Practical about plywood

[Paul G]

Plywood,

I know the subject has been thrashed but I cant seem to find a thread that succinctly deals with my questions.

After giving up hope of finding the right boat out there I am building a 20 foot lapstrake boat. So I want to get the fundamentals right. I have been told that no plywood is durable and all will eventually rot and delaminate if water gets in. Some are apparently better than others, regarding strength and longevity.

Many regard Occoume as the best ply but it is weak, light, nondurable and soft. My experienced marine ply supplier wont sell it as he has had rot problems. However it absorbs a lot of resin and glues well. Will it last the distance? Some builders I have talked to say only seal one side of ply with epoxy and use paint on the other which will allow the wood to breathe. theory being that even if epoxied both sides eventually water will get in, as epoxy is not 100% waterproof over time, especially given the usual variations in mixing, and environment variables that occur at home. Others say seal it up and it will last forever. Which is true?

One more. Is it better to use a thin strong ply or a thicker weak one? I cut a strip of 12mm meranti and a strip of 7.5mm hoop pine and the pine was only marginally weaker than the meranti! I figure that it costs less and the since I will be sheathing why not use the lighter thinner material. thoughts?

Paul.

[Captain Pre-Capsize]

Over the past several years I have read accounts of people boiling pieces of ply to test durability. Alternatively others have found pieces of ply washed up on shore that clearly had been floating around for a good long while. Weathered yes, delaminated no. It is much more dependable than you may think and I can assure you that if you are going to build a boat you are going to take mighty good care of it.

As to painting the outside, I'd do it. Much easier maintenance. Leave the interior bright. My two cents...

[ssor]

I have a Nymph pram that received indifferent care for about four years and developed some rot in the forward transom. The problem seemed to be the result of water getting into the ply and not having as easy an escape as an entry. Even after several weeks of sheltered drying the plywood was still damp. On the other hand I have a piece of the same plywood ( Home Depot 5 mm Meranti)laying out in the weather now for about a year and it is doing fine. There is no paint or other "protective finish" on either side. I often find that Meranti has been used under ceramic tile on bath room floors and has failed because of rot. Again it is easier for the water to find access than escape. Liquid water in, water vapor out.
Do I have an answer? NO. Some ideas? yes.
First of all plan all of your joints to present the least posible path for water to find entry.
Second if at all posible use copper napthanate on the edges of the plywood if it won't interfere with bonding.
As to the statement that no plywood is perfectly durable, neither is any other species of wood! Some are just better than others. There was a discussion here a few days ago about overlay plywood and as I recall there is a grade of plywood produced for highway signs that is at least as good as the best marine grades. Look through the latest 2 or 3 pages.

[ 06-11-2005, 10:43 PM: Message edited by: ssor ]

[Venchka]

Talk to John Welsford. I reckon he has forgotten more about small boats, plywood, how to finish them and how to make them last decades. John is in the middle of building a new house, office and boat shop so he may not answer immediately, but he will answer.

Contact John Welsford:

Phone: 64 (0) 7 357 5354
Fax: 64 (0) 7 3575354
email jwboatdesigns@xtra.co.nz
Post Po Box 314
Ngongotaha
New Zealand.

What are you building?

Wayne
In the Swamp. :D

[ 06-11-2005, 10:44 PM: Message edited by: Venchka ]

[seafox]

I don't agree with the boil test because who sails in boiling water? the delamination occures because their are gaps in the plys not gaps in the glues. seal it up the very best you can and there after repair damaged spots rot occures only if the moisture level is high enough will this boat be in the watter all the time?

I have two ply wood boats built in 86 and 87. they have never been covered they in fact have fiberflass over the joints one I think is polyester andthe other glovet ( a epoxy) no delamination I sealed them with thompsons waterseal before painting one has done better than the other. both built with AC exterior plywood

[Kevin5]

Talk to Sam Devlin, he has no qualms about using plywood. Large boats in the water all the time.

