Brief #012 · BIG SHIPS

Why a big ship can't just stop

Boat handling

A big ship has no brakes: stopping can take up to 15 ship lengths, the water close ahead of the bow can be hidden from the bridge, so you keep clear early.

Open water and fairways. Local rules for traffic lanes and harbours can add more.

Transcript

A ship this size has no brakes. So how does it stop?

It throws the propeller into full astern, and waits.

The international standard allows that stop to take up to 15 ship lengths.

For a 300-metre ship, that is four and a half kilometres.

And from the bridge, the water ahead of the bow can be hidden for up to 500 metres.

So a small boat close in front can simply disappear.

In a narrow channel, the rule is clear: small boats must not get in its way.

Cross early, cross behind it, and make your turn obvious.

It can't stop for you. Make sure it never has to. Follow for the next brief.

Sources

1. Wärtsilä Encyclopedia of Ship Technology: manoeuvring characteristics (stopping by stop engine, full astern)
2. IMO Standards for Ship Manoeuvrability, stopping ability criterion (track reach ≤ 15 ship lengths), via Wärtsilä Encyclopedia
3. SOLAS V navigation bridge visibility (view not obscured more than 2 ship lengths or 500 m ahead), S.I. No. 280/2021
4. COLREGs Rule 8, Action to avoid collision
5. COLREGs Rule 9, Narrow channels