The ulitmate plywood discussion?

[Howard]

Seems like all plywood boat forums kick this topic around ad nauseum....so maybe we can have it out once and for all.

I'm coming to this party late, having started (and hopefully will finish) my first boat at age 50. But having caught the bug....and knowing that what I want in my next boat may only come from me or someone like me building it, I'm trying to catch up in knowledge.

I know some of you have many years experience, so I respect what anyone else has to say. Having said that, it seems to me that the topics of which plywood to use and what to finish it with seem to get kicked around than they deserve to be. To an outsider, this appears to be a cross between some form of Vodoo and some other form of Vodoo, with "truths..."half truths" and contradictions everywhere you look. Surely there is a "best" way....and if not that....a "best" way....depending on what you are up to.

So with this in mind, I'll put forth just a small sample of what I've read this morning by doing a Google search for "marine plywood + fir":

Leading with Exhibit A:

http://www.boat-links.com/plyfaq.html

Followed by Exhibit B:

http://plywood.e-boat.net/plyhelp.php

Then there is this quote from the System 3 Epoxy book:

"Plywood is a very versatile material widely used in wood boat construction. It is dimensionally stable and needs only to be epoxy coated to protect it from moisture to become an almost ideal boatbuilding material. Several construction techniques are used to fabricate boats from plywood.

It is not necessary to use marine grade plywood in boatbuilding. Marine plywood is basically exterior plywood with a lower void content. Several years ago the plywood association that sets specifications started degrading marine plywood by allowing a higher void content. We believe that the extra cost for fir marine plywood over A-B exterior is not justified today.

Fir plywood boats that see continuous outdoor exposure should be sheathed on the exterior surfaces. Almost all fir plywood is rotary cut and exposed exterior surfaces will eventually check if unreinforced epoxy coatings are used. Sliced veneer plywood has almost no tendency to check. However, we know of no source of sliced fir plywood so plan to put a light layer of cloth on all exterior fir plywood surfaces.

Sliced veneer mahogany (I'm reading Okume or Meranti ...ha) plywood is readily available in many coastal areas. This plywood is considerably more expensive than fir. Builders using this for small boats rarely fiberglass the surface. Large boats are commonly fiberglassed if only because repair is far more costly if the epoxy coating is breached in impact. Better to build in the protection during production. "

One could chase his tail like this forever.

So with this in mind, I'd like to postulate some solutions to be kicked around:

Starting off with the idea that all marine and exterior plywood use the same types of formaldahyde based glue....essentially, resorcinol. The differences then are the density and characteristics of the wood fibers used and quality in which they are put together. Voids, no voids, patches, footballs, glue thickness, etc.

Okume: Source is a tree in Africa. Made in three different grades, with differences being face and internal voids. Unless the best grades are purchased, you will likely get the cheap stuff made in Isreal. It has small knots in the face and some core voids. The 1088 grade Okume is made to the highest standards of voids, glues, etc. but all Okume is made of the least durable wood of the bunch (rot and impact resistence). Characteristics are light weight and flexibility. So it does well in light weight boats with tortured methods of contruction. Sounds like perfect stuff for a Spindrift to me.

Meranti: Source is trees from Asia. Also different grades 1088 etc., which again relate to voids, knots, etc. Meranti has much better physical properties of rot and damage resistence....similar to fir, but does not check. Not as flexible as Okume, but is much heavier.

Fir: Exterior and Marine....difference seems to relate to surface and core voids....and whatever that brings. If the fir is glassed and sealed to the degree Okume has to be...what difference does the voids make? Anyway, fir is known for strength, but will also check...which cracks a surface coating of epoxy. So it has to be glassed, with perhaps the ultimate coating a layer of Xynole or Dynel polyester, with 3 coats of epoxy....sanding and fairing with additional coats of epoxy. Not light. Very heavy in fact, but strong and durable.