[Leon m]

web page (http://www.boat-links.com/plyfaq.html)

[Cuyahoga Chuck]

The boiling test is to determine if WATERPROOF glue is pesent. Interior grade glues will delaminate if boiled. The old BS1088 test was 24 hr. of continuous boiling. One builder put scraps of okuome in his steam box every day till it failed. When it did it was because the wood fibers fell apart.The glue line was still good.
Plywood is a man made laminate. The reason that okuome is specified for high end marine use is that it is a tropical hardwood that is capable of being verneered into 1 and 1.5 mm sheets of good size. Since it grows 12 months a year it is more homogenous and more stable than ply made with temperate zone softwoods. It is also eminently easier to finish and is the prefered ply for bright finishing.
The thickness of planking has a lot to do with the shape being covered. Since ply only comes in specific thicknesses going to the next increment may not be practical. Thicker ply may be too stiff to bend to the shape that's wanted.
6mm okuome is 5 verneers thick. Being a laminate is has much greater impact resistence than an equal thickness of most any dimensional lumber.
If by "sheathing" you mean fiberglassing I hope you keep us posted on how it goes. For many years Iv'e been stuggling to 'glass over hard angles and trying to put 'glass over lapstrake knuckles is something I would most certainly not attempt.
Charlie

[Venchka]

Ok, I've been harboring these thought for too long. Look out Martha, here comes the smut.

Once upon a time, in a rain forest far far away, there were real hardwood trees. Their strength, hadrness, appearance and durability closely matched western hemisphere mahogany. When Honduran mahogany got scarce and expensive, the African look and function-a-likes were used to produce marine plywood. And it was good plywood. Really good plywood.

Alas, the really good forests were depleted, just like the Honduran Mahogany earlier. Prices for the lumber and plywood rose.

Boatbuilders said, "Ouch! This stuff costs too much. We want cheaper plywood." Everyone knew that the really really good plywood was better. No one was willing to pay for it.

Enter okoume, a.k.a. gaboon. A trash wood that the lumber folks had bypassed to get to the good lumber. They now began cutting and exporting okoume for plywood production. The idea was to provide a low cost alternative to the really really good marine plywood.

"Please, Mr. Lloyd's, won't you certify our nifty new cheaper okoume plywood for use in marine structures?"

"No way," said Lloyd's. The wood isn't durable. It doesn't belong in the same places where the good stuff is used.

"If we add a fungicide to the glue, will you approve our okoume plywood?", the lumber mogules whined.

"OK, I guess that will work," Lloyd's sighed, caving in to the giant plywood industry.

And that, boys and girls, is how we got okoume plywood which is lighter, weaker, less durable and not as nice to look at as the really really good plywood.

Fast forward to the present...

Boatbuilders said, "Ouch! This okoume stuff costs too much. We want cheaper plywood."

Folks in SE Asia replied, "Take a look at our nifty new meranti plywood."

Thus ends the lesson for today. That's my story and I'm sticking to it.

Wayne
In the Swamp. :D

[RodB]

The Albert Strange "Wenda"..."Sally" was built glued ply lapstrake with 1/2" Sapele and fastened, very expensive but very good. The only epoxy was the lap joints. The exterior of the hull was then varnished several coats then painted, the interior was varnished 7-8 coats and the rest of the boat was built traditionally. This is a trailered canoe yawl that is in great shape going on 10 years, with only varnish and paint. The end grain was protected on the planks by gluing strips of Honduras Mahogany, but that was considered overkill and the builder would only coat the edges with several coats of epoxy next time. Perhaps the builder of "Sally" will chime in here.

My stitch and glue skiff has been built per recommendations of Tracy Obrien, designer and boatbuilder (he's probably built over 50 boats in the past 25 years). The entire boat is built with mostly Okoume (Malvaux- Lloyds approved) and 1/4" Merranti as an additional outer layer on the hull bottom. I sent for samples from a few suppliers and the French Malvaux (from World Panel) was heads and shoulders above the rest.

The construction was total encapsulation, all exterior surfaces glassed with 6 oz cloth , all other surfaces double or triple coated with epoxy. The entire boat will be primed with a hotter solvent (Xylene) high build primer and painted with Kirby's Alkyd enamel.

I have been assured this boat will be around long after I'm gone.

