Three shafts versus four

Propulsion systems, machinery, turbines, boilers, propellers, fuel consumption, etc.
alecsandros
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Re: Three shafts versus four

Postby alecsandros » Wed Jul 07, 2010 11:10 am

Lee: :clap:

A small addition to the discussion:

4-shaft designs were just as prone to debilitating stern damage as 3-shaft ones.
2 examples:
1 - Prince of Wales hit by 1 torpedo/tragic consequences
2 - VIttorio Venetto hit by 1 torpedo. This is less known, I think:
> the torpedo hit the ship in the stern, on the port side. 2000-3000tons of water were taken in. The ship immediately lost power and was dead in the water for about 20 minutes. The lucky part was that there weren't any more torpedo-bombers in the area...
After 20 minutes, VV started to move again, top speed 19kts.
Repairs lasted more than 3 months.

Cheers,
Alex

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Re: Three shafts versus four

Postby lwd » Wed Jul 07, 2010 1:27 pm

In the case of POW from my understanding she still had a significant amount of mobility after the hit. The problem was they restarted a damaged shaft. The problems in doing so are independent of the number of shafts. But 4 shafts close enough together should be more vulnerable to a total loss of mobility than two well spaced shafts. The latter might also allow for even better turning performance (or not).

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Karl Heidenreich
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Re: Three shafts versus four

Postby Karl Heidenreich » Wed Jul 07, 2010 9:28 pm

All authors on battleship design regarded the propellers and shaft as the Achilles Heel of these ships. No doubt. If the explosion is big enough at the underwater part of the bow I don't think there is a formula for being safe: two, three or four propellers, shafts and rudders too! Those cannot be protected.
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Ulrich Rudofsky
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Re: Three shafts versus four

Postby Ulrich Rudofsky » Wed Jul 07, 2010 9:53 pm

Was there an order in the RN or Kriegsmarine to try to hit or get near the drive shafts and rudders if possible? The modern pod propulsions systems must be really sensitive to nearby underwater explosions.
Ulrich

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Re: Three shafts versus four

Postby tommy303 » Thu Jul 08, 2010 12:07 am

I don't know of any orders in the Luftwaffe for targeting a ships props or rudders. Under the circumstances usually created by an air strike, I doubt that it would even be possible with the enemy ship manouvering wildly to evade. You probably could with a submarine, if you had not been spotted and was close enough, but from a plane, it would be very difficult in those days. Luftwaffe torpedo bombers did have a torpedo command unit very much like the analog attack table on U-boats, but smaller of course, which allowed for setting the torpedo gyros in flight for different angles on the bow, torpedo running depth and speed, enemy course and speed and spread angle since many LW torpedo planes carried two torpedoes which could be salvoed or dropped individually. All the bomb aimer or pilot had to do was keep his sight on the target and the unit would maintain target lock. However that is easier said than done on a plane which is subject to considerable buffeting around. I think most training established aiming amidships as normal to give the greatest amount of latitude for errors in data.

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Re: Three shafts versus four

Postby dunmunro » Thu Jul 08, 2010 4:51 am

alecsandros wrote:

4-shaft designs were just as prone to debilitating stern damage as 3-shaft ones.
2 examples:
1 - Prince of Wales hit by 1 torpedo/tragic consequences
2 .

Cheers,
Alex


PoW was hit by two torpedoes in the stern. 3 of her 4 shafts were damaged, and the rudder lost power, but was undamaged. If the flooding through B prop shaft had been contained, power to the rudder might have been restored and the ship brought under control. The RN deliberately chose a single rudder design for efficiency and because the rudder, if damaged, was small enough that the ship might still be steerable if the two outer shafts remained undamaged.

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Re: Three shafts versus four

Postby alecsandros » Thu Jul 08, 2010 8:37 am

Pow speed after the first torpedo hit in the stern droped to 12kts. I'd say that's pretty definitive.

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Re: Three shafts versus four

Postby lwd » Thu Jul 08, 2010 1:43 pm

Most ships when hit with a torpedo will slow significantly at least temporarily. Not doing so is not always a good thing either, Shinano is a case in point.

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Re: Three shafts versus four

Postby alecsandros » Thu Jul 08, 2010 2:44 pm

lwd wrote:Most ships when hit with a torpedo will slow significantly at least temporarily. Not doing so is not always a good thing either, Shinano is a case in point.


There are quite a few examples which show the opposite: Bismarck's first torpedo hit (in the armored belt) and NOrth Carolina's hit (also on the belt) are just 2 which easily come to mind.

When hit at the stern, that's a different problem, and having 4 shafts instead of 3 didn't solve the problem.

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Re: Three shafts versus four

Postby Bgile » Thu Jul 08, 2010 5:35 pm

alecsandros wrote:
lwd wrote:Most ships when hit with a torpedo will slow significantly at least temporarily. Not doing so is not always a good thing either, Shinano is a case in point.


There are quite a few examples which show the opposite: Bismarck's first torpedo hit (in the armored belt) and NOrth Carolina's hit (also on the belt) are just 2 which easily come to mind.

When hit at the stern, that's a different problem, and having 4 shafts instead of 3 didn't solve the problem.


The hit on North Carolina was not on the belt. It was below it, as are most torpedo hits.

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RF
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Re: Three shafts versus four

Postby RF » Sat Oct 09, 2010 9:14 am

Ulrich Rudofsky wrote:Was there an order in the RN or Kriegsmarine to try to hit or get near the drive shafts and rudders if possible? The modern pod propulsions systems must be really sensitive to nearby underwater explosions.


I believe the KM did develop a torpedo that homed in on the noise of screws for use by U-boats attacking convoys. The RN developed ''foxers' to distract the torpedoes from their target.
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