Judging Leeway

Any boat under way in a crosswind, whether it’s a rowboat crossing a lake or a powerful cruiser reaching along the coast, will be pushed sideways to some extent. The effect is called “leeway,” and even big ships are subject to it. Sometimes leeway is insignificant; often it is not.
Author:
Publish date:
Updated on
JudgingLeeway

Any boat under way in a crosswind, whether it’s a rowboat crossing a lake or a powerful cruiser reaching along the coast, will be pushed sideways to some extent. The effect is called “leeway,” and even big ships are subject to it. Sometimes leeway is insignificant; often it is not. If you don’t account for it when plotting a course, grief may be your reward.

If you can see your destination, you can check whether you’re being blown to leeward by lining up some fixed object near where you’re going with an object behind it. This effectively creates a range that works the same as those thoughtfully set up by the authorities to lead ships into harbor.

If there’s no significant current and your two range objects “open,” or move relative to each other, you are making leeway from your direct line. The solution is to steer “up” into the crosswind to close your markers and keep them lined up.

 Applying leeway to a course to steer: start from (A) the theoretical course. Protractor is turned into the wind by the expected leeway angle to find real course (B)

Applying leeway to a course to steer: start from (A) the theoretical course. Protractor is turned into the wind by the expected leeway angle to find real course (B)

You can see that the boat in the illustrations has to head up about 10 degrees in order to stay on the line. If she steers straight for her destination she drifts off course, the range opens, and she must steer firmly upwind to close it again.

When your destination is invisible because of thick weather or distance, you’ll have to plot a course. Estimating leeway is a part of the process. A small yacht close-hauled in a stiff breeze may slide to leeward by up to 10 degrees. As she bears away her leeway will diminish steadily as the wind draws further aft until, when running, there’s none at all.

 Applying leeway to a course you're already steering: turning protractor away from wind indicates actual course made good (C) if leeway has not been applied to the course to steer

Applying leeway to a course you're already steering: turning protractor away from wind indicates actual course made good (C) if leeway has not been applied to the course to steer

COMPENSATING FOR LEEWAY

It’s easy to get confused when numerically figuring leeway into a course-to-steer, so it pays to do the job graphically. Sketch a wind arrow somewhere on your chart, place your chart protractor on the course you want to sail, imagine your boat is sailing up the edge of the protractor and see which way to turn it to counteract her tendency to be blown downwind. Swivel it between 5 and 10 degrees toward the wind and read off the heading you’ll actually steer.

APPLYING LEEWAY

If you’ve already been steering a course and have not compensated for leeway, when the time comes to estimate your position you’ll need to know where on earth you are really tracking. The answer is to apply the same technique retrospectively. Sketch the wind arrow on the chart and lay your protractor on the course steered. Now swing it 10 degrees or so away from the wind, redraw the course and you’ve cracked the problem. 

Top Illustration (by Steve Sanford): Sailing on a beam reach, the boat above first falls to leeward, “opening” a pair of range marks on shore (left); the boat steers a high course to close them up again, but overcompensates, so that they are once again out of line (center); back on course, the marks line up correctly (center)

Related

sailingabove-2

Swan Flyer: A Hot New One-design

In a racing scene that’s bristling with innovation, legacy builder Nautor’s Swan refuses to be left behind in its quest to dominate the champagne end of one-design sailing. Arriving hard on the heels of the radical Juan Kouyoumdjian-designed ClubSwan 50, the ClubSwan 36 offers a ...read more

Maiden sets out for Uruguay during the 1989-90 Whitbread race

Making Maiden and the 1989-90 Whitbread Race

As recently as the late 1980s, the idea of an all-female sailing team in the Whitbread Round the World Race (the predecessor to the Volvo Ocean Race) seemed laughable to many. How could women handle the competition? They weren’t strong enough. They wouldn’t be able to take the ...read more

01-LEAD-J99

Four Very Different New Boat Designs

Following up on the J/121, which won a SAIL Best Boats award in 2018, the new J/99 represents a similar concept in a smaller package. Specifically, the new 32-footer’s deck layout and rig have been optimized for smaller and even doublehanded crews, with an eye toward meeting the ...read more

Dinghy Suggested CROP

Ask Sail: Dinghy Dilemma

DINGHY DILEMMA Q: We are in the throes of choosing a dinghy, and I would like to ask if you would recommend buying a RIB with a double-skinned hull rather than a single-skinned hull. Which provides better handling or stays drier? Also, aside from the heavier weight of a ...read more

Groupe Beneteau charging its boats in NEOLINE vessel

Transporting Sailboats Under Sail

Transporting sailboats under sail? That sounds like a cool concept, and it’s one that looks set to become reality in 2021 when shipping company Neoline brings its sailing cargo ships into service. Groupe Beneteau has committed to transporting boats between Europe and the United ...read more

01_vor120612_ross_0644

Sailing Master Ken Read

Images trigger memory. Preparing to interview the golden boy of American sailing, I thought I would find a picture that would show Ken Read at the peak of his sailing career, his heyday, to share and have a warm and fuzzy start to our conversation. It was a commanding image from ...read more

New-engine-being-lifted-over-stern

Know how: Replacing the Auxiliary Power System

One of the most complex tasks undertaken during Passion’s refit was the complete replacement of her auxiliary power system—engine, V-drive and fuel tanks. I needed more horsepower, which drove the need for more fuel capacity and a larger V-drive to handle the higher engine ...read more