One final note, most boats will last a very long time if maintained with any degree of care. A piece of furniture, varnished or not, will last many many years if left in a garage where it is protected from the elements and the sun. In boats, we abuse them, leaving them outside with no protection from the elements, and some do better than others, depending on construction and materials. Most boats would have surprising longevity with proper covers, ventilation, etc...all of which just takes a bit more time and effort.

RB

EDITED 6/12

PAUL G: The method described for an improvement on glued lapstrake construction where the planks are glassed on both sides prior to assembly should be worth considering for the boat you suggest building.

[ 06-12-2005, 01:30 PM: Message edited by: RodB ]

[Venchka]

Originally posted by RodB:
...1/2" Sapele

RBThe last of the really really good African hardwood plywood. Sipo, utile and khaya seem to have gone the way of the dinosaurs.

Wayne
In the Swamp. :D

[Jay Greer]

Most members of this list know my opinions of plywood.
It is all wrong and the rest of it is questionable! In over fifty years of boat building, I have worked on all manner of boats that have been brought to me for repairs of plywood components. Sadly the most damaging examples have been caused by plywood subdecks and bulkheads that have either, rotted, delaminated or both and contaminated sorrounding wood that otherwise would have been servicable had it not been for the plywood components that were used.
A case in point is a pretty little New England style lobster boat that in for repairs at our digs as I write this.
The hull is built of lap strake white cedar on white oak frames with copper rivet fastenings. The deck house was built of honduras with a glassed plywood coach roof. The plywood delaminated. Tore up the junction with the cabin sides, rotted and infected the side planking of the deck house. Result? The hull is good. However, the entire deck house must be replaced for the sake of the dimwitted builder trusting in the BS plywood advertising rather than using common sense and building the coach roof of T&G cypress, cedar or doug fir covered with white lead and canvas. Suffient evidence over the past fifty years should be enough to convince one that plywood is not a durable building material for boats. But then as P.T. Barnum so aptly stated, "There is a new fool born every minute!"

[RodB]

Maybe "mixing methods of construction" is part of the problem described above. How many of the problems encountered over the years involved polyester resin...and other mistakes of not building properly with epoxy and fiberglass and plywood... like unbalanced structures or poor quality materials. There have been many technical articles by many highly qualified "experts " singing the praises of quality marine plywood in boat construction. ...and the methods required for same... one advantage usually described is the glue layers in plywood slow the water ingress immensely compared to solid wood. I think protecting/sealing endgrain of plywood would always be the cardinal rule.

I would think plywood failure would have several explanations first of which would be using substandard plywood for construction in the first place. Second would be improper construction that would not provide appropriate moisture protection.

For example a few months ago a couple friends and I looked at a -for sale- "professionally built " NIS 18 " that was built in New England then brought down here. I noticed the deck house though glassed on the exterior... was standard exterior plywood left as bare wood on the interior surface of the roof. Although the exterior of the hull was glassed, the interior was only glassed below the waterline. Several items like these made my friend rule out the purchase of the boat straight away...simply because of overall construction errors (in our opinion)... and the boat was quite recently built.

Most of the rot I have seen in our hot, humid environment has been substandard materials like non-marine ply, improperly protected during construction and neglected over time.

Are there not many many very expensive coldmolded or strip/coldmolded sailboats with Dynel sheathed marine plywood decks that do fine and have great longevity despite the plywood? Are all epoxy constructed boats with plywood going to have catastrophic failure sooner or later?...sure are lots of folks going to lose lots of money.

Sailboat designs involving plywood: One problematic area in plywood built sailboats would be the lazarrette seats where solid wood 1X2's on edge would be epoxied to the outer circumference underside of the plywood cockpit seats, but not glassed (took too much time to radius the corners and wrap glass for professional builders). Now these 1 X 2's held all the weight and sat in water if water didn't drain properly from the perimeter of the lazarrette openings. One suggested fix was to buy treated wood that had been sitting around long enough to be really dry...then they could be glued to the underside edges of the seats ...painted, etc...and would withstand sitting in water much better without failure. A home builder could take all the time he wanted to properly construct the lazzarrette seats so that all end grain was protected plus solid wood was protected.

