Occume . . .
- Hi guys,
I see a lot about occume ply on the list.
Occume is a non-durable species (i.e. rots pretty quickly, when wet) and is never used in 'proper' marine ply (for example BS1088). Bruynzeel, a major manufacturer of occume ply to die for, describes it as 'exterior' grade. (In fact, browsing the Bruynzeel catalogue, I haven't seen any claims for their products (even the Regina Mahogany) to meet marine grade specification. That would leave the door open for litigation, I suspect.)
So - occume is only good for boatbuilding if thoroughly encapsulated in epoxy. It has many plus points, too - like easy to finish and very light.
For anybody not wanting to go the whole way with epoxy (3 coats, inside and out . . .) more durable species are likely to last longer - fir comes to mind.
I don't know about the US, but timber yards in the UK are full of luan ply that is claimed to be 'marine grade'. A quick glance shows that most of it is nothing of the kind - thin outer veneers, fat inner ones, voids, patches, . . . The staff in these timber yards are not to be blamed (apart from their lack of specialised knowledge) - they buy this stuff with the BS1088 stamp on the edges in good faith. Still, the better examples of this type (usually Far-Eastern, rather than South American) are very satisfactory for building small boats with epoxy protection - I use selected ply of this type for most of my small boats. Certainly I'm ready to move on to my next small boat LONG before the ply starts to give out.
For lapstrake ply construction, of course, only really good stuff will do.
My tuppence worth.
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- You have to be pretty careful with those paper thin
surfaces. I have used them happily for some boats,
but one particular situation that comes to mind is the
strength on a doubled bottom. With those thin plies,
you have only about 20% of your wood going accross the
bottom where it will do you any good, the rest is
runing for and aft, supported however by bulkheads,
and quite peelable from the blocks. Probably won't
come to harm with the indispensible glass coating, but
quite different structure than 12mm of fir with 60% of
the wood going crossways, and 30% of it outermost
where it will do the most good. My calcs suggest that
the former is stronger accross the sheats, while the
latter is stronger with the length, as intended. Both
are stiffer with the length, I imagine, which may be
By the way, as I mentioned before. Kurt Hughes got
USCG (not the golfers this time, right?) approval for
massive charter cats made of 3mm Luan doorskins, epoxy coated.
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