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Article by Tor Pinney                                                                                                                                        Back to List of Tor's Tips


© 2010 Tor Pinney - All Rights Reserved

Collision Avoidance Tactics for Offshore Skippers


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 into her anchor - and no one knows when or where it happened.

To an offshore sailor, merchant ships - freighters, container ships, bulk carriers, cruise ships, tankers, ro-ro’s - can be the real, modern-day sea monsters, capable of obliterating a yacht beneath their towering bows and spitting out the scraps through whale-size propellers. Imagine 80,000 tonnes of steel bearing down on you at 20 knots! What should you do? What can you do to avoid a collision?


Start by being conscientious on watch. That may seem obvious, but inadequate watch keeping is a major cause of collisions at sea. Stand up in the cockpit every 5 minutes and slowly scan of the horizon, 360º. It’s a simple yet vital routine.

Assess the Situation

When you spot a ship underway, first determine which side you're seeing. In daylight it’s usually obvious. At night, however, you have to read the navigation lights and these can sometimes be confusing. Ships use a variety of lighting configurations to indicate special circumstances like restricted in ability to maneuver, fishing or towing. (Note: It’s especially important to recognize tow vessels. Tows can extend as much as 1500 feet in open ocean, occasionally trailing two 300-foot barges in tandem. Always give offshore towboats at least a half-mile when passing behind them.)

Unless you’ve memorized all the navigation light configurations and their day shape counterparts, you’ll need a way look them up quickly when they appear. Keep a copy of Navigation Rules for International and Inland Waters on board. It contains illustrations and details of lights, shapes, sound signals and other aids and rules for avoiding collisions at sea. A plastic-coated quick-reference card is also handy for the cockpit.

In most cases, though, the nav lights on a ship are straightforward: port, starboard and stern (red, green and white) running lights PLUS a pair of white bow lights in alignment fore and aft, the after 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. They tell you which way the ship is headed, i.e., from the higher light aft towards the lower one forward, and therefore which side of the ship you’re seeing. One directly over the other means the ship is head on. You’ll often make out the white bow lights before seeing a ship’s red or green sidelight.

OK, you’ve determined which side of the ship you’re seeing. If her port side is facing your vessel’s port side (or her starboard is to your starboard), then there is no present risk of collision. Maintain your course and keep an eye on the ship to be sure she does the same.

If, on the other hand, her port side faces your starboard or vice versa, then it’s possible your courses are converging. In that case, immediately begin taking a series of compass bearings on the ship. A handheld compass with a nightlight is handy for this, but a binnacle-mounted cockpit compass works, too. Sit with the compass between you and the ship, scrunch down so you’re looking across the top of it, and line up the instrument’s center pin with the distant vessel. Then raise your head a little so you can read the mark with which the center pin is aligned on the compass card’s far perimeter. This is the ship’s compass bearing in degrees. Make a note of it. Then take another reading in a few minutes, and another a few minutes after that until you’ve established a trend. If the ship’s bearing is changing she will pass safely. If her bearing remains the same then your paths are converging; you’re on a collision course.

You can also use a radar’s EBL (electronic bearing line) to track a ship’s bearing, but your boat’s heading must remain perfectly constant. In lumpy sea conditions you’ll get more useful readings from a compass. Still, radar can track the target’s range, letting you estimate how much time you’ve got before the vessels are in extremis.

Suppose a ship changes bearing from 90º to 100º over a period of several minutes. She’s moving from left to right across your field of vision. If she’s off your vessel’s port side she’ll pass across your bow. If she’s off your starboard side she’ll pass astern. This change in bearing could also conceivably indicate that the ship is moving parallel to your course but at a different speed. However, since you just sighted her where she wasn’t visible 5 minutes earlier, either the visibility just got a whole lot better or (nearly always) the ship has been moving closer and will continue to do so until she has passed.

If the ship’s bearing does not change over a 5 to 10 minute time period, then assume you’re on a collision course. It is possible she’s running parallel to your course at the same speed – that would also result in a constant bearing - but again if she just recently hove into view she’s more than likely moving towards you. If nothing changes the two vessels will soon arrive at the same place at the same time.