RB

[ 06-12-2005, 02:19 AM: Message edited by: RodB ]

[Paul G]

This is the one

http://www.varuna.co.nz/images/scout.jpg

19 fthttp://www.woodenboat-ubb.com/ubb/icons/icon7.gif
250kg ballast
untold charm

I looked at a lot and this seems to fit the bill.....if you cant live on it , bring it home!

much bigger is a pain in the backside to handle by oneself. I dont want to pay the extra for a keeler and its maintenance. This one will probably be a yawl. galv fittings wooden blocks, NO stainless, built as economically as is seaworthy.

[Paul G]

The discussion on ply has brought to light a few new ideas, This boat will live on a trailer so that is perhaps one thing in its favour.

Who has a favourite ply?

The point about letting ply breathe a bit by epoxy coating only one side seems to have some merit. But isnt paint meant to be waterproof if its doing its job?

The boat by the way is called Scout, and is by the hand of John Welsford. He reckons he will have a few drawings to get me started in the next few weeks. I said that he better hurry as i have a friend who is itching to sell me his Cape henry 21 planset, and that is very tempting! The scout has a sweet look reminiscent of eun mara, which I sorely wanted but crossed of the list after speaking to a few owners
who loved the boat but said it wasnt very practical.

[BillyBudd]

Here in the USA I'm using meranti marine grade (they say it is BS6566 or whatever...) plywood (1/2" and 1/4" nominal, actually mm sizes). It comes from a plywood plant in Malaysia. That isn't too far from NZ and I'd think it is available to you for less money than here on the east coast of the US. Got mine from Noahs Ark in Toronto, Canada by way of Buffalo NY/USA. You might check out their website to see what they say about it. My canoe is the occume stuff, very thin 4mm, BS top-grade (BS1088-whatever) and is over 8 years old and going strong. But as a canoe it is mostly in the barn with only a day now and then on the water.

The meranti is heavier than the occume and perhaps that'll suit you?

[Scott Rosen]

Letting ply breath on one side makes no sense at all. The glue lines are waterproof. The only way water gets beyond the outside layers of a good marine ply is through the endgrain, which includes fastener holes.

Plywood has 360 degrees of endgrain. Seems that folks forget that when they are building with it.

My experience, while not as extensive as Jay's, shows that every plywood failure is the result of builder/designer error. Failure to seal endgrain, too many fastener holes and poor ventilation are on the top of the list.

Plywood subdecks or bulkhead-backings, with the outside layer mechanically fastened (i.e. screwed) to the plywood, and the plywood butt joints unsealed, are the worst offenders. Next are plywood cabin tops with endgrain unsealed, or worse, with endgrain glassed with polyester or covered with a trim piece which allows water to get between the trin and ply endgrain.

Use the best marine ply, understand the materials and build it properly.

[Tristan]

Use fir exterior or marine grade. Seal all edges with epoxy, or better, glass tape and epoxy. Keep water out of the plywood, inside and outside of the hull by glassing (with polypropylene if fiberglass is too heavy). A fellow in Coconut Grove (Miami) built beautiful boats about 45 years ago, decks and cabins all marine ply, no resin, tape, or cloth. The decks and cabins ALL rotted. I was involved in rescuing one of them by rebuilding the rotten portions and encasing the deck and cabin in cloth and resin.

[ssor]

One of the questions that needs asking is; How much rot do you find before you have to realize that there is a problem?

Just one improperly sealed penetration that allows water in will be suffient to start trouble with any non-durable plywood. Also unmentioned is the availability of pressure treated southern pine plywood. I know that it isn't pretty but "pretty is as pretty does".

[Gary E]

What kind of plywood were all those Chris Craft Sea Skiff's made with in the 50's and 60's? Fir?

Same for Lyman's and a of lot other names that escape me now.

They hold up very well for being so old.

[RonW]

I fail to comprehend the discussions on plywood.
Occomme has become popular due to the light weight, solid veneers, and it stains and paints well, not to mention the false advertising and hype concerning it's durability.

