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PLYWOOD FACTS
The two types of plywood acceptable for boat building are exterior and marine grade. The exterior veneer surfaces are graded alphabetically, “A” being best, etc. Douglas-fir is commonly available in the U.S. and imports with various types of veneers usually can be found. Exterior and marine plywood generally use the same adhesives. However, a marine grade has solidly joined inner cores while an exterior panel will have voids.
Can you use an “AC” exterior panel? If you’re building a 30′ craft that’s going to cost thousands of bucks, then go for the best. In contrast, if you’re working on a tight budget (aren’t most of us?), then a lower grade plywood can be considered.
When we would build a prototype of a small boat, we generally use an “AB” exterior grade. Not to save money, but to see if the panels with interior voids will make the bends without fracturing. We’ve had few problems with an exterior grade but, if an invisible void was at a point of stress, the panel could fracture.
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One Response to Boatbuilding Plywood Facts
As a former Columbia dealer and owner I would suggest that the typical AC or AB would be risky because of the possibility of a void in the vicinity of hte “tang” which is welded to the rudder post (vertical shaft). Regardless of the grade PW used, I strongly uggest increasing the size (area of the tang ) because they sometimes “twist” themselves through the rudder causing failure. Made large enough the possibility of voids is negated, so i fyou are willing to spend more for the metal tang then the less expensive PW will probably be satisfactory. As a minimum i would triple the area of the tang.