Naval History Forums

Hello all,

I know he IJN followed British Naval practice and philosophy in many areas, is this also the case in their naval machinery--perhaps at least as a starting point for developing their own ideas?

I find many mentions of Japanese warhsips being equipped with Kampon Boilers, but I haven't really found any clear description of the boilers themselves--were they similiar to Admiralty three drum boilers by any chance?

As usual, thanks in advance!

There is a very critical description of Japanese WW2 boilers at http://www.fischer-tropsch.org/primary_ ... -01-12.pdf. I am sure that the boilers were inferior to those of the USN. However, the inferiority is perhaps less dramatic than one might believe after reading the report. Thus Yamato made 153,553 SHP on trials burning 62.7 metric tons per hour while Washington at 27 knots burned 43.3 tons per hour. Unfortunately I don't know the SHP for that run but it was probably near 115,000. Thus USN machinery gave more power per ton of oil but not hugely more.

Washington at 27 knots burned 43.3 tons per hour. Unfortunately I don't know the SHP for that run but it was probably near 115,000

from where did you get this figure
FTP 218 figures for BB 55 class

based on max oil (95%)= 7554 tons at Mean displacement 40,700 tons
radius at 27 knots = 3640 miles
endurance at 27 knots therfor 134,8 h
fuel consumption(pure propulsion) = 56tons(long tons)/h

I took the data about USS Washington from a web page at http://usswashington.com/fuel.htm which references it to "BATTLESHIP AT WAR" by Ivan Musicant which I have not read. The Yamato data is in the report on IJN boilers and also repeated in “IJN Yamato” by W. David Dickson (so I believe it).

Thank you for the FTP 218 reference. It gives a range of rates of fuel consumption at 27 knots of 11,988-15,200 gallons per hour. I took the figure of 272 gallons per ton for crude oil from Wikipedia and that conversion gives that the best consumption was 44.07 tons/hr., which is close to the website. Thus, as usual, we find that an American site gives the best performance ever achieved by USS Washington. However, it is fair as the Yamato trials data was probably the best that Yamato managed.

question if you have 20 x Kanpon boilers and 4 x steam turbines how much horsepower do you get

Would one not expect Yamato to burn more fuel given that it's engines have to propel a lot more weight?

Hyperwar has some items that may be relevant. I'll dig if anybody wants to take a peek.

BuckBradley wrote: ↑Fri Oct 21, 2022 6:48 pm Would one not expect Yamato to burn more fuel given that it's engines have to propel a lot more weight?

Yes, via an indirect relation, more weight would need higher hp, which would need higher consumption.

But: would not even the same horsepower require more fuel to move more weight?

Example: Say I have a 500hp diesel running at maximum power towing 5,000 ponds. Now suppose I have that same engine running at maximum power towing 10,000 pounds.

Will it burn more fuel--or burn the same fuel but just move more slowly?

I would think both, but I am a lawyer, not an engineer like most of you guys....

BuckBradley wrote: ↑Sun Dec 04, 2022 2:58 am But: would not even the same horsepower require more fuel to move more weight?

Example: Say I have a 500hp diesel running at maximum power towing 5,000 ponds. Now suppose I have that same engine running at maximum power towing 10,000 pounds.

Will it burn more fuel--or burn the same fuel but just move more slowly?

I would think both, but I am a lawyer, not an engineer like most of you guys....

HI. Tricky question. First of all we have to clarify this, if you have an object of a weight of 100 pound you will need a 100 pound force to lift it, if you have an object of 200 pounds you have to duplicate the force. That is valid for vertical movement, where the main resistance comes from gravity. It is different from horizontal movement, where the main resistance does not come from gravity, but from other phenomena, mainly water pressure and viscous friction for a ship. So when calculating the power to move a ship at x speed you have to know the resistance, and it does not vary linearly with mass, for example a 3 000 t destroyer would need 60 000 hp to move at 30 knots, whereas Bismarck, displacing 45 000 t would do the same 30 knots with about 150 000 hp.