So in conclusion, I'm thinking you would want to use Okume in a lightweight dinghy type boat, where weight is an issue (both from physically picking it up...to less mass for the sails to drag around) and tortured ply methods can be used...keeping in mind that every square inch of the stuff has to be fully sealed or it will rot. On small boats, the cost is not that great in relation to labor. In the B&B boats, I'm thinking this applies to all the smaller paddle boats and dinghys, up to and including the Core Sounds....which are high performance boats....that are not typically left in the water.

On larger boats....with long term expectations...and/or serious crusing boats that may collide with objects....I'm thinking you go with Meranti or fir.....and know the evils that lurk within the fir. If you use that, you are going to have to do a serious coat job and it will be a heavy boat. If I was building a Princess (which I might be doing), and was ordering plywood today, I'd probably order 1088 Meranti. It looks to me like you build something like one of the Princess boats with Okume....you will likely get a lighter, faster boat... but one that may not hold up in the long run...either if it smacks into something...or if the skin is somehow breached so water can get in.

With that, I've run out of time and gas.....so let the discussion begin!

[Howard]

Okume is a great mystery to me. Seems to have the highest rating and recommendation of all of them.....but is the least durable...both from impact and rot resistance...at least as far as tests and reports of physical properties are involved. It appears to have it's place....as do all the others. But as I've said before....sorting all this out is a problem.

I plan to conduct my own little test. Coating panels of Fir and Okume with glass, epoxy and nothing.....clear cote or varnish them (so the progress can be watched).....and tossing them out by the back fence to see how they hold up.

[Barry Pyeatt]

I'll toss my 2 cents worth in here as well.

Having used various plywoods in boat fabrication, production and repair work over the last 50+ years, I've seen a dramatic shift in both production standards and actual product that is available on the market. I will have to point out that over the last roughly 7 years I've seen the greatest shifts and degradation of quality in the more commonly available types and grades of plywood. Primarily since other mfg. products have entered the general construction market offering much higher quality for competitive costs.

That being stated, there are some differences still between ACX Fir and Marine Ply that make the difference in cost worthwhile in my estimation. The numbers and thickness of laminations has shifted considerably as has the actual overall thickness of the material. The greatest differences have occurred in the 1/4" and 3/8" thick materials when applied to most of the boats we would be building. The center core lamination in the 1/4" has become thicker and the two outer laminations have become considerably thinner. End result is a decrease in structural integrity. This is representative in all softwood plywoods manufactured in North America. Both for general construction and Marine use.

The differences in 3/8' are the number of laminations with general construction grades having only three layers and Marine still having five layers resulting in a more structurally sound panel. The number and size of interior voids has changed but there are still far fewer and significantly smaller voids in the marine products. Quality control in the panels for marine use by most major manufacturers in North America is still quite good with edge and surface glued plugs in surface defects on marine and surface only on construction grades.

There is a significant difference in softwood plywoods sold in the North American market as well. Many use much lower grades of peeler logs than most Douglas fir used. In many areas, pine is used for peeler logs and other very cheap woods are used for the interior core laminates. This is fine for general construction, but not if you want to build a boat.

Exterior grades used to be suitable for a lot of our uses but that doesn't mean nearly as much anymore since the standards have changed.

Yes, Douglas Fir, other softwoods, and most other rotary peeled woods will check with changes in temp and humidity if not glassed. This is significant primarily on the outside surfaces and not such an issue on the interior surfaces although it does happen to a lesser extent.

Working with higher quality grades of marine plywood will provide a better result and a lot less frustration when it comes time to finish and in short order make repairs as needed. But with careful building techniques and care in fitting panels and working with them the amount of repairs that are required can be cut down significantly over the long run.

For example using the best side of the plywood on the interior side, not the exterior is significant in quality of finish work and ease of finishing as well as helping to maintain a quality finish. Since the outer surfaces are glassed, the best surface isn't essential, unless you are finishing with a bright finish where the surface grain patterns are being featured. With softwoods, even less so since they will most likely be painted or otherwise have an opaque finish over them.

