Efficiency of a paddle wheel steamboat

[Vikas]

We took a sightseeing tour on a steamboat (with a big paddle wheel in the back) while visiting New Orleans. The ship carried over 1200 people. It had boiler fired by diesel generating steam to power reciprocating pistons. What surprised me is that it had "only" 2000 hp. That is like 2hp/person. If your car had that efficiency, you will only need 8hp motor for a typical four door sedan! But we "need" at least 240 hp otherwise we feel our car is under powered.

Why 80x difference in efficiency?

- Vikas

 

[SWS]

Max HP rating is deceiving. I think that a typical car with gas engine requires less than 10HP to drive steadliy at 60MPH. Read that in Popular Science way back in the 1960's.

 

[expat]

How quickly did that paddle steamer accelerate?

 

[Kestas]

True, cars need that horsepower for acceleration, like getting on a freeway. The steamboat doesn't have that kind of acceleration.

 

[05GMC]

2000 h.p. , but how much torque ?

 

[Trav]

What measure of HP and at what RPM? How much torque is it producing?
Steam engines and ships use boiler or shaft HP while cars use BHP or WHP.

The City of Truro steam locomotive needed only 700ihp to pull its 118 tons at 92mph, max hp was 1000 hp at 200 psi boiler pressure. A diesel electric train needs approx 3200hp to accomplish the same.
It sounds like there is a lot more to HP figures than meets the eye.

 

[bullwinkle]

Question is-2000 HP at what RPM? Bet the torque curve is OFF THE SCALE!

 

[XS650]

Originally Posted By: Vikas
We took a sightseeing tour on a steamboat (with a big paddle wheel in the back) while visiting New Orleans. The ship carried over 1200 people. It had boiler fired by diesel generating steam to power reciprocating pistons. What surprised me is that it had "only" 2000 hp. That is like 2hp/person. If your car had that efficiency, you will only need 8hp motor for a typical four door sedan! But we "need" at least 240 hp otherwise we feel our car is under powered.

Why 80x difference in efficiency?

- Vikas


If you only wanted to go less than 10 mph on level ground and take forever to get to that 10 mph, 8 hp would be plenty of power for a car.

 

[Quattro Pete]

Originally Posted By: XS650

If you only wanted to go less than 10 mph on level ground and take forever to get to that 10 mph, 8 hp would be plenty of power for a car.

Or take any 50cc scooter for example. What does it have, 3 HP? It'll go 35 mph and won't even take forever to get there.

 

[XS650]

Originally Posted By: Quattro Pete
Originally Posted By: XS650

If you only wanted to go less than 10 mph on level ground and take forever to get to that 10 mph, 8 hp would be plenty of power for a car.

Or take any 50cc scooter for example. What does it have, 3 HP? It'll go 35 mph and won't even take forever to get there.


Good point. Mopeds (US definition) are limited to 2 hp or less and 30 mph or depending on which state and they can carry two people. Why is that boat so inefficient?

 

[Al]

Originally Posted By: 05GMC
2000 h.p. , but how much torque ?

Torque is meaningless. HP is what counts.

 

[andyd]

Originally Posted By: Al
Originally Posted By: 05GMC
2000 h.p. , but how much torque ?

Torque is meaningless. HP is what counts.
I think it is just the opposite. HP is good for acceleration, Torque is the power to turn the wheels. A steam engine has full torque at low RPM. That is why steam cars and locomotives dont have transmissions.

 

[Kiwi_ME]

Originally Posted By: Vikas
Why 80x difference in efficiency?- Vikas

I think you mean 30x and I'll guess the car in this example will get you there a lot faster, perhaps 30x. If your car had 2 hp per person it would probably be about as fast as the boat.

 

[Vikas]

Oops, you are right, bad math, it is only 30x!

 

[expat]

I understand that the average Joe can sustain about 1/3 hp for about 1 hour. On a streamlined bicycle that can give you about 40mph (I'm told)
Not bad!
Watercraft require VERY little power to move heavy loads, but at very slow speeds. consider the old Barges in the 1800's High tonnage at a walking pace, with only one (real horse) or pushed by a human.
I have to laugh when I hear someone say "My car produces 300 hp and gets 30mpg" No it doesn't! it gets 30 mpg producing about 35 hp.
Most reasonable sized cars can do about 100mph with about 100hp, but by then you are REALLY pushing Air. That's why a Bugatti needs a 1000 hp to crack 250 mph.

 

[XS650]

Originally Posted By: Al
Originally Posted By: 05GMC
2000 h.p. , but how much torque ?

Torque is meaningless. HP is what counts.


Al, you are correct, but you're wasting your keystrokes.

 

[Al]

Originally Posted By: XS650
Originally Posted By: Al
Originally Posted By: 05GMC
2000 h.p. , but how much torque ?

Torque is meaningless. HP is what counts.


Al, you are correct, but you're wasting your keystrokes.


I realize that...thanks for bringing me to my senses.

 

[mechtech2]

How does the diesel generate steam?
What is the system?

 

[Vikas]

Diesel fired boiler

 

[Shannow]

I doubt that a diesel paddle steamer is all that "efficient", a typical old firetube boiler being 60-70% efficient, even a multiple expansion steam engine is of the 30% range, meanign fuel to power would be lucky to crack 20%...pretty much why the forests of Oz disappeared along the muddy waterways.

Add that to the paddles which are probably the least efficient way of getting the power to the water, alternately wanting to lift the boat as they slap down, and lift a heap of water on the way back up, and it's not really the ideal commuter or long distance vehicle.

Torque at zero speed in a boat is as useful as lipstick on a pig (good for railroads with loads 'though), and as Al and XS650 have stated,in a boat, it's the power to displace the water around the boat, exchange momentum with the environment, and generally heat the place up.