
 
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Dear Broken fin guy,

I am a composites engineer so have alot of experience with this type of thing. Drilling a hole is a very good thing. Small is better and if the hole is raged you can wrap sandpaper into a tube and smooth the holes sides so it looks better. Then add tape but first clean with alcohol to get tape to stick. Try "3M 375 Packaging Tape" its really expensive clear shipping tape and works great for things like this. Cut the tape with the corners rounded so the corners won't peel and it will look better too. Use two plies of tape with one a bit wider like a wedding cake stacked up if one ply doesn't seem strong enough or tears. The tape should hold up well in the water though I am not 100% sure on that. Here is a link that shows the tape. They sell it at Wal mart sometimes too.
http://www.mypencil.com/mall/page12PackTapeDispenser.asp
Attached is photo of the tape
 
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Thanks wes - I found out that the duct tape was the weakest link in my quick fix - the fin was grrat to use, but the tape started peeling off after only 30 mins in the water (even though I cleaned the area very well with alcohol). Anyway, I've asked around and in a couple of days I should have 4-5 samples of different kinds of tape. Maybe you're right and I shouldn't go for fiber laminated, but just tough, thick plastic tape - if I see the fiber-based tapes fail, I'll try to get some of that stuff you've recommended. Is it very thick?

Thanks for your input on my training thread, too!

Cheers,
:) Ofer
 
Ofer-

You were on the right track with the duct tape; however, the fibers pull water in via capillary action. I have used the stuff for years as a quick fix for fins, surfboards, etc...but the biggest downfall is exactly what you have found --the silver cap to the tape quickly comes off. BUT, the new clear duct tape uses plastic fibers that do not pull in water. This stuff is great and has held extremely well for me. The best tape for the water that I have found by far.

Good luck-
Matt
 
Ofer-
The 3m 375 Packaging Tape I think is 2 mils or 0.002" thick. This is thicker than most cheap shipping tape but not super thick, maybe same thickness as 2 layers of thin masking tape or one layer of thick high quality masking tape. Another option would be clear "mylar sail repair tape", this is clear plastic tape with waterproof adhesive. You can do search online for it.

Cheers Wes
 
Thnx folks
i have same problem with my bi-fin i ll repair and i ll use it same way :)
 
Well, in the end I found a tape that's actually an adhesive aluminum strip (just sheet metal, no fibers). It adheres very well, but after 2 hard training sessions I see now that the aluminum is starting to break along the crack. The stuff just undergoes fatigue and is not resilient enough (though I can try to double it to slow the process down). Back to the fibered tapes, I guess, of which I have quite a few samples by now.
The "mylar sail repair tape" sounds like the perfect solution - thanks, wes! I'll look it up on the web (probably costs its weight in gold...).
Will keep you all posted,
:) Ofer
 
On impulse, I've just ordered some mylar sail repair tape - seemed like the right kind of stuff: salt water & UV resistant. Most important, it comes with a lining that you peel off before sticking on, so you can cut & shape it to size beforehand - it was very awkward to shape the adhesive tape with scissors while sticking it on, didn't come out too nice, either. Now this stuff is transparent, too - pretty cool!

Here's the link to where I bought it:
http://www.powerkiteshop.com/accessories/mylarrepairtape.htm

Happy diving!
:) Ofer
 
I have had the same damage on my mono, but instead of a tape I used a thin rubberfilm from a tube inside a biketyre and glued it onto my Waterway monofin with superglue on both sides of the fin. This has worked very good for almost a season with cw diving and pooltraining. It does not show any sign of coming apart yet.
 
Thanks, Aber - I was thinking along similar lines as one of the possibilities - something like using inner tube repair patches on both sides. Never thought of superglue, though.

By now I'm so given to experimenting with this, I'm just sure I'll find the best solution in the end. Meanwhile, I just enjoy trying different stuff. Guess I'm just a frustrated scientist at heart.

Cheers,
:) Ofer
 
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