HP gain vs MPH gain?
03-15-2006 | 09:15 PM
#11
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From: Wi/ Fl Keys
Re: HP gain vs MPH gain?
I have an Outerlimits speed vs engine option list,if interested, for the 37' single step, only merc power so once its above 525hp they show
speedmaster drives but will give approx. speed to HP.
speedmaster drives but will give approx. speed to HP.
03-16-2006 | 06:01 AM
#12
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AKA NoMoBoatin
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From: Can't remember.
Re: HP gain vs MPH gain?
Originally Posted by BBB725
I have an Outerlimits speed vs engine option list,if interested, for the 37' single step, only merc power so once its above 525hp they show
speedmaster drives but will give approx. speed to HP.
speedmaster drives but will give approx. speed to HP.
03-16-2006 | 07:17 AM
#13
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From: sint maarten
Re: HP gain vs MPH gain?
hp = cumulative drag x V cubed ( in ft /sec)
take what the known top speed of the boat is now in mph ...multiply that times 1.46 to get feet/sec
cube that and then divide THAT number into the total HP you have now... that answer is your cumulative drag figure.
now just work the formula backwards.... divide your NEW PROJECTED hp by that drag figure, and do the cube root of that for your NEW mph in f/sec.... divide that by 1.46 and get mph.... and it will be VERY very close to correct.
your neighbors 6th grader can tell you what a cube root is if youve forgotten
take what the known top speed of the boat is now in mph ...multiply that times 1.46 to get feet/sec
cube that and then divide THAT number into the total HP you have now... that answer is your cumulative drag figure.
now just work the formula backwards.... divide your NEW PROJECTED hp by that drag figure, and do the cube root of that for your NEW mph in f/sec.... divide that by 1.46 and get mph.... and it will be VERY very close to correct.
your neighbors 6th grader can tell you what a cube root is if youve forgotten
03-16-2006 | 08:00 AM
#16
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From: Omaha~LOTO
Re: HP gain vs MPH gain?
Originally Posted by Pat McPherson
My boat went from 67mph to 75mph when I swapped a 310HP7.4MPI for a 415HP/502MagMPI... 
03-16-2006 | 08:09 AM
#17
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AKA NoMoBoatin
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From: Can't remember.
Re: HP gain vs MPH gain?
Originally Posted by stevesxm
hp = cumulative drag x V cubed ( in ft /sec)
take what the known top speed of the boat is now in mph ...multiply that times 1.46 to get feet/sec
cube that and then divide THAT number into the total HP you have now... that answer is your cumulative drag figure.
now just work the formula backwards.... divide your NEW PROJECTED hp by that drag figure, and do the cube root of that for your NEW mph in f/sec.... divide that by 1.46 and get mph.... and it will be VERY very close to correct.
your neighbors 6th grader can tell you what a cube root is if youve forgotten
take what the known top speed of the boat is now in mph ...multiply that times 1.46 to get feet/sec
cube that and then divide THAT number into the total HP you have now... that answer is your cumulative drag figure.
now just work the formula backwards.... divide your NEW PROJECTED hp by that drag figure, and do the cube root of that for your NEW mph in f/sec.... divide that by 1.46 and get mph.... and it will be VERY very close to correct.
your neighbors 6th grader can tell you what a cube root is if youve forgotten
Huh.Are you saying i'm old and i forgot ?Your right. thanks.
04-26-2006 | 05:20 PM
#20
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From: frankenmuth michigan
Re: HP gain vs MPH gain?
The only problem with doing it mathmatecially is each increase in speed takes more hp per mph. My boat ran 62 mph w/415 hp,76 w/620hp (14.64 hp per mph),83 mph w/750 (18.57 hp per mph)92.8 mph w/944 hp (19.79 hp per mph),(the 750hp is a estimate) and the speeds were on gps BUT the first 2 speeds weren't labbed props which skews the data a little. If you took my current top speed minus original top speed and the 529 hp difference you would get a average of 17.17 hp per mph BUT if you factor it backwards with that my boat would have needed 655 hp to run 76 mph,Smitty
Last edited by articfriends; 04-26-2006 at 05:26 PM.
