Thursday, April 3, 2008

Displacement Hulls

There are two basic types of hull designs, they are the displacement hull and the planing hull. Displacement boats cruise through the water and planing hulls lift and skim over the surface. Displacement hulls will always displace (push away) water equal to its total weight. If its total weight is equal to the weight of the water that it's displacing, the boat will float.

As the displacement hull begins to move through the water, small waves appear at the bow and further aft along the hull. When speed is increased, these waves grow larger and the distance between them increases, until the boat is riding between the two waves that it is creating.

At this point, the hull has reached its maximum hull speed. Adding additional horsepower after this point only makes the waves bigger, with little or no increase in the speed of the boat.
To get a approximation of what the maximum hull speed of any displacement hull boat will be, you can use this formula:

1.34 x the Square Root of the Boat's Waterline Length (This is Theoretical Maximum Hull Speed).
Example: If your waterline length is 26 ft, multiply 1.34 by the square root of 26 (6.83). 1.34 x 5.48 = 9.2. This is the boat's maximum hull speed in knots.
Round bottom boats are the basic displacement hull design. Some advantages of a displacement hull are:

1. A relatively small engine can easily drive it, its ability to travel long distances is outstanding.

2. Because it's traveling through the water, not on top of it, it has a very smooth, and seaworthy ride.