Cockpit Floor Material

Discussion in 'Materials' started by rhewson99, Mar 24, 2013.

  1. rhewson99
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    rhewson99 Junior Member

    Hi. I am in the process of replacing the cockpit floor of a 36 foot power cruiser and I would appreciate your thoughts on replacement materials. Here are some details: The floor area is 70 Sq FT. The previous floor was one inch Balsa core. It had gone bad around the hatch hinges (there are four hatches, lots of fittings) so I cut the whole floor out. The main floor supports are about 49-50” from each side of the hull. To replace the floor I have considered Coosa Board, 3/4” Marine Ply and 5/4 Cedar decking. I eliminated the Coosa Board based upon my lack of experience with this material, local availability and cost. Next I considered 3/4” Marine Ply. My local cost for a sheet of 3/4” x 4 x 8 marine ply is roughly $200.. A 4x8 sheet weighs about 90 pounds. I need about 2.5 sheets for a cost of $500. Weight would be 225 pounds before glassing. I'd have to splice the plywood to span the 49” from hull to floor support. Handling 90 pound sheets, splicing the material, the weight and lastly the cost all work against this option, even though I do understand that marine ply would be the more “mainstream” approach. That brings me to the 5/4 Cedar decking option. Absent your input, my inclination is to edge-glue / biscuit-join 5/4 cedar planks into floor sections. Build a floor section, epoxy-saturate and glass both sides. This way I can easily fabricate my custom widths. The total weight before glassing would be about 60 lbs. The cost (for the cedar) would be about $200. total. I built one small section, it was straightforward and appears to be very light and strong.

    I would appreciate your thoughts / comments. And I want to emphasize the cost issue. The $500. for Marine Ply is not a big issue with me if there are compelling reasons to pursue this option. What am I missing?

    Thanks in advance for your help.
     
  2. rasorinc
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    rasorinc Senior Member

    Go with the cedar...........If you can cut tongue and grove, tight butt no V, you could cut the cedar in half you get 2 pieces out of one. 5/4 is a very thick board. When you glue T & G together you get a very rigid piece of wood. I'm putting down southern pine spanning a max of 36". 3 glued 1/2" thick by 3" spanning 36" do not deflect when my 270 lb. son stood on them. Cedar is weaker than pine but you get the idea. The weight savings and the money saved is great and you will have a beautiful floor.
     
  3. michael pierzga
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    michael pierzga Senior Member

    Normally I completly build and finish a component like a cockpit sole in the shop, then fit to the boat . Plywood makes this possible.

    I wouldnt look forward to working on my hands and knees , laying and fairing in a timber sole .

    Another nice material for flooring is Nidacore.

    http://plywood.boatbuildercentral.com/proddetail.php?prod=NIDA_H8PP_prefab_20mm


    Medium price . Nidacore needs engineering details similar to foam core.
     
  4. PAR
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    PAR Yacht Designer/Builder

    Woo, $200 bucks for 3/4" plywood? Is it made from gold? I can get XL Douglas fir (marine grade) for about $60 a sheet, though it's not the best looking stuff in the world. I can get meranti 3/4" with a BS-6566 grade (good stuff) for about $100 a sheet. I can get Joubert stock, BS-1088 okoume for about $160 (the real good stuff). I'll assume Canada has different suppliers, but the pricing can't be that much different.

    Coosa Board is about $330 a sheet (ouch). Nidacore with 18 ounce roving bonded to each side is about $280 a sheet. Nidacore with 1/8" meranti bonded on each side is cheaper at $170.

    Cedar rages in pricing depending on location and species. I'd recommend Spanish or Alaskan yellow cedar, as the two best suited. I wouldn't tongue and groove the edges with the stringer spacing you have, but would look to double plank the area. I don't think this is the best approach, unless you'll encapsulate and sheath.

    Lastly an exterior grade of big box store plywood, if well encapsulated and sheathed will do. This saves a fair bit of cost and is easily available.
     
  5. rhewson99
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    rhewson99 Junior Member

    Thanks to all for your comments. Very helpful. A few follow-up points to clarify and possibly help others in their planning:

    With some more shopping, I have found Meranti BS1088 Hydrotek 18MM (3/4”) 13 PLY for $159. CDN (+ 13% tax) which is an improvement over the previous $200. per sheet that I had quoted. Looks like another good reason for Canadians to move to Florida.

