gjgm
Active member
no, not never-never.. why are boat engines quoted in horse power and cars in bhp.Presumably they are both measured in the same way, so just convention?
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HP
- Thread starter gjgm
- Start date
Happy1
N/A
It's obvious really, you don't have brakes on a boat, well not mine anyway /forums/images/icons/laugh.gif
<hr width=100% size=1><font color=purple> "You only see what you recognise, and you only recognise what you know" <font color=purple>
<hr width=100% size=1><font color=purple> "You only see what you recognise, and you only recognise what you know" <font color=purple>
jfm
Well-known member
There is lots of fudging here but braodly:
brake hp=shaft hp = power (torquexrotation speed) at the output side of the engine, at the flywheel. Upstream of any gearbox, downstream of engine internal fiction
ihp = indicated hp = theoretical power computed from cylinder pressure. But this is always higher than bhp/shp because of engine friction losses. Bit useless to us, rarely quoted
SAEhp society of american engineers used to measure engine hp with all the auxilliaries like alternator and exhaust removed, so give a higher figure. Dunno if this is now ancient history
PS is the new metric horsepower. They picked the nearest round number to make a ps close to an imperial hp. Thus a ps was defined as 75kgm per second. That makes it 98.6% of an imperial horsepower. So an engine with 100ps is actually only 98.6bhp/shp. The letters PS stand for something in German, forgotten, but the P is pferd, german for horse.
I believe (others may know better) outboard motors are now invariably rated at the prop shaft, ie down stream of the gearbox. So they're a bit more powerful than the decals suggest
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brake hp=shaft hp = power (torquexrotation speed) at the output side of the engine, at the flywheel. Upstream of any gearbox, downstream of engine internal fiction
ihp = indicated hp = theoretical power computed from cylinder pressure. But this is always higher than bhp/shp because of engine friction losses. Bit useless to us, rarely quoted
SAEhp society of american engineers used to measure engine hp with all the auxilliaries like alternator and exhaust removed, so give a higher figure. Dunno if this is now ancient history
PS is the new metric horsepower. They picked the nearest round number to make a ps close to an imperial hp. Thus a ps was defined as 75kgm per second. That makes it 98.6% of an imperial horsepower. So an engine with 100ps is actually only 98.6bhp/shp. The letters PS stand for something in German, forgotten, but the P is pferd, german for horse.
I believe (others may know better) outboard motors are now invariably rated at the prop shaft, ie down stream of the gearbox. So they're a bit more powerful than the decals suggest
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gjgm
Active member
but presumably marine engines are also measured at the output... so its just a marine thing to say HP..coz most of them are American blocks anyway!
Happy1, i think you ve just found another safety feature for your boat!
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Happy1, i think you ve just found another safety feature for your boat!
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jfm
Well-known member
yes most boat engines excl outboards are measured at the output, so the ratings are bhp (=shp). The SAEstuff wouldn't carry over just cos it's the same block
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Sybarite
Well-known member
The letters PS stand for something in German, forgotten, but the P is pferd, german for horse.
Pferde Starke
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Pferde Starke
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DepSol
New member
Pferde Shiezer???
<hr width=100% size=1>Dom
<A target="_blank" HREF=http://www.soltron.co.uk>the website</A>
<hr width=100% size=1>Dom
<A target="_blank" HREF=http://www.soltron.co.uk>the website</A>