delcyros
Tech Sergeant
Super heated steam turbine = high pressure steam turbine (HPT)
Agreed, by its arrival this tech was revolutionary compared to the old low pressure trubine.
But Diesel by far isn´t a step back. Esspeccially for US purposes:
As we know, the US soon went to the all or nothing raft body armor sheme after ww1. Diesel engines really fit more to this specification than would HPT.
The only real disadvantage is that they were heavy.
I will calculate an example with roughly some estimations based on the original 1939 North Carolina BB design(sorry for using metrics):
The NC´s were the first true US BB to be builded after ww1 (Lexington BC turned into CVA and South Dakota fell victim to the Washington treaty), let´s compare the design with a proposed Diesel design:
displacement: 42.000 t. (actually 46.770 deeply loaden)
length(waterline): 214,6m
beam: 33 m
length/beam relation: 6.5
speed (trial):28,5 kts @ 125.000 hp (enforced) and 43.500 t.
armor weight: 13.976 t.
main armor length: 111,3m
propulsion: HPT, 4 shafts, 8 Babcock boilers, 121.000 hp (at 100%)
propulsion length (biolers + turbines): 59, 5m
engine weight: 1.881 t. (+ 845 t. auxilary and systems)
fuel complement: 6.592 t.
range: ? according to the datas from Iowa, which had a comparable hull shape, but beeing larger and having more powerful and efficient engines (as well as more fuel complement) I estimate around 10.000 miles /12 kts. It should be noted that the ship benefits a lot by the low weight HPT engine, which spared some weight.
Now I replace the HPT with a german Diesel engine (Graf Spee), and since Graf Spee had 8 engines and 2 srews and NC has four I (just for gaming) calculate with the exact doubling (which would result in 108.000 hp), by arranging the 16 engines in the same way (4 on each shaft):
What would change?
engine weight: 3.302 tons (+ 650 auxilary and systems)
propulsion length (gears and Diesels
54 m
fuel complement: 2.814t.
range: approx. 18.000 nm at 12 kts.
= if we calculate engine weight with fuel complement together, the Diesel driven NC propulsion weights 6.772 t (compare, the executed design is 9.318 t., that are 2.5 Ktons safed in the end for a nearly doubled range, not bad is you ask me). Now what happens with the speed?
at 41.500 tons (reduced trial) 108.000 hp could still drive the ship to 28,3 kts, no significant speed drop. (Variant A)
But it even goes further: Lets assume the 5 m shorter engine dep. would led to a shorter ship design, which probably would happen. Then another 2 (at least) Ktons could be safed due to the shorter vital armor box as well! Less deck armor zone, less main armor belt in spacial dimensions (important for the AON sheme), but all has the same thickness. In the end such a modified NC would only weight around 43.000 tons (deeply loaded), be a bit shorter, having a reduced beam-length relation (~6.3 instead of 6.5) and therefor a reduced speed (27.7 kts deeply loaden). In their appearenc ethis ship would look like a modified South Dakota(Variant B)
Another possibility is to keep the weight and take a reduced speed (26.8 kts) for 3.000 tons of additional armor. Less probable. (Variant C)
A last one (my favourite) could use the space for additional Diesels, one on each screw and a larger internally protected fuel bunker. This variant (D) would have little larger spacial dimensions like the original one due to 4 m increased length and therefor beeing 2 Ktons heavier (larger armor dimensions):
Displacement: ~48.000 t. deeply loaden
length:~ 218 m (waterline)
beam: 33m
length-beam relation: 6.6
engine weight: 4.127 tons (+~ 850 t. auxiliarys)
fuel complement: 4.221 tons
range: approx. 26.000 nm/12 kts
Engine power: 135.000 SHP
estimated peed: 29,02 kts at 135.000SHP and 45.600 tons
Compared to the original design this variant would more than double the range and a slightly increased speed as well as slightly less engine weight (9.200 t. instead of 9.318 t.)
Concluded some positives:
A shorter construction time due to reduced displacement (except Varian D)
A better TDS because of more void cells instead of oil filled cells
A much longer range
A reduced crew complement
Better Seakeeping because of higher freeboard
Some tactical advantages (smoke free)
And a reduced vulnarability because of impossibility of boiler hits.
The disadvantages would be as following:
uncomfortable vibrations, high degree of produced sound
higher engine height (neglectable, since the US BB design already placed the main armor deck one level higher, so the engines fit into the spacial subdivision)
Keep in mind that we calculated with old 1927/28 designed Diesel systems! Now explain me why it would be kind of step back?
