Keep well clear of large ships and their “blind spot”

If you cruise along the coast, offshore or enter a port or harbour with commericial shipping you will encounter large ships.

Large ships especially cargo vessels with the bridge and accommodation at the rear have a large blindspot which extends several hundred metres in front of the bow.Take care not to get caught inside this little known area called the “blind spot”. Inside this area, you will become invisible to both visual and radar scanning.

Cargo ships are often built with the bridge and crew quarters located at the rear to keep the forward decks open for freight and storage. Crew keep watch from the bridge, high up off the deck. The bow blocks their view in the area illustrated by yellow diagonal lines.

Rule 18: Responsibilities between vessels

In this rule of the International Collision Regulations (ColRegs/Steering Rules) the priorities of all vessels are specified. Power driven, sailing and fishing vessels are all required to keep well clear, give way and should pass  astern of these vessels.  They also must not impede their passage when in designated shipping channels as these vessels are restricted by their draft and ability to manoeuvre. When in a swing basin or berth they will likely be accompanied by tugs or other vessels.

What to do when you sight a ship
If you see a ship or another vessel heading your way, you can easily establish if you’re on a collision course simply by looking at the vessel and noting where that line of sight crosses your boat. Over a short period of time if that bearing does not alter, then you’re on a collision course.

Establishing line of sight by compass
Obtain a bearing by using hand-bearing compass or swing the bow of your vessel toward the ship and take a magnetic bearing. Write the bearing down. Note the location on the ship where you took the bearing (bow, beam, mast, superstructure, stern). Wait two to three minutes and take a second bearing to the same object. Take a third bearing with your compass two to three minutes later and then compare all bearings.

You are looking for a separation of at least 3 degrees between bearings. You want all bearings to increase or decrease in succession. Bearings that look like this: 004°, 008°, 012° are increasing to the right, called “right bearing drift”. Bearings that look like this: 108°, 104°, 100° are decreasing to the left, called “left bearing drift”.

If you note a slower rate of drift (less than three degrees of separation) or no change in bearings at all, this indicates a risk of collision. Take another bearing for verification if you have the time. If you still show little to no change, take action to avoid a collision. You could change course, change speed, slow down or stop. Avoid small changes in course or speed. Make your actions apparent to the ship to avoid confusion.

Remember to factor in your speed.  You may only be travelling at average speeds of  4 -10 knots so, you’ll need plenty of time to manoeuvre against a 20 to 30-knot cargo ship or tanker. A 20-knot cargo ship may cover one nautical mile in 3 minutes. A 30-knot cargo ship may cover one nautical mile in just 2 minutes. It’ll be on you before you know it!

Take action early and make any course or speed change substantial!


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