Flooring Material

Discussion in 'Fiberglass and Composite Boat Building' started by johnsonmtz, Apr 7, 2004.

  1. johnsonmtz
    Joined: Apr 2004
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    johnsonmtz Junior Member

    I am preparing to separate the hull and deck (top skin of hull?) of my 1981 SeaStar 18' runabout so I can repair the rotted transom. The floor is fair, but my thinking is if I have it torn down that far, then now is the time to replace the floor and be done with it. The condition of the stringers is unknown, but if they are rotted, I plan to use the same pourable material (Seacast) for them that I will also use in the transom.

    My primary question is what type of wood and what thickness to use for the decking? Should I get "marine plywood" or is green treated plywood fine? Or, should I use regular CDX/ construction plywood and coat the underside and edges with resin and use glass fabric/resin on the top? Finally, what is the typical deck wood thickness 1/2", 5/8", or 3/4". I'm not sure of the beam width, but the floor is about 72" edge to edge.

    Thanks for your help.
     
  2. bobber
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    bobber Junior Member

    Marine is the obvious best choice, but not always the most financial choice. hard to get true "marine grade" plywood these days, but maybe up around your way it is easier. Most of the time it is exterior ply. Im not keen on using treated wood. Normally that is intended for outdoor use, and is intended to dry. I'd also say, unless you plan on covering it, that it may become quite slippy when wet. id go for a good quality marine ply, if your budget, and availability will allow you. coating normal exterior ply with glass mat is the best option i think. and is the method i have used most of the time, without problems, on RIBs. Only hard thing is getting it smooth, if you want a smooth deck, have to get your belt sander out, also requires a gelcoat topcoat, else your going to have fibers sticking up, which play havoc on bare footed passengers. Unless you have carpet over it? trouble with gel coat is it is intended to be sealed from the air for it to cure. When laying it out of a mold, you need to use what we call "flow coat" but i think it is called something else in the US. basically its gel coat with wax mixed in. This allows it to cure, but is hard to put on smooth.

    Thickness depends on how big, and whats attached to it, and how often it is supported. i normally use 5/8" or 3/4". but with a 72inch width, id go for 3/4", although this will be heavy. But need to see how the deck is supported, and how often. Might get away with much thinner material, if it is supported well under it.
     
  3. johnsonmtz
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    johnsonmtz Junior Member

    Thanks good info

    The floor has supports every 18 inches. The decking will rest on the hull on the outside edges (obviously) and there are two stringers running down the middle about 18" apart.

    My intention was to coat the underside and edges of the wood with 2 coats of resin. Once dry I will paste some resin on the outside edges of the hull and on the stringers. When I lay the decking on that resin I will apply cloth over the edges and paste it with resin. In the middle I intended to screw the decking down to thestringers. Finally I would put two layers of mesh and resin on the top side of decking.

    The majority of the floor is only supporting seats & walking. I will be installing a ski pylon and I was thinking of adding a piece of 3/4" to the underside of that section and glassing it in as well. Yes the floor will be carpeted, so I only need to knock down the high spots when I'm finished.

    I was thinking that 1/2" decking might be okay since the supports are only 18" apart and with the mesh I will lay on top. My concern using "green treated" plywood was the amount of water it contains and the amount of shrinkage and twisting that occurs when it dries. I will check around to see if Marine Grade plywood is available. IF not, I guess I'll just have to hope I do a good job of sealing the exterior CDX plywood inside the resin.

    Any more tips would be greatly appreciated.
     
  4. bobber
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    bobber Junior Member

    1/2 inch should surfice fine, since it is supported on the stringers. The edges are where you are likel to get some problems with lifting etc. Laying fiberglass cloth, wetted out on the hull where the deck is supported would be a good idea, then placing the decking ontop of this, and fiberglassing it to thehull as much as you can get access too.
    Screwing in the middle is fine, as long as you use stainless screws, else your going to get rust seeping through your carpet and look ugly. If you dont intend to pull the deck again, its probably worth while applying resin to the stringers under the deck to hold it and stop the screws lifting out..

    No, dont use pressure treated plywood. i spoke to someone else about this, and what you say is true, the high water content means they are intended for outdoor use where they can dry over time. in this application, it would not be able to dry and would not only be soft, but will warp, and distort, possibly damaging your hull or stringers in the process if you have fitted it down securly. Also will tend to sag where it isnt supported, giving water traps and a weird looking deck!
    If your coating both sides and the edges, and doing it properly, exterior ply is fine to use. middle eastern ply is fine. marine is ideal, but expensive and overkill maybe since you are coating it.

    Definitely need some extra strength where the ski pole is going to go. How i have done it in the past is affix 3/4inch ply under the deck as you said, glassed in and screwed so it cant come loose. Making it as big as possible to spread the load, ideally attaching it to the stringers too. The more you spread the load the better. Then use a sheet of stainless steel on the topside, above, or under the carpet, depending on how you like the look, and bolting the pole through the steel, deck and the 3/4" ply using stainless steel bolts. however your problem will be getting the nuts on the other side, yuo can use anchors, or umbreller bolts, or you can take the opportunity of having the deck off to build a center, under deck, locker down the length of the boat to house skis etc, as well as allowing you access to the underside for bolting etc.
     
  5. johnsonmtz
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    johnsonmtz Junior Member

    Already has a locker

    The boat originally had a ski locker running down the center. I was too far forward for me to access the area where the pole will be, but I had thought of moving it back where I could access the pylon bolts.

