Marine Plywood

[Doug Canada]

Must marine plywood always be used?

With the high quality of fiberglasing and epoxy coatings today, is a marine plywood absolutely needed. How much is marine plywood a function of quality vs. cosmetics?

Nautical pureists, please be kind, but I am getting quotes of $80 - 120 per sheet, in Canada. I need 30 sheets.

My plans are too build a small trailerable sailboat, that may be in and out of the water a total of one month each year.

Thanks,

[Mike Vogdes]

For hull and deck, its best to use the good stuff, I like Okume for that, for bulkheads and frames its ok to go a little cheaper doug fir marine grade is ok. For bunk tops, cabinets, drawer bottoms or any non structural parts that will not see water then use what you want. You would be wise to use what the designer specs.

[DerekW]

Hi Doug

You'll get a range of opinions on this one, I'd guess. smile.gif

A thirty-sheet design might not be big, but it's certainly not small either. You will put in a lot of work before those thirty sheets float.

There's marine ply and marine ply. I've seen some pretty rough 'domestic' marine fir. MDO would make a better choice. 1088 Meranti is lovely stuff to work with, and the '6566' Meranti I've used was pretty close to flawless.

Other than for 'disposable' small boats, I would not choose to work with cheap ply - I've done it and the savings are not worthwhile.

just my 2c

Derek

[NormMessinger]

Since the answer to this question is pretty much a matter of opinion that makes me qualified to answer.

Must high quality marine plywood be used? Of course not. A lot of people, myself included have built satisfactory boats with everything from AC Exterior fir to luan underlayment. And, they (we) have gotten away with not glassing it, too. I've been thinking about building a boat from waffer or chip board just to extend the range.

Now, if we change the question to, should one use high quality marine plywood, the answer becomes a bit harder to pin down. Without writing a treatis one might begin by asking, how much will the wood cost compared to the total cost of the project, can you affort the cost up front, and will you remember that cost two or five years from now when what you will have then is a boat and pride in your accomplishment.

I've always used the best marine plywood for my best boats and the cheap stuff for the kids to learn on. The down side on non-marine ply is mostly the voids in the inner plies and the quality of the "B" face. I was told the glue in exterior plywood and marine ply is the same but marine may have a fungicide in it. (One knowledgable source, unconfirmed elsewhere.)

What I would call a small boat would take one sheet, um..., okay but no more than half a dozen. Tell us more about your design. Thirty sheet at $100 even if Canadian ;) is not chump change. Some of the Stevens Project Weekenders and Vacationeers I've seen which were built with good non marine plywood sure look nice when finished. And I've sailed with some thrown togeather with the cheapest of stuff that serve the builders needs. They would win no beauty contest but they serve.

So, bottom line, ya pays yer money and ya takes yer pick.

Best wishe.

--Norm

[Scott Rosen]

The difference in quality between good marine ply and construction grade ply is astounding.

You might be able to answer your own question by getting a scrap of good marine ply and a scrap of "other" ply and cutting them and playing with them for a few minutes.

[George Roberts]

Doug Canada ---

The APA website has engineering information for the various grades of plywood. You can at least compare the numbers there to get some idea of the relative quality.

You also might determine that a thicker lower grade of plywood might be more cost effective than a thinner higher grade of plywood.

[Badges68]

Hi,
just a 2c worth..
always use a ply with maximum layers for the thickness you want, usually the thicker the layer the poorer the inner layers are..
don

[Banjo]

Hi there,

Don brings up a good point. I recently bought some ply, they had "Marine" versions and exterior versions in the same 9 mm thickness.
The ONLY difference between them was the number of laminations. The "Marine" ply had one extra lamination and it's surface was marginaly smoother than the exterior one. Other than that they looked identical except on the price tag. The "Marine" sheet was $110 Au the other $47.50 Au.
I have decided to use exterior quality ply for the bulkheads, aligning the better face where it will be visible. The hull bottom sheets will be the "Marine" ones due to the extra laminations which add up to better puncture resistance , all other sheets will be a better quality exterior with the cheaper price tag. My boat will like most other trailer boats spend more time on the trailer than in the water, and when not in use will be under cover.
Therefore I feel the cost saving can be spent on the motor or other areas without degrading the boats longetivity.

[John Blazy]

A concept to consider is saving money on the ply and putting the money into heavier glass cloth and epoxy on the hull bottom. The best marine ply will still get water creep damage from a puncture through six to 10 oz cloth, but I used 'Superply' for my hull (17 bucks a sheet) and sheathed it with 38oz biaxial / CSM mat with an extra gallon of epoxy. Darn near bulletproof. It was put through the test in rough seas re-trailering it and the dings never went beyond my bottom paint.

Copied from another thread:

"You should look into Superply by Roseburg Forest Products. You can get it locally from a plywood distributor (possibly from a lumber yard too, tho plywood dist. sell to cabinet shops, and might sell to you in cash).
Superply is about 20% of the cost of Marine ply, and you can eliminate the shipping if you find a local stocking distributor. I only say "look" into it because it is not officially graded as BS 1088, and does not guarantee void free core, but I sure would use it again in any future boat I build.
I bought it for 17 bucks a sheet for 1/4" and the Luaun / Spanish Cedar face veneers are 1.5mm (very thick) over a fir core, and in all the cutting I did on five sheets I found no voids. If I did find some, I could use Norm's trick and just pour epoxy into the void. I heavy glassed (38oz) over it all anyway, so the grade/brand of ply didn't matter as much anyway.
The face veneers stained and finished very much like mahogony too - close grained, not subject to checking like fir."

