Old HP versus new HP

[achris]

Re: Old HP versus new HP

So then your saying that if my boat was a 1975 and was rated for 150 hp max and I put a brand new 150 hp motor on it I would now be over powering the boat??????

What??? Noooo.... Exactly the opposite... 150hp from a 1845 steam engine is exactly the same as 150hp from a brand new engine...

What I said is that your new 150 would be more reliable and use less fuel than the old one.... but still be only 150 horsepower.

Chris.......

 

[CaptainHook]

Re: Old HP versus new HP

That doesn't make sense to me. If an old outboard made 150 hp at the crank it would be less at the prop correct????

But the new motor is actually making the 150 at the prop so there would be more power actually propelling the boat...correct????

So if the boat manufacture back in 1975 tested the hull and rated it with a motor that didn't make as much power at the prop as a new one even though both motors wear the same badge......then new one would be actually more that the original test many many years ago.....am I right or just thinking to much?

 

[achris]

Re: Old HP versus new HP

The horsepower doesn't change. It can't, 1 horsepower is 33,000 ft-lbf/min. If the place where the horsepower is read from is different and there are losses between those points, then yes amount of horsepower the engine is producing MUST also have changed. So, in regard to your boat being rated as having a maximum horsepower engine of 150, then strictly by the book, yes, you're now putting more horsepower on it. Because the engine is producing more horsepower at point A, losing X horsepower in the drive train that wasn't accounted for in the original rating. Unless the tag says 150 crankshaft horsepower, I wouldn't worry about it... The tag says 150hp, put 150hp on it.

Chris........

 

[CaptainHook]

Re: Old HP versus new HP

I wasn't saying the horsepower was changing, just the amount that is actually making it to the water!!! Thanks

 

[madgadget]

Re: Old HP versus new HP

Actually every auto maker in the UK measures HP at the wheels, it is called BHP, Brake Horse Power.

No they don't. Its slightly different standard but all powers are flywheel over on this side

 

[TerryMSU]

Re: Old HP versus new HP

No they don't. Its slightly different standard but all powers are flywheel over on this side

Thanks, I was thinking the same thing. BHP is Brake Horse Power, but the brake is a De Prony Brake that is coupled directly to the flywheel.

http://en.wikipedia.org/wiki/De_Prony_brake

(the units in this presentation are metric, but the concept is identical.)

Also, depending on who is doing the rating, often the engine manufacturer will pull some tricks like disconnecting the water pump and running a separate water pump not powered by the engine and disconnecting the Alternator, etc.

By the way, older tractors, such as the old steam tractors would have both ratings on the tractor where the higher rating was BHP and the lower rating was drawbar HP. Many times, the Drawbar number was less than half of the BHP number.

TerryMSU

 

[carbineone]

Re: Old HP versus new HP

This is a the formula that used to rate Steam Engine HP

Power=work =force X distance = (180lbf)(2.4 X 2rr X 12 ft)=32,572 ft-lbf
___ _____________ _____________________ ____

time time 1 min min




I am no mathematical genius but I think that means the amount of weight a Horse could lift in one minute to a height of 12 feet or something like that.I could be way off but thats the formula they used in the "Old Days" I think later HP is rated differently but maybe not.Maybe someone else understands this Math crap better than me....Bruce

 

[madgadget]

Re: Old HP versus new HP

I don't know if this will be interesting or not, but I do a lot of car tuning on engine dyno's. Quite often the power I measure on a stock car will be within 5% of that quoted. I tuned a 2.0 turbo motor yesterday that mad 411bhp and 370lb/ft of torque not bad for a little 1200kg car