Bhp?

Discussion in 'Powerboats' started by Laranjo123, Oct 17, 2011.

  1. Laranjo123

    Laranjo123 Previous Member

    Hello gudday. I've been reading the PNA for about a day ago. I can't find any formula for BHP. My question is is there an exsting formula for BHP because i need to know the formula for BHP..... thank you.
     
  2. gonzo
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    gonzo Senior Member

    You got to be kidding!
     
  3. TeddyDiver
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    TeddyDiver Gollywobbler

    BHP.. Break horse power, the power of the engine no formula :)
     
  4. Submarine Tom

    Submarine Tom Previous Member

    Laranjo123,

    Explain yourself please.

    Do you mean calculating the required horse power for a hull?

    -Tom
     
  5. daiquiri
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    daiquiri Engineering and Design

    Laranjo, based on your recent posts, your technical knowledge seem to be shrinking day by day.

    BHP means "Break Horse Power" and is given by the engine manufacturer.
    If you need to estimate the BHP necessary to move the ship at the given speed, then you have to start from the effective power and go backwards by estimating efficiencies of every single item in the drivetrain, propeller included. When you get to the engine output shaft, you have the required BHP. http://en.wikipedia.org/wiki/Horsepower#Brake_horsepower
     
  6. lewisboats
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    lewisboats Obsessed Member

    There is no BHP or Brake Horse Power on a waterborne engine. There is Shaft Horse power though.
     
  7. pistnbroke
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    pistnbroke I try

    They put a brake (load) on the output shaft to hold it down to certain rpm at WOT .the power absorbed by the brake converted to HP (746w= 1 HP )gives the output......hence its called brakehorse power.
     
  8. philSweet
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    philSweet Senior Member

    It is an out of date motor term. It is one way to rate an engine. Historically, you applied a brake to a motor shaft and measured torque and rpm. Collect a bunch of data points and you have a performance curve for the engine. Rated bhp was the max hp calculated from the test. There are extensive standards for the test conditions- air and fuel temp, air pressure, fuel chemistry. All accessories, fuel pump, water pump, alternator, exhaust system, are stripped off or separately powered. Tests are corrected to standard conditions if they were conducted at different ones, say not done at sea level. It basically rates the potential performance of the iron. It shouldn't be capitalized, it wasn't named after a person. You need to know what it is so you can add the appropriate parasitic losses back in to calculate shp. Then correct for environmental factors to get some meaningful hp for the case in question. Actually, you probably don't need to know what it is. It hasn't been used much in the past 40 years.

    edit. Got the order wrong, correct for environment first, then do the losses.
     
  9. pistnbroke
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    pistnbroke I try

    not used for 40 years ...ford still quoting BHP ....and all the other engine makers I know .....
     
  10. Petros
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    Petros Senior Member

    the definition of a HP is 550 foot-lbs per second (which is also 33,000 foot-lbs per min.). It can also be converted to 746 watts or .746 KW (some engines are rated in kw).

    that is the HP "formula". The term "brake horse power" was a recognition of how engine hp was measured (with a "brake" dynometer) and is not really obsolete, it is just not usually relevant.
     
  11. DCockey
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    DCockey Senior Member

    "Brake horse power" was first used for steam engines sometime in the 19th century, to mean the power measured as the output shaft as opposed to "indicated horse power" or IHP. BHP was originally measured using "brake" on the output shaft which was setup to measure the torque the the output shaft was exerting on the brake mechanism. The shaft speed was measured and then the power computed. Today brake horse power can be measured using a variety of equipement but the term "brake horse power" is still used.

    Indicated power is determined by measure the cylinder presure vs piston position and then calculated the work done on the piston. Indicated power will be higher then brake power due to various energy losses between the face of the piston and the output shaft.

    Internationally there are several different standards for how much power constitutes one horsepower.
     
  12. philSweet
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    philSweet Senior Member

    Must be an Aussie thing. In the US, if car mfgs state a hp, it must be something called rated hp which is different. With modern electronics, I doubt you could keep the damn things running for a bhp test. Economy and emissions requirements have also played a roll in the rated hp definition, with an eye to gaming the system and perhaps slanted for domestic advantage.
     
  13. gonzo
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    gonzo Senior Member

    The rated HP is actual power measured at the wheels in the US. The rated HP hasn't been legal for decades.
     
  14. philSweet
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    philSweet Senior Member

    The proper term is certified horspower, not rated horsepower. Sorry.
     

  15. gonzo
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    gonzo Senior Member

    My typo
     
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