Epoxy encapsulating panels is encouraged by a few to protect the integrity of the panels, especially along cut edges. But simply coating the edges with epoxy will accomplish most of that since it is end grain moisture incursion that we are trying most to prevent. Some designers specify and recommend such practices and I endorse that concept completely.

Epoxy is as mentioned, moisture resistant, not waterproof, but it is uncommon for moisture to penetrate an epoxy coated panel on a trailerable boat, even with water inside it over the off season. But not uncommon at all for moisture to enter the cut edge surfaces of the plywood. Particularly in those regions of widely varying temperatures with below freezing temps occurring with thawing cycles. Also where humidity variations are quite wide. These cycles cause both the plywood (to a lesser degree) and solid woods to expand and contract with the internal moisture content expanding with freezing temps and contracting again when it thaws. This causes the checking in the rotary cut plywood surfaces and end grain to absorb additional moisture and swell. Then when it freezes it causes those joints to come apart or begin to and for finishes to get small cracks and splits in it. They may not be apparent to the casual glance when things return to more normal conditions but the result is moisture can enter the wood. Left to its own it can and does begin to cause rot and deterioration within both plywood and solid woods. Some woods are more prone to this than others. And thus many are not recommended for boat building use as in many cases the wood simply begins to fall apart and will not hold fasteners or have structural integrity.

Any plywood that has a hole in it is subject to incursion of moisture and will begin to compromise in integrity.

So...if you want to avoid issues with that potential, then learning to coat exposed end grain even in drilled holes can make a significant long range difference in how well a wooden boat will hold up.

Now then, if you plan on building and having the end product last for some time, (more than a season or two) and it involves the ultimate safety of both you and your family or friends, then the difference in quality of the materials will play a role in what you end up with. But the difference in initial cost is minor when compared to the overall investment if you consider that your time is worth something in addition to the cost of the raw materials.

If I were building a cruising boat that I expected to last or at least wanted to last for a good (long) period of time and be worth maintaining and repairing, I wouldn't cut any corners on the plywood for hull, deck, exterior or cabin surfaces. Or in motor wells, etc. I would pick out the best I could find and save a bit more if necessary to get what would last and be the easiest to work with ultimately. Even if it meant I had to go out of my area/region to get it.

A great deal of discussion is made and many that just don't have the experience of working with the materials will scoff and say that it isn't necessary. But then they are not building a boat for you or your family to use either. So the ultimate decision is always yours and only you can decide what is right or wrong for you.

Certainly you can use lower grades and quality of materials and make them work. The boat will float if you take the time to fabricate it well and stay close to the designers specifications. And it will probably give you a lot of satisfaction and enjoyment. But it will most likely require more to maintain it and keep it working well and it will not last nearly as long. If return on investment isn't a criteria, or long life either then go for it.

There are a lot of those out there sitting in back yards or in the weeds that are being forgotten and rotting away. A well built and maintained boat with good quality materials will last a lot longer than we will probably want to keep it and may have additional life with someone else beyond our use. Just something to keep in mind. But almost all homebuilts do not have good resale value period. So build for yourself and your enjoyment.

We will offer all the support and encouragement we can to make it and enjoyable build for you. Just don't let anyone tell you that there is only one product or way to do it. But glassing the exterior surfaces will make a significant difference in how long things will last and how well they will accept a variety of finishes and how long that finish will hold up.

How and to what level you decide to finish it is purely a personal choice and an entirely different topic which will bring out a lot more vocal opinions and comments. :roll:

[Scott Dunsworth]

I like the 1088 Meranti the best. I have used the 1088 okume and a lesser grade of meranti. Using meranti over okume would add 114 pounds to the weight of my Belhaven. Assuming that I used every last speck of the plywood. Of course that won't and didn't happen. But you must add in the fact that the meranti is much stiffer than the okume and less crossbracing was necessary. I like the extra stiffness of the decks, cockpit sole and seats that comes from the meranti.

If the meranti was more expensive it would still be my amateur choice.

