Strong Backs

Chapelle and Barto Plans

(to start of project)

 I’ll be working from a combination of printed plans along with measurements taken from boats of other builders, in addition to a few modifications of my own. Besides the one page Chapelle plans, I have the more complete set of plans from Wooden Boat Magazine by Marc Barto. I’ve also talked to Roger Crawford and taken measurements from his boats, as well as several other amateur and professional builders, all of whom you’ll hear more about later.

In comparing the Chapelle and Barto plans, I discovered some inconsistencies. Barto gave a steeper angle to his transom, perhaps to make it easier to plank in plywood, and this changed shortens the boat a bit. There also appear to be a few errors in the offsets of the Chapelle plans that Barto corrected on his version. As far as I can tell, these were either errors made when the original measurements, taken by hand in the field, were first recorded in 1888, or when Chapelle later transcribed them onto his final draft. I actually entered all the measurements into a spreadsheet to compare them. I haven’t talked to anyone else who noticed the differences, but some of them are quite large and obvious errors. I entered the final values in DelftShip, a nautical engineering program, just to be sure which values are correct, and then refined them further there.

Though builders of the Barto boats have encountered some difficulties, particularly around the transom area, I believe Barto’s plans are essentially correct; but he apparently assumes certain liberties will need to be taken according to the stubbornness or pliability of the wood you have on hand, and each boat will follow slightly different curves accordingly. In other words, just because he gives and exact measurement doesn’t mean that exact measurement will work.

In any case, I’ve settled on a final table of offsets, and printed out a final set of plans and mold templates. But regardless of which plans you use, the first task is to build a good “strongback” – the frame on which the boat will be constructed. It has to hold the weight of the boat for a long time, and stand up to all the sanding, sawing, pulling and shoving necessary to torture wood appropriately.

These two strongbacks, made of reasonably straight 12 foot 2×8’s and a bunch of scrap lumber, took most of a day to make. The legs are adjustable, so I can raise and lower to a comfortable height. I’ll add cross braces to stiffen everything up.

 

 

 

 

 


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