Fletcher-class acceleration

Propulsion systems, machinery, turbines, boilers, propellers, fuel consumption, etc.
Piorun
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Fletcher-class acceleration

Post by Piorun »

Hi

I'd like to ask, if anyone here knows what was the Fletcher-class destroyer's acceleration stop to flank and acceleration curve, mid-mission, boilers online etc.

Thanks in advance
Byron Angel
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Re: Fletcher-class acceleration

Post by Byron Angel »

Piorun wrote: Wed Sep 01, 2021 2:24 am Hi
I'd like to ask, if anyone here knows what was the Fletcher-class destroyer's acceleration stop to flank and acceleration curve, mid-mission, boilers online etc.
Thanks in advance
Hi Piorun,
This reply does not answer your question directly, but might prove of some related interest. The following data comes from a RN acceleration graph prepared for use in connection with the RN's 1929 wargaming rules. The following data relates to the RN destroyers HMS Amazon/HMS Ambuscade dating from the mid-1920s. Please consider all data below as APPROXIMATE.

Starting from stop (presumably) -
5 kts in 1 minute
10 kts in 2 minutes
15 kts in 3 minutes
20 kts in 4 minutes
25 kts in 7 minutes
30 kts in 16 minutes
31 kts in 21 minutes
32 kts in 24 minutes
33 kts in 28 minutes
34 kts in 33 minutes
35 kts in 39 minutes
36 kts in 46 minutes

HMS Amazon/Ambuscade - 319ft w/l length; 1,350t std displ; 42,000shp (31shp/ton displ).
USS Fletcher - - - - - - - - - 376ft w/l length; 2,050t std displ; 60,000shp (29shp/ton displ).

I am no naval architect, but, with shp/ton values of 31 versus 29 being slightly in favor of the British ships and w/l length being slightly in favor of the US ship, I suspect that the speed versus time graphs would not be differ terribly much up to 25kts or so; I'm guesstimating that the advantage would slowly turn to Fletcher's favor above that break point.

FWIW. Hope it helps.

Byron
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marcelo_malara
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Re: Fletcher-class acceleration

Post by marcelo_malara »

Hi guys. I would say that Fletcher´s longer hull and more extreme machinery would better the RN numbers.
Byron Angel
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Re: Fletcher-class acceleration

Post by Byron Angel »

marcelo_malara wrote: Sun Sep 05, 2021 1:21 am Hi guys. I would say that Fletcher´s longer hull and more extreme machinery would better the RN numbers.
Hi Marcelo,
My totally unqualified layperson's guess is that you are probably correct. The greater W/L length of the Fletcher design would postpone the advent of serious wave-making resistance. OTOH, Fletcher's ~50pct greater power is offset by ~50pct greater tonnage and acceleration is closely related to power to weight ratio. That's why my instinct suggests that the difference in acceleration times, although likely to favor Fletcher, will probably not be dramatic.

As they say - "the devil is always in the details". There are IMO far too many unknowns for me to make anything remotely resembling a firm pronouncement. Hopefully, someone better informed will jump into the discussion.

Byron
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marcelo_malara
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Re: Fletcher-class acceleration

Post by marcelo_malara »

Hi Byron. You are thinking about the problem in Newton´s Second Law terms:

F = m * a

More specifically in this form:

F/m = a

But, that would be right if the excess of F (the propeller thrust) is instantly available, which is not so in a steam ship. So I would say that the ability to raise more steam (boiling more water) is the variable that we would need to study. An in this I think that the higher temp/higher pressure USN boiler has the edge.

Regards
Byron Angel
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Re: Fletcher-class acceleration

Post by Byron Angel »

marcelo_malara wrote: Sun Sep 05, 2021 4:12 pm Hi Byron. You are thinking about the problem in Newton´s Second Law terms:

F = m * a

More specifically in this form:

F/m = a

But, that would be right if the excess of F (the propeller thrust) is instantly available, which is not so in a steam ship. So I would say that the ability to raise more steam (boiling more water) is the variable that we would need to study. An in this I think that the higher temp/higher pressure USN boiler has the edge.

Regards

Hi Marcelo,
I was approaching the issue from the simplest common starting status - that both ships had full steam pressure in hand. To do otherwise would introduce a whole new array of influencing factors that I am even more unqualified to comment upon ... :wink:

Byron
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marcelo_malara
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Re: Fletcher-class acceleration

Post by marcelo_malara »

You can have full pressure, but that would fall quickly if you full open the throttles without enough steam volume to replace the used one. I think that a slow sailing ship has some boilers out of line, and going to full speed requires lighting them (or at less allowing more fuel to the burners if they are already light) and waiting for the water to boil.
Piorun
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Re: Fletcher-class acceleration

Post by Piorun »

Byron Angel wrote: Sat Sep 04, 2021 11:55 pmFWIW. Hope it helps.

Byron
Your post and the following discussion is super helpful, especially that there's so little exact data around. Thank you all very much.
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