Seal the edges with epoxy and cover it with epoxy and fiberglass cloth, now bolt it to the front of a building and paint a name on it and call it a sign. Let it set there day and night through rain and shine, heat and freezing and watch it go to hell in probably a couple of years at most.
So this is great stuff for building a boat hull out of, yea right.

Build a kayak or canoe from ocummee and use it gently, wash it out after each use and hang it upside down in your garage and it should last a very long time.In fact forever if it isn't exposed to the weather or hard useage, might even end up in a museum 200 years from now. Now use 3/8 or 1/2 inch and nail or screw it a frame system and call it a BOAT, that sits on a trailer outside and has areas that will collect dirt and water, after all you can't roll it over and rinse it out and hang it upside down in the garage, and problem areas devolop.

Ken Hankinson highly recommended mdo or hdo sign panels, devoloped for the state goverment for making road signs around 50 years ago.But you won't find it in 1/4inch or some millimeter for making kayaks.In the last 20 years or so all the marine architects that design plywood boats also sell epoxy and fiberglass cloth to subsidize there income.After all good marine plywood- good old american made douglas fir marine plywood looks terrible with just a paint job and the grain shows through. So laminate fiberlass on top of it for a nice paint job. The sign material already is made to avoid this problem.

http://www.woodenboat-ubb.com/ubb/ultimatebb.php?ubb=get_topic;f=1;t=011666

My next boat, very shortly, will be highway hdo.

Wayne's remarks above on his thoughts,are dead on, and Scott's remarks concerning construction method are dead on.Proper Plywood construction is different from carvel. In the 50's plywood was attached directly to the frames in place of carvel, as in sheet construction, which again is different from lapstrake, but the flex of the frame put pressure on the fasteners and caused egg shaped fastener holes which allowed a place for water to enter and cause delamination. Now frames have length wise stringers for additional stiffness and to allow air circulation.Total air circulation is the big secret. And not having the ply attached directly to a frame, even with limber holes, there will be a dirt residue that collects behind the frame, and the dirt residue will suck moisture from the air and you have a damp substance laying next to the frame on the ply.Trapped moisture.

[ 06-12-2005, 10:14 AM: Message edited by: RonW ]

[Venchka]

Paul,

You and John have been keeping secrets, eh? A slightly shorter Penguin. Good on you! I repeat: Listen to John. He knows where the good plywood is in New Zealand.

Thanks for the first peek at a new Welsford design. Now I know why the little two berth cruiser keeps slipping down the list. Nice looking boat.

Wayne
In the Swamp. :D

[Bob Smalser]

Originally posted by Jay Greer:
...In over fifty years of boat building, I have worked on all manner of boats that have been brought to me for repairs of plywood components.

Sadly the most damaging examples have been caused by plywood subdecks and bulkheads that have either, rotted, delaminated or both and contaminated sorrounding wood that otherwise would have been servicable had it not been for the plywood components that were used...
Plywood was developed and became popular in the '30's and '40's because we had cut all the forests down, making good wood scarce. Plywood was cheaper than the remaining good wood.

Today, the forests have all grown back, there is a modern portable sawmill somewhere in almost every arborist operation, both urban and rural, and the plywood and plywood boat industry has evolved into one of those consumerist monsters eating every brain they can. Plywood has dramatically declined in quality over the decades and the stuff suitable for boats is very expensive, along with the crude-oil based plastics needed to build with it.

1) Today, traditional boats can be done much less expensively than plywood boats.

2) Old carvel boats suddenly relegated to trailer life leak. New carvel boats beginning life on a trailer don't have to leak any more than plywood boats do. They are also much easier to repair than plywood boats.

3) Solid wood is much more satisfying to work than plywood and goo.

4) The folks who tell you that you don't have the skills necessary for traditional joinery, yet have you bevel or butt those crumbly, unpleasant plywood edges accurately to take a batten and fillet, are hyping you.