All said and done my guess at the extra weight of using the meranti would be 70 to 90 pounds for my 19 foot boat.

Scott

[Howard]

Barry if your time is worth anything, I think we got $20 worth! Same for Ray. It takes time and thought to write that much.

On the Spindrift, I'm making extra sure that every square inch....and any and all holes, are epoxy coated. With use, it may get holed.....it may get dinged...but it's leaving here intact. If anything...it's packing too much epoxy.

I'm not advocating using the cheap crap. I abhor the cheap stuff. I was taught things by my father who is known for overbuilding anything and everything. Knowing weight is an issue, I have a tough time getting him to plane wood to 3/4" if that's what is spec'd. His hardwood stacks were cut to a full inch or more, and planes to 7/8" or nearly an inch. That's what he uses instead of 3/4. My tendency is to overbuild just like he does.....I just wish I had his skills (and tools) so I could do a better job of it.

Nope...my quest is to find out what the best is, and how to do it right...hopefully without spending an arm and leg to do it. Again, I'm not new to boats, but am new to building boats myself, so I'm trying to learn fast. But I'm firmly in the "quality doesn't cost it pays" camp. I don't understand why anyone would build a 30 footer...or any other boat out of ACX, slap one coat of epoxy on the outside, paint it with porch paint and then wonder why it's gone south in 2 years. Why waste all that labor on junk? I understand the hobby aspects of it, but why not go the extra few steps and make something that will last?

On the other hand, I wouldn't want to spend $200 for sheet of plywood if something that cost $80 per sheet is the same or better product for that application. It's just amazing to me that some guys will spend $20 and some $200 to do the same thing, and both think they are better off for it. Not trying to be too judgemental, just an observation.

[Charlie Jones]

Barry - would you please do me and my trifocals a favor? Please edit that great post with some spaces between the paragraphs. I can hardly keep my eyes focused on it and I want to read it carefully.

Thanks

[Guest]

Its the devil getting old, Charlie Brown. :wink: But you gotta point here, with the spaces. I have enough problems with double sentences myself and teh speeling of Capt. Jakes . :twisted:

Dang, you can't write the on the board, now, [T E H] without it correcting you.

[wkisting]

Hi guys,

I lack much of the expertise of some of the other posters here. I've only built two complete boats to date: a cedar-strip kayak and an ACX/BCX fir ply Pocket Cruiser.

I used the ACX fir on purpose, knowing it wasn't the ideal material, because the Pocket Cruiser is a small, 14' boat for kicking around for fun. Not something I wanted to "preserve in stone" so to speak.

For the next boat (a Princess 22), I'm considering Okoume or Meranti. Anyway, here's what I've gleaned about these two types of ply (aside from the already excellent info posted above by others). I'm not sure how accurate this info is, so maybe the experts can set me straight if I'm wrong.

I've heard that the major reason(s) for choosing Okoume are as follows:

- undeniably lighter weight

- excellent strength (more than adequate for most designs) once sheathed in 'glass

- extremely high standards of quality under the BS1088 standard

I've heard that Meranti is "better" (subjective opinion, of course) only insofar as it is stiffer and more impact resistant, but the trade-off is that it is also about 16 - 17% heavier than Okoume.

Now here's the part I'm least certain about: Somewhere I read that the major argument for preferring Okoume over Meranti or other types of ply is that Okoume ply tends to be manufactured with much better quality control than other BS1088 rated plys... One article I read suggested that the best "kind" of Okoume (especially for brightwork) is called Brunzeel, while the second best (still very good) is called Shelman. The same author recommended against the kind of Okoume that is Israeli made, but the author couldn't remember the name of such Okoume (Kelet perhaps?).

