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can't remember! is it 2 mph per each 50 HP?

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Old 04-18-2007, 11:05 PM
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Default can't remember! is it 2 mph per each 50 HP?

Guys ! Can't remember what was the rough calculation for how much more HP do we need to get 1 more mph for example...

If we are talking about twins, then I guess it would be, let's say, 50 HP per side more for 1 or 2 mph???
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Old 04-19-2007, 12:27 AM
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i go off of the 20hp per 1mph
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Old 04-19-2007, 12:43 AM
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It's not linear, so the formula doesn't work. For aerodynamic drag it goes up by the cube root of the horsepower ratio. Hydrodynamic drag is probably close to this. Maybe some of the navel engineers can chime in.

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Old 04-19-2007, 02:58 AM
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All boats are different and it also depends on what speed you at. Most boats with stock power will gain about 1mph for every 20hp increase. For twins it would be 20hp per side for a 1mph gain.
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Old 04-19-2007, 03:48 AM
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Check BAM marines speed calculator
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Old 04-19-2007, 06:13 AM
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Or you figure it this way

about 2 mph per $2600.00...I spent 3900.00 and only got 3 mph...do the math )
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Old 04-19-2007, 06:30 AM
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Deep V no steps...

Once over 60 MPH it's roughly 1 mph for every 30 HP

http://www.go-fast.com/boat_speed_predictions.htm
Deep V Constant @225
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Old 04-19-2007, 07:37 AM
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I always use $50 per additional 1 hp after the initial engine cost.
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Old 04-19-2007, 08:44 AM
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I increased the power of my motors 51 hp per side. Got 3 mph more, maybe 4 under the right conditions.
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Old 04-19-2007, 08:55 AM
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There was a thread about this a LONG time ago.

A simple equation that I believe will get you close is:

New Speed = Old Speed times [ the squareroot of (New HP / Old HP) ]

or

New HP = Old HP times [ (New Speed / Old Speed) squared ]

Some people say that it should say "cubed" instead of "squared" but "squared" and "square root" will get you close.

Do the math!

http://www.offshoreonly.com/forums/s...ad.php?t=42529
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