Plywood Choices

[John Stevens]

I've been checking prices of plywoods. I used fir on my pram but got some checking where I didn't glass.

I'd like to go with something different.

Can anyone give me some insight into the different plywoods?

I've seen Okoume, Meranti 1088 and 6566. There is a good difference in price. What it the difference in the wood.

I'm thinking of "not" glassing the boat, just a few coats of epoxy.

TIA,

John

[Greg Luckett]

I like Okume BS1088 when I can get it and/or afford it, mostly because it is the lightest. My second pick is Merianti BS1088. 3rd is either in the next best grade. I will not use Fir anymore if I can avoid it, and never anything but marine grade.

[wkisting]

The Okoume BS1088 seems to be pretty much the stitch-and-glue premium standard... light, tough, strong for its weight. When you browse around the internet, you'll hear people voicing reservations or discussing the "downsides" of Okoume and recommending alternatives (not unlike you see with discussions of fiberglass vs. all the higher-tech alternatives: S-glass, Xynole, Dynel, Kevlar, Carbon, etc.), but if you look into it long enough, you eventually come full-circle to the conclusion that the Okoume BS1088 is pretty much ideal, as any "weaknesses" or "drawbacks" of the wood turn out to be relative, and outside the margin of concern for boat-building. (i.e., Okoume is weaker than some species, but strong enough for boat building; Okoume can rot more easily than some species, but is not likely to do so if its sealed-and-sheathed properly; etc.) Certainly there are cheaper alternatives, but cheaper too is a relative term when you consider long-term maintenance and durability. Common boat-building wisdom says if you want a boat to last and last, Okoume is one of the better/best ways to go.

At least that's what I've found after much, much investigation over the years.

Having said that, since you mentioned ONLY sealing it with epoxy (no 'glass layer), there may be a few woods which are better choices. I'll leave that to the smart folks here to answer... Most of my knowledge of Okoume is based on the assumption the hull will be sheathed in 'glass, but I have seen some warnings that un-sheathed Okoume is not a good idea. I'm not sure how seriously to take those warnings... they may turn out to be unwarranted concerns like most other reservations I've heard about Okoume, but perhaps not.

Guys?

[Barry Pyeatt]

You might want to read the information on appropriate plywood and woods for boat building use on the www.Glen-L.com website. Good information and pretty comprehensive.

Also do a "Search" of topics in this forum. There have been long and informative threads posted in the past with some good information on what other builders have used. And what they avoid.

[John Stevens]

The Minuet is built from frames not stitch and glue. So... Would that make a difference in my selection of plywood?

TIA,

John

[wkisting]

John, I don't think so. My comments should apply to virtually any building method that utilizes ply Okoume in a sheathed-in-glass application. Sorry, I can see I probably confused you by calling it the "stitch-n-glue premium standard"... I should have called it the "plywood-boat standard".

I was only hesitating to tell you that it will work in an epoxy-only (no glass) application because I have heard reservations from many about using it that way. On the other hand, I've also heard success stories... better to defer final judgment to those smarter than I.

Interestingly, if i remember correctly, the Glen-L site (possibly not the same link, but somewhere on the Glen-L site) that Barry suggested is one of the places I first ran across some reservations about using Okoume without sheathing in glass. I don't recall what the info said, but something to the effect that Okoume is not ideal. Then the folks here reminded me that Okoume-sheathed-in-glass is a different animal entirely. Since you're talking about letting your Okoume run around naked, you might want to check around in the Glen-L materials to see what they say. I'll check it myself, and if I can find the short blurb that gave me concern, I'll post it.

[Tom Lathrop]

I saw some sobering evidence in plywood this morning.

A friend who was spending last week here from cooler lands brought a Bolger Lily electric launch along. We were looking it over and discovered that the plywood not covered with sheathing was checking extensively. I thought at first that it must be fir but it is meranti.

I have not heard of that hapening to meranti before. All had been epoxy coated and painted and all horizontal surfaces had checked badly.

Anyone have other experiences with meranti checking. It is bad enough to prevent me from using or suggesting meranti if this is a general fault.

[Charlie Jones]

I'm with Greg on this. I refuse to try to use american fir plywood any longer except maybe for interior, non structural parts. The consistency and quality of Okume (lighter) or Meranti (slightly heavier) is so far and away above the US made stuff it isn't even funny. And the overall costs aren't that much more. The one exception is fir in 1/4 thickness- it seems to still be pretty fair stuff. Over that has turned to junk.

Another place you save is in the finishing. Epoxy coated okume finishes SO much easier and better than fir ply it's not even in the same league.

Personally I like the Okume.

And no, building a framed boat won't make a difference. I think also that you'd be making a mistake to NOT glass the exterior of the boat. Not really that much extra work or expense and sure pays off in lower maintenance later.

