Factors for Longevity

I have come across some great discussions of building issues for longevity of plywood boats.

The first source is from John C. Harris at Chesapeake Light Craft.  John has done an interesting investigation of wear and tear on his fleet of demonstration and prototype boats.  The fleet probably has an accelerated wear rate based on its heavy use and transport to boat shows.  John goes through many case studies of various types of damage, probable causes and required fixes.  The blog posts can be found here.

A 15 year old CLC Eastport Pram, perhaps oversanded during the build.

The second paper is from Jim Brown and is titled Building for Longevity from the Searunner Construction Manual.  I found this over at Small Trimarans.  Jim shares his long experience on essential building  techniques using epoxy and plywood.

Thirdly, there is a post by Dudley Dix discussing painting and coating requirements on plywood boats.

These three texts overlap and reinforce each other.  My takeaways are:

• Pay extra attention to make sure all plywood is triple coated with epoxy.  Jim Brown says that this includes the edges of plywood that will be bonded (eg. bulkheads).  I had mistakenly thought that the bonded edges would be OK with a primer swipe and the glue layer.
• Carefully avoid any over sanding. Of course you don't want to hit the glass, but beyond that you must maintain the full thickness of the epoxy envelope over the glass.
• Consider extra protection in high wear areas.
• Immediately take action to repair and seal any dings or scrapes.
• Maintain UV protection inside and out.

Basically, protect the full epoxy encapsulation of the wood at all costs.

First Epoxy

I applied a coat of epoxy to some parts that don't get any fiberglass.  Start small.

Above are interior parts that form part of the pod/bunk area.

This is one of of the forestay bulkheads that will get three layers of carbon at the top, but is only coated with epoxy at the bottom.  You can see tabs/ears that will anchor the bulkhead to the main hull panels.  The notches are for spruce stringers.

Besides these parts, I spent most of the day sanding small pod/deck inserts.  These parts will be embedded in the foam core cabin top to support deck hardware and winches.  They are small bits that were nested in with much larger parts.  I decided to get them sanded and then I'll store them in bags until much later.

It has been ranging from the mid 20s to the mid 30s in town.  The heaters have been cranked up to get the shop up to 60F. The shop humidity is about 45% and a few couple larger panels on the top of the parts stacks are arcing slightly.  I'm trying to weigh those down.  A wood stove would probably drive the humidity out better.  The panels have been moved about five times in the last two weeks and have been in five storage areas.  The best storage was in Russell's shop for a few days.  He has excellent flat tables and a large wood stove.

Task Time: 6 hours

Project total time: 28 hours