Thread: edge fastened deck planking

Originally Posted by HUON

look forward to your replies.

He's looking in the wrong direction isn't he

Richard
(that comment can be safely interpretted as "I don't have an answer")

I've done it again. I'm SURE I saved it! Maybe there is a new time limit?

I waxed eloquent
I waxed lyrical

And then gave all my writing the ultimate brazilian I think.

grrrrrr
MIK

Upshot was that the usual method was to put a couple of screws (or bolts in bigger boats) through the middle of each plank at each intersection with the deck beams - caulk and paye to prevent water getting in as the planks move around.

Edge nailing sounds a lot weaker if it is to hold the deck to the beams - if it is like a concealed nailing - sometimes done through a rebated edge in the plank - but I think it is more likely to be something else.

But it could be to stop the deckplanks from moving round between the deckbeams. There were also many strategies to overcome the fundamental weakness of planked yachts - their poor resistance to torsion - by putting big long threaded rods edgwise through the planks that make up the decking to try and prevent them from sliding past each other as the boat twists and bends.

Basically you can view a carvel planked boat like a garden gate without the diagonal that prevents the unsupported end of the gate from sagging. Add the diagonal or a flat panel of ply over the area and it is fabulously rigid. It is the diagonal that counts. putting more structure square to the centreline is of very limited use.

More sophisticated methods were to use bronze straps set up at about 45deg to the planking and decking. Or to use two layers of planking at an angle to each other.

This is a common method for bulkheads in larger old wooden ships by the way - at least the bulkheads can be dimensionally stable (and shape stable).

Plywood, steel, fibreglass, composite, cedar strip, all provide a truer monocoque with relatively little torsion distortion of the hull. Even a very lightly built boat like the PDR can exhibit huge torsional stiffness providing you include a few boxed in areas in the construction.

Ply decks can give an older boat a structural stability it may be losing with an older planked deck.

The best method is plywood if it is acceptable - but it might not be at all relevant to a restoration job.

I think that PAR and some of the other people here with wide experience in boat repair and restoration might have something interesting to say too.

I might be wrong about what the edge fastening means.

Laid decks come in a few different forms and edge nails usually serve two purposes. They can be used to effectively hide fasteners. This is common on small craft where the decking material can be too thin to successfully receive bungs of the screws, without sacrificing decking material strength. If they are placed at alternating angles, they are quite effective at pullout, particularly if ring shanks.

Edge fasteners on larger craft are usually employed to help stabilize the decking material. When a traditionally built boat, with a laid deck, is underway, the seams rub against each other, length wise. This movement is normal, but tests the strength and pull out resistance of all the fasteners. After a few years the decking starts to "spring" in places, which leaves some of the decking stock more proud (standing taller) then it's neighbors or worse, slightly lower, which captures boarding water (it pools in the low spot). Edge nails can help keep unruly planks aligned. In this country, these types of decking systems are called strip planked.

Many building techniques have attempted to address this, such as spines, tongue and groove, etc. but the forces that cause the deck panting or seam movement is just too great.

If your rebuild will permit, the best deck is one carrying a plywood substrate. You can seal this and place a laid deck over it. It'll look just like a laid deck, but it will not move and the seams will stay put.

One trick I use to make a very convincing laid deck, but one that doesn't leak is to use a bead board plywood over the deck beams, with the beads facing down (painted) and then, seal it up with 3 coats of epoxy and two layers of 6 ounce cloth. Over this, I then place the laid decking, but dimensional thinner stock is used (especially if weight is an issue). The decking material is laid in 3M 4200 (polyurethane adhesive/sealant) and fastened to the deck beams in the traditional manner (screwed down and bunged). This deck will be stronger and much more stable then the original. It looks the same from both sides, it will not leak and it can be removed and replaced, without exposing the interior of the boat to mother nature.