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Generally longer means faster, at least on flat water. But all of the other characteristics below interplay with length to affect speed, and work differently in waves as opposed to flat water. The closer waves are together the more that length typically starts to interfere with turning and agility particularly for flat boats with little or no rocker.
Is the width at the widest point of a boat. Beam in surfskis occurs close to the seat and surfskis usually do not have abrupt transitions in width so beam can be used for general comparisons of surfski width - generally “narrower is faster” but less stable (flatness of the bottom interplays with this)
Chines are the transition shapes from the bottom to the side of surfski (a hard chine is an abrupt transition or corner, a soft chine is a more gradual curve). Harder chines in a surfski can contribute to quirky or abrupt transitions in handling.
refers to the amount of curvature in the bottom of the hull along its length from bow to stern. More rocker reduces the tendency of a surfski to spear waves, rather the ends “rock” up. Rocker typically also makes a surfski easier to turn because resistance from the water against turning is more centralized and not extended as strongly to the bow and stern.