Tacking a Square Rigger

[Daniel]

The average square rigged ship could sail about six points from the wind according to Harland; other sources vary, but six points is the most commonly given figure.

Dusting off some old trigonometry skills, I figured that if a square rigger can lie six points from the wind, then to reach an objective in the wind's eye that lies 1 nautical mile distant, the ship must cover 2.613 nautical miles to tack to it. The actual distance would be somewhat greater because of leeway. Although I understand that modern sailboats often do some of their best sailing close to the wind, I think that a square rigger sails at its very slowest on the wind. If the wind is strong enough, the leeway may be so bad that the objective is completely unreachable.

I've wondered how this fact combines with the inability to determine longitude accurately to affect navigation methods. If you are aiming at an objective to the north or south, and you set course directly toward it, you have an essentially 50% chance to arrive east or west of it. But arriving to the downwind side effectively leaves you more than 2.613 times further from your destination than arriving an equal distance upwind of it. Given that fact, I imagine an earlier 18th century navigator might deliberately "aim to miss" to the upwind side of his target, then turn and sail downwind to his mark once he reached the correct latitude.

Consider, for example, someone sailing from Martinique to Cape Verde, a frequent stopping point en route to Guinea. We've all heard of sailing on the latitude line to protect against errors in longitude estimation, but if you try to sail to Cape Verde on the latitude line, you'll be tacking against the trade winds all the way, and you'll effectively turn a 2,170 nautical mile voyage into a 5,670 mile one. On the other hand, you can sail due north to the horse latitudes at about 31 degrees North, then northeast across the horse latitudes until you reach the prevailing westerlies at about 36 degrees North, then sail east until approximately the longitude of Cape Verde. Then you point not at Cape Verde but approximately at Dakar (Africa is too big to miss, no matter how bad your longitude estimate is). Once you hit the African coast, just turn west when you've reached the latitude of Cape Verde. Total distance is about 4,283 nautical miles, a lot better than the 5,670 mile distance you travel tacking along the latitude line.

I don't know for sure if "aiming upwind" was actual Golden Age practice. One thing I do notice, though: of the various Cape Verde islands, Maio (the "Isle of May") seems to have been by far the most commonly mentioned as a stopover place by sailors coming from America. Maio is the easternmost of the major islands, and is the first one you hit if you sail from a little above Dakar on the African coast due west along the latitude line.

[Dutchman]

overcorrecting to windward was a common practice. Captains and navigators are well documented to adjust north of the mouth of the Chesapeake to avoid the outer banks.

don't assume too much on leeway. it depends on the boat. a faster vessel can override the leeway sometimes- its a wind variable. the other consideration is current- if current is stronger than wind, you can be swept to leeward. its odd to see a square sail pointed almost off the wind loosing ground to current.

A squaresails aeordynamic set is dead down wind, which conveniently enough also creates the least ammount of drag on the hull. because you are going with the wind, it makes the passengers feel as if they are standing still sometimes.

If a squaresail is filled it will create pull regardless of position to the wind. some points are more advantageous than others and it is up to the crew to balance the hull to sail position to take full advantage of the combination. Some positions are just wrong, such as backwinding and can actually push the vessel backwards. We used to do this on Lasers. Sometimes we would make a windward, leeward race course and sail it with the main backwinded and the boats going backwards.