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:
Updated:
Original:
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

pirate-marlin-logo

Pirate’s Cove Billfish Tournament

This Spring has felt a bit like a slow day of fishing but it’s almost time to time to Bait…and Switch. The Pirate’s Cove Billfish Tournaments offer something for every member of your crew. Exceptional fishing, fun times with family, old friends and new. Our run is short, our ...read more

Tusk.00_00_16_21.Still001

Tusk by Spyderco

Spyderco's Tusk knife combines a blade and marlinspike to create a multitool perfect for marine use. Made with corrosion resistant materials like titanium and LC200N steel, a nitrogen alloyed steel, and Spyderco-exclusive locking mechanisms, this knife is one of the toughest ...read more

IY11.98_fTaccola©DJI_0200

Italia 11.98 Performance-cruiser

This past winter, SAIL principal editor, Adam Cort, check out the new Italia Yachts’ new 11.98 performance-cruiser at the boot Dusseldorf show in German, and says he can attest to the fact it’s a boat more than worthy of the attention of North American sailors. Available in ...read more

01-LEAD-2017_IDALEWIS_0219

Racing: Doublehanded

I was born in 1955, and although I was a tad young to actually follow the first Observer Single-Handed Transatlantic Race, I grew up in the age of the pioneers of solo offshore sailing—Francis Chichester, Robin Knox-Johnson, Alec Rose, all Knighted for their singlehanded ...read more

newport-400c-updated

Spectra Watermakers

The world's quietest and most energy-efficient watermakers. Our product line ranges from hand operated desalinators that can make 6 gallons a day to our largest system that produces 20,000 gallons of fresh, potable water per day. Spectra Watermakers has the complete package: ...read more

CAPE-COD---Under-sails

Boat Review: Cape Cod

The concept of “daysailer” has grown ever broader over the years. These days the label can be pasted on a boat as small and simple as a Sunfish, as fancy as a 40-footer with a nice big cockpit and plenty of brightwork, or any number of concoctions in between. This Cape Cod ...read more

C-1002-600px

Sirius Signal

Be seen with the brightest SOS Distress Lights Available C-1002 Two Color Distress Light Flag & Whistle The Sirius Signal model C-1002 SOS eVDSD (electronic visual distress signal device) is the first product to be engineered to the new RTCM standard 13200.0 — accepted as ...read more