[wkisting]

Tom, I've heard that unglassed Meranti and even Okoume (indeed, most woods) can check, eventually... just takes a lot longer for some wood species to do it. Never seen it myself, but certainly have heard that.

John, this other messing-about thread is LOADED with good info about plywood... check it out. It will probably answer 90% of the questions you never knew you had about plywood! Here's the link:

http://www.messing-about.com/forum/viewtopic.php?t=3888&start=0&postdays=0&postorder=asc&highlight=okume+okoume+glenl

Oh, and I found the Glen-L blurb that gave me concern long ago:

Speaking of saving weight, Charlie... Did you use Okoume ply for Travis' boat? I've always heard good things about Okoume, but then I just spotted this little snippet of info on the Glen-L webpage concerning Okoume:

------

OKOUME

(gaboon)

27 lbs. per cubic foot, 2.08 lbs. per board foot.

This West African wood produces large, clear logs of uniform straight grain. The heartwood is salmon pink or pale pinkish brown resembling some types of Philippine mahogany. The sapwood is grayish. It is only fairly strong considering other woods, but strong for its weight, although low in resistance to decay. The wood splinters easily and is best sawn with carbide tipped blades. It has little use in plywood boat building except in smaller boats where lightweight is more important than durability. Some imported plywood is made from this wood.

-----

I was surprised to read this. I thought Okoume was the premier plywood to use for ply boats... Is it better to go with something stiffer/stronger (albeit heavier) like Meranti? Or is the post on the Glen-L site just too pessimisstic regarding Okoume's strength?

If you want to see the responses I got, it comes from this thread: http://www.messing-about.com/forum/viewtopic.php?t=3875&start=0 which also includes much great info about plywood.

Hmmm... maybe Frank would want to copy and snip from these two threads and move them into the Articles section with a title like "Plywood for Boatbuilding" or something like that?

[Pipefitter]

I chose the 1088 meranti because it was somewhat more durable in rot resistance. I also wanted a more weighty wood because my boat was originally built with solid planking. In my case,the ply is glassed just above and below waterline. The topsides are just epoxy sealed/painted except for where I used D-Fir on the sheer deck to stop the checking.It was already checked when I bought the fir. The meranti or okume will hold up well above waterline without glass. I think if I was to use unsheathed plywood,I would opt for the more exotic mahogany plies.I was under the impression that the face veneers on the meranti or okume is too thin to stand up to long term submersion. If one was wanting to use fir ply,it doesn't hurt to cover it with a light cloth and consider it part of the priming for paint stage. I used epoxy/ 4oz. cloth as a veil over the fir but now that has probably made it cost as much or more (read fairing and sanding work plus the cost of epoxy and glass)than if I had bought the 1088 ply in the first place. Since the sheer deck on my boat is structural,I wanted the tougher more rigid D-Fir.

Here is the meranti clad pan of my boat glassed.

Here is the topsides just epoxy coated.It was built outside and left in this condition for many months and never did check and still hasn't.

I should also add that I have heard that meranti bends kind of funny. In my case,being that my boat is rather narrow in respect to it's length and it was built of seperate narrower planks of glued lap,this wasn't a concern in my situation. Maybe some others know about this aspect of the different plywoods.

[Greg Luckett]

We are using 12mm Merianti on the 18ft Lobster boat. I believe it is BS1088 grade.

[Pipefitter]

When my buddy gets by to take the recent photos of my boat,I will get some pictures of the meranti scraps that have been sitting outside in the weather for the last 2-3 years. They have not delaminated or changed much at all. The fir didn't fair so well. Not the still useable scraps but the small bits and cutoffs. Wish I could have had some of the okume to subject to this as well.

[John Stevens]

Again, thanks for the advise and the links. I started pricing the plywood already. There seems to be a difference in the Meranti 6566 and the 1088. Is the 1088 that much better?

As I said I built the pram of fir. The plywood part has checked but the solid fir has not. It the checking only a problem in plywood laminate? I was planning on using DF for the frame work, chines and such.

TIA,

John

[Pipefitter]

I would opt to use the better 1088 below the waterline and use the lesser above maybe. Also,if this plywood I used gives me a problem with checking,I will sand all the paint off next refinish time and glass it. My boat will be covered and stored in the shade other than to let it air out so that is another consideration when choosing what material you choose. If it is going to have an exposed existence,I would opt to use the very best I could afford or glass sheath the lesser. I think if I was to use the fir,I would try the MDO sign plywood with the paper on it.

