Game Development Reference

In-Depth Information

barrier for some fuller hulls. Note that the speed for the 40-foot sailboat is the hull speed

of a 40-foot full-formed (not slender) hull. We can calculate the hull speed with the

following formula:

V
hull
≈ 1.34 ×
LWL

Where
V
hull
is the hull speed in knots and L
WL
is the length on the water line. Some

modern displacement boats, especially racing kayaks, can exceed their hull speed if they

have very fine ends, long hulls with narrow beams, or some other optimized hull form.

Propulsion

There are a variety of methods to propel a boat through the water. The oldest is by way

of sails using the wind. The physics of sailing could fill several chapters on its own, so

we won't go into detail here. If you are interested in that topic,
The Physics of Sailing

Explained
(Sheridan House), by Bryon Anderson, is a good starting point. You can also

check out the airplane chapter in this topic and note that a sail is just a vertical wing.

We will say this: if you choose to put a sailing vessel in your simulation, make sure to

remember the golden rule! You cannot generally sail within 45 degrees of the direction

the wind is coming from.

There are many different kinds of propulsion: rudders, shafted fixed-pitch propellers,

shafted CPP propellers, azimuthing thrusters, propellers in nozzles, water jets, pump

jets, contra-rotating, and the very odd Voith Schneider type. We can't get into all of them

here, but the aforementioned list should get you started if you are interesting in mod‐

eling the specifics of different propulsor types.

The major propulsion relationship for your simulation would be the thrust-to-propeller

RPM or thrust-to-throttle curve. The fly in the ointment here is that thrust is also de‐

pendent on forward speed. As the boat moves faster and faster through the water, the

inflow velocity of the water into the propeller is higher and higher. This means that the

difference between the velocity of the intake and the velocity of the output is smaller,

reducing the amount of thrust. In general, the thrust curve versus boat speed will look

like
Figure 16-6
.