Plywood Bulkhead scarfs-Verticle or horizontal?

[Roly]

From a cosmetic point of view, if clear finished, verticle grain would look better.That means 3 scarfs to get the width. Which dimension would it be
best to orient the the most grain for structural reasons, athwartship, or in the mast axis? Or is it splitting straws?
Thanks.

(12mm meranti)

[Landlubber]

Roly, the bulkheads are usually covered with the desired veneered ply, so it would not matter how you run the scarfs, it is normal though to have them vertical, the length of the sheet of ply, unless of course the bulkheads are only to sole level, where it would not matter at all, whatever is convenient. The scarfs are made at a minimum of 8:1 and should be more 12:1 as the importance of strength becomes the priority.

[CTMD]

45 degrees, but you'll use a lot more ply and the grain will look "funny". Really its splitting straws however, I'd align the sheets along your primary load path. Good 12mm ply will usually have 7 vaneers 4 one way, 3 the other. This means the play will be approx 30% stronger in tension along the face grain axis.

[PAR]

Typically scarfs in traditional construction, are arranged so that any moisture that might intrude, will drain out from gravity. You'll find this simple rule applies to all joints. A deck beam to carlin or shelf is a classic example of this with an inclined ramp, tilting away from the inside corner of the mortise or beam pocket.

With modern epoxy and plywood building methods, it's not as important a consideration, other then grain orientation for load transfer across the panel.

[Roly]

how is ply in compression?

[CTMD]

very good, ask your supplier for the exact data on the stock you are buying