Game Development Reference
In-Depth Information
traveling and plows its way through the water. The cross-section of a displacement hull has a
relatively constant U shape from bow to stern. Displacement hulls are used in long-distance
powerboats such as cruise liners and trawlers. They are the most fuel-efficient type of hull, but
they also experience the highest drag forces in the water, which limits their speed to relatively
low values.
With a
semi-displacement
hull, the forward section of the hull is V shaped, which allows
the front end of the boat to lift up when the boat is traveling forward. The lifting motion reduces
the water drag (also called
hydrodynamic drag
) experienced by the boat. The top speed of a
semi-displacement hull is higher than that of a comparable displacement hull. Lobster boats
and coastal trawlers will typically have semi-displacement hulls.
High-speed powerboats and jet skis have what is known as a
planing hull
. This type of hull
has a V shape over much of the hull, allowing the hull to rise up out of the water when the boat
is traveling forward. The angle that the hull rises out of the water is known as the
planing angle
(see Figure 9-2).
Figure 9-2.
A planing hull can rise up out of the water.
Since the portion of the hull still in the water is reduced during planing, the hydrodynamic
drag experienced by the boat is reduced as well. Planing boats can achieve speeds of 160
km/hr
or more. The downside is that planing boats have the highest fuel consumption rates and are
the least stable in heavy seas, but that is rarely an issue in game programming situations. Since
most boat game simulations involve speed, you will probably most often be dealing with
planing hulls.
Basic Force Diagram
Just like the projectiles, sports balls, and motor vehicles that we have studied in the previous
chapters of this topic, a boat traveling across the water is subject to various forces that deter-
mine the acceleration, velocity, and position of the boat. The basic force diagram for a boat is
shown in Figure 9-3.
Gravity
Thrust
Drag
Buoyancy
Figure 9-3.
Basic force diagram on a boat
