268 seamanship secrets
peaks and rush down the other side to the sea. They have local names—a
williwaw in Alaska, a Santa Ana in Southern California, or a mistral in the
Mediterranean. At the surface, fall winds reach gale to hurricane force. Vessels
30 miles at sea in an Alaskan williwaw have reported winds up to 90 knots!
Breaker eff ect. Narrow, docile bays turn chaotic when the wind opposes
the current. High winds blowing into a bay against the current cause breakers
to form across the mouth. Small craft must not attempt to cross the breakers
until the current slackens and conditions moderate.
Cape eff ect. When a prevailing wind blows parallel to the coast and runs into
a cape, winds and seas increase. Cliff -lined capes may have huge seas and winds
twice as high as the prevailing wind. Small craft must stay several miles off shore
for safety.
Strait eff ect. Winds increase in velocity when squeezed between two land-
masses. Some examples include two islands, the mainland and an island, or a
narrow, high-sided canal.
Land disrupts wind strength and direction. On this idealized coastal sketch (and on actual
weather charts), wind arrows are used to show direction and wind speed. Th e shaft and
arrowhead show direction. Each tail feather, called a barb, represents 10 knots. One-half
of a tail feather is 5 knots. Note the increase from 15 knots of prevailing wind to 30 knots at
the cape (gale force). Speed also increases inside the strait between the island and mainland.
Study your chart and track the weather to help determine the safest path to follow.