[ 06-12-2005, 10:46 AM: Message edited by: Bob Smalser ]

[Dave Lesser]

Following is a cut and paste from the link provided by Leon M yesterday:

MDO (medium density overlay) is excellent for boatbuilding. It is usually produced to state highway department specifications and is supposed to last in extreme weather conditions with no checking, with only paint for protection for as I remember fifteen years with no deterioration. It is usually pressed up with douglas fir cores and centers, with a thin face on either side of lauan then over that the MDO, which is a phenolic resin impregnated paper which is stippled to easily take and retain paint. The MDO is impossible to separate from the plywood and is the reason why highway signs last practically forever.

HDO (high density overlay) on the other hand is not good for boat construction. While it is even more indestructible than MDO, paint won't stick to it, and not much else will either. HDO is built using the same process, the paper is a heavy phenolic coated paper, but it is constructed to be used primarily for concrete forms, and formulated to be slippery so that nothing will stick to it.

[RonW]

Couldn't agree more with those that say real wood is the way to go. BUT.
But there is a place for plywood boats (IF) designed and built properly.
Look at boats like the pacific dory, what better design could you find for plywood. Solid frames, longitudial stringers with hopefully a quality plywood over with plenty of air circulation. There are plenty of them still fishing that are 40 years old and going strong.Nice size trailer boats.

Anyone building from plywood should get Glen-l's book boatbuilding with plywood, after all he does have 50 years experience in designing plywood boats. Ken Hankinson plans as well, and Ken actually worked for glen for a long time.

Properly designed, built and plenty of air circulation with hopefully a quality ply that will stand up to a marine enviorment.

Dave's cut and paste comment on mdo is right on. But the part on hdo is half right and half wrong.
For the most part it is right,most hdo panels are designed for concrete forming and will not hold paint. And believe it or not is not quality enough for boat hulls. They allow voids in the hdo that they do not allow in ply that is designed for signs, and the finish is harder and slicker, more of a plastic, and on the higher quality concrete panels a real thick and very slick plastic type overlay that nothing wants to stick to including paint.
BUT the highway hdo is designed specifically for state goverment highway signs, ready for paint or vinyl lettering. It is the ultimate in resein overlay sign material and should be the best ply you could buy for a boat hull, bare none.
It is also cheaper then occumme and sell for about $80. a sheet for 1/2inch and no reason in the world to epoxy and fiberglass the outside. More money and labor saved.No worry about delaminations.

[RodB]

In all fairness...


Seal the edges with epoxy and cover it with epoxy and fiberglass cloth, now bolt it to the front of a building and paint a name on it and call it a sign. Let it set there day and night through rain and shine, heat and freezing and watch it go to hell in probably a couple of years at most.
So this is great stuff for building a boat hull out of, yea right.
Ron W
----------------------------------------------------------
What kind of longevity would you get with a little primer and decent paint on the exterior of your "sign".... ? With a little UV protection this sign could last a long time...


2) Old carvel boats suddenly relegated to trailer life leak. New carvel boats beginning life on a trailer don't have to leak any more than plywood boats do. They are also much easier to repair than plywood boats.
Bob Smalser

-----------------------------------------------------------
Bob, please describe the particulars on "new carvel boat's" construction.

RB

[ 06-12-2005, 12:20 PM: Message edited by: RodB ]

[Leon m]

I'm suprised nobody has mentioned Bruynzeel Suprahect Mahogany ply, thats what I'm building my Sharpie out of ,and I must say,I havn't seen a better ply on the market...5 ply,20yr. Loyds regestered...Good stuff.

[RodB]

Ron W

I would think most folks choose Okoume because of its weight and cost... and you pays your money and takes your chances. Using Okoume would especially require one to "build properly" per Scott and Tristan above....it would go without saying. There are certainly some really good plywoods still available, although expensive such as Sapele.
---------------------------------------------------------------------
It would be interesting to see how much one could build a reasoable craft such as, say a hard chined 25 foot sailboat, built either with quality marine plywood or using traditional construction and quality solid woods. I personally would not choose Okoume for such a major project, but pay the extra for Sapele if building with plywood. The cost of materials is not all that much in such a large project when considering all the labor and time involved. I would have suggested a Sharpie but most folks building a sharpie would not be as likely to select any higher quality wood than neccessary if building traditionally. This would be an interesting comparison as many folks comment on the "less cost" of building traditionally. Perhaps this less cost applies ot smaller boats.

