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Breaking Monofin

Discussion in 'Freediving Equipment' started by mattbigblue, Mar 18, 2010.

  1. mattbigblue

    mattbigblue Limitless - Mateusz 'Matt' Malina

    Local Time:
    6:07 AM
  2. diver87

    diver87 Active Member

    Local Time:
    5:07 AM
    Hey Matt,

    That looks bad...
    one possibility is to drill a hole at the end of crack that it can´t get bigger. but maybe not the best?
  3. REVAN

    REVAN The Right Stuff Supporter

    Local Time:
    10:07 PM
    That’s a tough one because it goes under the rubber leading edge cuff. I don’t know if you can peal that back to get access to the composite blade underneath or not, but any good repair would remove the entire crack including the part you can’t see. However, you can always experiment to see how well something works.

    The first thing I’d do is stop drill the crack. Then I’d take a 90 degree high speed hand held grinder with a 1 inch 80 grit sanding wheel to scarf-sand the crack down to a knife edge on both sides. Try to slope it about ½ inch per layer of fiberglass if there is enough room for that. Like I said if there is a way to remove the leading edge cuff, make the repair and then glue it back on again later the repair will be much more likely to last.

    Once you have sanded away the damage, you need to lay-up fiberglass to replace the missing material. Taper the layers to match your scarf sanded slope. Try to find a glass weave that looks like what was used in the original panel and lay it up using the same warp alignment if you can tell what that was. Usually you can see evidence of the alignment in the different layers where you sanded through them. Since it broke before, I’d put down a couple of extra layers beyond what it originally had. If you are not repairing the hidden part of the crack, I’d consider doubling the number of layers for the first 2 inches of the crack and then taper it down from there along the length of the crack.

    To make it strong and flexible you need the right ratio of resin to fiberglass. By weight, you don’t want to have more resin in the repair than you have fiberglass. Too much resin will make the repair brittle. The best way to not have too much resin is to bleed it off. Look into techniques for vacuum bagging composites for details. On something like this you can achieve similar results without the vacuum bagging by laying up the bleeder layers and then clamp pressure plates over the repair until the resin cures. The alternative is to just do a wet layup. Weigh out you resin so that you don’t apply too much and try to work out all of the bubbles as best you can with a paint brush. It won’t be as strong and flexible, but like I said, you can try it to see how it goes.

    If this sounds like a lot of work to you, it probably is and your time may be better spent working extra shifts to afford a new monofin. However, if you know what I’m talking about and have access the tools needed, it really is not that bad of a job. With all the necessary equipment at hand, this should be a job you could do in about 3 or 4 hours. If that is not the case, you could spend a lot of time and money just getting the tools and supplies together only to make a repair that might not last.
    Last edited: Mar 18, 2010
  4. mattbigblue

    mattbigblue Limitless - Mateusz 'Matt' Malina

    Local Time:
    6:07 AM
    I think i will not fix it myself cause I don't have any tools.will contact manufacturer and work it out.

    The thing is on Saturday I have big competition that I was preparing a lot. Is there anything I can do just to make one dynamic with these monofin?
    Should I drill a hole at the end of the crack?if yes how wide? And what easy accessible material I can use just to make temporary filling for one long dynamic?

    Thank You

    Matt Malina
    Posted via Mobile Device
  5. REVAN

    REVAN The Right Stuff Supporter

    Local Time:
    10:07 PM
    I would not use it as is, because the crack will continue to propagate. The only question would be, how fast and will you be able to finish the race before the fin stops working well enough that it is even worth trying to race with it.

    The first thing to do is to stop drill the crack. I’d make it at least 0.25 inch and maybe as much as 0.5 inch in diameter. Hopefully that will at least stop the crack from propagating for a little while.

    Without actually repairing the crack, you may be able arrest the crack propagation better still if you can find an effective method for distributing stresses around the hole you drill. You could go to the hardware store and look for big fender washers (1 to 2 inches in diameter) and a really short bolt. Put the bolt through the stop hole you drilled with the washers sandwiching the composite panel and pinching it tight. This may keep the panel from flexing and straining the immediate region near the stop hole at the end of the crack. You could even go as far as to put some epoxy under the washers to also bond them to the panel, but you may have a hard time getting them off again if at some point you want to try to do a better repair.

    If you do try bonding them, sand the surfaces of the washers and the region of the fin blade they will be contacting to rough them up and clean them with acetone to remove any grease. If you can’t get acetone, at least clean it with soap and water followed by rubbing alcohol. It would also be a good idea to soak the washers in acid to etch the surface microscopically. Once cleaned, avoid handling the bonding surfaces with your bare hands or you will put grease back where you just removed it.

    I hope this helps, and good luck.
    Last edited: Mar 18, 2010
  6. mattbigblue

    mattbigblue Limitless - Mateusz 'Matt' Malina

    Local Time:
    6:07 AM
    Together with my friend, we fixed it.


    I took 2 stainless steel plates, cut them in shape.
    At the end of the crack we have drilled a 2mm hole just to stop the crack.
    Then we drill 6 holes as You can see each one 4mm. Connect plates by rivet aluminium bolts. Rivet is better than welding, people used to built bridges this way in the past, and now they are going back to this technique. I think it should be stronger than before.
    After a while I will post here more details how it works.