If You’re On a Collision Course

Once you’ve concluded you’re on a collision course with a ship, decide who has right of way. It’s each captain’s responsibility to know the applicable rules and act appropriately. Again, Navigation Rules for International and Inland Waters is your best information source.

Being under sail doesn’t necessarily give you right of way. In addition to the more commonly known Steering and Sailing Rules governing vessels on converging courses, Rule 18, Responsibilities Between Vessels states in part: “… A sailing vessel underway shall keep out of the way of: a vessel not under command; a vessel restricted in her ability to maneuver; a vessel engaged in fishing.” An earlier part of the book defines these terms; a later section describes the day shapes and nightlights these vessels exhibit so you can identify them. Of course, when your engine is running – even if your sails are up – then a ship approaching from your starboard side has the right of way.

If you determine that you’re on a collision course with a ship and that she has the right of way, alter your vessel’s course abruptly and substantially to pass behind her. Continue observing and taking bearings until it is clear you’re passing at a safe distance. Resume your original heading after you see the ship’s transom or stern light.

If, however, you have the right of way, then your responsibility is to maintain your course and speed… up to a point. The question now is whether the ship’s crew sees you, whether they even know you’re there. Don’t take it for granted. In an alarming number of cases they do not, and here is where yachts sometimes get into trouble. 

There are many reasons why a ship’s watch officer might not see a yacht:  He could be busy attending to all manner of ship’s business, or simply absorbed in a good book or some similar distraction. He might even have dozed off. Not all commercial vessels maintain a proper watch at all times. This is why you must. 

Even if they are watching they might not see you. Ships carrying stacks of containers forward of the bridge often have a substantial blind zone ahead, and even with a clear view the night watch in a ship’s wheelhouse may not see your running lights. Yacht masthead lights are more visible than lights mounted on the pulpit, which can be obscured by waves, but it’s still difficult to pick out a lone red or green running light in sufficient time for a ship to do anything about it. Against a background of shore lights or in foul weather it’s even more difficult.

Neither should you assume your boat is visible on their radar screen. A seagoing yacht should carry a radar reflector aloft - this helps a lot – but some ships turn their radars off at sea to reduce maintenance.

Considering all that, perhaps we should be grateful they ever see us at all. When they do and the ship’s watch officer determines that you have the right of way, he will alter course to avoid you, usually (but not always) passing behind your vessel. You might perceive a change in the ship’s angle, though it may be slight. Then you’ll note changes in her bearing, confirming that she will now pass safely.

If She Keeps Coming

When you have the right of way and the ship does not alter course early and obviously, you should assume they haven’t seen you. Call them on VHF radio channel 16 while they’re still a few miles away. All ships are required to monitor VHF 16; that’s the only correct radio frequency for hailing a nearby ship.

If you’ve managed to read the ship’s name through binoculars, hail her by her name. Otherwise, initiate VHF radio contact by saying something like, “Calling the ship heading (their approximate heading, such as ‘southeast’) near latitude (your position) and longitude (your position).” Repeat this a second time and then add, “This is the sailing vessel (your boat’s name). Over.” Repeat the call several times at 15- to 30-second intervals.

If they respond, say something like, “Good evening. This is the sailing vessel, (your boat’s name), about 3 miles off your (port/starboard) bow. We appear to be on a collision course. I believe I have the right of way. Do you see my vessel ahead of you? Do you intend to alter course? Over.”

There may be a delay while they scramble to find you through binoculars. Then (hopefully) they’ll say something like, “Roger, captain, we see you and we’re altering course to pass astern of you.” At least, that’s how it goes sometimes.

Unfortunately, when sailors call ships on VHF 16 in these situations, more than half don’t answer. More than half! Maybe the watch officer doesn’t understand English. Maybe he’s just not listening.

Become More Visible

If you can’t raise the ship on the VHF and they still haven’t changed course, at night switch on your spreader or deck lights, bathing the foredeck and sails in thousand-candlepower brilliance, hoping to startle the ship’s watch from their torpor. You could also flash a spotlight at their wheelhouse, but only momentarily so it won’t interfere with their ability to read your navigation lights. Then redirect the light onto your sails.

