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Old 21-09-2016, 12:46   #1
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Marine Ply - Okoume or Douglas Fir

My zodiac tender is just about coming to the end of it's life so I'm about to embark on building a new nesting pram for the winter project

I'm fairly certain on the design etc but as far as construction is concerned I can source douglas fir based marine ply locally or travel a couple of hours to get Okoume marine ply - does anyone have any experience of either or both and what are the pros/cons of each (from my limited research Okoume seems to be preferred but not sure why)

Thanks,
Grae Morrison
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Old 21-09-2016, 13:13   #2
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Re: Marine Ply - Okoume or Douglas Fir

I have built many boats with both materials. Okume is my choice. Much nicer finsh. Easy to work. Uniform grain.

Steve.
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Old 21-09-2016, 13:27   #3
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Re: Marine Ply - Okoume or Douglas Fir

The down side to Okoume is of it gets wet it will rot in a heart beat. You have to pay a lot of attention to the epoxy coating. Fir is much more resistant but it checks and cracks. The marine rating only addresses the glue used and lack of voids. Rot resistance is not considered.
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Old 21-09-2016, 13:37   #4
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Re: Marine Ply - Okoume or Douglas Fir

Go to this site. They have a description of the various marine ply's and are great to work with. http://www.boulterplywood.com/MarinePlywood_4.htm

I have used both and fir checks very bad. Okume is great to work with. I have also used Merranti and Teak. All have their place.
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Old 21-09-2016, 13:57   #5
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Re: Marine Ply - Okoume or Douglas Fir

I lean toward Okuome of your choices. But I assume when you say "fir" you mean what they sell today as fir which is Hem-Fir fast growth Hemlock hybrid. Soft and no rot resistance like old growth Douglas Fir. In addition it's full of knots/ plugs as it comes from small trees.
My best preference would be Bruynzeel
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Old 21-09-2016, 14:07   #6
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Re: Marine Ply - Okoume or Douglas Fir

Okoume for sure. Easy to work with and a lot lighter than fir plywood.
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Old 21-09-2016, 14:40   #7
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Re: Marine Ply - Okoume or Douglas Fir

I have worked with both, I wouldnt drive two hours to buy less durable plywoood and pay twice as much but that's just me. Here's why-

Weight - Building the rowing only version of chameleon out of Okoume instead of Douglas Fir will save maybe around ten pounds or ten percent of the designers suggested weight of a hundred pounds. A little bit more than the weight of a gallon of water.

Quality - 5 ply 6mm BS 1088 rated Okoume will feature a better quality lay up than a domestic 3 ply 1/4" APA marine grade Douglas Fir. The DF will also likely have a couple footballs on the A-side but if you are epoxy coating you should be painting anyway so whether the wood is pretty wood or is ugly with footballs in it doesn't matter.

Cost - True Llyods certified BS 1088 Okoume will easily cost twice as much as domestic DF not including shipping. Be advised there are others claiming to be built to the BS 1088 spec from France and Israel but not certified for less money and others still that are made in China and marketed as marine grade available for even less money. Know what you are buying or beware.

Strength - Douglas Fir has nearly 50% greater modulus of elasticity and 30% greater crushing strength than Okoume. When you are dealing with very thin material to begin with that difference in strength is significant. Be advised the spec for 6mm BS 1088 allows for finished product to be as little as .21" thick. FWIW my domestic 1/4" DF is . 267" thick. True, very thin Okoume will be that much lighter than DF, but it will also be much much weaker.

Durability- unlike Douglas Fir which is rated as moderately durable, Okoume is rated as non-durable. Sure, you're epoxy coating it so no worries right? All depends on how much abuse you dish out and what kind of maintenance you are willing to put into it. Rot happens. Repairing rot on stitch and glue construction can be a pain.

Ethics - Okoume is listed on the IUNC Red List as vulnerable. Douglas Fir is listed as least concern.

If you live in the states consider that Okoume plywood starts out life as a raw material in an African equatorial rainforest, gets cut down and shipped across an ocean to a European nation for manufacture, then gets shipped across another ocean to this country before it finally gets shipped one last time to your doorstep so you can build yourself a dink.

Meanwhile, the domestic DF comes to you from a temperate forest in your own country which means all your money stays right here instead of being spread around countries like rape capital of the world or it's neighbors where there is little accountability for environmental issues or human rights.

Danny green chameleon nesting dinghy
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Old 21-09-2016, 15:26   #8
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Re: Marine Ply - Okoume or Douglas Fir

Lots of good points above, in Delancy's post. That said, you should probably study on such things a bit yourself as well. And there's lots of information available at Edensaw (woods/hardwoods) in WA. Marine Plywood | Edensaw Woods, Ltd. - Port Townsend, WA

On their website there are a few more options aside from what you've already listed, though the 2 you picked are probably the best choices. Much of the why behind such being listed in the above post. But there are other marine plywood types available. The strength properties, densities, etc. are denoted on Edensaw's website.

