Navigation rules - page 4
3.4 Rule 12
The Rule - Sailboats vs Sailboats
(a) When two sailing vessels are approaching one another, so as to involve risk of collision, one of them shall keep out of the way of the other as follows: (i) when each has the wind on a different side, the vessel which has the wind on the port side shall keep out of the way of the other; (ii) when both have the wind on the same side, the vessel which is to windward shall keep out of the way of the vessel which is to leeward; (iii) if a vessel with the wind on the port side sees a vessel to windward and cannot determine with certainty whether the other vessel has the wind on the port or on the starboard side, she shall keep out of the way of the other.
(b) For the purposes of this Rule the windward side shall be deemed to be the side opposite to that on which the mainsail is carried or, in the case of a square-rigged vessel, the side opposite to that on which the largest foreand-aft sail is carried.
Examples: Sailboats in same tack (a) ii
From the set of the sails, the wind is obviously from bottom to top on the image. Therefore, Blue is on Port, Red is also on Port. Red is the leeward boat and therefore is the stand-on vessel. Thus, Blue must give way. The best action here would be for Blue to steer up into the wind, turn to port. However, every circumstance is different and a "judgment call". The reason we'd recommend an immediate turn to port for Blue is because it would be turning away from Red. Trying to duck (going behind) is risky because you are turning towards Red and depending on your speed you could hit Red. A turn to port will allow Red to give room without any risk of collision.
From the set of the sails, the wind is coming from the bottom left to the top right on the image and Red and Blue are both on Port. Red is the leeward boat. Blue must Give Way. The best course of action would probably be to turn upwind and tighten sails, although a gybe would work as well depending on Blue's desired course and taking into account that in high winds, gybes are dangerous for the crew and for the rig.
Example: Sailboats in different tack (a) i
From the set of the sails the wind is from bottom right to top left on the image. Therefore, Red is on Starboard (wind blowing sail to port), Blue is on Port (wind blowing headsail to starboard). Thus, Blue must Give Way. Blue could release sails and turn down wind or tack. We'd estimate here that Blue is better off letting sails out and bearing away from the wind to pass behind Red. In this example, if Red turns to starboard, the chance of collision would be significantly reduced.
Example: (a) iii
From the set of the sails the wind must be blowing from top left to bottom right on the image. Therefore, Blue is "on starboard" and Red is "on port". Red must Give-Way. The best course of action would probably be for Red to turn further downwind to starboard - perhaps even causing a gybe.
The two boats below are Running. The forward boat is on port. The rear boat is on starboard.