what wood can be used for bulkheads?

coolista · Jun 18, 2015

I know we can now get cyprus, http://www.cypresswood.net/content/index.php and I do not know how well suited it is for blue-water structures. When your vessel was built, cyprus might not have been available (moratorium restricting harvest in the past), and I know cyprus does well for immersion in water. Might be a conversation piece as it stains in unique hues.

Jeff · Jun 18, 2015

I used mahogany for an interior air conditioning cabinet. Matched very well.

centerline · Jun 18, 2015

many types of wood are acceptable to use, but MDO plywood would be my choice, except where it wont be seen... then regular exterior plywood is fine.
or if it will be completely encapsulated in fiberglass, in which case the plywood is only used as a mold to hold the polyester build up....
any decorative wood and trim can be added later, which is more expensive.

no matter the product, where the bulkheads or partitions are tabbed in and not completely sealed and moulded in with a heavy build up, the tabbed portions MUST be secured with mechanical fasteners.... because if the wood ever gets moisture in it, the "fiberglass" will delaminate from it and allow the bulkhead to float around in the tabbing.

Gunni · Jun 18, 2015

Negative Homer. For bulkheads, you are looking for marine plywood rated BS1088. This is as structural part and you want void-free certified marine ply. Try McEwen, they may be able to get you something within easy driving distance of the Queen City. They also distribute mahogany veneer plys that work well for boat cabinetry.

justsomeguy · Jun 18, 2015

Half-inch Baltic birch plywood works just fine in that location. Just finish all six sides well.

I like shellac!

As to your side question, it might be nice to have something to keep the compression post from getting knocked from its position, eh?

centerline · Jun 18, 2015

Gunni said:
Negative Homer. For bulkheads, you are looking for marine plywood rated BS1088. This is as structural part and you want void-free certified marine ply. Try McEwen, they may be able to get you something within easy driving distance of the Queen City. They also distribute mahogany veneer plys that work well for boat cabinetry.

I would agree... but the bigger the boat the more important it is to use the high dollar certified stuff.
many small boat manufactures in the past have used far less quality plywood than most of us would buy for building a dog house

small boats with small loads, the workmanship is more important than the certified materials used.

as this is an owner project and not a boat manufacture, the requirements one needs to follow can be different.

the MDO plywood is good but the HDO plywood exceeds marine plywood, but does not carry the rating.
it cannot carry the rating because the the laminates that compose the HDO are not actually constructed from "rot/mildew/fungal resitant" wood as the british standard 1088 calls for, but it is artificially created in the HDO laminates by saturating them with resin during layup... HDO plywood is stronger and will outlast marine plywood in any enviroment, but as its a lot stiffer and a bit heavier due to its saturated cores, its unbending quality may make it harder to work with for some projects.

MDO, which does not have the saturated cores, used to be, and I assume still is used as the structural plywood support under the v berth, quarter berth and settees, where fiberglass liners are absent, due to the finished surface of the MDO product.

so dont count it out where a good strong stiff flat panel is needed

shemandr · Jun 18, 2015

Seating area = settee in salty talk
Table = table
Table area could be dinette. Or as I like to call it - a complete waste of space.
Unless you use your boat A LOT differently than I, it's berth, not birth. Sorry to correct you but you might as well know now before re-posting the same error.

Brian S · Jun 18, 2015

Gunni said:
Negative Homer. For bulkheads, you are looking for marine plywood rated BS1088. This is as structural part and you want void-free certified marine ply. Try McEwen, they may be able to get you something within easy driving distance of the Queen City. They also distribute mahogany veneer plys that work well for boat cabinetry.

I second Gunni. I'd use either okoumi or meranti BS1088 ply. 1088 is A/B face grade, BS6566 is B/C face plies. BS rated plywood specifies more plies than average fir "marine" plywood available from your local lumberyard, and boil proof glue. Plywood rating systems are all over the place. I was able to buy submersible "marine" ply from my local lumberyard (they call it "marine ply" because it was immersion rated glue), but it was fir, and didn't have as many plies per thickness as a BS graded ply. Fir is less desirable because it will crack and check, even if painted with epoxy resin.

