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Wood and Plywood Facts

I can't find douglas fir 1 x 12s. What else can I use?

The Stevensons hail from the west coast, where douglas fir is a plentiful and common boat building wood. But in the other parts of the country (and the world!) builders either pay a premium for douglas fir, or simply can't find it at all.

Here's a list of species builders have used instead of douglas fir:

• Southern yellow pine (SYP)
• Hard pine
• Poplar
• Phillipine mahogany
• White oak

You may not be able to find any of these at a good price. But there are many more; for a more complete list see Glen-L's great site about boat building woods at Wood and Plywood, Chapter 5 (if that link doesn't work, go to Glen-L.com  and scroll down in the left frame and select "Boatbuilding Woods").  The trick is to find the wood that is priced fairly in your area, and use that.  If you really want to get technical, go to the Forest Products Laboratory Guide, published by the US Government, for specs on various woods.

Very soft woods like redwood are not appropriate, but there are quite a few rot resistant woods with even grain that can be substituted for douglas fir. I used construction grade lumber, which was re-sawn into 1 x 12s, but you do a bit more work that way.  Some have asked the local lumber yard to plane down 2 x 12's to the 3/4" thickness needed for to simulate a 1 x 12 (they usually charge for this service, but it might not be as expensive as ordering in 1 x 12s and paying the freight).  Ask at the local lumberyard what wood they sell for outdoor stair tread (real wood, not that plastic stuff!) or for fascia on homes, etc., which commonly comes in 1 x 12 sizes.  Compare that wood to the description either on the Glen-L site, or at the Forest Products Laboratory Guide.  Or, ask on our Main Forum.  Chances are, the wood available locally that is used in exterior applications will work fine for your trailer-sailer keel.

Think Safety!
Boat building involves inherently dangerous activities, and each builder must be responsible for his own safety. Information presented in our Shop Tips are "builder to builder" communications, rather than from experts in the use of tools or techniques. We encourage all builders to read manufacturer’s instructions, follow all safety precautions, and be pro-active in seeking out more information on reducing the risk of injury or illness. I found an alternative wood, but not in 1 x 12 size. What can I do?

Some builders have reported using a 1 x 8 and a 1 x 4 to "simulate" a 1 x 12 when they start lofting the keel. Because the keel is laminated, and really quite strong, you can do this without worrying about scarf joints or the like. You just have to stagger the long horizontal joint by putting the 1 x 4 above a 1 x 8 when lofting the first lamination. Then, when making the "middle" lamination of the keel, put a 1 x 8 above a 1 x 4 below. 

This overlaps the long horizontal joint (its easier to do than to describe!) For the final layer, make it exactly like the first, and all three layers will be staggered. When you glue up the keel, this long butt joint will be fine. (Just remember that when lofting the first layer, you still have to measure down from the top edge 4", because that 1 x 4 is really not 4" wide!)

Should I use marine grade plywood, or exterior grade from Lowes/Home Depot?  What is "exterior grade", anyway?

Marine ply is pretty expensive, but it is good stuff. Compare prices in your area. If you want to spend the money, it is well spent.  It finishes easier, will probably last longer, and ... well, who can argue against quality?

That being said, I'm a cheapskate, and used what people commonly call "exterior" grade plywood from Home Depot. I'm not planning to leave my boat in the water, and if it lasts 5 - 10 years or so, that's fine with me. Here's what I found out about plywood.

People commonly think that the "ACX" grade of plywood is exterior because of that "X" at the end. That isn't true. The voluntary grading system of the APA - Engineered Wood Association uses the first and second letters to tell you about the faces of the plywood. An "A" face has no voids or putty filling knot holes. A "B" face may have football-shaped wood glued in where knot holes were. A "C" face will have knot holes, sometimes filled with putty, and sometimes not. A "D" face looks like the surface of the moon, with unfilled knot holes in the face.

So a "AC" grade of plywood has a good face, and a poor face. But what about the "X" at the end? Does it stand for exterior? No, the way I understand it, it specifies that the inner core is of undetermined species. So how do you know if plywood is rated for exterior use? Here's an example of what to look for, the grade stamp:

The APA's Grading Stamp
You see the now-familiar "A-D" rating for the faces of the plywood. That "Group 1" designation specifies the strength of the wood used for the faces, with "Group 1" being relatively strong woods like douglas-fir. The next word, in this case "Exposure 1" tells us if the plywood is rated for exterior use.

Plywood is made in four exposure durability classfications by those manufacturers agreeing to the APA standards: Exterior, Exposure 1, IMG or Exposure 2, and Interior.

Panels marked with the word "Exterior" are made with fully waterproof glue and composed of C-grade or better veneers throughout. That means that most of the knot holes are supposed to be filled with putty or wood on the inside plys. This is the best non-marine grade of plywood, and you probably won't find it at Home Depot!

Exposure 1" panels are usually the ones stacked under a sign proclaiming something like "ACX Exterior Plywood." Exposure 1 plywood is made with the same fully waterproof glue, but may include D-grade veneers in the core. That means there are voids on the inner plys. For boat building, those voids mean that moisture will collect there, especially if the boat is kept in the water or in humid conditions, and will eventually rot from the inside out. And, on boats where you are bending the panels extensively, the voids will cause an unfair bend (or cause it to crack at that spot!) The APA says about this common grade of plywood: "Because of the veneer grades used, panels under prolonged severe moisture conditions may occasionally develop limited, highly localized glueline delaminations coincident with grade characteristics."

IMG (intermediate glue) or Exposure 2 plywood is not required to be made with fully waterproof glue to get this grade; it can have a glue that will delaminate if exposed to a lot of moisture, but will hold up under moderate humidity and exposure. Interior plywood is not required to have exterior glue, but must be made with moderately moisture resistant interior glue.

I used "Exposure 1" plywood. I'm day sailing my boat, and I know it will spend far more time on its trailer than in the water. And even though I love my boat, its not my wife, and I know I'll tire of her someday (the boat, that is). Probably within 5 years. Then I will callously toss her aside and buy or build another boat. Now if you plan to leave your Weekender in the water all the time, or want it to last 15 years, I would plan on using marine grade plywood. Builder's choice, once again

US made marine grade plywood usually has douglas-fir faces, and some builders have decided if they are going to spend the money, they want the mahogany-like faces of Okume or other imported species plywood. The Glen-L site has quite a few descriptions of the imported marine plywood. One other factor: if you are planning on saving some real money, and are not going to use fiberglass cloth and resin or epoxy, stay away from fir faces on the plywood. The fir ... even on marine grade plywood ... will check and crack each season. For non-glassed boats, use a marine grade plywood with Okume, sapele, or another imported species that will not crack.

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