Plywood options for interior

[heartofgold]

Greetings one and all!

I would like to announce my return to form. Ahem, I mean my return to the forum. Ivan hit us down here harder than most people realize, and I am just now coming up for a breath of fresh air and to catch up on the important things in life, like sailboat refinishing.

I am preparing to rebuild my interior, beginning with the vee berth, and I was hoping I could find some suggestions on different types of plywood to use. I read on the daysailor site where Tim had used 9mm, 3/8" and 13mm Meranti plywood, each for a different purpose. What is this product, where does one order it, and what should I expect to pay for it retail? And, of course, are there other products I should be considering? As always, any and all suggestions and/or information is welcome.

[Tim]

I often use the terms "9mm" and "3/8"" interchangeably, as they refer to basically the same thickness (9mm is actually 0.35433"). Meranti plywood, however, is sold in metric thicknesses, so 9mm is the correct term.

13mm plywood is approximately 1/2". I had one sheet of this on hand that I used for the cabin sole. The other interior structures are 9mm meranti; the three main structural bulkheads are 18mm (3/4"). One should choose a plywood thickness that is appropriate to the strength requirements of the job, and taking into account the unsupported spans involved, if applicable.

Meranti is a type of Phillipine mahogany. The meranti plywood, which meets the stringent requirements of BS 1088 (the benchmark for the highest quality plywoods), is made from this type of mahogany. The facing surfaces are clear and free of those annoying "footballs" that you see on lesser plywoods. Some sheets look almost too nice to hide in a structural application, but in general it looks like plywood and lacks any real character that you might want to show off. But the surface is smooth and much nicer than the best A-face standard plywood that you could find. Plus, since it is in fact a mahogany species, it looks more like real wood and less like trash.

The king of marine plywoods may be okoume plywood, which is manufactured to the highest construction standards in the industry. Meranti as a wood is actually more durable than okoume, but plywood made from okoume (hence "okoume plywood") is technically preferred because of its high manufacturing and quality standards. It also meets standard BS 1088.

That said, marine meranti plywood is constructed to the same regulated standard for the end result, and this means that it is a high quality, void-free plywood with more plies per thickness than the plywood you might find at a lumberyard. This makes it extremely strong and stable, and you know that when you cut into it you shall never find a void.

Note that the adhesives used in a true marine plywood are not necessarily different than those used in standard exterior grade plywood. However, true "marine" plywood refers to the construction of the interior laminations of the product, and is certified void-free, and with no flimsy interior laminations. Interior lams in true marine plywood are, to my knowledge, the same as the exterior, other than in appearance and not accounting for any attractive veneers used in some types.

Meranti is not inexpensive, but is a good value when you want to do the job right. Its price tends to be only a small percentage higher than something like fir exterior plywood, but for a much higher quality product. Meranti is significantely less expensive than okoume.

From my recent plywood order, here are the prices for three sizes of meranti plywood:

6mm (about 1/4"): $33.55/sheet
9mm (about 3/8"): $44.54/sheet
18mm (about 3/4"): $84.74/sheet

Obviously prices vary depending on location and other factors. It should be available locally at any vendor that sells marine plywood. Or search online, though I'd hate to have to ship plywood long distance.

I believe that in this day in age, only the best quality plywood should be used in boat construction, at least for structural applications. To me, this means any of the marine plywoods meeting BB 1088. You can cut price, but only at the expense of ultimate quality. Note that I have no problem using interior grades of veneer plywood (i.e. cherry), but only in surfacing applications, and never for structural.

For your boat, I'm sure all interior structures could be made from the 9mm plywood.

[heartofgold]

Tim,

Great information. Summed up, do you feel that 9mm is sufficient for applications such as the vee berth and setees/quarter berths? And are those quoted prices retail or wholesale?

[Tim]

Doug,

Those prices are from Maine Coast Lumber. It's a retail outfit.

I used 9mm for the entire v-berth in the daysailor, including the top. You definitely need to build in some additional supports for the top (or in any wide horizontal span), as the 9mm is a little lightweight to avoid bending on its own in this application. It won't break, but it will bend if not supported adequately.