Another claim that interests me, but is not for certain: The major argument against Okoume tends to be its lesser resistance to rot, but several authors I've come across claim that if sheathed properly in epoxy so that air and water vapor cannot reach the wood, there is no way that it can rot. (These claims suggest that, in theory, the wood will NEVER rot... not ever... until the boat is finally damaged enough to allow water penetration from a structural scratch, dent, or ding... in theory, then, if you were vigilant enough with the epoxy brush, you might never have your boat rot out from under you... hmmm, not sure if I believe it to that extreme, but...) I find this claim interesting because, as Ray pointed out to me on another thread, you can purchase Okoume that has been treated with a fungicide to discourage rot, but if these other authors are correct, the fungicide would be redundant and unnecessary--assuming, of course, you carefully epoxy the Okoume panels.

Anyway, some of that might have been mentioned in the long unbroken paragraph above, but my eyes too had trouble reading it all (it's not just your eyes Charlie! and I'm only 28, so age has nothing to do with it!), so apologies if a little of this was redundant. I just wanted to point out that, despite the comparative "weaknesses" of Okoume, the general consensus among most of the experienced builders/authors I've run across is that Okoume is still the premier choice for a high-quality, reasonable weight, sufficiently strong craft, with all other plys gaining advantages (like greater strength) only as a trade-off for something else (like heavier weight).

Cheers.

[wkisting]

One quick follow-up question that I am surprised has never occurred to me earlier....

I just realized I don't usually (maybe never) hear about builders using multiple species of ply. Is there a compelling reason not to mix species? Otherwise, maybe the ideal compromise would be to use a heavier, tougher, more rot-resistant wood like Meranti below the waterline (hull bottom panels, for instance), and Okoume everywhere else... might lower the CG a very, very, very tiny bit? Certainly couldn't hurt, could it?

Just curious.

[John Weigandt]

Here's a picture from a few years ago when my first boat had an oak branch fall on her from about 50 feet up. She was probably 15 or 16 at the time.

She's 20 years old this year, and I just spent the Labor day holiday, lovingly sanding and repainting her butt ugly rough finish. Only her 3rd painting ... 1 at construction 2 some years ago and 3 this year.

She's been stored outside every day of her life with the exception of 2 winters where she got to stay in the garage. She's had some rot in the bottom of the cockpit from standing water (my fault not hers), and has had that and a soft spot in the top deck fixed with epoxy resin/glass.

Construction... ACX 1/4 inch plywood, stringers. Pl glue from a tube (they didn't have premium then) glue brass screws and glassed the sides and bottom with polyester resin (Yikes !!) Top deck has no glass.

She was sailed as recently as June, but was getting just too ugly to be seen with, thus the new paint job

I still love this little boat, since she's the one I cut my real sailing teeth on. She's also the one who gave a nephew his start, and the Boat Katie solo'd in, and the boat that Thomas first sailed with dad as just "passenger" We even go out on the mighty Mississippi on occasion.

Her finish was very rough, because at the time my only power tools were a jig saw and a corded power drill (drilled and drove the screws and sanded with that drill)

I laugh at the comments that polyester and or epoxy aren't waterproof. They sure come a damn sight closer than wood alone does. :shock:

So for a small boat, Fear not the cheap stuff, but Keep her painted, and Keep her moderately dry. and above all HAVE FUN !!

In my subsequent boats, (Weekender, Moccasin like canoe, and Birder) I have used epoxy resin for it's superior properties.

I would use marine ply on anything on the scale of the Princess, but I laugh when folks use it for a little boat like the Mini Cup.

Guess that makes me the "old man of the AC" :wink:

John

[wkisting]

I agree with you, Ray, about the encapsulation issue. Right after I posted above, I got to thinking... since some degree of penetration is virtually inevitable (sooner or later you're bound to hit something or run aground or bang a dock or scratch against the side of the trailer, etc.) I think you're probably right about the desirability of fungicide. Even if it's redundant while the wood remains encapsulated, it's bound to be some help if (when!) the wood gets penetrated by water.

I'm thinking about this mixing wood species idea now. Ignoring weight, what do you all think would be the single best plywood a person could use to build a strong, stiff, ultra-rot-resistant hull-bottom? (still pretty sure I'd built the rest of the boat out of Okoume... but "upgrading" the most scratch-prone portion of the boat (the bottom... maybe the cockpit sole too) to a better wood might not be a bad idea.