[Barry Pyeatt]

Checking can be an issue with almost any wood given the right set of conditions. It is more prevalent in woods with wider/thicker growth rings and more of a difference in hardness between the seasonal growth of the tree. Hardwoods tend to grow more evenly so they generally have more consistent densities to their rings. Softwoods tend to have greater differences between the rings. New growth softwoods in particular as compared to older growth trees.

When the wood has to live in an environment that has temperature and humidity extreems and goes thru freeze/thaw cycles, the internal moisture in the wood itself causes the wood to swell or expand when it takes on increased levels of moisture (humidity) and if it freezes then it causes it to expand further. Then when it thaws out and drys out it shrinks. That causes the more rigid coatings to have hairline cracks. Some are visible but most are not apparent until moisture gets beneath the finish. Then it gets into the wood and can't escape. Heat and moisture cause rot. Not addressing the issue leads to more rot and eventually extensive damage.

The surface eventually gets an uneven pattern of small cracks in it. That is where the moisture gets into it. It is more of an issue on the exterior of the hulls, decks etc. Less so on the interior surfaces. One good reason for a lot of the pros recommending using the best face to the interior side of the boat. Less prone to checking than lesser quality surface. Also easier to paint. Charlie Jones likes to finish clear with epoxy so he can see changes in colors of the wood which is the first indicator of moisture geting below the surface finish.

Unfortunately, epoxy doesn't prevent checking on any plywood, only glassing and resin can prevent it. Checking is less of an issue where there are more even temperature ranges and less of a chance of freezing.

Boats that are covered up and left sitting seasonally will be more inclined to have checking issues. Keeping good air circulation helps prevent mold from forming. Keeping things from laying around on the surface helps preventn mold too. Let things dry out and there is less mold. Less mold, less rot eventially for the most part.

Personally I use high quality alkyd primers, then a good quality exterior Porch and deck latex enamel on the interiors with a lot of attention to caulking all the interior exposed seams. Not to keep water on the outside of the boat but to keep it from intruding from the inside of the boat. I also prefere using either the same over the glass on the exterior or polyuethanes which are harder and wear a bit better.

[wkisting]

John,

As I understand it, the ratings specify the likelihood/frequency that voids will appear between layers. No matter what the wood species, the biggest enemy of plywood is these voids, so I would highly recommend you go with the BS1088 rating (the highest) regardless of which wood you choose... particularly below the waterline.

The prices seem significant, but really, if I weren't going the ultra-cheapie route of AC Fir and going to make the investment in marine ply, I'd go all the way and get the best... the extra hundreds will pay you back in peace-of-mind, potentially higher resale value, and longer boat life.

[Charlie Jones]

Yes, The Princess was built using Okume, BS1088, as is the Core Sound 17 currently in the shop. So were the CLC Mill Creek 16, the Eastport Pram and the John's Sharpie I built. The Weekender sevderal years ago was done with fir marine- it was after that, when I was rebuilding the interior of Necessity (AND Tehani) that I found the horrible state of fir plywood. They even attempted to sell me a 1/2 sheet of "Marine" that was FOUR PLY!!! I passed on it.

As to the checking, it also has to do with the way the plywood is made. Virtually all US ply is rotary cut, whereas the Okume is normally sliced across the log. Rotary cutting can lead to "chatter" as it's being cut which can contribute to checking. If the log isn't wet out just right, they will also chatter and be more prone to checking. But just the nature of rotary cutting also contributes to it. You are getting a variety of grain structures across the sheet of plywood that aren't necessarily present in sliced veneers.

As to voids- I've probably cut up somewhere over 100 sheets of Okume in various thicknesses in the last 4 or 5 years and have NEVER EVER found even a 1/16 wide void.

[John Turpin]

This thread demonstrates the value of this forum. You couldn't buy the advice given here. Keep it up.

[Greg Luckett]

This thread demonstrates the value of this forum. You couldn't buy the advice given here. Keep it up.

Amen to that

[Pipefitter]

I intend to keep my boat in an environment comparable to that of my house that stays looking good the longest. Filtered UV via the poly tent and only covered when it is outside to keep the rain and leaves out of it. As of now,being I have no sides on the tent,the boat does get wet when it rains sometimes and there is enough air movement to dry it out decently but not like it would in the sun ofcourse but I have no "visible" checking as of yet going on 3 years. I saw one of Oysters small skiffs and it looked quite well kept and intact. He was careful to keep the leaves out of it and only covered it when it was going to be parked under trees.Seeing him take care of his skiff and how it still looked after all these years was about what I had intended for my own. Didn't seem like alot to it. I do have the advantage of a longer season than alot of people here but it will be interesting to see what works or what doesn't.I appreciate this extra info and input.

Barry,good points about the mold and being too well covered.At my work when I take the covers off the boats sometimes,I can smell the dankness/mold and even see it on the upholstery.I can only imagine what it would do to alkyd paint.