[windrose]

Heart of Gold, I put "ceiling boards" on the sides of my vee berth and it looks great. Basically, I ripped off the lovely blue shag carpet and killed all the mildew and painted everything white with a mildew inhibitor in it. I then laminated some vertical strips of wood every 18" along the vee berth walls and painted them white as well. I then took Cetol and stained birch strips that are about 2" wide (front and back, so they would not warp) and used stainless screws to attach them to the vertical stringers with a 1/4" gap between each birch strip to allow for air flow. It made an incredible difference in the appearance of the vee berth and really helped the boat look not so dated. It was cheap, but time consuming to do and I admit I am pleased with the results. I will attempt to post a photo. Good luck. Ang

[PeteB]

Hi Tim,
When you rebuilt the interior of Glissando, you discussed using 1/4" cherry plywood to replace the original ugly woodgrain laminate. Can you elaborate on what type of plywood you used for this? Interior vs. exterior grade, etc.?
Thanx

[Tim]

The cherry plywood used in my interior is just standard interior-grade plywood--nothing special. At the time, anyway, there was no "marine" grade cherry plywood available, at least locally. I don't know if such a product exists even today; given the wide use of cherry in boat interiors now, perhaps there is.

None of the cherry ply in my interior is used in a structural way, but nonetheless there have been no problems to report as a result of the construction of the plywood. I see no problem with using it for this application. I would not choose it for anything structural, however.

[David VanDenburgh]

The cherry plywood used in my interior is just standard interior-grade plywood--nothing special.

I've been reading some older posts with interest as I am nearing the point where I can begin installing the bulkheads that will form the engine compartment, galley, and icebox/nav station on the Alberg. I was preparing to drive anywhere from 1.5 - 3 hrs tomorrow to pick up some meranti or okoume, but coming across this post has me thinking that I may not need to be that extreme for this part of the project.

So, the question is: What is the recommended plywood for reconstructing the galley, etc.? Here's a picture of the area to give you an idea of the space I'm talking about.

Now, to complicate things a bit, the picture below shows one of the bulkheads that is tabbed to the overhead beneath the deck. Should this bulkhead be meranti or some other structurally sound plywood?


Thanks for the input and please pardon my ignorance.

David

[Figment]

How securely is that bulkhead tabbed to the underside of the deck and the inside of the hull Does that tabbing appear substantial enough that it's meant to transfer actual hull stress, or is it most likely just there to hold the piece in place?
I'm guessing the latter. The deck doesn't span any great distance at that location, and I doubt that there are any high-stress fittings nearby.

The items you're dealing with are really just furniture. Furniture-grade material will suffice.

But then I'm the nut that uses liquid nails instead of 3M5200 for interior adhesive applications.... ;)

[David VanDenburgh]

Figment,

It was - in my limited experience - "loosely" tabbed to the overhead. In fact, there was a gap of about 1/2" between the top of the bulkhead and the overhead, so whatever structural support the thing might have provided was resting solely on the tabbing.

Thanks for the response.

David

[Tim]

For interior partitions and "furniture", you can use just about whatever you want. If you're going for a nice wood look, then choose a good grade (as good as you can find) of veneer plywood in the species of your choice for these non-structural members.

The tabbing on these pieces is designed to hold them in place, and to each other; they don't provide necessary structure. In you A-30, just the aftermost bulkhead (aft of the galley under the cockpit) and the forward bulkheads provide structural strength to the hull. Most of the rest of the interior is "furniture" only. Every boat is different, so take one case at a time.

This veneer, cabinet-grade plywood is of lower overall quality, at least as compared to a better quality marine product like Meranti, but will suffice for non-structural applications, like your galley area. Just stay far, far away from the fir plywood junk they sell at your local big box store.

Make all attempts to seal the end grain, in all cases, as well as to finish the back sides of pieces that might be susceptible to moisture.

For general interior work, structural and non-structural, I recommend marine meranti plywood, though it should be used mostly in hidden areas, or else covered with some other product for a final finish. Some sheets of meranti look almost finish quality, but it's not really intended as a finish product.

