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whirly round things


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#1 markh

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Posted 23 February 2009 - 11:17 PM

right then, any prop calc boffins out there?/

ours is all to shit, wrong box ratio & wrong prop

currently 1.5:1 and swinging a 22" fan, engine rated 2750rpm, 6knots is what we get (and we don't get full revs either)

my reckoning is slower box and bigger prop

3:1 box then and maybe 26"

we're just under 44' long, what would anyone reckon she should make speed wise?? or what's anyone with 44' boats of a similar build getting?

any suggestions for size/pitch?

#2 Kevin Munro

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Posted 24 February 2009 - 01:06 AM

Have you tried FAL in Buckie Mark?

http://www.falpropel...alculations.php

#3 markh

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Posted 24 February 2009 - 03:43 PM

yeah, done a few of the theoretical calculations, most of them work on the fact your calculating for a nice shiny modern boat, some even say we're propped correctly at the moment, based on the box ratio, prop size and length, which we might be if it were a modern boat

sorta convinced that the answer for boats of this type are big slow props, given the 1.5:1 box, means we're trying to spin the prop at getting on for 2000rpm to shift 25 ton of boat

pushing a big tide, we struggle at 4 to 5knots, but the hull speed works out about 9 

#4 KEVIND

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Posted 24 February 2009 - 06:06 PM

MARK SPEAK TO DAVE AT A&E WOODWARDS AT HULL HE IS THE BEST U CAN GET WERE PROPS R CONCERNED   01482 329185



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