SVN solovelanet

37 SVN Solovelanet Global A boot bulb. These kinds of shapes are used both for cast iron and for lead keels.This shape is mainly suitable for cruise boats. While the centre of gravity is slightly higher compared to that of a T-keel, on the other hand a boot keel is very unlikely to get tangled on a rope or chain when entering a harbour Three keel types If you take a tour of a shipyard, the drydocked bo- ats you see you will usually have one of the fol- lowing: the trapezoidal keel, widely used from the 1970s to the early 1990s, the boot- or L-shaped keel, and the inverted T-shaped keel. The two latter types are both found nowadays in the latest desi - gns, with L-shaped keels favored on cruise boats, and T-shaped keels being the standard for racing ones. The biggest difference between these three types is the positioning of the centre of gravity. Given the same keel depth, the more the weight is concentra - ted at the extremity, the more the righting moment will be. The keel with the lowest centre of gravity is the T-shaped, in which almost all the weight is at the extremity, followed by the L-shaped and final - ly the trapezoidal keel. The trend of the last twen- ty years has been towards lowering the centre of gravity as much as possible, and a modern racing keel will have a sharp and thin fin, with a very ta- pered T-shaped bulb at its extremity. Cruise boats designers however opt almost exclusively for the L- shaped keel. The reason for this is practical: com- pared to a T-shape, an L-shape is less fragile and offers less grip for lines, chains and other obstacles you can hit when mooring in a marina. The advantages of T-shaped keel with a low cen - tre of gravity are mostly evident when sailing close hauled: all things being equal, the leeway decrea- ses and the righting moment increases, allowing for a more generous sail plan. Alternatively, designers can exploit the advantage to design a lighter keel with the same center of gravity, resulting in a qui - cker boat. In terms of performance, trapezoidal keels are the Cinderella of the group. Yet, they do have some significant advantages. To begin with, their shape makes them more resistant to impact regardless of the construction material. Furthermore, they are easier and less expensive to build because they require only one mould. Boats equipped with fin or torpedo need specific structural features desig - ned to absorb the loads imposed on the hull by the superior righting moment of the appendage, which also increases the cost of the boat. The sailing experience will also vary depending on the keel type. With rough waves and wind, a boat equipped with a T-shaped keel will be slower be - cause pitching tends to expose the upper face of the T, increasing hydrodynamic resistance. This will make the boat more difficult to control and require a more experienced helmsman.

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