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I would like to get your opinions on how best to construct slatted decks, in particular, how to attach the gratings to the bearers.
I have seen various examples:
- some just used wood screws with countersunk heads, flush with the grating surface.
- others use wood screws and burry them into the gratings with a wood plug on top.
- others use machine screws screwed into exact fit holes in the bearers, with heads either flush to grating surface or burried with wood plug.
All of the above have the risk that water may travel along the screws into the bearers and sooner or later cause the screws to get loose, and the bearers to exhibit wet rot.
- The most recommended way seems to be to burry a nut into an epoxy bed in the bearer, and use machine screws to fix the grating.
Attached you find a schematic in which I tried to envisage the process steps. I would be glad to receive comments on this.
I would carefully wipe the screw threads with a very thin coating of grease to make them easier to remove. I would also suggest making the holes slightly deeper than the screws need when holding the grating down, so that you can be sure you'll be able to tighten them sufficiently when you fit the grating.
It may sound crazy, but what if you make a 10mm dado in the bearer so as to fit each grating and then you fix them with rope? Easy to see if it has a problem, easy to fix, easy to do. If you would want to do some more work just make sliding dovetail joints, you make a dado dovetail slot in the bearer and the pin would be the lower half of each grating, this way you just slide the pieces together and you won't need any fastener.
Quick and practical, you make dado in bearer for gratings and epoxi glue both parts.
This method is fine and will be fairly strong but its a lot of extra work. Two things to consider one is that regardless of the fastener you use the epoxy needs to protect the wood for the full depth and beneath the fastener to effectively prevent water intrusion into the wood. the second is that your fastener strength is now limited to the boding strength of the epoxy. I'm assuming you're considering these concepts because you're using a lighter softer wood. I would suggest using a high oil content tropical hardwood like Teak, Tigerwood, or Ipe and stick to traditional fastening methods. calculate the weight difference and just carry less stuff. I used tigerwood for my decks and have loved them for lots of reasons.
check this, would be easier
I am currently doing a minor refit of my boat (TIKI 31, standard design), painting mainly, and can confirm that the untreated accoya I fitted for deck slats approx 8 years ago is still in good condition.
There is no need to treat accoya and wide (8") boards do not cup.
I used A4 good quality contersunk stainless screws and A4 coachbolts. Screws were counterbored in the usual way. I used mastic sometimes according to whim.
Some of my deck slats are lashed to bearers using 4mm dyneema, as my centre platform is slatted and not a ply composite as is the design construction method.
I would not hesitate to use accoya again for this purpose. It is softwood treated with a chemical process which precludes moisture entering the wood pores. Therefore the timber does not get much heavier when there is a lot of water about. Average movement on an 8" board is about 2mm in the width over the seasons.
I used to kiln dry timber to sell for a living so I am attuned to these things.
The accoya itself needs to be straightgrained as the timber is only as strong as spruce.
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