Agreed, by its arrival this tech was revolutionary compared to the old low pressure trubine.
But Diesel by far isn´t a step back. Esspeccially for US purposes:
As we know, the US soon went to the all or nothing raft body armor sheme after ww1. Diesel engines really fit more to this specification than would HPT.
The only real disadvantage is that they were heavy.
I will calculate an example with roughly some estimations based on the original 1939 North Carolina BB design(sorry for using metrics):
The NC´s were the first true US BB to be builded after ww1 (Lexington BC turned into CVA and South Dakota fell victim to the Washington treaty), let´s compare the design with a proposed Diesel design:
displacement: 42.000 t. (actually 46.770 deeply loaden)
length(waterline): 214,6m
beam: 33 m
length/beam relation: 6.5
speed (trial):28,5 kts @ 125.000 hp (enforced) and 43.500 t.
armor weight: 13.976 t.
main armor length: 111,3m
propulsion: HPT, 4 shafts, 8 Babcock boilers, 121.000 hp (at 100%)
propulsion length (biolers + turbines): 59, 5m
engine weight: 1.881 t. (+ 845 t. auxilary and systems)
fuel complement: 6.592 t.
range: ? according to the datas from Iowa, which had a comparable hull shape, but beeing larger and having more powerful and efficient engines (as well as more fuel complement) I estimate around 10.000 miles /12 kts. It should be noted that the ship benefits a lot by the low weight HPT engine, which spared some weight.
Now I replace the HPT with a german Diesel engine (Graf Spee), and since Graf Spee had 8 engines and 2 srews and NC has four I (just for gaming) calculate with the exact doubling (which would result in 108.000 hp), by arranging the 16 engines in the same way (4 on each shaft):
What would change?
engine weight: 3.302 tons (+ 650 auxilary and systems)
propulsion length (gears and Diesels
54 mfuel complement: 2.814t.
range: approx. 18.000 nm at 12 kts.
= if we calculate engine weight with fuel complement together, the Diesel driven NC propulsion weights 6.772 t (compare, the executed design is 9.318 t., that are 2.5 Ktons safed in the end for a nearly doubled range, not bad is you ask me). Now what happens with the speed?
at 41.500 tons (reduced trial) 108.000 hp could still drive the ship to 28,3 kts, no significant speed drop. (Variant A)
But it even goes further: Lets assume the 5 m shorter engine dep. would led to a shorter ship design, which probably would happen. Then another 2 (at least) Ktons could be safed due to the shorter vital armor box as well! Less deck armor zone, less main armor belt in spacial dimensions (important for the AON sheme), but all has the same thickness. In the end such a modified NC would only weight around 43.000 tons (deeply loaded), be a bit shorter, having a reduced beam-length relation (~6.3 instead of 6.5) and therefor a reduced speed (27.7 kts deeply loaden). In their appearenc ethis ship would look like a modified South Dakota(Variant B)
Another possibility is to keep the weight and take a reduced speed (26.8 kts) for 3.000 tons of additional armor. Less probable. (Variant C)
A last one (my favourite) could use the space for additional Diesels, one on each screw and a larger internally protected fuel bunker. This variant (D) would have little larger spacial dimensions like the original one due to 4 m increased length and therefor beeing 2 Ktons heavier (larger armor dimensions):
Displacement: ~48.000 t. deeply loaden
length:~ 218 m (waterline)
beam: 33m
length-beam relation: 6.6
engine weight: 4.127 tons (+~ 850 t. auxiliarys)
fuel complement: 4.221 tons
range: approx. 26.000 nm/12 kts
Engine power: 135.000 SHP
estimated peed: 29,02 kts at 135.000SHP and 45.600 tons
Compared to the original design this variant would more than double the range and a slightly increased speed as well as slightly less engine weight (9.200 t. instead of 9.318 t.)
Concluded some positives:
A shorter construction time due to reduced displacement (except Varian D)
A better TDS because of more void cells instead of oil filled cells
A much longer range
A reduced crew complement
Better Seakeeping because of higher freeboard
Some tactical advantages (smoke free)
And a reduced vulnarability because of impossibility of boiler hits.
The disadvantages would be as following:
uncomfortable vibrations, high degree of produced sound
higher engine height (neglectable, since the US BB design already placed the main armor deck one level higher, so the engines fit into the spacial subdivision)
Keep in mind that we calculated with old 1927/28 designed Diesel systems! Now explain me why it would be kind of step back?
