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One of my favourite stories from my summertime job in a Vancouver Island sawmill in 1967 was the joke that workers liked to pull on naive newbies to the mill. They would tell the unsuspecting victim that a certain pile of lumber had been cut too short and would then send him in search for the “lumber stretcher” to remedy the problem. The unfortunate victim would go from one area of the mill to another, asking for the device, only to be told that he should try in yet another place, until he had covered most of the mill and someone would relent and let him in on the joke. Fortunately for me, the mill workers thought that a farm boy from the prairies would have too much common sense to be caught by such a prank and they didn’t pick on me!

Boat building does have a similar problem to that posed by the mill workers – how to make short boards into longer ones in order to build boats beyond the length of available lumber. Various methods have evolved in the history of boat construction, including the scarf joint (which we will encounter in a future post). The advent of CNC directed routers, able to cut out patterns with great precision, has enabled one modern version of “lumber stretching” that the Mana “cat kit” incorporates – the jigsaw puzzle joint.

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On the Tiki 21 that I built in the 90’s and on most of the modern designs from James Wharram Designs, plywood panels are joined, end for end, in a butt joint with a piece of plywood epoxied over top of the joint. This method is effective and requires no specialized scarfing equipment or expertise but it does not leave a smooth panel on the interior of the hull. The jigsaw joint used on Mana 24  gets around that limitation – a 100mm strip of fibreglass tape reinforces the joint instead of a piece of plywood.

 

The puzzle joint ensures that the joined panels line up correctly. I followed the advice from JWD and placed MDF board above and below the joint along with plastic sheeting, weighed things down overnight while epoxy cured, and the results were a nice smooth, 23 foot long panel.

 

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