[Designer]

This is a emotional subject that is full of myth and mis-information. While working my way around the world I have used all kinds of weird and wonderful plywood with good success.

I will use any breed of plywood that is available that will do the job providing it is properly made with phenolic glue and has no voids. Fir is at the bottom of my list because unless it is glassed, it will check. The grain prints through even when glassed. Also, 1/4" ply is made with only 3 veneers and often has poor quality control.

Okume is usually the first choice because it is available, affordable, works nicely, has a pleasant color when varnished and is lighter than most other plywoods, and when glassed, overcomes it's not very durable rating.

The marriage of epoxy and plywood has created a wonder material for boat building. There is no other material available that combines the stiffness to weight ratio, cost, workability and repair-ability (in spite of a comment made earlier in this string).

The picture shows me planking a 24 footer in Israel in 1977. While passing through Israel, I was commissioned to design and build a small ocean cruiser. As the owner's means were meagre, we decided that it was better to build a small, high quality boat, rather than a larger quick and dirty one.

We drove to Kibbutz Taal and they peeled about 1000 square feet of okume veneer for me. The hull was made of 4 layers of 1/8" veneer glued with epoxy and held down with 150,000 staples while drying. They were all removed. The deck and cockpit was made with 1/2" okume ply, also from kibbutz Taal. The whole exterior was sheathed with 10 oz. glass and epoxy.

By a strange twist of fate I have that boat here in North Carolina. After sailing over here on her own bottom, she has been sitting here in our hot, wet and humid climate for a long time, and at 27 years young there is no sign of that, "not very durable", okume rotting. I am sure that she will outlive me.

If I was building a Princess and overall weight was not a big issue, I might make the bottom out of meranti, where the weight could be advantageous and to save a few bucks. But, I would make the rest out of okume.

[wkisting]

Forgot to ask... Has anyone ever heard of a bad experience with CPES? (Clear Penetrating Epoxy Sealer... from Rot Doctor)

http://www.rotdoctor.com/boat/WBcoatresin.html

I've run across this stuff on all kinds of boat-building forums. I've never--I mean NEVER--heard even the slightest negative comment about this stuff, and usually it gets rave reviews... I'm talking reviews so good that you almost think they're exaggerated comments planted by the manufacturer (I'm sure they're probably authentic, though).

I'm considering using it to treat the cut edges of the ply when I get around to building my next boat. Sounds like you can use the CPES with outstanding results on ANY wood, solid or ply, regardless of species, provided the moisture content is reasonable (too much moisture... say, above 15%... and apparently the CPES doesn't penetrate)

I found this site where a guy ran a test on the sealing properties of CPES.

http://www.smithandcompany.org/firstwood/firstwood.html

In the first picture, they use purple-dyed CPES to show how deep and thoroughly the CPES penetrates the wood. This also shows how deeply water could penetrate.

In the second picture, they used clear CPES to seal the wood (i.e., allowed it to cure). Then dipped the pieces again in purple-dyed CPES... the result? No visible penetration whatsoever (an impressive difference) of the purple dye.

What makes the CPES attractive over regular epoxies is the depth at which it penetrates (and the thoroughness of the penetration). The drawback is that it's very volatile, but if you apply it outside with a particulate respirator, it would be safe enough. Rot Doctor claims the CPES is an ideal bonding primer for epoxies, paints, varnishes, etc. so there shouldn't be any bonding compatibility issues, at least not with the major and well-known brands (West, Raka, etc.). The CPES also apparently stiffens the wood as a result of bonding the wood fibers so thoroughly.

By the way, I have no affiliation with Rot Doctor. I'm just extolling the potential virtues of their product here because it sounds like it might be just the sort of thing to address some of the limitations to some of the types of ply mentioned above.

Anyway, just curious if anyone has ever heard a downside or a dis-recommendation concerning CPES...

[Howard]

Hard to argue with Graham's logic....and doubly so when he has the proof siting right in front of him.

