Game Development Reference
In-Depth Information
Figure 16-6. Speed versus required thrust
An important physical phenomenon concerning propulsion that you may want to in‐
corporate is cavitation . Cavitation occurs when a propeller is moving fast enough that
the low-pressure side of the blade starts spontaneously creating vapor bubbles. These
bubbles exist for a short while, and then as the propeller turns, the static pressure
changes. This higher static pressure causes the bubbles to collapse violently. This collapse
is so fast and furious that it can cause metal erosion at a high rate. It will eat away at a
propeller until it is no longer producing thrust. It is also very noisy. That is why sub‐
marine propellers are shaped very differently than other ships' propellers. They seek to
limit cavitations so they're not heard by enemy vessels. The damage caused by cavitation
also creates a speed limit on RPMs for a propeller. Cavitation is a real-life phenomenon
you can exploit to penalize the player for driving around at high speed all the time.
Another aspect of ships and boats that is often oversimplified is maneuverability. Ma‐
neuverability is also a very complex topic whose numerical simulation is beyond the
current realm of real-time simulation. However, with some simplifications and as‐
sumptions, it can be more accurately modeled than if you do not know the underlying
framework. Almost all vessels maneuver by way of two methods: rudders or thrust
vectoring. The users generally won't care about the differences, so you can model both
by angling the thrust vector off-center.
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