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→Roll Stability
There are several kinds of roll or heeling stability: [[#Ballast Stability|ballast]], [[#Hull Form|form]], [[#Static Stability|static]] and [[#Dynamic Stability|dynamic]]. These are important in determining a boat’s resistance to capsizing from a beam-on wave, and the type of rolling motion. The rolling motion dictates your comfort.
Dynamic stability and large angle stability must be considered as equal partners with the vesselboat's static stability.<ref>http://www.kastenmarine.com/beam_vs_ballast.htm</ref>
Inherent in the design of every boat is a restoring force from rolling called the righting moment (RM), and a point of instability. A boat capsizes when the force of a wave causes it to heel over to its point of instability, called the Angle of Vanishing Stability. Beyond this point, the boat capsizes and may stay inverted. The wider the beam, the more difficult it will be to revert. The upside down boat sits on the water like a flat-bottomed boat. The deeper the keel, the greater the counterbalancing force to the superstructure and the easier it is to revert.
Many displacement boats will self-right from 65-70 degrees before they turn turtle. Unlike sail boats very few have positive stability to 130 degrees.
A vessel’s boats’s stability can be divided into two performance categories: initial stability and ultimate stability.
Initial stability defines the angles of heel that are normal to a vessel's operation. This is also the [[#Static Stability|static stability]]. This is usually between zero and 15 degrees of heel. A wide-beamed boat heels less (has greater stiffness), and is more comfortable. But a narrower-beamed boat has more ultimate stability. Ultimate stability is the angle of vanishing stability.
