Boat structures 101

[Blue_Heron]

So, I’ve explained what cored laminates are. They are a successful construction method for conventional fiberglass boats. Maybe I should also talk about what they are not. There are construction methods that aren’t true cored laminates, but kinda look like them. Some are quite successful, others not so much.

A good example of a successful alternative to the cored laminate is the type of plywood/epoxy construction used in stitch and glue boat building. Stitch and glue is a process of wood boat building that uses reinforced epoxy joinery to build hulls and other boat components of plywood. They are then covered with an epoxy/glass laminate inside and out to protect them from moisture, abrasion, and puncture. Typically, the laminates in this type of construction are not as thick as in a pure cored laminate. The plywood core contributes more stiffness to the assembly than in the cored laminates I described in my previous post. This method can be used in lieu of pure cored laminates to successfully repair a fiberglass boat. But if you use an epoxy plywood construction method, you want to do it right, or it may not hold up.

Probably the most important thing to remember about plywood/epoxy construction is EPOXY. You can’t use polyester boatyard resin in a thin laminate over plywood and expect the same results. Cured epoxy resin has far superior physical properties for this application. It is more flexible than polyester, it bonds better, and it is much more impervious to moisture.

You can build a deck by coating plywood on both sides with a couple layers of mat and polyester resin, but it won’t be anywhere near as durable as a plywood/epoxy deck, particularly if you live in an area with high humidity and lots of rainfall like I do. It will appear quite strong when first installed, but over time it may absorb moisture and/or delaminate. This was the method used on the previous “restoration” of my Hewes Bonefisher project boat , and it lasted probably less than10 years. By the time I got the boat, the deck had been mostly removed, but what was still there was a delaminated waterlogged mess.

For more info on stitch and glue, or plywood epoxy construction methods, I would refer you to Joel Shine, our resident expert on the subject. Or you can learn quite a bit from his web site:

http://www.boatbuildercentral.com/

Dave