Tech Tips #18, Give Me a Little
Leeway
By Bill Whitney
As Friendship Sloop sailors we all have experienced
leeway at one time or another. All vessels are subject to it, except
with the wind dead ahead or astern. Sailing vessels make lots of
leeway when hard on the wind and less leeway when well off the
wind. Light airs and heavy winds have more impact than moder-
ate breezes. When you are trying to get from point A to point B,
leeway is one of the elements that you have to consider along
with currents, tides and wind direction. Admittedly, current and
wind direction usually have more of an effect on a vessel, but if
you are on a long leg, vessel leeway can really add up.
There are several ways to estimate your boat’s leeway;
the most effective ways deal with looking astern and watching
where you have been. Choose either of these methods to make a
rough estimate of your boat’s leeway angle:
The first method is to simply watch your wake as you
steer a straight course. Take a bearing on your wake trail using
your primary compass (if it’s binnacle mounted and high enough)
or a handbearing compass to estimate leeway angle. Using either
compass, take a bearing dead astern. Wait several minutes, then
sight along the wake line to windward. The difference in the two
angles gives you your leeway angle.
The second method is to use a bearing to an object
astern. First find a landmark, light structure, or buoy dead astern.
Take a bearing with your compass. Hold a steady course for
several minutes, and then take a second bearing. The difference in
bearings is your leeway angle.
Now that you know how much the boat is slipping
sideways you can correct for it by adding or subtracting your
observed leeway angle from the compass course you are steering.
Be sure to apply correction to your steering course in the proper
direction. You want to steer the boat closer to the wind to
counteract the effect of leeway. If the wind blows from the port
side, subtract the angle from your course. If the wind blows from
the starboard side, add the leeway angle to your course.
For example, you are close-reaching on the starboard
tack, steering a course of 300 degrees magnetic. You sight astern
with the handbearing compass for a reading of 120 degrees
magnetic. Five minutes later, you sight down the wake line, and
the bearing is 114 degrees magnetic. The difference gives you a
leeway angle of 6 degrees. You’ll need to point 6 degrees higher,
so add the angle to your 300 degree course and steer a new course
of 306 degrees magnetic.
Note that this correction may also include a component
of current correction because you could easily be in an area where
the current is pushing the boat sideways. Normally the current has
an equal effect on both the boat and the wake it leaves but in
some areas the currents can be quite tricky, flowing faster in one
part of a bay than in another. After you have estimated your
boat’s leeway in different wind velocities and at different wind
angles a few times you get a good feel for the corrections that you
need to make and can make them on a “seat of the pants” basis.
See you on the water!
