Outward flange repair strategy

Discussion in 'Boat Design' started by ChadRider, Feb 4, 2013.

  1. ChadRider
    Joined: Oct 2009
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    ChadRider Junior Member

    A Precision 21 sailboat with the port hull to deck joint badly damaged by rubbing against a piling in a storm. Two options:
    Repair in place - Means rebuilding the flange on the hull and the flange on the inner liner pan AND rebuilding the molded toerail on the edge of the deck without easy access to the back. Good: no major disassembly. Bad: hard to get a this area from the inside.
    Remove deck - Means hundreds of aluminum rivets and then prying open the 5200 sealed joints. Good: get to peel the moldy carpet off the inner surface with the deck where I can get at it, get to repair both the deck edge and the hull flange with full access. Get to easily fix any wet core. Bad: hundreds of rivets, 5200, keeping everything straight when putting it back together.

    Opinions??

    Thanks Chad
     
  2. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Welcome to the forum and yep, storms suck sometimes.

    There are less then 200 rivets in the flange joint on your boat (approximately 60 - 70 per side). Removing the deck cap and liner is a daunting job, particularly for a novice. They rarely come apart without more damage, though with care this can be mitigated to an acceptable degree. It's also unlikely you're repair the extruded rub rail. Replacement rails can be had, likely the exact same one, though these aren't especially inexpensive.

    3M 5200 can be loosened with heat, or cut. Trying to pry the joint apart, usually just breaks stuff. I use a home built hot knife, made from an old hacksaw blade. A heated putty knife works too, as does lot of elbow grease and a utility knife.

    I'd recommend some photos and a would suggest you're best advised to consider the exterior repair option.
     
  3. ChadRider
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    ChadRider Junior Member

    Hey, thanks for the quick reply. Yes, the hotknife seems like a great idea. I know someone who has one he uses on car windshields. Might be too thick though. I took some 5200 apart on my last boat with heat and it worked well. I'll snap some pics tomorrow and put them on here.
     
  4. ChadRider
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    ChadRider Junior Member

    Pics of the offending flange

    First one pic and then another. As you can see the flange was pretty mangled.
     

    Attached Files:

  5. ChadRider
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    ChadRider Junior Member

    The worst of the damage

    This is the worst area. The edge of the deck is smashed, and the flange is worn away.
     

    Attached Files:

  6. viking north
    Joined: Dec 2010
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    viking north VINLAND

    Had to do the same repair on a 19ft Halman/Nortica. I went at it from inside and glassed over the hull to deck joint. --Pain in the neck to get at especially up in the bow section but with a helper passing me wetted out GRP strips served on a piece of 1/2" in. mdf I got it done. Next I went at it from the outside cutting the flange completely off and again glassed over the hull to deck joint building up a heavy layer which allowed me to attach a rub rail. I was fortunate that the boat did not have a liner. ----
     
  7. philSweet
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    philSweet Senior Member

    From any sensible standpoint, the boat is totalled. If you want to have a go at learning boat repair, that's a hell of way to begin!

    you need a covered workspace for the better part of a year.

    you need the cooperation of the manufacturer, and you need them to splash you a piece of deck to replace the chewed up area. That won't be cheap. You need to strip out about half the boat's interior. The hull needs a thorough going over to detect delamination and damage. Is the hull cored, or just the deck?

    Personally, I'd say it's just a P21, and go find an abandoned hulk that can be buffed out and then transfer all your goodies onto it. Its the difference between sailing this year or sailing next year. Of course, we don't always do the sensible thing, else we wouldn't have a boat to begin with- would we?
     
  8. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    What percentage of the flange and deck cap is misaligned, after the damage?
     
  9. ChadRider
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    ChadRider Junior Member

    Yep, it is totalled!

    Paul, about 8' of the hull/deck joint is crushed and the deck as sprung up away from the deck.

    I know this is a big repair. I am leaning toward putting the whole thing in my garage and yanking the deck off, yanking the liner out and rebuilding each where I can get at it.

    My plan with the deck is to putty it up so it LOOKS right and then use that to make a mold with which to make a replacement for the crushed part. Then I'll build myself a new skin in the female mold and then graft the new section of deck back onto the old deck replacing the crushed part. I actually will talk to the Precision folks. If they can save me a month of screwing around it might be worth some $$ to me.

    Then I can bolt it all together just the way it was done originally.

    I have been looking for a second P21 from which I can put together 1 nice one. So far no good.

    Chad
     
  10. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Find a P-21 to pull a couple of molds from . . . Over them a nice buff and wax as you borrow their boat for a weekend, while the goo sets up.
     
  11. Red Dwarf
    Joined: Jun 2012
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    Red Dwarf Senior Member

    Can you post a picture of the same area on the undamaged side? I would like to see what the shape was before the damage.

    If the shape is fairly simple you could recreate the damaged area in wood. You could use the undamaged opposite side for templates. Make many templates from a thin material and it is easy to flip them for the mirror image you need. Once you are happy with the shape, make a mold and create a replacement section.

    Good luck.
     

  12. ChadRider
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    ChadRider Junior Member

    Good ideas

    Both are excellent suggestions. I like the idea of not having to spend a lot of reconstruction time on the existing edge only to cut it off.

    The wooden plug has the advantage of using materials (and a boat) that are right here. No time pressure, no surreptitious removal of someone else's rub rail, etc.

    The mold off an existing boat has the advantage of avoiding all the modeling of the wooden plug, gives a more exact mold, and is faster. But, ...

    I guess I just have to start getting dirty. If I can get both the deck and the liner out before the end of March I'll be pretty well lined up to get this done. If I miss that milestone, I know I am in for a long haul.

    Thanks
     
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