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rtrapasso -> RE: Ship handling info needed... (12/25/2007 7:17:05 PM)
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quote:
ORIGINAL: juliet7bravo
I'm trying to figure some ship data;
SITUATION; 9000 ton WW2 fast freighter traveling at 15 knots (cruising speed) eats a torpedo, knocks out the (diesel) engines. The freighter saw the torpedo 45 seconds out, and rang up full speed and ordered a hard starboard turn (Captain heard lookout direct and was standing next to helm). Sea state is calm to moderate.
My questions;
(1) What would the ships speed be when the engines were knocked out?
(2) How many degrees could the ships head have been turned before torpedo impact?
(3) Once the engines were knocked out, how fast would the ship slow down, and at what rate?
Attack Plot shows ship continuing on the same heading she was on when torpedo hit...maybe swinging slightly to starboard (which is the current direction).
(4) With engines out, at what point does the rudder become ineffective? Isn't she going to keep going in a circle until almost to a stop or drifting?
(5) Or did they zero out the rudder (if attack plot is accurate)?
I know it's impossible to answer "accurately" without more data, but I'm looking for "informed" SWAGs.
Too many variables to answer accurately.
The engines being "knocked out" could be from flooding in the engine room, or it could be the engines were physically knocked off their mounting blocks* or otherwise separated from the drive train. So, if the latter - it would happen immediately, if the former, it could take some time. Rupturing a fuel line would probably stop diesels pretty quick as well.
As for how far could it turn - it would depend on the ship. Different ships have different size rudders in proportion to their size (or have twin rudders, etc.) It also would depend on the sea state, currents, etc. There is a big difference between "calm" and "moderate". For large ships, it takes a while to start turning, but once the ship starts to turn it can turn pretty quickly. This also may be load dependent, it think. But, i'm guessing it would be AT LEAST 30 seconds before anything happens - and could be 2-3 minutes.
Rudder becomes ineffective when speed gets below a few knots ("steerage speed" - usually 2-3 knots in larger ships, iirc.)
The rate the ships slows down is also dependent on sea state, current, wind, as well as how deep the ship is riding in the water.
(*Allied ships built later in the war had special "shock mounts" on their engines to prevent this from happening.)
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