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Speed calculator Guru's needed

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Old 12-17-2003, 12:10 PM
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Default Speed calculator Guru's needed

Expert opinions needed on theoretical speed. Besides if it prevents arguing on the Kramer thread this is good!

I went to http://www.go-fast.com/boat_speed_predictions.htm and put in my information and got 72 MPH.

I need any other thoughts from the experts around here with these parameters:

Boat:
2000 Cigarette Tiger Non Stepped hull 9800#
Engines according to Dyno Sheet:
601ft @3700 rpm
547 HP @5400 rpm
Drives:
#6's Dry-Sump (from information I got I figured losing 30 HP/each to turn these monsters)
Transmission:
I put 10hp each to turn tranny

This gives me 507 HP to the prop.
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Old 12-17-2003, 12:22 PM
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What Pitch?

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Old 12-17-2003, 12:53 PM
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A buddy's 01 Tiger with Bulldogs and Bravos ran 70 before he added the 8-71s...runs 81 now.
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Old 12-17-2003, 01:19 PM
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Pretty close to what I was thinking...now I just have to get there.
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Old 12-17-2003, 02:05 PM
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GLH,
That chart is very close to being correct. Don't forget to factor in the weight of fuel. I hit the exact gps speed of my boat using 235 as the constant.
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Old 12-17-2003, 02:18 PM
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HEY CORD COORECT IF I'M WRONG,YOU HAVE THE WEIGHT AT 4000 WHICH IT IS 9800LBS AND ONLY HP FOR ONE MOTOR.
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Old 12-17-2003, 02:18 PM
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Default SPEED FORMULA

RPM Diveded by sterndrive ratio X pitch of propeller Diveded by 1056 minus 12 percent should get you pretty close.
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Old 12-17-2003, 02:21 PM
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I GOT 72, ON CORD SAME THING. I JUS CAN'T POST IT.
9800LBS 1014 HP 225 FOR A HEAVY V BOTTUM COMES UP YO 72MPH.
I USED IT A COUPLE OF TIMES AND ITS PRETTY ACCURATE.
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Old 12-17-2003, 02:29 PM
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Quote:
Originally posted by outer42
HEY CORD COORECT IF I'M WRONG,YOU HAVE THE WEIGHT AT 4000 WHICH IT IS 9800LBS AND ONLY HP FOR ONE MOTOR.

That was for my boat. Guess I was saying that if the right info was put in, that the calculator sees to be generating a accurate speed.
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Old 12-17-2003, 04:29 PM
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It is most accurate once you calculate the exact constant for your particular set up. The constant can change though, a set of labbed props may be worth a couple of MPH, but obviously the HP or weight did not change.
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