Game Development Reference
Rudders and Thrust Vectoring
Although rudders and thrust vectoring have the same result, there are some important
differences. A thrust vectoring system, like a jet boat, can steer only when the vessel is
producing thrust. A rudder, on the other hand, works only when the vessel has forward
speed. If the boat isn't moving forward with enough speed, then the rudder can't produce
a turning moment.
If you keep in mind those differences, you can model both systems the same way. The
most important thing to keep in mind when modeling larger ships in your games is that
they take significant time to respond to control inputs. Figure 16-7 tracks the heading
of a ship over time during what is called the 10/10 maneuver .
Figure 16-7. 10/10 zig-zag test
A vessel is moving in a straight line, and the rudder is put over 10 degrees in one di‐
rection. Once the vessel's heading changes 10 degrees, the rudder is moved to the op‐
posite side at the same angle. The initial turning time is the time it took for the vessel
to change its heading 10 degrees. As large ships have enormous momentum, they will
continue to turn even though the rudder is in the opposite direction. The maximum
deviation from the original heading minus the 10 degrees at which the rudder was
flipped is called the overshoot angle . The size of this angle is one measure of how slow
the vessel is to respond to the helm. For larger ships, this can be between 15 degrees
when light and 45 degrees when loaded with cargo.
The time to check yaw is the time in seconds it takes for the overshoot angle to be
achieved and the vessel to start changing its heading again. This is repeated for the other
side to detect any bias a vessel may have for turning in a particular direction. The moral
of the story is that for anything other than a high-speed small craft, boats and ships can
take a significant amount of time to respond to the helm. Your simulation should strive
to reproduce a turning ability that matches Figure 16-7 for extra realism.