When constructing a lapstrake craft, the boards (strakes) overlap each other, much like the shingles of a house. Besides aesthetic appeal, the advantages of this system are twofold. Firstly, the overlapping areas are doubly thick, meaning that they act much like stabilizing stringers running from stem to stern. Because of this, it is possible to create a clinker craft using relatively light material. In addition to adding strength, lapstrake construction also aids in maintaining a dry interior, as the ridges on the outside of the hull serve to direct spray downwards. When sailing in adverse or cool conditions, this is incredibly valuable! Because of the craft’s design, The bottom board, or garboard, is the first plank to be laid, as it is the base on which all of the other strakes will rest. In all boatbuilding books, authors seem to regard the garboard as a formidable challenge. This is primarily because, on round-bilged boats, the first strake must accommodate for the compound curve present at the lower extent of the hull. However, because Willy Winship is a flat-bottomed craft, we were able to avoid many of the issues that generally plague the garboard. Still, we were faced with the difficulty of deriving the correct plank profile in order to minimize stresses exerted on the strake during assembly and use. Although it may appear that a correctly-spiled craft has planks that are slightly curved, or scimitar-shaped, in reality, strakes can be incredibly odd. For example, the sheer on this boat had to be distinctly “s” shaped in order to take the contours of the hull. Thus, it is important to devise a process through which the proper plank form can be determined. When faced with this challenge, the amateur boatbuilder may be tempted to panic, as some experts tout methods that entail the use of several spiling battens, dividers, and transfer marks. Fortunately, there is a simple method of establishing strake shape, sometimes called the “truss method”, consisting of three straightforward steps:
1. After obtaining two flexible, true battens the width of the laps in question (Plywood seems to be the ideal material for this application, as it is not subject to the natural stresses found in natural woods), clamp one to the previous lap, or, in the case of the garboard, to the chine or keel.
2. The second batten should be affixed to the molds at the positions predetermined through spiling the hull. It is important to remember to place the batten with the top edge aligned with the mark, as the width of the batten represents an area that will be covered by the following strake
3. Using a few dozen short scraps of batten material, attach cross braces in a triangular fashion akin to that employed in truss bridges. This will result in the formation of a rigid replica of the plank that can be used to transfer the correct shape to the waiting board.
Okay, enough theory....here is what really happened:
1. We took one of our scrap planks that we made while we were practising scarfing and bent it around the molds and marked the chine and battens on the inside with pencil lines. We cut the plank to the lines and put it back on the molds. A total failure--it needed about 6" of edge setting to get it to lie properly on the molds.
|4 . Plywood plank being fitted to the boat. Success!|
|6. Lines on the plank, ready to be cut to shape.|
|8. Hood end cut to shape (trial and error to fit) and the gain cut.|
|9. First plank in place and the spiling battens positioned and ready for the truss webs to be added.|