Game Development Reference
only a single compartment. If they capsize, they will sink readily; indeed, this is the way
that most small boats sink.
As we mentioned before, accurately computing all degrees of freedom for a nontrivial-
shaped body in real time would be difficult to accomplish with today's computer hard‐
ware. In general, you want to follow a few high-level rules:
• The higher the center of gravity, the more likely it is that the boat will tip over.
• Large vessels are always compartmentalized. Damage should be limited to the wa‐
tertight compartment in which it occurred.
• The vessel will heal or trim in the direction of damage. If damage occurs on the
starboard side, the boat will heel to starboard. If the damage occurs in the bow, the
boat will list forward.
• A boat will remain floating as long as the undamaged compartments have a volume
in cubic meters of at least the weight of the hull in metric tons divided by 1.025.
• After being damaged, even if a vessel has enough undamaged volume to remain
afloat, it doesn't necessarily mean it will float upright.
• Sinking almost never occurs as quickly as depicted in video games; however, cap‐
sizing can occur rapidly and is probably a more realistic way to model a stability
Closely related to ship stability is the subject of ship motions. Knowing how vessels
work in a random set of waves will greatly help you to increase realism in your games.
The most important aspect of this is coupled motions, which we will talk about shortly.
First, some more vocabulary! As discussed before, there are six degrees of motion any
rigid body is capable of; for boats, some of these have special names and are described
next and illustrated in Figure 16-3 .
Figure 16-3. Floating-body degrees of freedom