Saturday, February 16, 2008


The tiller is the connection between your mind and the heading of the boat. You exert pressure on the mahogany, it moves the rudder in the gougeons attached to the boat and the balance of the pressure of the wind on the sail and the water on the rudder puts the boat on the desired heading. The helmsman spends most of their time with a hand on the tiller, so the feel should be right. Not too big, small, sharp, just right.

Here is another interesting way to use pressure. We exist in a fluid medium, our atmosphere. The air above and surrounding us has mass. We use that mass to clamp layers of composite materials together using a method called vacuum bagging. In this case we are making the sneakbox centerboard, a device to resist lateral pressure and keep the boat from sliding sideways over the water and wasting drive energy. This centerboard is utilizing some reused plywood and scraps of unidirectional glass mat and carbon fiber in a composite sandwich. The duckboat has a very smooth bottom and round bilge like the bowl of a spoon. When the wind blows on the sail from abeam, it tends to roll the boat over on it's side and slide it across the water sideways. The centerboard counteracts this force by pushing on the water and resisting the sideways force translating it into a forward motion. It also has to slide through the water with as little resistance as possible so it has a foil shape.

The core of the board is plywood, faired to a sharp trailing edge. The next layer is glass set in West System epoxy. The outside layer is carbon fiber for stiffness also set in epoxy. Both layers are rolled on, the board flipped and the other side laminated. A bag is constructed from plastic and mastic. A layer of release fabric that doesn't stick to epoxy is put on and then a layer of breather fabric, kind of like felt. The entire sandwich is sealed inside the bag and then the air is pumped out until we reach a vacuum of about one atmosphere. That means there is about 14 lbs per square inch over the entire surface, top and bottom, of the board, squeezing the epoxy into the wood as well as evening out all the layers.

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