Friday, July 23, 2010

The Formation of a Hull

It is a pleasure to be able to blog again! As has been the case many other times, recent building activity has conflicted with our ability to keep our readers updated. However, although our blog was silent, the boatshed was abuzz with activity. I am pleased to report that we have made significant headway since the previous post. As shown below, we have completed the side planking and have begun the process of laying the flat bottom. After our most recent efforts, our project is truly starting to take on the likeness of a ship. After such a significant lapse in reporting, it is probably most appropriate to recount the month of June in chronological order. Because the last post detailed the installation of the transom onto the strongback, the last step before planking, it seems appropriate to begin with the garboard.

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 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.

2. Having already been burned once we were too chicken to just jump straight into cutting a valuable plank so we decided to cut up a piece of plywood first to see if we could put the theory into practise. Here is our first truss.

3. Laying out the truss on the plywood.

4 . Plywood plank being fitted to the boat. Success!

5. Transferring to the mahogany plank.

By using this process, we found that it was possible to obtain board form quickly. After reviewing the lines on the completed craft, we concluded that they closely followed the initial spiling batten locations that we had deemed to be fair earlier—the objective of any spiling technique. No aspect of this method is difficult to master, and, as such, it is ideal for any first-time builder. Despite its simplicity, however, the accuracy of the above system rivals any of the other spiling methods presented by experts.
6. Lines on the plank, ready to be cut to shape.

7. Planning to the line after rough cutting with the circular saw.

After transferring the proper dimensions of the plank to the scarfed boards using the assembled truss, it was relatively easy to shape the strakes. In most books, authors recommend using a circular saw for this step, as most planks have too much curve to be cut using a tablesaw. Initially, we were somewhat apprehensive about this prospect, as, for us, the circular saw has been a tool usually reserved for basic cuts requiring little accuracy, or for jobsite construction. It seemed to have no application in the fine craft of boatbuilding. However, having now cut ten boards with this tool, we can attest to the fact that it is effective in this use. By using the saw for rough cuts and reaching our final shape using the hand plane, we were able to combine accuracy and efficiency. Although the saw was useful for this task, we were reminded of the sheer versatility of the hand plane. Although it appears a simple tool, we have reached for the plane countless times for tasks no other tool could do in the construction of Willy. From leveling the chines to squaring the planks at the transom, our two planes have been indispensable in this undertaking. In addition, they are a sheer joy to use! There is something about the rhythmic motion and the whisper of the blade in use that has an entirely unique sensation. Unlike with power tools, where all senses are obscured by the incessant vibration and din of the motor, the user is able to wield a plane purely through feel. Although one could write extensively upon this topic (and that shall probably come), it will suffice to say that any shop that lacks planes is inadequately equipped. 
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.



1 comment:

  1. Hello - How are the truss pieces attached to the battens besides the single screws? If you glue, it can't be re-used for other planks. But if 1 screw, I thought it would pivot on that screw and move around?