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All Forums >> [Current Games From Matrix.] >> [World War II] >> War In The Pacific - Struggle Against Japan 1941 - 1945 >> Ship handling info needed...

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Ship handling info needed... - 12/25/2007 5:21:32 PM

juliet7bravo

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Joined: 5/30/2001
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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.

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RE: Ship handling info needed... - 12/25/2007 7:17:05 PM

rtrapasso

Posts: 22653
Joined: 9/3/2002
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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.)

< Message edited by rtrapasso -- 12/25/2007 7:19:14 PM >

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RE: Ship handling info needed... - 12/26/2007 7:47:37 AM

Feinder

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Joined: 9/4/2002
From: Land o' Lakes, FL
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Enough calculus & physics on, "what it takes to turn a ship", to make your head explode.

< Message edited by Feinder -- 12/26/2007 7:57:31 AM >

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RE: Ship handling info needed... - 12/26/2007 10:28:21 AM

Doggie

Posts: 3244
Joined: 9/19/2001
From: Under the porch
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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.

That's pretty simple. First off, a freighter is not likely to use diesel engines. If it has a funnel; it's not diesel.

With no engines, the ship's speed would be the same as what ever current the ship happend to be in.

With no headway, the rudder would be useless.

The "heading" would be the same as the wind direction, though the bow could point in any direction.

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RE: Ship handling info needed... - 12/26/2007 2:15:23 PM

rtrapasso

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Joined: 9/3/2002
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quote:

If it has a funnel; it's not diesel.

Possibly true with freighters, though i have my doubts... there certainly were warships (i.e. German pocket battleships) running on diesels that had a funnel.

i agree most large freighters didn't have diesels during WW2.

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RE: Ship handling info needed... - 12/26/2007 7:01:53 PM

crsutton

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Joined: 12/6/2002
From: Maryland
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Virtually all large merchant ships in WWII were oil or coal fired steam ships. Large low compression diesels really did not begin to see service until the early 1980s.

They (diesels) still have stacks though. They still make a lot of smoke.

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RE: Ship handling info needed... - 12/26/2007 9:00:30 PM

mlees

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Joined: 9/20/2003
From: San Diego
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IIRC, the USN Destroyer Escorts had diesel engines. Stacks are present.

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RE: Ship handling info needed... - 12/27/2007 6:26:18 PM

msieving1

Posts: 526
Joined: 3/23/2007
From: Missouri
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Most of the major Maritime Commission type freighters were built in both turbine and diesel versions, so diesel power is not that unlikely. And of course diesel powered ships have stacks; they have to get rid of exhaust gases just the same.

Maximum speed of these ships would be about 16 kts, so if the ship is already at 15 kts, the speed isn't going to change much in 45 seconds. Even a hypothetical faster ship with a maximum speed of 20+ kts isn't going to accelerate very quickly. And WW2 freighters aren't generally noted for manueverability, either. I wouldn't expect that the course would change more an a few degrees. Ordering full speed and a hard turn is mostly a pro forma response to sighting a torpedo. In a freighter, it's not likely to have much effect.

Is the data based on a real life attack? If so, I'd assume the attack plot is accurate. After all, the person who made that plot was there.

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Post #: 8

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