So, for your question, if I tow a 5 000 pounds ship with an engine of 500 hp, imagine the 500 hp applied to a winding winch to eliminate propeller propulsive losses and other questions, the towed ship would achieve say 15 knots, if I take a 10 000 pound ship it would not be towed at 7.5 knots, say it would at 10 knots. So the engine would be running at lower rpm, but at a higher torque. Torque you can think roughly of it as the power instantly applied at the crankshaft (a physical inconsistency but a fairly valid simplification), and power (hp) as the sum of that instant power in the revolutions the crankshaft makes in one second.

So, you would have in the case of the 5 000 pound ship the engine running at a certain torque and rpm giving 500 hp. In the case of the 10 000 pound ship the engine would run at a higher torque and lower rpm, giving the same 500 hp. The question so would be how the fuel consumption varies with torque and rpm, nevertheless I can assure you that both values would be very close.

Very interesting. Thanks for the response. I had not considered the fact that one is not moving so much against gravity as other forms of resistance. I guess this would also apply to a lesser extent to semi-trucks going down a level highway.

BuckBradley wrote: ↑Sun Dec 04, 2022 8:08 pm Very interesting. Thanks for the response. I had not considered the fact that one is not moving so much against gravity as other forms of resistance. I guess this would also apply to a lesser extent to semi-trucks going down a level highway.

Yes, any vehicle running on wheels would have a resistance, mainly frictional (mechanical) and air drag at high speed. It is clear that you can move a car weighting a ton with your bare hands, and for sure you can not lift it. For a ship, we move 35 feet sailing vessels with the hands in the peer with very little effort, I would say a force of about 5/10 kg would move it fairly easily.

"So when calculating the power to move a ship at x speed you have to know the resistance, and it does not vary linearly with mass, for example a 3 000 t destroyer would need 60 000 hp to move at 30 knots, whereas Bismarck, displacing 45 000 t would do the same 30 knots with about 150 000 hp"

This is indeed correct, but it should also be considered that the total resistance to a ships' forward motion increases with speed, and this relationship is also not linear; that is, resistance increases more steeply at higher speed, so that any minor increase in speed progressively requires larger and larger power increases. In broad terms, the power required for a given ship to attain a given speed is roughly proportional to the CUBE of the speed. Thus, the Bismarck attained 30 knots with 150,000hp, but an increase by 3 knots would have required close to 200,000 hp.

ebonsi wrote: ↑Tue Dec 27, 2022 7:29 pm
This is indeed correct, but it should also be considered that the total resistance to a ships' forward motion increases with speed, and this relationship is also not linear; that is, resistance increases more steeply at higher speed, so that any minor increase in speed progressively requires larger and larger power increases. In broad terms, the power required for a given ship to attain a given speed is roughly proportional to the CUBE of the speed. Thus, the Bismarck attained 30 knots with 150,000hp, but an increase by 3 knots would have required close to 200,000 hp.

Hi! Yes, you are right. A moving body in a fluid (a bullet for simplicity) has drag from two causes:

-the form drag: the area of low pressure behind the body, that sucks it to the rear, retarding its velocity

-the friction of the skin

Both these vary with the square of the velocity. For a ship there is a third cause of drag (or resistance as naval architects call it), the wave making resistance, the bow and stern waves that a ship creates in its motion and whose energy comes from the engines (propelling the ship). The variation of the wave making resistance depends heavily on the combination of the bow and stern waves, canceling each other or reinforcing each other, and this depends on the speed and waterline length.

Now, the power to move a ship is:

resistance * speed = hp

Note the correctness of the physical magnitudes:

kg * m/s = kgm/s

So, from purely form drag and skin friction causes (a sub or a torpedo for example), the square variation of the resistance and the cube variation of the power are quiet correct. Problem arises when the ship speed is so high that the waves combines, and here the variation can go up with the 4th or 5th power. Tomorrow I will post an excel with some examples.

Regards