    The Cedar Option: This option uses 5/4 cedar decking which can be hand-picked easily at Home Depot. The quality of these boards appears good however I realize that it is lower quality than that used in more visible applications like kayaks and canoes. My floor will be painted with non-skid (as it had been) so no cosmetic worries. I would build each floor section (3 of them) at home. I would trim the edges from each plank, and use a biscuit joiner and glue to form a finished 10” x 72” panel. Run that through my planer down to about 15/16 thick. Join the 10” panels into a floor section. Run 1” thick floor supports in high-traffic areas perpendicular to the plank direction. Encapsulate the whole section, top and bottom, in glass and epoxy. Estimated section weight: before glass: 20 lbs.

    The Plywood Option: I have had two local boat builders suggest the regular exterior-ply option, encapsulated in epoxy. I remain concerned over the risk of delamination using regular exterior ply.

    Using plywood leaves me with the challenge of splicing the plywood in spots (some spans over 48”). There would however be far fewer seams versus the Cedar option which one could argue is full of seams. That leaves me with the weight issue, more from a handling perspective than a finished perspective. Estimated section weight using Meranti is 48 lbs (versus Cedar at 20 lbs) before glass. I am frequently working this project by myself. I am in OK shape but lifting and fitting a 48 lb floor section I think would be a challenge.

    Double Planking: I really like this idea however my knee-jerk reaction is the work and possibly the cost would exceed the Marine Ply option.

    Other Materials such as Foam, Nidacore: My current hang-up with these materials is securing the hatches and the fittings. That's exactly where the old floor failed. I have more experience with wood, I know how to reinforce it in high-load areas. Other core materials – I have little to no experience, and don't want to learn on a large project such as this.
     
  6. PAR
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    PAR Yacht Designer/Builder

    Solid laminate by way of any openings, will solve the problems with the softer core materials. Plywood can also benefit from this approach too.

    Plywood's advantage is it'll tie things together, offering lateral and longitudinal stiffness and support. The cored products will do the same if well bonded. You can tackle this with all the materials mentioned, though application will vary slightly with each.

    Regular, exterior plywood will do, but you must be careful about the plywood type. If it's an APA sheet, it must say "Exterior", not "Exposure 1" or "Exterior Exposure 1". The Exterior grade will work, though not as strong as a real marine grade. It needs a good encapsulation and sheathing, especially the end grain and any holes.

    5/4's cedar is really too thick to consider encapsulation, as an effective moisture barrier. Cedar moves a lot with moisture content and stock over 3/4", I've found will overwhelm an epoxy coating, causing splits and cracks. If it's heavily sheathed (over 16 ounces all around) it'll do okay, but the heavier the sheathing the better. This drives up costs and effort. I also don't like the volume of fastener penetrations necessary for a "laid" deck, each being a potential leak point. Biscuit joints are a waste of time on this type of deck and only work with water based adhesives, which is what causes them to swell and lock in the groove. Epoxy will not cause them to swell, so they'll just be sloppy, in their grooves. Tongue and groove will help alignment, but is more trouble.

    This is why plywood is so attractive; cost, large surface area, stiff, strong and takes goo and fasteners well. Plywood can be scarfed or a butt block or a Payson butt joint can be used. In this application I'd use a Payson butt joint, for a simple, flush seam.

    Ultimately, cost and familiarity are what forces most material decisions. You have some wood working skills and plywood is easy to work. Using good plywood will help a lot, but techniques (and goo) will bail you out, if you're the wood butcher most of us are.
     
  7. alan white
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    alan white Senior Member

    You should probably use an exterior grade plywood as suggested. If you totally seal the underside with epoxy (three coats minimum), all the edges, all holes------ basically anywhere where water could find its way in------ before installing, then you ought to get a good long life out of the plywood (which shouldn't exceed $40.00 a sheet).
    cheaper plywood has fewer layers and more voids due to knot holes. It would help to add a layer of 8-12 oz fiberglass on top after installation to seal fastener holes and strengthen top veneers that have voids directly under them.
    It's mostly the voids in plywood that make it problematic where water's concerned so prevent it from getting in. That means everywhere as water loves to migrate around laterally inside wood----especially plywood where the grain goes both ways.
     
  8. michael pierzga
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    michael pierzga Senior Member

    If properly engineered foam or Nidacore will work perfectly.

    Plywood is forgiving and easy to use. I would use plywood, epoxy and fiberglass sheathing

    Spend some time engineering the hatch frames and drainage system. No standing water around the floor perimeter and no standing water in the hatch frame gutters.
     
  9. missinginaction
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    missinginaction Senior Member

    Something I learned here that has helped me greatly is the idea that you have to be thorough in sealing out moisture from plywood. Others have mentioned this. With regard to your hatches, consider the following.

