Number of Propellers?

[PhilipF]

While I am aware that Trawlers appear to run with just a single screw I am amazed to be told that far larger ships usually have just one. The size of this propeller must be massive. I'm talking of large 'box' ships here, also I suppose massive oil tankers.

I thought cruise ships had at least two, and I seem to recall seeing a design with four - not certain my memory is correct.

Any comments?

Philip.

 

[trev]

Its quite usual for any comercial vessel to have only one propeller, some have two engines geared to the same shaft. In the late 1940s to the 1960s it was common for cargo liners to have twin installations, but this ceased by mid 60s. Passenger liners used to have multiple installations, and the larger vessels being built today are multiple. The occassional container ship and the odd tanker have twin screws, but its more the exception than the rule.

 

[Mirelle]

Modern diesel engines are incredibly reliable.

There used to be an "un-official" limitation of 40,000 shp down one shaft - more than that and you needed twin screws - but in recent years this figure has been exceeded quite comfortably.

I run a fleet of ships which put 60,000 bhp down a single shaft, for 24.5 knots; we've never had the slightest problem with the main engines, shafting or propellers.

Mind you, we've had half the rudder fall off one ship - nobody noticed until we had divers down for something quite different!

A single engine is significantly more fuel efficient.

 

[petehoehill]

Yes the majority of commercial ships run on one main engine and one propellor.
the difference being they have at least a continual engineer watching and constantly maintaining the whole system. On the bigger ships it maybe a full team on a 24 hour watch
rotation.
On the smaller ships it maybe the master has an engineer watch qualification, and provided he has sufucient engineering back up from shore, (he can get it to a safe port with advice), he is cerrtified to sail.