Interestingly, while okoume is often regarded as the "granddaddy" of marine structural plywoods, meranti is actually a more durable species, but is somewhat heavier in weight. Both marine meranti and okoume meet the same BS1088 standard for construction and void-free certification.

[Ryan]

Where does Lauan plywood fall in the rankings for marine plywood? Many references consider it to be the same as meranti, but I have a hard time beliving that since I can buy Lauan at Lowes.

[Tim]

Lauan plywood is junk! It is most certainly not marine grade.

Lauan and meranti are both species of mahogany, and the species themselves may be similar, but the products made from them could hardly be more different.

The key to the quality of the meranti plywood is in the number of laminations, and the fact that all laminations are certified void-free. This makes for a stable, solid product. In fact, it's the laminations and the void-free certification that make a marine ply a marine ply; the glue is rarely any different than that found in exterior grade.

[CharlieJ]

I agree with every thing Tim is saying except- Luan is not a form of mahogany- it's related to the cedar family instead. It's just CALLED mahogany by many people. Same way with Okume- it ISN'T actually a mahogany- different family completely. Okume is an african hardwood, named Okume.

On the fir plywoods, standard and marine. Be VERY careful with the stuff should you decide to use it. I've been seeing stuff, labeled as "Marine" with only 4 plys in 1/2 thickness. Run, don't walk, from that kind of junk.

Actually, American made plywood has been going downhill for a number of years, and has now gotten to the point where I don't even consider it as a viable material for boat building. It's pretty much trash. I did use some good grade fir marine in building the interior of Tehani, but I was quite careful in what I got. I'll probably not use fir again. Okume, ( or Meranti) just isn't that much more expensive, considering the time and effort put into a boat. A boat like my Rhodes Meridian or the Triton's should serve well for YEARS once restored- no sense in shortchanging yourself or the boat, by cutting corners on quality woods, just to save a few pennies.

As an example last year I delivered a 22 footer to a customer. When I did the orriginal cost estimates on that boat the difference between French made, BS1088 Okume and American made AB fir marine came to about 600 dollars- on a 20,000 dollar boat- just not worth using cheaper grades.

[Tim]

I agree with every thing Tim is saying except- Luan is not a form of mahogany- it's related to the cedar family instead. It's just CALLED mahogany by many people.

Well, I learn something new every day! I guess when you hear something enough, you start to believe it. I'd always heard that Lauan was a mahogany...which I guess is a misnomer.

[heartofgold]

Several years ago, I purchased a cd from this source. The contents of the cd are invaluable in wood identification and purpose. Tells a lot about uses, density, rot resistance, and such. It's awkward to navigate (ancient version I am using), but once you figure out the system, it is a terrific tool.

[Tim]

Several years ago, I purchased a cd from this source.

Which source?

[heartofgold]

Oops! Sorry about that. Look here: http://thewoodexplorer.com/.

This is now an on line source, but I believe the cd is still available.

[Tim]

Another good (if overly exhaustive) source is the book Understanding Wood, by R. Bruce Hoadley.

[David]

I have always know luan as a form of mahogany also.

From a kayak building site on marine plywood:

Another less common variety of marine plywood is 'Meranti'. It is made from many subspecies of the 'Shorea' tree species which also happens to be the source of wood for the common Lauan (luan) plywood. Both Lauan and Meranti plywood are also referred to interchangeably as Philippine Mahogany and the wood is harvested in Indonesia and the South Pacific rim forests.
Now, there is also White Lauan made from Shorea almon, Red Lauan made from Shorea negrosensis which happens to be the Red Meranti. Other 'Meranti' plywood is made from Shorea curtisii, S. hypochra, S. leprosula, S. multiflora, S. platiclados, S. pauciflora to name a few. Confusing enough ?

the site is:
http://www.oneoceankayaks.com/stitchglu ... ytype1.htm

David

[bcooke]

Stop. My head hurts.

-Britton

[dasein668]

Stop. My head hurts.

I agree!