Do a web search on Superply.

[Railmeat]

Something else to consider: Workability. Designs that require that the plywood be worked with a plane (like my Penobscot 14) would probably not fare too well when built with other than higher quality marine materials. I'm thinking of the splintery mess that the sheet of luan that I used for pattern-making turned into when cut. I couldn't imagine attmepting to plane lower-quality stuff.

Don

[JimD]

Doug, where are your price quotes coming from and what type of wood are they quoting? Noah's in Toronto has a very nice web site with price and wood characteristic comparisons for several kinds of wood. For example meranti compared to okoume is about 20% less expensive but also about 20% heavier. And except for brightwork doug fir might be a better choice anyway so long as its being painted.

[whb]

Doug

Seems that the price (between various marines and standard ply) differential is bigger in Canada somehow. The fir marine that I have seen here does not impress me nearly as much as the MDO that I have seen and the MDO is less than half the price. I am thinking like John Blazy.

Use the MDO and then put a good quality glass layer on.

Howard

[Badges68]

Hi,
dont see the gain in building in ply then adding a heavy layer of glass.. you may as well build in glass to start with.. all we do now is saturate the outer layer of the ply with a 50/50 mix resin and thinners then an epoxy paint..
don

[Dan Cavins]

Hi Doug. I am hardly the expert but can offer a couple of notes from my experience. One, on MDO, I used quite a bit of it with no reservasion. But I used it in the cockpit and interior. Also, I found MDO that was just crap and MDO that was great. All called MDO. I dunno'? Check around. The great stuff was half the cost of marine ply. Now on the hull I forked out for the marine. It's good stuff. Think about a sensible mix of the plys. Also keep stiffness in mind for anything to be bent. I had some marine ply mahogany, great, but won't bend much. MDO about same. Marine ply fir -flexy! Again, think about a sensible mix of the stuff if cost is an issue. Just a hackers thoughts. Dan

[Banjo]

Dan said,

"Just a hackers thoughts. Dan "

It sounds to me like your far from being a hacker Dan, what you said is good common sense.
Well done.

[L.W. Baxter]

Also to keep in mind-- some exterior plywood is quite good. And some of it is total crap. And the face veneer grades have nothing to do with actual structural qualities. CDX is structurally superior to most AB or AC graded stuff, because the A and B surface veneers are super-thin (because they cut them that way, as they are worth more) and the inner cores are correspondingly thicker. And I suspect the inner cores of CDX are usually DF, as CDX is expected to do structural duty in homebuilding, whereas the inner cores of the fancier stuff are almost surely hemlock or some other garbage, because those grades are used in non-structural jobs, like soffiting and paneling.

If you want to build a boat with exterior ply, use CDX or CCX with an odd number of plies, fill the cracks, paint with epoxy, then cover with latex house paint! That might be how I built my little boat, but I'll never tell. ;)

[davef]

Lots of good comments on here but here is my two cents.

Based on my limited experience, I agree that there appears to be a dramatic difference between the cost of construction grade marine plywood and the premium marine plywoods such as meranti and okume.

I bought marine plywood from Alpine Plywood in Milwaukee, WI and the only cost premium was around 15% over conventional plywood. It's certainly not as pretty but there were no internal voids and the adhesive is waterproof. I used this plywood for the stations and any place where the wood would never be exposed, even if painted.

As a test, I boiled water and dropped samples of the plywood into it. I know that conventional plywood delaminated and the marine plywood would not. Other than that, it looked pretty conventional.

For the cockpit and exposed surfaces I bought Okume and Mertanti. Both had more plys and the face ply was much nicer. The Meranti was much cheaper but proved to be very heavy (unexpectedly so) and if I had it to do over I would have chosen the Okume even at the cost premium.

[davef]

Oh yea... sorry... Here's the web site for Alpine Plywood. They were nice and the prices were very reasonable. Don't know if they're a good choice outside of Wisconsin....

What boat are you building?

Good luck to you.

http://www.alpineplywood.com/

[davef]

Sorry... one last comment before I sign off.

On the Alpine web site, their marine grade is listed under softwood fir and shown as an AB finish....

Available in 1/4, 1/2, 3/4 and 1-1/8.

Any idea what Okume and Meranti actually are? Is that a type of wood? Is it just the facing ply? Someone on here knows....

They were a fraction of the cost of Okume but maybe I just didn't have a good source fo Okume. Once again, the Okume I bought looked like the stuff you make furniture out of, which seemed a waste under painted surfaces.

It would be interesting to compare prices and performance here...

-D

From their web site...

Fir

Description Dimensions Unit Size Alpine Item Number
EXT AB MARINE 1/4" (.25) 48X96 120 15-025-001-48096
EXT AB MARINE 1/2" (.50) 48X96 60 15-050-001-48096
EXT AB MARINE 3/4" (.75) 48X96 44 15-075-001-48096
EXT AB MARINE 1 1/8" (1.125) 48X96 30 15-112-001-48096