below the waterline

[Doug Canada]

I known this will be sacrilege on a Wooden Boat forum, but is (ply)wood the best choice below the waterline? With the wide variety of synthetic materials out there today, is Marine plywood still best?

The marine plywood that I would be using will be glassed and (painted) covered. The wood will be completely sealed.

Wood is 100% more eye catching than any thing out there. But if it not going to be seen, why wood?

Is the cost for synthetic material (sheets / panels) more or less than marine plywood. In Canada BS1088 Okoume -Lloyds Approved is $110. Polymer panels?

I promise to use all wood in the cabin and deck!

Thanks,

[TimothyB]

Hi Doug!

Well, I think you'll have to give us more detail about what your boat project IS before we give you our valuable advice ;)

Marine plywood is fine for bottoms, wood is fine for bottoms, glass works too. We happen to like wood boats here, though. ;) Plywood comes in under that wire nicely, but you would need to fully encapsulate it with epoxy and glass unless you only wanted a lifetime of a few years. Also the concensus seems to be unless you are building a trailer sailer, don't use anything but good quality marine plywood. Its easier to work and likely won't fail you long term.

Thats about all I can say till I know what you are intending to build. Got any pictures? Restoration or new? Sail or power?

--T

[Doug Canada]

It would be a trailer sailer of lapstrike construction (~Cape Cutter 19, see my past posts). Something that would be in the water a week or so at any give time. It is not my intention to have it moored, but for a week or two (summer vacation).

I guess that I am suffering from sticker sock for a piece of marine plywood ($110) in Canada. I need 30 pieces.

I have built a cedarstrip canoe and kayak over the past three years, and it has not even been required to use waterproof glue (I did though). With the glassing of the hull it would be sealed. Any scratchs / bumps would be healed at home.

I guess my question is that if (ply)wood is sealed in epoxyed glass, does it still need to be "marine" plywood.

Please understand that I completely respect the superior quality of Okoume (marine) plywood. Not to mention the natural beauty of the wood. Again, just trying to get other options for hull construction. With out compromissing quality or structural integrity.

Like I said sacrilege.

Thanks again,

[Ron Williamson]

Doug
You might consider MDO,which is high quality exterior Doug.Fir,with a smooth overlay of fiber and resin.It is used for highway signs and the like,and has an excellent reputation.1/2"unprimed should be less than $50/sheet.
R

[WWheeler]

Doug:

You may want to try noahsmarine.com in Toronto. You could pick it up and save the freight too. Prices are much better than you've been quoted. See below for the Meranti price. We could debate the merits of the different grades, but this is apparently decent quality.

B/BB Meranti face & core veneers. 1.5 mm face veneers. Equal or nearly equal laminations. WBP Gluelines. Medium weight, good bending & finishing characteristics. Excellent structural plywood. Meets BS 1088 Standards Pending Lloyds certification.

Thickness
Weight
# of plies
Price/sheett
Price/10+ sheets

1/4" (6mm)
24 lbs
5
$ 57.25
$ 51.53

3/8" (9mm)
38 lbs
5
$ 80.00
$ 72.00

1/2" (12mm)
50 lbs
9
$ 87.50
$ 78.75

5/8" (15mm)
60 lbs
11
$ 108.00
$ 97.20

3/4" (18mm)
75 lbs
13
$ 128.00
$ 115.20

[Paul Griffin]

Doug

The 18'6" sailboat that we sail was made of fir ply at least 20 years ago. It was glassed over, and it's still doing fine today. Our is a sailboat not a piece of art. We are happy with it.
As for cost, I have a $5,000 pile of lumber out back just for the deck of our 26' boat we are building. :D

[TimothyB]

All good advice. MDO is a great alternative to Marine ply, especially if you are excapsulating.

But.. if she is going to be a trailer sailor, and cost is a concern, then maybe you should think about building her in real wood? No goops and stuff because heck, that stuff costs money! And make her out of white pine! That stuff is cheap, or even free depending on if you can find a friendly sawmill guy to throw you the offcuts, or if you can find a guy with a few trees in his backyard that you can cut down yourself and use for timber. Find a local guy with a wood mizer!

Heck, you could use galvanized nails and splurge on some real enamel paint for the thing, and still be way under the price of using marine ply and epoxy. Make your own wood blocks, use ordinary rope for line, and you'd be in like flint with nary a dent in ye olde wallet.

