 | Power boat hull form |
|
At the opposite extreme to a pure sailboat is a boat that is strictly a power vessel. Such a boat will not need a deep keel like a sail boat. A power vessel will always benefit from some sort of roll dampening scheme. A power boat will have several hull shape differences from a sailing vessel. For example, a power boat will not require as much beam, and a power boat will benefit from optimizing the prismatic coefficient in terms of a higher expected operating speed on a voyage.
If you study the vessel designs presented in either issue, there are very few of them specifically optimized for making passages at efficient displacement speeds (the optimum long range voyaging speeds between S/L 1 and S/L 1.2).
Naturally, there are many valid reasons to make use of a "semi-displacement" hull form. It must be realized though, that semi-displacement shapes are not necessarily optimum for long passages. Instead, their place is coastal cruising where rapid transit is the primary requirement, and where fuel use and survival in ultimate conditions are secondary considerations.
Semi-displacement types require more "lift" in the after body to give them higher speed potential. Therefore, a semi-displacement boat will have fairly straight and fairly flat buttock lines aft. Greater speed will certainly be possible, however speed comes at a much greater cost in fuel, and often in the displacement required to carry that fuel. While speed is improved, range is diminished considerably. For many travelers this is the correct choice, since they may only have weekends and short vacations to spare. For the true long distance voyager however, quite different requirements exist.
For seaworthiness in ultimate conditions there is little question that a true displacement vessel is the most suitable platform, having a more sea kindly behavior, a deeper hull, and ordinarily a larger range of positive stability.
A common misconception is that a displacement vessel must be "heavy" and must consequently be slow. Whether a boat is or is not a displacement type is not so much a matter of her weight, but rather a matter of her shape, mostly in the after body. If you study good sailing vessel shapes, you will be looking at what are also essentially excellent hull types for Voyaging Under Power...!
One common change made when optimizing such a shape for power rather than sail is to widen the stern. This is beneficial for power boats, and if the change is modest, sailing performance will not be adversely affected.
|
 |
| | Roll dampening |
|
As noted, all ocean going power vessels will require some sort of Roll Attenuation scheme. Aboard a motorsailor, this is to a large extent provided automatically by the sail rig itself. The sails contribute as well, but the rig itself also provides an effective roll stabilizer even with the sails furled due to the added inertia of the spars and rigging.
|
|
| | Sailing synergy |
|
As noted, all ocean going power vessels will require some sort of Roll Attenuation scheme. Aboard a motor sailor, this is to a large extent provided automatically by the sail rig itself. The sails contribute as well, but the rig itself also provides an effective roll stabilizer even with the sails furled due to the added inertia of the spars and rigging.
|
|
| | Controllable pitch propellers |
|
As noted, all ocean going power boats will require some sort of Roll Attenuation scheme. Aboard a motor sailor, this is to a large extent provided automatically by the sail rig itself. The sails contribute as well, but the rig itself also provides an effective roll stabilizer even with the sails furled due to the added inertia of the spars and rigging.
|
|
| | Rig type |
|
As noted, all ocean going power vessels will require some sort of Roll Attenuation scheme. Aboard a motor sailor, this is to a large extent provided automatically by the sail rig itself. The sails contribute as well, but the rig itself also provides an effective roll stabilizer even with the sails furled due to the added inertia of the spars and rigging.
|
|
|
|
|