Okoume is relatively light, not terribly rot resistant, but certainly ok for interior use, and used in many hull building projects where encased in epoxy and glass. Meranti can be good too, but I understand it's more brittle and prone to cracking while being worked. Sapele is expensive, but has some beautiful grain patterns, if you had something that you wanted to look especially nice. Chesapeake Light Craft uses okoume for hulls and bulkheads in their kayak kits, and sapele for decks.

You can order BS graded plywood from Noah's Marine, and they will ship full panels, 1/2, 1/4, and possibly down to 1/8 size panels. http://www.noahsmarine.com/index.asp

centerline · Jun 19, 2015

solodare said:
So 1/2 inch for the bulkhead? I would have thought it was 3/4. I have not check the current bulkhead though. I guess it does look more like 1/2.
But what ever species I go with will need to be "sealed"? I was going to stain it. I guess thats not a seal?

if its a stiff plywood like marine grade or better, 1/2" will work great for your boat.... bigger boats will need 3/4 or even 1"...
my mac25 has the original bulkheads that are 1/2"... no problems.

to seal it, go to a home improvement center and get a varathane (brand name) product, stain with a poly sealer and glossy or satin finish will work nice and is easy and quick to work with... or use a spar varnish, but thats the slow way to go.

Daveinet · Jun 19, 2015

Depending on the function, I might be inclined to use counter top laminate over foam. Most of that is Acrylic which is pretty strong. Frame the panel in Teak. That is the way the interior on my RV is done. it is very strong, although not puncture resistant.

RIVERCRUISER · Jun 21, 2015

Re: Sealing marine plywood

IMO that means coating the edges w/ at least three coats epoxy resin
the first coat should be thinned
I also coat the flat surfaces w/ a thinned epoxy resin

Indysailor · Jun 21, 2015

I sealed the edges of my new bulkheads with CPES. After using it I was pretty convinced that it was really just epoxy thinned with acetone. But I liked the results and used it on a recommendation from a wooden boat shop owner I met, who also sold me a sheet of 1/2" Okoume to do the job. I'd be surprised if you need 3/4".

I've seen boats where people have used all sorts of plywood for bulkheads. The key is to buy good quality with no voids. And seal the edges; there really is no reason to seal the entire bulkhead since water that may leak in is going to gather at the bottom and soak in to the top.

centerline · Jun 21, 2015

Indysailor said:
seal the edges; there really is no reason to seal the entire bulkhead since water that may leak in is going to gather at the bottom and soak in to the top.

exactly... this is the reason that epoxy is not needed. but just something that will resist a splash.
epoxy being stronger is a good option on an edge that will remain raw and uncovered, as it will glue it better and prevent the plywood from having slivers or getting a rough edge to it.
the bottom will likely be tabbed in with polyester so there is no real need to seal it twice.

foam is NOT a good choice for a structural bulkhead, no matter how its edged.
when the rigging is tensioned properly, the mast pushes down on the top of the boat, trying to push the deck into the interior, which in turn will cause the sides to bulge outward, flattening the boat like a oblong pancake with turned up ends... you need the structural support inside so the boat will hold its roundish shape under what can potentially be a couple thousand pounds of downward force....

Captain Mud · Jun 21, 2015

CPES is a very sophisticated epoxy made largely from the resins in wood. It has a propriety blend of solvents to help in its natural affinity for sealing, and it is somewhat flexible as well so the wood can "come and go"...and excellent choice for sealing anything, especially before painting or varnishing.

Daveinet · Jun 22, 2015

solodare said:
Not sure I follow you davinet,?

When I stated depending on the function, I was meaning if the boat has a compression post, so the bulkheads are not supporting the mast load.

Basically what I was trying to describe was a sandwich construction. Basically you build a frame and then glue panels on either side and use foam in the center for a core.

Technically even if the boat does not have a compression post, one could just make the frame section closest to the center out of a larger piece of wood. Or just cap the end with a thicker wood post. Then you get the function without the weight. While this may seem like a lot of work, it will not be as prone to rot, and will be much lighter.

Gunni · Jun 22, 2015

solodare said:
So 1/2 inch for the bulkhead? I would have thought it was 3/4. I have not check the current bulkhead though. I guess it does look more like 1/2. But what ever species I go with will need to be "sealed"? I was going to stain it. I guess thats not a seal?

Most likely something like 18mm. Bulkheads are prone to weakening from standing water and saturation. Seal it with marine-rated epoxy.

what wood can be used for bulkheads?

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