    I guess I'll go with 1/2" exterior plywood and coat the daylights out of it. I hadn't thought of using cloth out on the edges but it is a good idea. What if I laid the cloth and wetted it on the hull and left a few inches extended above the decking so I could wrap it around and wet it on the top side in addition to laying and wetting cloth down from the topsides of the hull? Would that help hold the decking better than just cloth on the underside?

    For the stringers, I was going to replace them and the transom with Seacast composite material from these guys http://transomrepair.com/ I figure with this stuff I'll have a stronger than new boat that won't rot from the inside! I've never used this material but it seems to be a good option and will allow me many years of worry free boating.

    Again thank you for the advice. I'm capable of doing most any work, I just needed the knowledge of where to start.

    Thanks,
    Kevin
     
  6. bobber
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    bobber Junior Member

    you mean wrap it around the edge of the deck? i dont really think you will gain much from doing that, but i dont see what harm it would do, for peace of mind.
    Ive never used the seacast product, so i couldnt advise on that, i dont know how well it does, or what its properties are.

    The under deck locker is a good idea i think, just remember, if you move it back, to make sure you put in a floor to the locker, properly laminated and fitted to the stringers, and not use the hull itself as the floor, else you may end up with skis falling out the bottom of your boat. To avoid noise, what i have used before is the foam they use on bowling greens. i dont know if you have bowling greens around you, i think its more a european thing, but its basically a foam, looks kind of like egg boxes. This sticks to the locker with resin and is about 2 inches thick, so stops things banging around, as well as absorbing impact. I use it in anchor lockers to stop the anchor smashing its way through the bow in heavy seas.
     
  7. kapnD
    Joined: Jan 2003
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    kapnD Senior Member

    pourable filler

    I'm interested in the "Seacast" material mentioned earlier. Have never heard of it, and am in dire need of such a product. Have you used it before? My plywood stringers are pretty rotten, not really a problem, as the glass around them is heavy enough to maintain strength, however now I'm repowering, moving engine mounts which bolt through stringers, and need a filler material strong enough to keep the bolts from squashing the glass in.
     
  8. johnsonmtz
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    johnsonmtz Junior Member

    Suppose to work

    I'll definiltely keep you posted on the progress. I have removed all the rotted transom wood and cut out the old flooring today. The Seacast is suppose to ship out Monday so I should be pouring the new material next weekend.

    KJ
     
  9. bobber
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    bobber Junior Member

    just make sure you spread the load on engine mounts as much as possible. the engine bearers, which often are the stringers are designed to spread the engines load and weight along the entire length of the boat. so avoid just having the local area around a mount strong and ignoring the rest. Spread the load as much as possible
     
  10. johnsonmtz
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    johnsonmtz Junior Member

    Decisions to make

    Funny thing, when I removed the flooring I found the stringers were hollow. There is a 1/2" strip of plywood in the top of each which I assume is there for screwing the decking down, the rest is just a woven fabric glass shell. Is this a common building technique? There are 4 stringers so the floor has much more support than I previously thought. I cut out the floor leaving 2" of the old decking all around the sides (see picture).

    The main decision I must make is how to connect the new decking on the edges. Should I screw strips to the underside of the old floor to use as a support for the new decking and maintain the original floor level? Or, should I glass in the edges of the old decking to seal it, build up the stringers by 3/4" and just set the new decking on top of the 2" overhang of the old deck?

    Finally, as I pulled up the floor I discovered all the foam was completely saturated. This boat was carrying about 400 lbs of water in that foam which I removed completely. My final question...do I need to replace the foam? Can I glass in some horizontal supports to give the stringers lateral stability and leave out the foam? IF I need to replace the foam, what should I use? And, how do I prevent the foam from getting wet again and holding water?

    The engine is an outboard, that's why I wanted to use the Seacast for the greatest strength in the transom and rot resistance.

    I appologize for all the questions, but I want to do this right the first time so I can have years of trouble free boating.

    Thank you all.

    Kevin
     
  11. bobber
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    bobber Junior Member

    [Its not a method i have used, but i believe it is a practiced method.

    getting into the techniques now, which would be better comming from someone who does this a lot, as i dont to this extreme. But i would imagine attaching strips to theunderside of the old decking, glassed and screwed, would be the easiest and neatest way to do it. one you have the new deck in place, i would then glass over the whole thing, to seal any joins and tie it all together.

    The foam, im not sure about, that i will leave to someone who has had experience with this design. As far as water getting in, it depends on how the hull was sealed, if at all. For instance any lockers, are they all watertight lockers. Fixing points for fittings, if they arnt sealed water will go down through the holes. May not seem like a lot of water, but once its in there, it cant get out again, and so builds up over the years. Best thing is to check any points that potentially could allow water in and seal them properly with marine sealent. If your outboard mounting bolts go through the transom below the deck line, make sure they are sealed fully both sides, as this is a common place for water to get in.
    if you are worried you might end up gathering water in there again, you could always fit a bailer to the transom, that allows you to drain the hull, you can use one of the plastic screw in bungs, that remain water tight, but allow you to drain the hull periodically, or after every use to prevent the build up of water. Also helps dry the hull if you leave it open when not in use. How you would do it would depend on if your hull has any bulkheads, and if they are water tight or not. but since you got the deck off, you could easily fit a bailer below the deck line in the transom, IE as close to the keel as possible without actually cutting into it, and seal it well inside and out.
     
  12. FibrSupplyDepot
    Joined: Sep 2013
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    FibrSupplyDepot Fiberglass Supply Depot

    Do not use pressure treated wood ever in a boat if you are going to glass over plywood.
     

  13. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    This is a 9 year old thread . . .
     
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