Replacing deck

Discussion in 'Materials' started by mariner 40, May 9, 2008.

  1. mariner 40
    Joined: Nov 2005
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    mariner 40 Junior Member

    I have to replace the deck on my sailboat, plywood. I talked to an owner of a repair shop. He thinks I sould replace plywood deck with foam core. Can anyone help me with information on pros and cons of each?
    thanks
    mike
     
  2. PAR
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    PAR Yacht Designer/Builder

    You could do a foam cored deck, but it's more difficult then the way your old ketch is built (plywood decks and structures with a 'glass sheathing). This assumes you have a Mariner built after 1970, when they were 'glass hulled. If it's an earlier version and all wood then you can't easy use the foam cored deck.

    The reason it's difficult to do a core deck on your boat is because the foam has to be completely incased in laminate and bonded to the hull. The head liner side will be very difficult to make and insure a good bond over 100% of it's surface. You could build a mold and layup the inner skin, but this is much more work then necessary.

    Seal up your plywood decking and cabin pieces with three coats of epoxy, then sheath it with the amount of fabric you'll feel comfortable with, after you've assembled it on the boat. The fabric offers little in strength, unless you use several layers, it's really only there to improve abrasion resistance. A good deck surface will have 2 layers of 6 or 8 ounce cloth. The cabin sides don't need as heavy a fabric layup, but the roof(s) do. Fair and paint.

    Attaching the plywood should be easy enough, just screw it down to the beams, carlins and clamps. The cabin structure will likely require some clever woodworking skills (they all do), but well thought out placement of fastener cleats and corner posts will get it done.
     
  3. mariner 40
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    mariner 40 Junior Member

    Thanks Par
    The boat I have was built in 73. Fiberglass mold with 1" plywood decking. Decking was covered with approx 5/16" of glass. I think 2 layers of 1/2" covered with glass is the way I will go. Thanks again for the info.
    mike
     
  4. PAR
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    PAR Yacht Designer/Builder

    Your boat was way over built, you could easily save some weight (not a bad thing) by using two layers of 3/8" plywood. Just tab it in well and insure the sheathing is heavy enough to receive some abuse.

    I wouldn't be surprised if your boat has 1.5" thick laminate along the garboards and an average hull thickness of .75" (or more). This is typical of the Mariner 40 build, very heavy construction and why so many are still around.

    The polyester covered plywood deck and deck structures is a weakness. Not that they didn't make it heavy enough, but the use of polyester doomed it to rot and delaminate.

    I recently replaced a roof on a similarly built powerboat. Since the beams were intact, but the roof gone, I simulated tongue and groove, by using 1/2" bead board plywood (exteior grade, waterproof glue), with the beads facing down, then a sheet of 3/8" marine ply over this, with 2 layers of 6 ounce, set in epoxy to seal it in. The painted bead board looks great, but can't leak. On the second layer of cloth, I didn't attempt to fill the weave, just squeegeed the excess resin off. This produced the look of a canvas covered roof, but with the toughness of cloth and epoxy (under paint of course).

    The nice thing about epoxy is it's so much stronger then poly and it sticks much better too.

    You could also use the same bead board trick on the deck (again facing down), with 3/8" inside and a 3/8" sheet over this. Skin this with two layers of 'glass then bed some teak or pitch pine strips for a natural wood deck. This is more work, but it's a great look.

    You have a number of options. Post some pictures, I haven't seen the nice clipper bow of a Mariner 40 in a few years.
     
  5. FAST FRED
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    FAST FRED Senior Member

    The polyester covered plywood deck and deck structures is a weakness. Not that they didn't make it heavy enough, but the use of polyester doomed it to rot and delaminate.

    I would disagree , the deck covering is not the cause of rotten plywood , the breakdown of the sealants at chainplates , windlass and stanchons or any other penitration that are not rebedded at defined intervals causes leaks.

    Get any wood wet and dry often and it leaves.

    The epoxy is a fine glue , and very strong , but it wont help the ply rot from leaks.

    FF
     
  6. PAR
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    PAR Yacht Designer/Builder

    Yes, the penetrations into the ply that weren't addressed (bedding hardware, etc.) caused moisture ingress, but the plywood rotted because polyester doesn't seal wood very well. Polyester doesn't stick very well to wood either.

    Fred, you're correct in that most of the time, these issues are maintenance related, not necessarily materials.
     
  7. Steve W
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    Steve W Senior Member

    I agree with Par on the way to do the repair,2x3/8" layers is enough, 1 layer of dynel is enough,survives dropped winch handles etc better than glass and nice to use,especially if doing the deckhouse.Ive also used the beadboard method and it looks great,ive also made my own beadboard where ive used 4mm okume and run the beads on a tablesaw using a sears molding head when ive wanted the look but in a ply/foam/glass sandwhich for lighter weight.We have a cold molded boat in the shop right now with a deck of 6mm ply,3/4" klegecell and 2 layers of 10 oz glass in epoxy which has a leaking prism and its held up much better than any other cored deck ive seen.
    Steve.
     
  8. mariner 40
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    mariner 40 Junior Member

    Where can I find good instructions on installing a new deck? When I bought the boat, I had a different lifestyle, now, if I get the boat fixed, it will be on a tight budget. Does anyone know a person or people interested in doing the repairs at a reasonable rate?
    mike
     
  9. PAR
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    PAR Yacht Designer/Builder

    There are a number of books covering the various different repair and building techniques and methods. I don't know of a specific deck repair type of text, other then previous threads here.

    There will be several skills you'll need, during the deck and cabin structure replacement process.

    If you're on a tight budget, then doing as much of the work as you can will be your biggest savings. Shop rates vary, but none can compete with a dedicated owner, willing to perform the tasks for themselves. I don't know enough about you area to comment on the availability of qualified shops to perform your repair, but labor costs will surely jack the cost up substantially.

    Dynel is a nice fabric to drape, especially on curved decks and deck structures, but it uses a lot more resin then cloth. A budget build would benefit from a just cloth approach, with Dynel or Xynole being better materials, but more costly to apply.
     
  10. mariner 40
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    mariner 40 Junior Member

    Here is the repair steps as I can best determine: Remove all old fiberglass where deck was glassed to hull. install 3/8" plywood, to deck supports using epoxy and screws. install 2nd layer of 3/8" plywood using epoxy and screws with all seams seperated. use 1' plywood for cabin walls. use two layers of 3/8" plywood for cabin top. All plywood cut to size and encased with epoxy prior to installation. Where the plywood meets hull sides, should that area be filled with thicken epoxy to seal? Should I try to use one continous sheet of glass to cover deck or overlap seams? Due to health reasons, I will not be able to do much work, only watch. If I can determine correct installation methods, I will hire indivual who wishes to learn as he goes. The other option I have is selling or parting the boat out and buying a smaller one ready to sail. I really like this hull design. It's slow but, I not in a hurry to get where I am going. Any help will appreciated and please do not get upset with my ignorance.
    mike
     
  11. the1much
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    the1much hippie dreams

  12. PAR
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    PAR Yacht Designer/Builder

    Mike, you're on the right track and no one is getting upset about your questions, it's why we're here.

    The cabin sides will benefit from the same double layer of plywood as the deck and cabin roof. The advantage of using a double layering is you don't have to scarf the seams or other wise go to any big difficulty sealing them. This of course assumes the seams in the plywood are well staggered.

    If you're going to job it out, costs will soar as labor, particularly skilled isn't cheap.
     

  13. mariner 40
    Joined: Nov 2005
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    mariner 40 Junior Member

    I hope it will be livable spending about $40,000 on repairs. I have to see how it goes. thanks par
     
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