White “attention” flares – handheld, meteor or parachute - are excellent for this application. Keep them close to your steering station, ready for immediate use. With meteor flares fire at least two, 10- to 15-seconds apart; the first to catch their eye, the second to help them pinpoint your position. Do not use any other color flare! Use only white flares for collision avoidance.

Do everything you can to alert an approaching ship to your presence early, while they’re still at least a couple of miles away. The watch officer needs time to assess your range, bearing, heading and right of way, and to alter course. Ships cannot change direction quickly.

If They Still Don’t Respond

You’ve done all you can, yet here comes this deaf, dumb and blind gargantuan bearing down with no sign of turning to avoid the impending collision. You clearly have the right of way, but as the old sailor’s adage goes, you could be dead right. Now what?

There comes a point when you simply have to get out of their way. With some fast, timely maneuvering aboard a sailboat, sometimes involving a 180-degree about face and a prodigious burst of auxiliary engine power, you can avoid an oncoming ship. Announce your intention on VHF 16. Then change course abruptly and substantially so that it’s obvious to an observer.

Above all don’t wait too long to do it. One mile is about as close as you should ever let an unresponsive ship get on a converging course before taking evasive action. Farther is better. Remember, if she’s approaching at 20 knots, one mile is a mere 3-minute window of opportunity. Once you’ve changed course, immediately take more bearings to be sure your nemesis didn’t simultaneously change hers and so put you onto a new collision course.

The AIS Advantage

Today there is new hope for besieged boaters. The marine automatic identification system, or AIS, takes much of the guesswork out of collision avoidance, providing real time data on commercial carriers within its +/- 25-mile range. It can plot potential collision courses on a display screen, tell you the ship’s owner, classification, speed, heading, and of particular interest in close encounter situations, her name.

Your VHF transmission will reach every radio in a 25-mile radius. It’s extremely helpful to identify the specific vessel that’s about to run you down and call her by name on channel 16. This clarifies which ship you’re trying to warn off, encourages a non-English speaking watchman to fetch someone who understands what you’re saying, and virtually forces them to answer your call because they know that you know who they are. If they don’t respond and then endanger your vessel, you can later file a complaint with the ship’s owner. No captain wants that sort of black mark on his record. In most cases he will reply if you call his ship by name on VHF 16. You can then advise him that your vessels are on a collision course, that you have the right of way, and that you would appreciate it if he’d alter his course to avoid you. Invariably he will comply.

Class B recreational vessel ‘send & receive’ AIS transponders cost $500 to $1,000, a modest investment for such a potentially valuable tool. However, in deference to the KISS principle the prudent mariner will still take multiple compass bearings early on to determine whether his vessel is on a converging course with a ship. And while a ‘send & receive’ transponder will also put your vessel on the ship’s AIS display screen, be prepared to get out of their way - just in case the ship’s watch officer isn’t watching.

Quick-Reference Summary

1)  Scan the horizon every 5 minutes.

2)  Determine whether a sighted ship is:

a.  Passing you safely port-to-port or starboard-to-starboard, or

b.  Potentially converging port-to-starboard, starboard-to-port or head-on

3)  Be familiar with Navigation Rules for International and Inland Waters and keep a current copy on board, plus a quick-reference card.

4)      If there is a possibility that your courses are converging, take a series of compass bearings on the ship. Use radar (if available) to track the ship’s range and rate of approach.

5)      If converging, determine who has right of way. If the ship does, alter your course abruptly and substantially to avoid her. Give fishing trawlers and especially tows a very wide berth.

6)      If you have the right of way and the ship does not alter course to avoid you while more than 2 miles away:

a. Call the ship on VHF channel 16 and ask the watch officer to alter the ship’s course. If the ship does not respond on VHF 16;

b. At night make your boat more visible with spreader and deck lights, a spotlight, and white flares.

7)  If the ship still does not respond:

a. Announce your intention to alter course on VHF channel 16;

b. Alter course obviously and substantially, using ample engine power if necessary.

c. Observe the ship and take bearings to determine that she has not also changed course.


~ End ~

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