In Which I Worry About Plywood

Most of my boat is built from plywood, so choosing the right kind was my first concern. Most of the plywood sold in lumberyards and home centers is not waterproof and not suitable for boats. That leaves boat builders with two choices. The first is exterior grade plywood, which, as the name implies, is intended for outside use. Basic, run of the mill “ACX” exterior plywood looks just like regular plywood found at any lumberyard or home center, but its redeeming virtue is that it is held together with waterproof glue. It’s more expensive than interior plywood, but not by much.

The second option is “marine grade” plywood. This kind of plywood, I learned, is fundamentally identical to exterior grade plywood, with one important difference: it is made without voids. Apparently, most plywood has small air pockets in the interior laminations. These gaps can allow water to seep in, weaken and eventually rot the hull no matter how conscientiously the boat builder paints or epoxies the exterior. Prices for the least expensive marine grade wood is roughly twice that of exterior plywood; the cost climbs rapidly for marine grade plywood made from exotic, imported woods, especially something called “okoume,” a tropical hardwood that seems to be much prized by the boat building community.

The concern about “voids” sounds worrisome (“Voids: The Hidden Killer”), but I resist spending more than necessary on a first time effort that is not meant to be an heirloom. I remind myself of my goal: build a boat that can gracefully sail down the Chesapeake Bay and maybe last for a few more years while I plot my next steps. Spending too much money on unnecessary quality is simply wasteful. More than that, it starts to take the fun out the whole enterprise. Where’s the sense of adventure when my small act of middle age rebellion starts to cost more than the family minivan?

But am I making a mistake? For insight, I start searching the many online boat building forums. I quickly learn that among professional boat builders and ambitious hobbyists,  ACX carries as much clout as Spam and Cheez Whiz. Again and again, I watched hapless novices ask, in some fashion, the following question:

Hey guys! I’m new to boat building, but can’t wait to get started. I want to build something with my son that won’t break the bank and will give us some fun on the local lake. I’m wondering if I can use exterior grade plywood. Marine grade plywood sounds nice, but, gosh, it sure is expensive! Let me know what you think.

Here’s a typical reply, posted on one forum by a builder with the moniker “Betelgeuserdude:”

“Quality of plywood has generally been falling into the abyss for decades. ACX will do the trick for a quick and dirty boat, upon which you will place little value or trust. The use of ACX is very poor economy, in my opinion. My labor is by far, the more expensive portion of the construction of any boat. If I have to burn the boat after a few years, or replace the poor initial materials with the materials which I should have used, my expensive labor is wasted.” (

Fair enough. But aren’t there times when less expensive materials make sense? When I was a novice woodworker, I developed my skills by cutting and shaping inexpensive pine boards, not oak or cherry. Only when I had confidence in my skills did I begin experimenting with more costly woods. So if I view this as an experiment, a way to test the water, as it were, isn’t ACX good enough? Betelgeuserdude offered grudging endorsement of this philosophy. “If all you wish to do is slap together a small boat, upon which you will endeavor to enjoy a few seasons of use, by all means use ACX.”

Not all boat builders have such a low opinion of exterior grade plywood. Among the “get it done and get sailing” crowd, there is a tolerance for mid-priced materials and shorter life spans. An article posted on Messing About captured the zeitgeist of this community. “I’m a cheapskate,” the author wrote, without sounding very apologetic, “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.” (

Five to ten years sounds fine to me, too–plenty of time to build my next (and better) boat.

By now my plans arrived and the Stevenson’s bill of materials helped settle the question. At the top of the page it called for twelve sheets of “ACX exterior grade plywood.” That tipped the balance, although I had—and still have—some reservations about my choice.


Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

%d bloggers like this: