additional concepts and formulas 309
B/D ratio 25% to 35%
Average roll period = (beam/3.3) × .90
Medium displacement sailboats
B/D ratio 35% or more
Average roll period = (beam/3.3) × .85
Cruiser/racer sailboats
B/D ratio 35% or more
Average roll period = (beam/3.3) × .80
Racing sailboats
Deep draft and low deck profiles
Average roll period = (beam/3.3) × .75
Longer-than-average roll periods indicate an inherently unstable vessel. These
vessels are called tender or crank, and for good reason: they’re top heavy. Even mod-
erately tender power vessels heel over to one side when making turns in flat water.
Any seaway imposes the threat of capsize.
Shorter-than-average roll periods indicate excessive stiffness. These vessels give
an uncomfortable ride with short, snappy rolls. They are designed to carry extremely
heavy ballast and light topsides. Only a few vessels in the world need this extreme
stiffness. One of these, the Coast Guard motor lifeboat, carries most of its weight in
the keel and is designed to recover from a 360-degree rollover.
PITCHING
A vessel pitches, or rises and falls up and down, on its athwartships axis. This un-
comfortable motion often results from loading one end more than the other. Hull
design also plays a role. Boats with long overhangs tend to pitch more, and might
hobbyhorse (rise up and down in place when slowed by a sea). Pitching causes crew
fatigue and induces seasickness. The smallest tasks take tremendous effort to perform.
Move weights from the bow and stern and place them near the keel. Slow down and
change course slightly to improve pitching motion.
YAWING
A boat rotates horizontally around a vertical axis in a motion called yawing. Sailing
vessels experience yawing while running downwind in gusty weather. Power vessels
running before seas and swell may yaw from side to side. Add weight astern to help
cure yawing. In large seas when running before the wind, consider towing warps; in
extreme conditions, stream a drogue.
Weight Distribution and Performance
Throughout the loading process, make a continuous check on your boat’s list and trim.
List is the tendency for a boat to lean permanently to one side. Even a small list of
1 to 2 degrees can affect underway performance. A boat is trimmed when it shows no
inclination at the bow or stern. Boats out of trim pitch and hobbyhorse in a seaway.