Cedar Planking for bulkheads

[Pat McD]

I am still trying to decide on what type of material to use for my companionway bulkheads on my Seasprite 23 daysailer. While one obvious and most popular choice would be 5/8 marine plywood, I am concidering other options. I was thinking of going with hemlock but cannot find kiln dryed and dressed boards locally. Regular good one side plywood properly treated would probably work, but given that my boat does not have a selfdraining cockpit the bulkheads may be exposed to water from time to time.

Has anyone used cedar planking for bulkheads? I was thinking of using 1", 1X6, tongue and groove, glue the joints and add some bracing on the cabin side.

Any thoughts or comments?

Thanks,

Pat McD
Captain of the project boat Azul

[Hirilondë]

If it is a structural bulkhead, then nothing comes close to plywood for strength and stability. Solid wood bulkheads can be built that work, but they will never match the stability of plywood. If they are merely space dividers, then less structural, less stable materials are suitable.

Gluing tongue and groove, then using battens, then tabbing it all to fiberglass is looking for trouble. As the wood tries to expand and contract with moisture changes the tabbing will hold while the glue joints will break, or the wood will. You would have to build the bulkhead with mechanical fastenings (screws and bolts) and attach it to the hull mechanically (cleats glued to the hull and fastened to) to assure expansion and contraction could occur without damage. This would be no where near as integral as quality marine ply that has been sealed well and tabbed well to the hull.

Teak is one of but a few woods where gluing of pieces with joints (half lap, mortise and tenon, etc) and pieces oriented in different directions are stable enough not to try to explode when moisture is added.

If you really like the look of cedar, then I propose the following. Build and tab in a marine plywood bulkhead. Then either veneer or cover it with thin pieces of cedar. If you use the thin pieces do so with a little room for expansion and contraction like ceiling is done. Use rounded or chamfered edges and leave small gaps between slats. You could epoxy thin slats with tight joints to the plywood. This would require a lot of epoxy, and sealing the cedar well would be required. Any future compromise of the sealer could mean trouble.

[Pat McD]

Thank you for the great advise. I was pleased to see you are a marine carpenter by trade and appreciate your sage advice.

I believe the companionway bulkheads on a Seasprite daysailer are structural as the berths butt up against them as well as the cockpit seats. So I guess I will abandon the planking idea for all the good reasons you cited.

While marine plywood is the best alternative, if it was not readily available were I live, how would you treat good one side ordinary plywood for a bulkhead application and berths?

I am hoping you will have some good advice and be able to avoid your saying:" Nothing is more expensive than trying to save a little money."

Thanks again,

Pat McD
Captain of the project boat Azul

[Rachel]

One thing to keep in mind is that it is quite possible to "mail order" marine plywood. I know of a number of US sources, but I'm sure there are Canadian ones too.

You can also often have a local "real" lumberyard order it in as well.

Rachel

[LazyGuy]

Pat,

If you can't get marine ply, try MDO (Medium Density Overlay) it is the stuff they used to make highway signs before metal. Then make sure you seal the entire thing in epoxy, particularly the edges. It is great for paint as there is no wood grain that shows through the paper.

[mmarken]

I just salvaged a bunch of 4" wide cedar tongue and groove paneling from a buddy's fixer upper home (the kind used in closets - for some reason the last owner had a wall of it). I was thinking of covering plywood bulkheads in the head and other closed spaces. My plan is to not install using glue, but to "frame" it using teak or mahogany trim. Interior, out of site cabinets I would use ss screws. Is there a downside to this, or a better way?

[Hirilondë]

I have lined lockers with aromatic red cedar (since it came from closets I am guessing this is what it is). I installed it with brads diagonally through the tongues into the plywood. This allows some expansion and contractions without buckling. If you capture the pieces in a frame/trim be sure to leave room for the pieces to move, expand and contract.

[Duncan]

While marine plywood is the best alternative, if it was not readily available were I live...

You might want to try Noah's, down in Toronto- shipping might not be too bad?

[BALANCE]

Remember, when using cedar, if you varnish, polyurethane or paint it, you no longer have the benefits that come with cedar - aroma and moid.

[mmarken]

The plan was to use it unfinished - for aroma and mold - thanks for the insights!

[Quetzalsailor]

All advice above is bang on.

The currently-available marine plywoods are made with wood species which are much less rot resistant than the once-available; some are so poor that they make the Standards (Lloyds, etc.) only by having had their veneers treated. So, it's more important than ever to seal (with epoxy) the end grain and preferably the adjacent areas which are concealed by other details.

Most plywoods these days are laid up with water resistant glues; it's the veneer quality that makes the plywood meet Standards. (Witness CDX grade sheathing once universal but now rarer in house construction; it won't delaminate or come apart, but voids and rampant imperfection in the veneers make it look awful when soaked.)

You can preserve less-than-appropriate plywood by coating it out in epoxy. The money you save in wood, you may spend in epoxy and trouble. though. I've used Home Despot's Red Chinese smooth-veneered (oukume?) plywood for non structural but prone-to-damp work in Quetzal, coated in epoxy; the one piece that I can see every weekend is fine after several years and I know it gets wet.

[Hirilondë]

There are so many grades of plywood it is mind boggling. I doubt the Home Depot stuff is okoume. Like anything else the first step is to decide which characteristics you need your plywood to meet. From there you can choose what you need to buy. For boat building BS1088 okoume or meranti marine are the top choices. You really don't need them for a bulkhead though. Sealing tabbed in bulkheads, concentrating on the edges is always a good idea. This also means you can use a structural but lower grade of plywood and meet all necessary characteristics.