A boat is on port tack when the wind is coming over her port (left) side and her mainsail and boom are carried out to starboard. That is the beginner’s definition and it is nearly always enough. The precise definition, which the racing rules and the collision regulations both use, is that a boat’s tack is named for the side opposite the one her mainsail is on – so a boat running dead downwind with the boom to starboard is on port tack even if the wind feels as though it is coming from behind. The one thing every sailor must know is that a port-tack boat is the give-way boat when she meets a boat on starboard tack, at sea and on the race course alike.
How to tell which tack you are on
Look at the boom. If the boom is out to starboard, you are on port tack; if the boom is to port, you are on starboard tack. This works on every point of sail, including a dead run when the wind direction alone would be ambiguous. On a broad reach or run, when a boat is sailing by the lee, the wind may actually be coming across the starboard quarter while the boom is still out to starboard – she is still on port tack, and still the give-way boat.
The rules
The give-way rule is the same whether you are cruising or racing. Under COLREGS Rule 12, when two sailing vessels are approaching so as to involve risk of collision and they have the wind on different sides, the vessel with the wind on the port side keeps out of the way of the other. Under Racing Rule 10, “when boats are on opposite tacks, a port-tack boat shall keep clear of a starboard-tack boat.” The port-tack boat tacks, bears away to pass astern, or, if she can safely do so, crosses ahead.
Two refinements matter. First, COLREGS Rule 12 also says that if you are on port tack and see a sailing boat to windward and cannot be sure which tack she is on, you must assume she is on starboard and keep clear. Second, in racing, a port-tack boat that tacks too close ahead of a starboard-tack boat may break Rule 13 or Rule 15, so a lee-bow tack needs room to spare.
Port tack on the race course
Port tack is where much of the tactical drama in sailing happens. At the start most boats set up on starboard tack because it gives them right of way, so a boat approaching on port is threading through a fleet that does not have to move for her. A port-tack start – crossing the fleet from the pin end – is one of the boldest moves in the sport and works only when the line is heavily port-biased or the fleet is small.
On the beat, port-tack boats duck starboard-tack boats. A good duck loses very little: bear away early, ease sheets to accelerate, pass close under the transom and harden up in the other boat’s wake with speed on. Boats that tack to avoid a starboard boat and land on her lee bow in dirty air lose far more. A well-timed lee-bow tack, on the other hand, is the port-tack boat’s revenge: tack just in front and to leeward of the starboard boat so your backwind forces her to tack away.
Trim and the sailmaker’s view
Sails should set identically on both tacks, and when they do not, the boat is telling you something. A mainsail that looks flat on starboard tack and full on port tack usually indicates a mast that is not straight athwartships – uneven shroud tension, a spreader out of line or a mast step off centre. Headsails that sheet differently on port and starboard reveal tracks or cars that are not symmetrical. Before blaming the sail, a sailmaker will sight up the mast on both tacks and check that the jib leads measure the same from the centreline. Most “the sail is wrong on one tack” complaints turn out to be rig.
Frequently Asked Questions about Port tack
Which side is the boom on when I am on port tack?
Starboard. A boat’s tack is named for the side opposite the mainsail, so on port tack the wind is over the port side and the boom is out to starboard.
Who gives way, port tack or starboard tack?
The port-tack boat keeps clear of the starboard-tack boat, under both the collision regulations and the racing rules. The starboard-tack boat holds her course so the port boat can avoid her predictably.
Can I be on port tack while running downwind?
Yes. On a run the tack is decided by the side the mainsail is on, not by the exact wind direction. Boom to starboard means port tack even if you are sailing slightly by the lee.
Port tack is half of every beat and half of every run, and it is the half where you owe the other boat room. Know which tack you are on from the boom, look to windward, and when you meet a starboard boat make your decision early and cleanly. Do that, and port tack becomes just another way of sailing fast rather than the tack you worry about.