reducing horsepower required for speed in destroyers

[christian]

machinery for destroyers is currently quite a bit higher than it should be in horsepower

i will show 6 ships as example and their recreated examples (i will merely recreate the hulls of these ships and not their armaments as that does not change the horsepower needed)
all these ships will be recreated in 1970 with maximum level 27 tech modded on (reduces chance of bugs from doing 1920 with max tech)

i will show 6 ships which are shimakaze/le fantastique in game their hulls are basically the same fletcher and kagero and Z class destroyers and L class destroyers
2500 tons 39 knots 85.6k horsepower needed : real life values were 75k horsepower for shimakaze for 39 knots and 74k horsepower for 45 knots on le fantastique both ships were around 2500 tons or slightly more (still less than 2600 tons) 

it is also to be noted the remaining weight on the hull (every setting being standard except speed and weight) was 4 tons thus this hull is basically useless as anything but a ram stick
fast destroyers like these are impossible without cramped speed and short range in which case you still only have around 285 tons to play with

second group of ships is the kagero
1900 tons 35 knots which required 34k horsepower to run while in real life it needed 50k horsepower to run at 35 knots at a weight of 1900 tons
fletcher 38 knots 2300 tons 68k horsepower needed to run at that speed in real life it needed 60k horsepower to run at that speed at 2300 tons

last is the 2 british destroyers
Z class needed 44k horsepower to run at 37 knots at 1700 tons in real life needed 40k horsepower to run at 36.75 knots at 1700 tons close to real life
L class needed 40k horsepower to run at 36 knots at a weight of 1900 tons in real needed 48k horsepower to run at 36 knots weight 1900 tons 



boiling down the suggestion is increase machinery horsepower required for ships below 36 knots slightly while decreasing machinery weight for ships going faster than 36 knots and significantly decrease the horsepower needed for ships going faster than 37 knots 

also each machinery horsepower might weight a bit too much although im not sure

[dorn]

I think it is because savings on machinery was higher in real history, I will try to check it.

EDIt: meaning saving through technology

[rimbecano]

Jun 22, 2019 5:49:23 GMT -6 christian said:

fletcher 38 knots 2300 tons 68k horsepower needed to run at that speed in real life it needed 60k horsepower to run at that speed at 2300 tons

Wikipedia gives Fletcher's speed as 36.5. Do you have a source for 38?

[oldpop2000]

There was a preliminary designs dated Sept 30,1941 of a B and B-1 destroyers which led to the Allan B. Sumner class design. It was an updated Fletcher class destroyer. It had an estimated speed of 37.6 Knots. There was a request in 1939 to provide the new Fletcher class with 38 knots but that would have required 20% more power. It would also make the ship 10% heavier and a requirement for more space. The decision was to have between 35 and 36 knots. The General Board decided on 36 knots. Now, that is the estimated speed but if you overpressure the engines, you could attain 37 Knots but not for long because that would use all the fuel so, the best maximum speed was 36 Knots.  

Sources: SpringStyles #3 and U. S. Destroyers by Norman Friedman Page 113 Paragraph 2.

Just a note: I put together an accurate design in Springsharp for the Fletcher. At 35 knots, power was about 61,776 but if I ramp up the speed to 38 knots, the power goes up to 87,330 hp. Now, Springsharp is a little off on engine horsepower but it close. This confirms that if they had tried to go to 38 knots, the engines would have required far more power as is normal with ships. At 37 knots, the hp requirements are 77,994.

Some random data shows that from 20,000 hp on Scharnhorst, you would gain about 4 knots in speed. For Hood, from 14,020 hp @ 15.8 knots to 24,720 hp, you would gain about 3.3 Knots. Most ships have an designed overpressure that can be implement but if you go higher, you can damage the engines. This figure is generally 20%.