    Where ever you need to install a thorough bolt for a hinge, use a forstner bit to drill an over sized hole. Then, fill the over sized hole with epoxy. Once the epoxy has cured drill the resin out to accept your fastener. This creates what is called an epoxy grommet, which permanently seals out water from your plywood.

    The link below shows the concept....it's on a fly bridge, a 1/4x20 bolt holds part of a railing in place and passes through the resin.

    http://www.boatdesign.net/forums/at...74-flybridge-came-out-my-head-img_0268-1-.jpg

    Good luck with your project,

    MIA
     
  10. PAR
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    PAR Yacht Designer/Builder

    With hatches and other openings the very edge, which usually incorporates a drip rail or drain system, is also very vulnerable. Water can pool and this causes problems. These areas should be built of solid laminate, which can be cast over a mold and bonded in place. They can also be made from inert materials (HDPE, PVC, aluminum, etc.), then screwed and/or bonded down.
     
  11. rhewson99
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    rhewson99 Junior Member

    Given all of your good feedback, my decision is to go with 3/4” plywood for the floor. I am still pondering the marine ply versus exterior ply decision. Again your input on this point has been helpful.

    I plan to make three floor sections at home. Two sections will be about 50” x 72” wide, so I will need to splice the ply and I am OK with that. The floor sections will be joined over the existing 3” wide centre floor supports. Here I plan to remove a strip of material 2” wide by 1/4” deep from each section edge that I want to join. Once the sections are together, I will fill the channel with epoxy and 4” glass tape.

    Regarding hatches, openings and gutters: Yes - these areas were a big problem with the old floor. The gutters were too narrow and not deep enough (3/4 X 3/4”) which did not allow for proper cleaning and drainage especially in rough seas. A good friend builds aluminum yachts, he is giving me a price on 4 custom hatch/gutter assemblies built from extruded aluminum. I anticipate a big price tag for these. So my Plan B is to build hatch openings and gutters using mahogany and integrate into the floor section such that there are no exposed plywood edges. All will be soaked in epoxy.

    The top of the plywood floor will be covered in one layer of cloth and resin for abrasion resistance. The underside of the plywood and edges will be simply epoxy coated. I do plan to set all fasteners into reinforced epoxy.
     
  12. PAR
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    PAR Yacht Designer/Builder

    I'd recommend you use two layers of 3/8" plywood, instead of a single 3/4" sheet. This serves two purposes, the first is the seams can be over lapped, so joining them together for a larger panel is easy and no leak potential. Second is, it's stronger and offers more veneers and an extra glue line. 3/4" exterior will have 5 veneers and some will only have 4, but two layers of 3/8" will provide 6 veneers, plus the extra glue line, where they are bonded together. Yeah, it costs a little more to do it this way, but it's a lot stronger, stiffer and makes the joints a lot simpler to approach. Lastly if you damage the top layer, you can just route out the area, down to the lower sheet and glue in a repair patch, without cutting through the whole sole panel.
     
  13. rhewson99
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    rhewson99 Junior Member

    The two-layer approach makes sense given all of the advantages that you state. A question about gluing two 3/8" pieces together: Page 10 of the Canadian Plywood Handbook talks about gluing plywood and the need for consistent pressure to create an effective bond. They talk about one technique - "nail gluing" - using nails on 2" centres to create the bond. Is there a better way to apply consistent pressure? I wonder also about the weight factor. Which would be lighter - two 3/8" panels laminated or one 3/4"? My guess is the laminated 3/8 - more veneers, less heavy glue. Thoughts?
     
  14. PAR
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    PAR Yacht Designer/Builder

    With curved panels, you will need to force them to conform, which can be do a few different ways, from sand bags or vacuum bagging. Nailing, or preferably screwing being the easiest, next to some sand bags or concrete blocks. If you use epoxy, you don't need lots of pressure, like other adhesives, just enough to insure glue line contact, that's it. With PVA's or other adhesives, you'll need a fair bit of pressure. Two layers will weight within a few ounces or a single 3/4" panel. The extra glue line will weigh something, but in the big picture, not a significant amount. If you do use screws, work from the centerline out with the fastener pattern. This works out trapped air and forces the panel into the curve.
     

  15. michael pierzga
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    michael pierzga Senior Member

    Clamping pressure is always an issue.

    In the perfect world you would use a vacume bag.

    A mixture of nails, screws , staples, clamps, weights is also possible .

    Review the Gougeon brothers book.

    http://www.westsystem.com/ss/assets/...k 061205.pdf

    They speak about clamping pressure with fasteners and the correct pattern of the fasteners
     
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