Dodging Sea Monsters
Most commercial ships are run by competent professional crews. Still, close encounters with yachts are not uncommon. Every once in a while a ship arrives in port with a mast wedged in her anchorand no one knows how it got there.
To an offshore sailor a large merchant vessel can seem like a modern-day sea monster, capable of obliterating a yacht and spitting out the scraps through whale-size propellers. Imagine 80,000 tons of steel bearing down on you at 20 knots. What should you do? What can you do to avoid a collision?
Watch and Assess
Start by being conscientious on watch. That may seem obvious, but inadequate watchkeeping is a major cause of collisions at sea. Stand up in the cockpit every five minutes and slowly scan the horizon. Its a simple yet vital routine.
When you do spot a ship underway, first determine which side youre seeing. In daylight its usually obvious. At night, however, you have to read the navigation lights, and these are sometimes confusing. Ships show a variety of lights in special circumstances, such as when they are restricted in their ability to maneuver. Unless youve memorized all the variations and their day mark equivalents, you should keep a copy of Navigation Rules for International and Inland Waters on board as a reference.
In most cases, nav lights on a ship are straightforward. There are port and starboard (red and green) sidelights and a stern light (white), plus a pair of white bow lights fore and aft, with the aft light positioned higher than the one forward.
Also called masthead lights or steaming lights, bow lights are visible from ahead in a 225-degree arc and are normally the first lights you can make out from a distance. They tell you immediately which way a ship is headed and which side youre seeing. If the higher light aft is on the left, the ship is moving to the right with its starboard side toward you, and vice versa. The closer together the lights are, the smaller the angle of the ship in relation to your position. One directly over the other means you are looking at the ship head-on.
Having determined the ships orientation, you can assess whether its a threat. If her port side is facing your port side (or you are starboard to starboard), there is no present risk of collision. Maintain your course and watch the ship to be sure she does the same.
If, however, you are port to starboard or vice versa, your courses may be converging. In this case, you should take a series of bearings on the ship. A handheld bearing compass with a nightlight is handy for this, but a binnacle compass works, too. If the ships bearing is changing she will pass you safely. If her bearing remains constant you are most likely on a collision course.
You can also use a radars EBL (electronic bearing line) function to track a ship, but to do so your boats heading must remain constant. In lumpy conditions youll often get more useful readings from a compass. The advantage with using radar is that it allows you to track a targets range as well, which gives you a much better idea of how quickly a ship is approaching.
If a ships bearing does not change over 5-10 minutes, you should assume youre in danger of colliding. The ship may be running parallel to your course at the same speed, a situation that would also result in a constant bearing. But if she only recently hove into view shes most likely moving toward you. If nothing changes, the two vessels will soon arrive at the same place at the same time.