Before the planks in any carvel-planked boat are fitted, any joints in the backbone structure of the boat that cross the rabbet line need to have stopwaters fitted. That is, any joint between two backbone members (such as the keel and the forefoot, or the keel and the sternpost) that crosses the rabbet line, therefore crossing the line between the outside of the planking and the inside of the planking) need to be blocked otherwise there is a pathway for water to enter the boat. Stopwaters are made from any durable softwood, and are driven into holes drilled through the joint, starting exactly where the joint crosses the back rabbet line, that is the line where the inside lower edge of the plank will sit. The holes are drilled a little undersize, in our case 11/32" for a nominal 3/8" stopwater. The timber intended for the stopwater is machined oversize and overlength, and shaped roughly round. The timber is then driven through a 3/8" hole in a steel plate or a plumber's pipe-flaring tool, which shaves off the excess timber and compresses it a little. The stopwater is then driven into the undersize hole in the backbone structure, then the excess on each side is chiselled back so as not to protrude beyond the rabbet surfaces. Do not be tempted to use store-bought dowels, they are made from the wrong timber and will likely not expand as the water reaches it, which is how the softwood stopwaters work. With those fitted, it's now back to planking. Watch this video which goes through the whole process.
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AuthorIan Smith, Boatbuilder (ret'd) Archives
January 2024
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