Official Fleet submarine ranges are far from the truth?

Rosencrantz · 08-03-16, 05:38 PM

Has anyone else here ever checked the official ranges given to the Fleet type submarines? I'm asking, because when I made some calculations for both Porpoise and Gato classes, I started to get weird results. A short, simplified example of my calculations:

Class: Late Porpoise (Perch and later)
Fuel oil load: 89 945 gals
Weight of fuel: 647 604 lbs (7.2 lbs/gal)
Assumed consumption: 0.46 lbs/BHP/hr
Overall lenght of the submarine: 301 feet
Waterline lenght of the submarine: 288 feet
Displacement, official: 1 350 - 1 370 tons surfaced
Estimated displacement, surfaced, diving trim: 1 634 tons
Range at 10 knots, official: 11 000 nm
Calculated SHP need for 10.25 knots, propeller: 665 shp
Calculated KW need for 10.25 knots, generator: 515 KW
Calculated BHP need for 10.25 knots, engine: 735 BHP

735 BHP x 0.46 lbs/BHP/hr = 338.1 lbs/hr = 47 gals/hr
89 945 gals/47 gals/hr = 1913 hr
1900 hr at 10 knots = 19 000 nm

0.46 lbs/hr shoud be more than enough for diesel-electric drive of those days. Geared systems used fuel even less and straight systems even less than geared. So 0.46 lbs/hr should be really enough. Steam turbines used typically 0.66 lbs/hr on those days. Now, if we take the official range of
11 000 nm at 10 knots, we get 1 100 hour endurance at 10 knots.

=> 89 945 gals/1 100 hrs = 81.77 gals/hr = 588.7 lbs/hr

588.7 lbs/735 BHP = 0.80 lbs/hr

Conclusion: either Wintons, GM's and FBM's used by the US Navy were very thirsty to the extreme levels (getting even steam turbines behind) or official ranges for fleet boats are either:

1.) Intentionally misleading (which I doubt - any qualified naval engineer is able to make pretty good estimates based on the previous details)
2.) Meant to be used as aid for operational planning like: "the boat is able to proceed about 5 000 nm to the area of interests, stay there about 30 days and make it back without refuelling".

Calculations for Gato gave exactly the very same directions. Official ranges seem to be about 40 - 45 % off. Any thoughts? Please, if you did find a mistake, report it.

Greetings,
Rosie

08-03-16, 05:38 PM	#1
Rosencrantz Grey Wolf Join Date: Dec 2004 Location: Finland Posts: 758 Downloads: 78 Uploads: 0	Official Fleet submarine ranges are far from the truth? Has anyone else here ever checked the official ranges given to the Fleet type submarines? I'm asking, because when I made some calculations for both Porpoise and Gato classes, I started to get weird results. A short, simplified example of my calculations: Class: Late Porpoise (Perch and later) Fuel oil load: 89 945 gals Weight of fuel: 647 604 lbs (7.2 lbs/gal) Assumed consumption: 0.46 lbs/BHP/hr Overall lenght of the submarine: 301 feet Waterline lenght of the submarine: 288 feet Displacement, official: 1 350 - 1 370 tons surfaced Estimated displacement, surfaced, diving trim: 1 634 tons Range at 10 knots, official: 11 000 nm Calculated SHP need for 10.25 knots, propeller: 665 shp Calculated KW need for 10.25 knots, generator: 515 KW Calculated BHP need for 10.25 knots, engine: 735 BHP 735 BHP x 0.46 lbs/BHP/hr = 338.1 lbs/hr = 47 gals/hr 89 945 gals/47 gals/hr = 1913 hr 1900 hr at 10 knots = 19 000 nm 0.46 lbs/hr shoud be more than enough for diesel-electric drive of those days. Geared systems used fuel even less and straight systems even less than geared. So 0.46 lbs/hr should be really enough. Steam turbines used typically 0.66 lbs/hr on those days. Now, if we take the official range of 11 000 nm at 10 knots, we get 1 100 hour endurance at 10 knots. => 89 945 gals/1 100 hrs = 81.77 gals/hr = 588.7 lbs/hr 588.7 lbs/735 BHP = 0.80 lbs/hr Conclusion: either Wintons, GM's and FBM's used by the US Navy were very thirsty to the extreme levels (getting even steam turbines behind) or official ranges for fleet boats are either: 1.) Intentionally misleading (which I doubt - any qualified naval engineer is able to make pretty good estimates based on the previous details) 2.) Meant to be used as aid for operational planning like: "the boat is able to proceed about 5 000 nm to the area of interests, stay there about 30 days and make it back without refuelling". Calculations for Gato gave exactly the very same directions. Official ranges seem to be about 40 - 45 % off. Any thoughts? Please, if you did find a mistake, report it. Greetings, Rosie Last edited by Rosencrantz; 08-04-16 at 12:57 AM.