One thing which you do get in the non-Fir plywoods, is more layers per a given thickness of plywood, & greater quality/quality consistency. Which in thinner plywood is important. And in some of the other non-Fir plywoods you can get stuff which is purpose built to be more flexible, which can come in handy when doing things like stitch & glue, where you'll be doing a lot of bending of the wood.

I know it's probably said a bit too often, but on projects like this, I can't see the extra cost of one wood vs. another being a giant consideration. Given that in tender's especially, you want to use the best quality stuff that you can find. As they do get worked really hard. Plus a lot of time goes into their construction.

Also, a 10-15lb weight savings may not sound like a lot. But when you're dragging the dink 50yds uphill on a beach, that extra weight really adds up! AKA you do genuinely notice it.


PS: From time to time you also hear of guys glueing up their own plywood. Either from veneers, or by using multiple layers of quality 3mm plywood. Which might be worth looking into. As then perhaps you could optimize the strength of the final plywood, as well as boosting it's waterproofness (this via enhanced glue saturation of more of it's internal layers).
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Old 21-09-2016, 16:59   #9
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Re: Marine Ply - Okoume or Douglas Fir

It is a little hard to find these days but Medium Density Overlay plywood makes a great paint surface. Typically Fir core/ waterproof glue and while not quite up to marine core standards but pretty close and don't think strength will be a big issue.

I have built several boat exterior parts and after 10 years still look like molded FG. I saturate with WEST epoxy, sand and paint with Imron. Lightweight, strong, stable, and shinny.
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Old 21-09-2016, 18:06   #10
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Re: Marine Ply - Okoume or Douglas Fir

Quote:
Originally Posted by Frankly View Post
It is a little hard to find these days but Medium Density Overlay plywood makes a great paint surface. Typically Fir core/ waterproof glue and while not quite up to marine core standards but pretty close and don't think strength will be a big issue.

I have built several boat exterior parts and after 10 years still look like molded FG. I saturate with WEST epoxy, sand and paint with Imron. Lightweight, strong, stable, and shinny.
MDO is great stuff, but he's building a small dinghy and the smallest MDO is 3/8". You need plywood that bends well.... Hydrotek or Okoume works well for this.

Matt
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Old 21-09-2016, 19:08   #11
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Re: Marine Ply - Okoume or Douglas Fir

That issue had occurred to me as 3/8" was the thinnest I have ever run across. Most of my projects are with 1/2". 50 years back we had a local boat builder that used it for a line of small outboard runabouts. Having watched fir plywood surface check over the years, it was a real eye opener to see how well that impregnated surface held up to the elements with a little paint.

"Back to the drawing board" as they say.
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Old 22-09-2016, 01:22   #12
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Re: Marine Ply - Okoume or Douglas Fir

One can always use Fir or MDO for the floor/bottom of the dink, since it is what takes the hardest beatings. And then use a lighter ply like Okoume for the other parts. Thus you get the best of both in your build.
Plus, of course, most of the interior bits can be built using much lighter materials than the hull anyway. Including even going to a cored composite for the interior furniture & structures. Though from about 5mm on down, the strength to weight ratio in plywood is tough to beat. Well, unless you use cored carbon fiber for your structures.
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Old 22-09-2016, 09:49   #13
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Re: Marine Ply - Okoume or Douglas Fir

I built a small pram style dinghy (stitch and glue method) using Doug Fir plywood. Very happy with the results.

While I can't compare with Okoume because I didn't use that, I have no complaints or unhappiness with the fir product. Easy to source. Go and pick out the exact sheet you want - minimal voids, smooth surface, few "football" plugs, etc.

I used plans from Bateau (free). http://bateau.com/free/D4.pdf. Added a sailing rig.

Love it - very happy with results.

~markb
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Old 22-09-2016, 11:01   #14
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Re: Marine Ply - Okoume or Douglas Fir

Has anybody thought about using FRP panels from Home Depot to fabricate a dinghy instead of plywood? I realize you might need to add a few stringers for stiffness but the benefit is a uniform material and no rot.
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Old 22-09-2016, 11:36   #15
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Re: Marine Ply - Okoume or Douglas Fir

Hydrotek Meranti ply is my choice. Good quality, more rot resistant the Okome, and much less checking than DF. It is heavier, but stronger, and it does cost more. But for a few sheets for a dink, it hardly matters.

Dave
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