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?
1
whirly round things
Started by
markh
, Feb 23 2009 11:17 PM
3 replies to this topic
#2
Posted 24 February 2009 - 01:06 AM
#3
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
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