If you really really wanted an encapsulated bottom, you could then do it with one course of dynel or Xynole cloth and epoxy for not too much money. Probably something like $100.

http://www.gartsideboats.com/catsail2.php#doherty

http://www.gartsideboats.com/catsail3.php#24canoe

Theres 2 for some inspiration smile.gif

--T

[Venchka]

Don't go away. I'm pondering and cyphering on cutting materials cost. We need to look at the whole picture. Stay tuned.

[Bob Smalser]

But.. if she is going to be a trailer sailor, and cost is a concern, then maybe you should think about building her in real wood? No goops and stuff because heck, that stuff costs money! And make her out of white pine! $3500 bucks for plywood for a small boat?

$3500 here and in BC will buy you a whole truckload of DF export-grade 41' sawlogs....enuf for a small house frame.

Got any small sawmills cutting local oak and cedar up there?

Use the search feature for "sawmills" and you'll find portable mill websites glad to tell you who owns one nearby.

[Venchka]

This is the kind of stuff you should be looking for.

Wood Find (http://media5.hypernet.com/ubb/ultimatebb.php?ubb=get_topic;f=4;t=001997)

Also, A&M Lumber is an hour east of you. They had green 8/4 black locust air drying this time last year. It would be perfect for structural framing down low, around the and below the mast, chocks and cleats on deck, etc. They also stock doug-fir, white, yellow and red cedar.

More on plywood, fiberglass, etc. later. Stay tuned. Film at 11.

[JFH]

Doug,

I am south of you on the lake, just outside of Langton, Ontartio and I build/restore mostly lapstrake boats. The plywood you need should cost you about $50.00 CAD per sheet of 1/4". Marante is about $10.00 a sheet cheaper. You can download Noah's catalogue and price the stuff yourself. An 18' boat with good frame support and made of 6mm would be light and fast. Going thicker will cost you more and remember that if your plans call for 3/8 solid stock, you will get similar strength from 6mm quality plywood. You will just need to consider that when lofting your molds.

To answer you question of using cheaper stuff,...I would use it if I didn't really care about having it for more than 10 years and if it was sealed with Industrial Formula's S1 epoxy first (check Noah's for that stuff too). Because I want my grandchildren to be able to use my boats when I'm long gone,...I only use the best materials and to hell with trying to save a couple of hundred bucks.

Let me kow how it goes.

Jim Hammond
www.innerbayboats.com (http://www.innerbayboats.com)

p.s. just finished a 1958 Century Raven...will post pics soon...

[Bob Smalser]

http://www.sawmill-exchange.com/index.htm

http://www.mobilemfg.com/

http://www.baileys-online.com/

http://www.woodmizer.com/welcome.html

Check the phonebook and the mill manufacturers/sellers for portable sawmillers locally. Local tree service guys will know of them, too. Few advertise.

[Stargazer14]

I have to question these estimates on the life expectancy of the plywood bottom. Even shethed in epoxy some expect a few years?
Well if plywood today is a better quality than it was 35 years ago, I'd say your boat can outlast you by a few years. My '67 skiff still has its original 1/2" ply bottom, and it's shethed in nothin' but old bottom paint..... :rolleyes:

Plywood sounds like a great way to go for your trailered boat.

[Venchka]

Originally posted by Doug Canada:
...is Marine plywood still best?

The marine plywood that I would be using will be glassed and (painted) covered. The wood will be completely sealed.
...
Is the cost for synthetic material (sheets / panels) more or less than marine plywood. In Canada BS1088 Okoume -Lloyds Approved is $110. Polymer panels?

I promise to use all wood in the cabin and deck!

Thanks,Ok, first things first...

http://www.dixdesign.com/cc19plysec.gif

Interestinly, the Cape Cutter 19 cross section is nearly identical to my Caledonia yawl up to the sheer. She's planked with a 12mm bottom and 9.5 mm topsides. Floors and bulkheads for lateral support. Darn stiff boat she is.

Moving right along.
The marine plywood that I would be using will be glassed and (painted) covered. The wood will be completely sealed.Why glassed? Is it because:

A. The designer said so on the plans? If he said so, is it because the underlying 9mm OKOUME plywood all by itself isn't strong enough for a 2,000 pound boat? Okoume plywood might be great in a wee pulling boat, tender or canoe. Maybe not so great in a ton of boat with coastal cruising in mind.