Another thing that would apply to either of the Princess boats, or others made this way with multiple layers of laminated strips in the critcial bow section, is that each strip is essentially encapsulated on four sides with epoxy (exterior...between layers and in the butt joints between strips). So any damage is confined to the impact area. If you did have damage or rot develop, you could go at it with a router and flute bit....and dig out the bad spot, scab in a new piece and off you go.

[Tom Lathrop]

Ditto what Graham said. A few years ago Graham decided to add some more ballast to the boat he describes by cutting out a section in the plywood keel and inserting a plug of lead. After whacking out the wood, there was absolutely no sign of any degradation, rot or otherwise. His original Catspaw dinghy is still in great condition after extensive offshore and inshore use.

I see many small plywood racing sailboats that are 40 or more years old and still in sailing condition.

Almost all wood needs some kind of protection to endure long in the marine environment. Denigration of plywood by the plank on frame crowd is often no more than an attempt to create an aura of uniqueness about themselves. For the home builder, plywood is hard to match for its broad and useful set of characteristics.

Rot requires water and free oxygen, deny either of these and rot has a hard time making a foothold. The idea that you should epoxy only one side of planking to let the wood breathe makes no engineering sense. Wood is DEAD, it doesn't need to take a breath, at least it should be really dead before you put in your plywood boat. The best results I have seen for longivity are when all surfaces have been well coated with epoxy. I am most definitely not talking about large timbers that can see a lot of dimensional movement. Fabric sheathing adds another layer of protection in that it toughens the surface. Glass is good but for abrasion resistance, the synthetic materials like Vectra polypropylene, Xynole polyester and Kevlar are far better, in that order. In my tests, Dynel comes out poorly.

If A/B exterior fir plywood of the quality available at most local builder's supply houses 40 years ago were still around, it would be a good choice for low cost boatbuilding. The stuff I see now is, for the most part, pretty disgusting and I never see the A/B grade anyway. I have used the BS6566 grade imported plywood with good results although admit that BS1088 is a better and safer choice when money is not a factor.

[Charlie Jones]

agree on the Fir plywood. One other thing to really be careful of- I recently went to purchase some fir MARINE plywood from the yard where I had been buying the stuff. They tried to unload some 4 ply crap on me - 1/2 inch thickness with FOUR plies, labeled AB Marine. What a load of crap THAT would be. I accidentally got a sheet of that once before - you CANNOT keep it from warping without cleats at regular intervals.

As I said on another thread here or on the other board, I choose Okume, because for all around use it's really hard to get a better bang for the buck.

I'm also really saddened to agree with Tom Lathrop- the good quality American made marine plywood we saw 25 years ago, when I was building my 35 foot trimaran, are long gone. He said the Lumber yard stuff, but I think the MARINE has gotten just as bad. Hell- I think Luaun might even be better- at least IT's got balanced plys!!!

[Howard]

I keep looking at different sites for these discussions. The big kick on Okume seems to be it lacks durability.....but what does that mean exactly? What objective description comes with that?

Does that mean it rots quickly? I read where the Shelmarine product is treated to prevent rot and fungus and that removes the non-durable label and stigma.

Does it mean it's soft and won't take an impact? In terms of dimension lumber, I'm thinking of the difference between white pine and white oak?

Do them mean than under stress, it will come apart?

Just curious about what happens with the stuff to earn that label.

[Frank Hagan]

I have enough problems with double sentences myself and the speeling of Capt. Jakes . :twisted:

Dang' date=' you can't write the on the board, now, [T E H'] without it correcting you.

Now that is SO NEAT!

Hat's off to you Frank!

Now if we can add some programming language to clear up boat and maybe half a dozen sticky fingers words I can come up with in the next month or two....

Clear up what? Boat? :twisted:

[Frank Hagan]

I've run across this stuff on all kinds of boat-building forums. I've never--I mean NEVER--heard even the slightest negative comment about this stuff' date=' and usually it gets rave reviews... I'm talking reviews so good that you almost think they're exaggerated comments planted by the manufacturer (I'm sure they're probably authentic, though).

