Fir plywood

[clancyb]

Hi all

I'm seriously considering building Arch Davis's Jiffy V-22. He recommends using marine fir plywood for the construction, due to its greater durability than Okoume and other plywoods.

However Sam Devlin says in his book to run screaming from the stuff.

Should I go with Arch(who after all did design the boat) and the the fiberglassed fir hull, and save a few bucks? Or is that a false economy and get the more expensive(and more fragile) plywood? BTW this will be a nice boat, but I'm not going to obsess about getting it perfectly yachty.

Thanks in advance

[mariner2k]

My 2cents. My boat has a fir plywood deck. It has been on in excees of 20+ years. I recently pulled off the old fiberglass/epoxy. Despite the fact that there was wetness between the glass and the plywood, the plywood was in like new condition. True, it is a deck, not a hull, but I would definately give it two thumbs up in this situation. mariner

[Ken Liden]

Fir marine plywood has been a mainstay of wooden boat building for more than 60 years. The trick is to be sure that you are using Marine plywood. Marine plywood is free of voids and will have a core of either Fir or Larch and a Fir face and will have resorcinol glue. There are lots of Fir plywood hulls out there that are more than 50 years old. In the US compliance to plywood standards is voluntary and the panel will be stamped with the name of the association under which rules the plywood was produced. God alone knows what standards are used for imported plywood.

[Wayne Jeffers]

Clancy,

You'll get all kinds of opinions about fir plywood.

A lot comes down to personal preference. Choice of plywood is one of the many decisions/compromises we make in building a boat.

A few objective facts:

Fir plywood has a propensity to check unless covered with glass cloth. Epoxy coating alone, or paint, won't stop it from checking. I've read that liberal application of raw linseed oil will prevent checking, but I haven't tried it yet. Most (maybe all) other kinds of marine ply do not check.

Douglas fir is more rot resistant than Okoume.

Marine Douglas fir and A/C Douglas fir from the lumberyard are made of the same wood and with the same glue. The marine grade is manufactured to better tolerances, may have more plies, and should be free of internal voids. These are all advantages.

A lot of people think that A/C is plenty good enough. OTOH, for anything more than a simple skiff, the cost of the best plywood is a pretty insignificant part of the total cost, so why not spend a little more for the good stuff that has proven to last many decades?

Wayne

[clancyb]

To give you all perspective, rough estimates(from Harbor Lumber website) for the plywood are $2000 for marine fir, $3400 for okoume, or $4200 for Shelmarine okoume(what's this?). Big difference in some ways, but not really a big percentage in final completion cost of the boat.

[almeyer]

I'm having the same internal debate myself. Two years ago I built a pirogue out of 1/4" luan ply, cheap stuff but with a good marine sealer and varnish it has held up fine. I also give it a good rinse (I use it in a brackish environment) and dry it off every time I'm done and store it in the garage. Now I'm looking to build a Penobscot 14 from Arch Davis plans and wondering about using marine ply or AC ply. The AC is about half the cost of marine, which makes a difference. Wouldn't mind hearing some more thoughts on the subject. The Penobscot will also be stored in the garage - it will take too long to build to store it outside in the weather.
Thanks,
Al

[Mr. Know It All]

The marine Douglas Fir plywood that my Lyman's lapstrake planked hull was made with has lasted 41 years with no rot. The other parts of the boat that were made with the more expensive mahogany plwood and most of the oak frames are all rotted and needed replaced or repaired. I guess the cheap stuff is the good stuff. :D
Peace---> Kevin in Ohio

[imported_Conrad]

For what it's worth, I just bought two sheets of 1/4" fir marine to build a six hour canoe. The stuff was terrible, no mid ply voids, but one face was full of putty and badly checked. Unfortunately I didn't catch it until I was home.
On the other hand I've bought non-marine fir ply from Greenwood Forest Products out of Oregon that was exceptional, better than most marine. A lot of MDO fir ply is excellent also, so it probably comes down to checking the individual sheets as you pull them off the stack. The quality from batch to batch and mill to mill seems to be highly variable regardless of the label.

Okume will rot in short order if not completely protected/sealed.

[Dave Carnell]

Persson Mfg. is building their line of skiffs of "high quality AC fir plywood". AB or marine plywood carry a surcharge.

<http://www.perssonmfg.com/>

[Albie]

I've used both--fir in a Wittholz 18" "Downeaster" and more expensive Israeli stuff for a Joel White "Nutshell". I coated both with three coats of epoxy and have had no trouble at all. The "Downeaster" is almost 15 years old(same as my good dog,Clancy)and has been no problems except for two oak floors developing rot which was from use of bad stock. Do make sure it is a good grade of marine ply.Good luck.

[ 05-14-2002, 07:48 AM: Message edited by: Albie ]

[clancyb]

Thanks all. Marine fir it is. Any particularly good suppliers in the Mid-Atlantic? I'm probably going to have to have them select and deliver the boards, and I'd like a reputable yard doing it(I just had a local yard deliver lumber for a 400 sq. ft. deck - they dumped it all at once onto my slate patio).

BTW, Arch Davis's plans are fantastic. For the Jiffy V-22, he sends 3 sheets of Mylar with full size renderings of major components, 6 sheets of blueprints with detail views and comprehensive overviews, and a 25(?)page booklet of instructions.

I'll start a new thread on the dimensional lumber I need.

clancy

[Albie]

Boulter Plywood in Somerville,Ma. is excellent-except I've always picked up. Harbor Sales(?) in Baltimore. I had good luck with Condon in White Plains,NY. They shipped 4'x20' pieces to me. However, that was delivered to a factory with a loading dock and receiver and I took over from there. Those three also deal in dimensional lumber. Good luck.

[ 05-14-2002, 10:09 AM: Message edited by: Albie ]