B. Adding fiberglass to protect the plywood gives you a warm fuzzy feeling?

C. You feel a need to add a covering to protect the bottom from bad nasty stuff? Xynole might be a better choice for abrasion resistance. Search here for Tom Lathrop's test results of various cloth used for abrasion resistance.

If the answer is "A", write to Mr. Dix and ask him if the fiberglass can be omitted if you use stronger plywood. If the answer is "B" or "C", keep reading.

Look at the cross section again. How do you propose to get the cloth around the plank laps? If you do add cloth, what's the bottom going to hit? This isn't a flat bottomed boat you drag over rocks and sand. Sure, you might hit the sharp edge of a rock ledge with the garboards, but I don't think fiberglass will keep the water out in that case. If you really think it's a good thing to do, you could put fiberglass or Xynole on the garboards. Why am I telling you all of this? I went through the same discussions during the last year and came to the conclusion that it wasn't going to do enough good to justify the effort. In fact, if water vapor gets past the cloth, it can do more harm than good.

You said the wood would be completely sealed. Amen to that. But, there's sealing and then there's sealing. C.P.E.S. and Kirby's paint seals wood very nicely at a reasonable cost. That's not the only way, but it's one way.

Now, for the alternatives to marine plywood. MDO was suggested earlier. Good stuff. Not expensive. The doug-fir core is stronger than okoume. Professional boatbuilders use it and stand behind it. I couldn't find a source in Canada with GOOGLE but I came up with some numbers from Harbor Sales in Maryland.

"Medium Density Overlay-Exterior plywood panels that have a resin impregnated fiber overlay that has been fused to the surface of the panel. The overlay virtually eliminates surface checking, and looks better, longer after painting. Available unprimed or primed."

MDO 2-sides, 4'x8'x3/8" @ $42.50CDN
MDO 2-sides, 4'x8'x1/2" @ $51.00CDN

It is also available in MDO 1-side as well as 4'x10' and 5'x10' sizes. Thickness range is 5/16" to 1-3/8".

If it were my Cape Cutter 19, I would use 2-sided MDO for everything except parts that are glued up from 2 or more layers. In those cases, I would use 1-sided MDO and or plain doug-fir plywood to get a wood-wood glue line with MDO exterior faces. Fill any voids with thickened epoxy. Seal the plank edges with strips of doug-fir set in epoxy.

I would use 1/2" for the bottom and maybe put in 2 fore & aft stringers equally spaced between the keel and outboard edge. The rest of boat would be 3/8" or less in non-critical areas. For framing, black locust or white oak down low and for anything that I didn't want to break. Ever. The rest of the structural framing could be a mix of doug-fir and Alaska yellow cedar. White cedar for soles, floorboards and anyplace I wanted to keep weight down that wasn't heavily loaded.

Seal the real wood and any plywood you want finished bright with C.P.E.S. Paint with Kirby's. Bright finish is up to you. Epifanes rapidclear looks great new. I'll let you know later how it holds up.

Or, build a strip planked + cold moulded hull out of native Canadian woods. Call Paul Gartside. His 18' Spartan is tres nice!

[Ron Williamson]

Regarding MDO,Commonwealth Plywood,Waterloo.
1 800 563 6081.They have a place in London,IIRC.
Good guys to deal with in Waterloo.They're wholesalers but don't mind dealing with decent retail customers.They have lots more than plywood but ya gotta ask.
R

[High C]

There are a lot of plywood trailer boats out there that are well over 20 years of age that were built with lumber yard ACX plywood. Many of them are painted only, no fiberglass. A trailer boat with fiberglass (5 or 6 ounce) cloth and epoxy should outlast you, regardless of the type of plywood.

Be careful with the inevitable voids, though. Non marine ply will have voids in the plies here and there. Be sure to fill the ones you see with thickened epoxy before you do that first wetout.

[Doug Canada]

I assumed that glassing the hull was the only way / option to seal and show (the beauty of) the wood.

All the best,

[Venchka]

Originally posted by Doug Canada:
I assumed that glassing the hull was the only way / option to seal and show (the beauty of) the wood.

All the best,You mean, like, an all bright finished hull? All the plywood? Good luck. You'll need to put the best available highest UV protecting marine varnish on all that epoxy. Lots of varnish. Double digit coats. And recoat often.