A Comparision of Plywoods

The Windmill requires seven sheets of plywood to complete. It might be possible to get by with six, but it would be risky, since shipping costs would make buying an extra sheet very dear. The only leeway in the scantlings on plywood thickness is on the choice of material for the air tank walls and the internal bulkheads. These may be built from either 4mm (5/32") or 6mm (3/8"). This is a matter of weight control. If the builder wishes to fiberglass the exterior, I recommend using the 4mm instead of 6mm to keep the finished hull weight nearly the same. So the requirements are: five sheets of 6mm and two of 9mm OR two sheets of 4mm, three of 6mm and two of 9mm.

The prices in the box are based on the 1996 catalogs from Boulter and Harbor Sales and today's quote from Plywood & Door Mfg. Corp. (P&D).

Shipping costs are significant. They are not bad per-sheet in a large order, but terrible for a single sheet. My costs for shipping the seven sheets I received today from P&D as part of a 2400# order was $17. If I had ordered just the seven sheets, it would probably have been about $70.

As you can tell from the following letter, I am high on the plywood from Plywood & Door Mfg. Corp. (imported from France). This stuff is not quite the quality of the BS 1088 plywood, but when used with a modicum of care, it is plenty good enough for the Windmill. It will finish out much superior to fir and there have been some nice Windmills built from that. Chances are that it will be impossible to tell whether a boat was built with P&D or BS 1088 plywood. It's all okoume. Now for the bad news. P&D does not currently have any US distributors and all orders have to be shipped from Bridgewood, IL (near Chicago). This means that the minimum order quantity is 20 sheets of any thickness. However, two people could order 20 sheets, build two Windmills and have enough plywood left for two Optimist Prams for about the same cost as ordering for a single Windmill from the other sources. 21 sheets will build three Windmills at very little more cost than one boat built with BS 1088 plywood. My guess is that using the P&D plywood will save a bit more than 10% on the cost of the ready-to-race Windmill including trailer. (Total cost estimated at $3,000. Figure 1/3 each for wood, hardware and sails)

P&D is trying to set up some distributors so that this minimum order will no longer be a factor. Of course you must expect the price to be higher from a distributor. They tell me that it will still be possible to order direct at the 20 sheet minimum.

Template and handbook sales are slow now with only three being ordered since the Nationals. That seems to be normal for this time of year. I have developed the dimensioned pattern layouts for the hull panels and bulkheads and they are now included in the Handbook, so it is no longer necessary to buy the full-sized templates.

Tom Lathrop

Plywood Sources and Prices as of December 1996 British Standard 1088 Non Standard Source: Boulter Harbor P&D Quantity Ea. Total Ea. Total Ea. Total 4mm 2 45 90 54 108 17 35 6mm 3 75 225 69 208 23 69 9mm 2 79 158 94 187 36 71 Totals $473 $504 $174

A letter to Plywood & Door Mfg. Corp. from Tom Lathrop in 1996

John Mazziotta
Plywood & Door Mfg. Corp.
1435 Morris Ave
POB 1212
Union, NJ 07083

Dear Mr. Mazziotta,

I have had a chance to examine and run some simple tests on your okoume plywood. I conducted a boil test on several samples of your plywood and samples of okoume plywood from Israel, Greece, France and The Netherlands, plus one sample of lauan from Indonesia. All of the other okoume plywood was of marine grade and met the specifications of British Standard 1088. It is not known whether the lauan met BS 1088 or not.

All samples were boiled for 12 hours per day over a three day period, leaving the samples in the water a total of 72 hours. All samples passed this test with no visible degradation or delamination of the glue line. Upon complete drying, all samples showed some small voids in the interior plys caused by shrinkage of the stressed fibers. I consider this to be normal and unavoidable. Your plywood was as good as any of the others in this test.

While inspecting several sheets of your plywood I did find some voids and/or overlaps of the plys at flitch joints in the structure. An occasional joint gap was observed on one side of face veneer. This was never seen on both faces. The face veneer quality usually appeared equal to the other marine plywood I have used, but some sheets showed knots or other small imperfections not seen on the BS 1088 panels. This might be of some consequence if the panel is to be bright finished. I would find it necessary to inspect each sheet for voids and repair or avoid them where they present problem.

One other difference I noted was that in thicknesses of 3/8 and above, the face plys of your plywood are about 15% thinner than the others. Your face veneers appear to be approximately 0.050 inches thick on all panel thicknesses. While thinner face veneers are less desirable for structural use, I consider 0.050 inch to be acceptable.

In conclusion, I find your plywood to often be the near equal to plywood manufactured to BS 1088. In those cases where there are imperfections affecting the structural integrity of the panel, it is either repairable or can be relegated to less demanding applications. This could be a problem to large shops where the worker might not have the skill to inspect or repair the defect. This is not the case with any wooden boat builders that I know of.

As you know, Graham Byrnes and I participated in the recent boat building challenge at Georgetown, SC, where I had the opportunity to look at about 20 plywood sheets that your company graciously provided. I was favorably impressed with it and have no hesitation in using or recommending your plywood for marine applications. While it is somewhat inferior to the BS 1088 standard, the quality/cost ratio is definitely in your favor. Since I participated in a joint order of 92 sheets (just received today), I expect to get good results from it.

Sincerely, Tom Lathrop
Mildred's Cove Boatshop
POB 752
Oriental, NC 28571
(919) 249 2646

These are John Harris comments on the above. John Harris has built quite a few boats himself.

We once ordered several hundred sheets from Plywood and Door when our regular suppliers got low. In general, I agree with Tom about its good quality, although for the record there were a couple of things besides the lack of the BS1088 rating that bothered us. One was that the 4mm pile we got was a little thinner than 4mm, which drew complaints from some finicky builders. The sheets had an unsightly seam in the veneer on one side that we had to cut around, though I wouldn't have worried about it in my personal boat. Also, the inner core was alleged to be birch, not Okoume. I can't say for sure whether that's true or not; it sort of looks it. Birch rots fast, but then again, so does Okoume, so it doesn't bother me. I've also gotten some BS1088 French-made Okoume that seems to have a birch core. We boiled our Plywood and Door stuff and it was fine.