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  1. #1
    Join Date
    May 2011
    Posts
    2

    Ski Boat - Floor Replacement

    Hello, I have a 1989 Ski Challenger with a rotten floor. I have torn out the floor and am seeking the most economical, but still durable, solution to replacing the floor. The carpet is in good shape so I do not care about looks.

    First question:
    1. Marine plywood v.s. PT plywood? I plan to cover it with fiberglass and resin anyway so does it matter? The research I have made states both use the same glues but pressure treated will have voids in the plys. Will this matter if I seal it with resin?

    2. What is the best and most economical resin to use to seal the plywood prior to installation? I have previously used the West system, which works great but was not cheap. Are there acceptable alternatives?

    3. For the floor, I understand the top should be covered in fiberglass. Should the bottom also be covered? Does the fiberglass aide in sealing the plywood? What is the ideal type of fiberglass? (woven sheet, mat, etc.)? It appears the original plywood was painted with a white sealant paint and stand fiberglass put lightly on top.

    Anyway, I know this a lot of questions but any answers are greatly appreciated. We do not have much expertise in my area and I have heard nothing but good about your store.

    Thank-you,
    Chris

  2. #2
    Join Date
    Mar 2001
    Posts
    399
    Real Marine Plywood is made with water and boil proof glue, you can check this by boiling a sample for an hour or so. Some lumber yard plywood advertised as water proof is actually water resistant and will come apart when boiled, or exposed to the damp environment of a boat bilge for a few months. Marine ply is also void free in the cores so no place for water to collect and therefore initiate rot. Marine ply usually has more plys than Fir and is made with Mahogany so is also stronger. Pressure treated plywood is very rot resistant, but the carrier for the fungicide is usually petroleum distillate/varsol that affects resin adhesion so does not work well with epoxy and polyester resins. Exterior grade (boil a sample) non pressure treated fir ply will work if you can find some that is reasonably void free.
    When installing a new floor in a fibreglass boat the plywood needs to be fitted with a bevel that matches the hull, but with about a gap, use a 3M Bubbles/Cabosil mixture with resin to fill the gap when you put the floor down. Use a mixing stick or cut a plastic spreader to make about a radius fillet between the floor and the side of the hull. The floor needs to be fiberglassed to the hull, this keeps water out of the bilge and helps stiffen the hull. You can just use a 4 or 6 tape, but if you cover the whole floor and run the glass 3 or 4 up the side of the hull it will also protect the plywood. The manufacturer probably used 1.5 oz mat and polyester resin because most of your boat was built with this combination, however this resin does not stick well to wood. Epoxy is easier to use for repair and works well with wood so is usually used for retrofits, however it does not work well with mat so go to 6 oz or 10 oz cloth. You can put the floor down with the fillet, let it cure and sand before fibreglass, but it saves a step if you do the glass right on the wet filler.
    For finishing your floor either sand and paint, glue down carpet, or Seadek peal and stick is easy and works well. You can also roll down thickened gelcote to make a non skid, but gel does not stick well to epoxy so you may have some chipping.
    Boat floors usually rot from the bottom up so if you want to seal the plywood use epoxy after you have done all the fitting and trimming, use at least 2 coats, being sure to seal exposed edge grain. System 3 makes an excellent penetrating epoxy sealer called S1, but any high solids epoxy such as East, West, MAS, or System 3 will work. These are all quality epoxies but East System is a little less expensive, good stuff, just no money spent on the advertising budget. Polyester resin without fibreglass should not be used as a sealer as it will crack.
    While you have the floor up it is a good idea to check the stringers, motor mounts, transom and any other wood bits. Most runabouts also have pour in place flotation foam under the floor that may have gone to mush. This a closed cell foam so will not absorb water, but water sloshing around will eventually break down the cell structure. It is a good idea to replace the wet stuff as it will keep the boat afloat if you get a hole. Just mix and pour before installing the floor. A pour will rise about 6 in hr. so you can just keep adding until full, trim excess with a bread knife.

  3. #3
    Join Date
    May 2011
    Posts
    2
    Thank-you for the detailed and thorough response. You have saved me a lot of time trying to hunt for answers and helped with my decision. It is greatly appreciated!

  4. #4
    Join Date
    Sep 2012
    Posts
    2

    86 ebbtide

    Hello, I am new to replacing a floor on a ski boat. I am a mechanic by trade, and love to have a project to work on. I recently bought an 86 ebbtide, that turns out to be very rotten. I have all the decking, stringers and bulkheads cut out and i'm ready to start cutting out the engine mounts and the transom once i get that engine hoist. I want to do this floor replacement the right way, so i'm doing it one step at a time. The thing that I'm stuck on right now is the floor under the open bow. How do I get under that thing with out having to cut it out of my way. I was able to cut the stringers out with a cut off wheel on the grinder by laying down on the bottom if the hull, but the edges of that piece of decking is almost impossible to reach with any type of cutting tool, much less a grinder to clean out all the old glass. Any help that you can give is greatly appreciated, cause i'm not quite sure which way I should go.

  5. #5
    Join Date
    Mar 2001
    Posts
    399
    Good news, sounds like you need to pull the deck! There should be an aluminum moulding with a plastic insert covering rivets or screws that hold the hull and deck together, remove these to pull the deck off. You now have easy access to all the internal structure of the boat. Just keep in mind that the deck helps keep the shape of the boat so try to support the hull before you pull the deck so you can get it back on looking more or less the same.


 

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