Three years ago I purchased 30 sheets of high quality 1/2" and 3/8" Okoume for about $1700 including shipping from Miami to Dallas...to build my 18 foot flats skiff. I chose Okoume mainly because of weight and because I was assured it would last a long time if built with properly. I also purchased a few hundred dollars worth of honduras mahogany and about $1200 worth of epoxy and cloth, etc .... Leaving out the outboard motor and trailer it still comes to a chunk of money...which resulted in a very strong, fully encapsulated custom flyfishing skiff that would cost around $16K if you purchased a similar craft built of fiberglass(hull only).

Considering trailering as one of the main criteria, I would be open to suggestions as to other methods of construction to have considered and estimated costs? (18' LOD, 19' 6" LOA, 66" bottom, 84" beam, 12" wide sheer decks, large decks fore and aft, center console, 11 feet of cockpit floor/sole).

http://www.imagestation.com/picture/sraid168/peeec0a8943d9106f86f10c10a1cc1204/f4286233.jpg

RB

[ 06-12-2005, 01:08 PM: Message edited by: RodB ]

[Gary E]

Are those bait tanks hanging on the transom or just more floatation?

or maybe a sorta swim platform?

[George Roberts]

The fact that I can go out and buy solid lumber sufficient to build a 30' boat should be proof that there is no shortage of boat building lumber and that there never was.

Plywood is popular for production building because the properties are more predictable than solid lumber. The wholesale/retail markets are also better.

I expect that plywood boats could be build and maintained as well as any other style.

[Bob Smalser]

Originally posted by Jay Greer:
... plywood subdecks and bulkheads that have either, rotted, delaminated or both and contaminated surrounding wood that otherwise would have been serviceable had it not been for the plywood components that were used....
Resaw thru the gluelines of a plywood scrap and toss the lams into a pint jar of linseed oil. Do the same with the same thickness, moisture content and volume of Doug Fir lams resawn from solid heartwood.

Then remove the lams from both jars and compare how much linseed is left in each. The plywood is clearly missing something for it to soak up that much oil.

Besides the unnatural grain structure remaining in rotary-cut lams, what it's missing is mostly lignin, the "glue" that holds the cellulose fibers together.

It's gone because the plywood lams are tortured pretty severely in the manufacturing process. The log is steamed to ease the passage of the knife thru the spinning log, then the wet lams are quickly and severely dried before gluing.

Doesn't surprise me a bit that the longevity of plywood doesn't match the real stuff.

[ 06-12-2005, 04:31 PM: Message edited by: Bob Smalser ]

[Billy Bones]

I've heard of dismastings.

I've heard of capsizes.

I've heard of all manner of rigging failures.

I've heard of rudder posts failing leading to sinking.

I've heard of prop shafts failing.

I've heard of keels falling off.

I've heard of planks failing.

I've heard of fasteners failing.

I've heard of rust and rot in all types of boats.

I've heard of UV degradation.

I've heard of seacocks, stuffing boxes and keelcoolers failing.

I've heard of poor building techniques leading to failure.

But I've NEVER heard of a maritime casualty resulting from any of the inherent qualities of high-quality marine plywood, properly used.

(and I've also heard a LOT of noise about plywood from people who haven't built a boat or are building their first.)

BTW, I much prefer meranti to okoume, having now used both.

edited to add, plywood is harder if not impossible to repair in some cases. One of the joys of a traditional wooden boat is its repairability.

[ 06-12-2005, 09:22 PM: Message edited by: Billy Bones ]

[RodB]

No, not bait tanks...the boxes are for additional floatation to keep the hull level when accelerating from a standstill. Those boxes are called "sponsons" and are extremely common on the gulf coast flats boats.

Amen Billy Bones.

RB

[Jay Greer]

Trying to convince a confirmed plywood user that the material will not last, is about as easy as convincing a confirmed smoker that they will, most likely, die of a disease that is directly related to the use of tobacco!