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BUIZILLA
07-26-2008, 05:52 PM
a 4 blade 22" Apollo prop turning 5600 rpm's.. how fast would you be going??

how's about a 3 blade 21" at 5800 ??

just curious..

onesubdrvr
07-26-2008, 06:07 PM
a 4 blade 22" Apollo prop turning 5600 rpm's.. how fast would you be going??

how's about a 3 blade 21" at 5800 ??

just curious..

That's some pretty high RPM's,..... Assuming a .8 efficiency constant (for both props) I get 94 on the 4 blade, 90 on the 3 blade,....math may be way off, and what the hell do I know, I don't even own a boat, right?

But you know these numbers already, I'm assuming you have some interesting hints and hidden facts for us now :wink:

Wayne

BUIZILLA
07-26-2008, 06:15 PM
sorry..

outboard gearcase, i'm assuming about 1.80 maybe??

onesubdrvr
07-26-2008, 06:19 PM
See, I am an idiot,.... lol,... sometimes I kill myself :bonk:

Wayne

onesubdrvr
07-26-2008, 06:24 PM
OK, sorry,

Using a 1.8:1 ratio, both props "calculate" right at 64-65mph. That was with no efficiency losses though.

Wayne

BUIZILLA
07-26-2008, 06:41 PM
confirmed gear ratio to be 1.75-1

twin engine boat

let's guess the actual GPS speed...

onesubdrvr
07-26-2008, 07:13 PM
Ok, I've redone my calculations,

I don't know why, but I'm going with a very high efficiency factor

4 blade - calculated 66.6
3 blade - calculated 65.9

I'm going to say a gps speed of 64.2 and 63.4 respectively

:crossfing::bonk::yes:

Wayne

BlownCrewCab
07-26-2008, 07:21 PM
I'm gonna say 60.1mph actual speed...I usually use 1157 for a constant, instead of 1056.. 1157 knocks off 10% right off the top and is usually much closer to actual speed (But I'm up here where we only have fresh water & and thats 10% slip by it's self)