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How much fasted should 75hp make it go?

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Old 05-19-2005, 09:49 PM
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Default Re: How much fasted should 75hp make it go?

Here's the link, sorry

http://www.go-fast.com/boat_speed_predictions.htm
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Old 05-19-2005, 10:11 PM
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Default Re: How much fasted should 75hp make it go?

I forgot about that calc. It is pretty close. Their recommondations for a constant aren't very good(at least it wasn't for me), but if you figure out your own with the present motor out like Rick did it works.
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Old 05-19-2005, 10:14 PM
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Default Re: How much fasted should 75hp make it go?

The calculator claims a 5 mph gain for 75hp.
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Old 05-19-2005, 10:20 PM
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Default Re: How much fasted should 75hp make it go?

Quote:
Originally Posted by FX10
The calculator claims a 5 mph gain for 75hp.
For a 30', 4500lb boat. I guessed the boat we were talking about was in the 28 ' range.

Now, take a 3000lb boat with 260hp and add 75hp. Lookie there 10 mph increase!

Weight and hull efficiency play a big role. That's why the "1mph for Xhp" rule doesn't work. The calc takes these into consideration.
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Old 05-19-2005, 10:31 PM
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Default Re: How much fasted should 75hp make it go?

but you have to determine "your " constant. If you know the top end, mph, weight, and hp, the calculator will give you the constant.
The site also has a gear ratio calculator. I tried it with the standard 1.5 bravo XR. Given the 88mph claim. I then tried the 1.35 ratio . And came up with 91mph.
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Old 05-19-2005, 10:32 PM
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Default Re: How much fasted should 75hp make it go?

Quote:
Originally Posted by FX10
it came within 1 mph of actual, cool.
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Old 05-19-2005, 11:41 PM
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Default Re: How much fasted should 75hp make it go?

Quote:
Originally Posted by FX10
The calculator claims a 5 mph gain for 75hp.
I don't believe it will gain that much?


what would it be if ya had twins at 75hp each??
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Old 05-20-2005, 04:02 PM
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Default Re: How much fasted should 75hp make it go?

Quote:
Originally Posted by JCPERF
Well a 525 makes 560 and a 600 makes 600 so you will pickup about 2 MPH
And if the 525 was really making 560 HP to push Eddie to 83, then what will 40 more ponies do? 1MPH? Maybe 2.

FX10, I'm getting part of the story but I wanted see what the colaberative OSO thinktank had to offer. I think anything over 85 will make for a winner. Otherwise, what's the point?
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Old 05-20-2005, 04:45 PM
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Default Re: How much fasted should 75hp make it go?

Ron,
I totally agree. Even at this point 85 sounds good. I was readind an article in a Feb. issue of Powerboating mag. The article was on a Formula 380 Fastec hull, which formerly had 575's (not 525's) in it. It was rigged with the new 600 Merc's, and claimed a gain of between 4-6 mph. And that was with only 50 more hp. Does that sound right to you. I was going to bring the article home and scan it, then put it online here. Maybe Monday I'll do it.

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Old 05-20-2005, 04:50 PM
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Default Re: How much fasted should 75hp make it go?

"generally" bout 2-3 mph for every 50hp. seems about right.
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