<SNIP!>

I found this site where a guy ran a test on the sealing properties of CPES.

http://www.smithandcompany.org/firstwood/firstwood.html

[/quote']

Smith and Company is the originator of CPES, so their results might be biased.

I don't have any experience with it, but some of the claims seem a bit out there to me. What I have heard is that it is a very thin epoxy, and will penetrate as much as any thin epoxy will, and where it penetrates, it seals the wood. That CAN stop rot, but I have heard of cases where the wood just continued to rot where the stuff didn't seal it up.

[PAR]

According to West System tests and a few I've conducted, the amount of penetration epoxy has on the wood substrate has little to do with its ability to keep out moisture. The protection comes from no breaches in the coating, not the amount of penetration. Smith's rants about the "organic compounds" used in their CPES products is just plan silly, frankly. The keyboard I'm typing on also has organic compounds in it's matrix, but no more resembles the leaf bearing organisms it once was. Stealing a few molecules from organic sources is quite common in thermo plastics, most having them or mimicking them in structure.

It's a big commitment using epoxy in a build. By this I mean epoxy is a decision that has a big impact on the material choices, additional labor, mess, shop supplies, health hazards, cost and maintenance of a boat. These are above and beyond the more traditional construction methods using plywood or lumber not embalmed in goo.

My 1960 Chris Craft has original plywood planking (except the garboards), I just replaced original plywood planking on 1965 and 1958 powerboats. They are and were well constructed, alkyd painted (oil) without any plastic coatings, surviving near 50 years. Not such a bad thing to ask of planking material.

I expect the plywood was good stuff in it's day and the same quality will cost as dear today, but our labor costs are much higher in comparison. Adding the additional costs and labor of epoxy encapsulation, would have added how much more life to these boats? I'm not convinced it would have and am in direct contradiction to myself twenty years ago, when I believed encapsulation was the only way to insure long life in wooden structures.

After countless builds, repairs and restorations I find myself falling back on more traditional methods and strategies in regard to epoxy and plywood. I've been at this over 30 years now and have seen it come full circle. I remember when everything was getting a sheathing in polyester and cloth (remember all those home built cats and tri's from the 60's and 70's). That didn't pan out, in spite of ridiculous zealots carrying on about how it might if we just did this or that. Then epoxy was used on everything. The repairs came in and now it's epoxy, but only in thin laminations and only with the correct construction methods. Now I've seen it come around to 50 year old (and older) plywood that hasn't been coated with anything other then a fresh coat of oil based paint and reasonable, timely repairs to damaged areas.

Some construction methods wouldn't be if it were not for goo and cloth and I enjoy these designs as much as the next.

Plywood construction and imports, particularly from the far east, have dropped in quality dramatically in the last ten years. This makes the call for exterior grade ply's use in boat building much less a no brainer. A few of the boat building lumber suppliers don't even carry Douglas fir plywood any more because of the complaints over checking. Exterior ply has such poor quality construction (over lapping ply's, many voids, repairs, low number of layers of unequal thickness, etc.) that it's difficult to justify it's use. You don't save much, when it takes more to finish and more frequent repair and maintenance can be expected. It's not that the this stuff can't be used, it can find a place in parts of the structure that will not receive as harsh a treatment as the bottom of a boat. Traditionally, the boat's planking is the best material used on the build and generally isn't a good place to cut corners. Cabin furniture, internal structures and all sorts of uses can have the lesser grades of material. I've bent, scarfed to length sections of good plywood (a recent 23' plank comes to mind) when CRACK an unseen void, inside the good 60 bucks a sheet stuff, let go like a shot gun blast (that'll piss you off) as I wrapped it around the waist of the boat. The voids in exterior grades make bending ply very difficult and then there's the rot pocket issue. I'll only use high quality plywood if it's on the weather deck or hull of a boat. It will not come back and bite me 5 years later.