Large ships - what weather do they carry on into, in the Channel?

[Athene V30]

It is often the case of being safer to stay out at sea if blowing hard rather than going into shallower water to try and anchor / berth alongside etc.

Another Aircraft Carrier, think current Ark Royal, as the story goes, couldn't get tugs to berth in Australia as the crews were on strike so they ranged the Sea Harriers strategically on deck, chained them down and used the engine thrust to help berth the ship. At last a use for WAFUs!

/forums/images/graemlins/laugh.gif

 

[homa]

Limiting factors

I drive a large Ro-Pax. The limiting factor for us is the wind strength and direction of the wind. With a Length overall of 790ft and height of 100ft that's a lot of sail area. Problems start when we slow down and want to steer at slow speed with a beam wind. We have learned that we can loose steerage at a certain wind speed and water speed. On my particular ship we have set ourselves a limit of 50kts wind. Above this and we don't enter or leave port. Mainly because we can only make the tugs fast at a relatively low water speed. Sea conditions generally are not a problem unless we get a northerly for a period of time, then its a question of setting a course to keep the worst of the weather on the quarter or a couple of points off the bow. As regards knowing that we are going out into poor weather, If the weather is severe, I always inform our passengers of what to expect and a rough ETA, and give them the choice whether to sail with us or not.
On ships such as bulkers and tankers we generally didn't deviate our course unless there was a typhoon or Hurricane forecast ahead. And only then if deviation was possible. Otherwise we just rode out the weather as best we could.

 

[cliffordpope]

Re: Limiting factors

I don't think Nelson stopped for the weather did he?

 

[Anonymous]

Re: Limiting factors

That is a large Ro-Pax! Your description of the problems with steering at low speed reminds me of the problems with a twin/multi engined aeroplane. Below a certain critical speed the rudder is not big enough to compensate for asymmetric power (e.g. in the event of one engine failing) so below that critical speed, if one engine fails, you are going down even if there is sufficient power in the remaining engine(s) to climb or maintain altitude. It is normal practice when flying to get out of that zone as soon as possible since you are in a dangerous position all the while your speed is less - unless you have the altitude to build up speed, of course.

Are you able to use your bow and stern thrusters under way to assist when the speed through the water is too low for the rudder to compensate for the wind? Are these thrusters continuously rated or only for intermittent use? I have often wondered whether you could deploy the thrusters in a close-quarters near-collision situation....particularly thinking of the recent Ouzo incident in which the stern of the Ro-Pax is believed to have swiped the yacht when altering course; the stern thruster could have been used to keep the stern clear, maybe?

 

[homa]

Re: Limiting factors

We only have bow thrusters (3 of) and no stern thruster.
However we can split the engines and the rudders so can actually compensate for loss of steerage by reducing the leeward and increasing the pitch on the weather propeller.
Bowthrusters are continuously rated but are pretty ineffective at speeds above 3-4kts water speed.
You need a lot of power to supply these thrusters - ours require the shaft alternators to be running - not a quick thing to do in event of a close quarters situation. Rudders are VERY effective at any water speed, we have twisted leading edge, becker, fully balanced rudders.