Plywood Observations

[Howard]

This may be news or it could be I'm the only one who didn't know this, but I have a couple samples of some marine plywood I'm looking at. They are 18mm Hydrotek (Meranti) and 18mm Okume, both from Edensaw. Just square cuts off scraps. The Hydrotek piece weighs 15 oz. The Okume 14 oz, but see below.

The Okume measures 23/32nds and is in fact 18mm. The Hydrotek 3/32nds less and slightly under 21/32, but is also called 18mm. Most places represent 18mm as equal to 3/4 inch, but these are not. The Hydrotek not even close. The Hydrotek has a couple small voids, splits and rough edges along one side, but that is probably a function of the scrap it came from. The Okume, as near as I can tell from the samples, is flawless. However, the Okume appears to have been made by gluing two 3/8" panels together. There is a clear seam in the middle. Said to be 13 plys but there are really 14. Has anyone else observed these kind of irregularities in sizes?

Dropped a ballpeen hammer on both and the dent in the Okume is at least twice as deep as on the Meranti. I'm translating that into the idea that Hydrotek might take more abuse than Okume and is what you would use for the bottom and sides, and maybe bulkheads.

For color choices, and matches, I painted some epoxy on some wood scraps. Meranti is really dark, almost like walnut. Finished bright, not much matches up to it but the ash.

The other scraps are red oak, white oak, yellow pine, and ash. Not shown is a gorgeous piece of cherry. It is a bit darker than the Okume but is a close match to it. Very similar to the red oak.

No conclusions, just some observations.

[Joe Nelson CS#35]

I used Aquatek on my CS 20, which is a grade below the Hydrotek (6566 vs. 1088). I am please with every trait of it other than for the weight...it weighs more!

I think it depends on the boat you are building. Small boat where weight is important, I would go with Okoume. On my next boat, Larger sailboat with ballast...I will use Aquatek on all things below the sheer. Decking, cabin, etc. will be Okoume. This will keep the weight down aloft and reduce the cost of construction. You can use the weight in the hull. But I am talking 1" bottom panels and 1/2" side panels.

I am building a tender. It is all Okoume.

If you epoxy encapsulate, I dont think that it matters if there is a marginal difference in quality. With a 30% difference in cost, I think it worthy of consideration.

[Kidd]

I also built my CS17 out of Meranti. It is probably heavier, but she sails fine for my purposes. I have never used Okume but I hear that Meranti is stiffer than Okume when it comes to making bends. I did find the wood stiff. I did not ,however, have any problem with the bends in the bow of the CS17. If, as you observed with your hammer test, Meranti is tougher, that would be a definate plus for my sailing locations. All the lakes in Georgia are very low right now.

[Greg Luckett]

Howard,

I like your thinking and looking at the panels. Nice insights. I too wonder about the splicing two panels together to make a thicker panel. I have seen that done on non-marine grade but did not expect to find it on okume marine grade panels. That is disappointing. Are these BS1088?

[Eric]

I have built my boat almost entirely out of apitong (AKA keuring, Dipterocarpus grandiflorus). It's heavy, extremely stiff, but very strong. I had a few problems getting things to bend, but eventually got it done with much cursing. Apitong ("Yang" in Thai) seems the be the most common wood here in Thailand for general contruction, weighing 44 pounds per cubic foot. The exterior grade sheet wood seems very durable, and I immersed some in water for over a month with no change. I also banged some with a hammer, impressive strength, which I may need as the bay near my house is so damn shallow. About 20 dollars a sheet for 10mm, which seems pretty outrageous for Thailand prices since beautiful interior grade ply is about 8 bucks a sheet, but whatever. It also takes epoxy well.

Actually, the boat is basically finished, sitting in my yard, but the monsoons have been so heavy lately that I haven't been able to get out. What a drag, watching it rain all the time. Sailing is better in the winter here.

[Greg Luckett]

Eric,

I think I know how you feel. Winters and snow here have a similar effect.

Any pics of the boat yet?

[Howard]

Greg:

The Okume is 1088. The Hydrotek is also supposed to be the 1088 version of Meranti. That the thickness of the Hydrotek was more than 1/16th short was a surprise. Most sites will list the 18mm ply as equal to 3/4 inch. Neither one was. But perhaps close enough to equal the specified scantling size of plans. That would be the concern I guess. That and if you mixed them up, they are not going to be the same thickness. Can't think of a time when that would matter, but it would be something to be aware of.

But both superior to some 3/4 inch marine fir I bought about 4 years ago. That has a surpising number of voids, bad surfaces and bad edges. At least the remnant I have left does.

[Greg Luckett]

Howard, I noticed that too on 3/4 fir marine grade. That is used a lot in this area for transom repairs on power boats. I bought a 2x4 foot piece for making motor mount pads. Really crap panels which required my filling voids on even small detail pieces. I thought maybe it was the exception, so went to the yards and looked around. It is the common.