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Old 05-24-2011, 04:21 AM   #1
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Default prop pitch

Anyone ever have a problem with excessive cavitation or changed their props pitch to bet better performance??
Mine are 24P and Im not happy with them.
twin bravo 3 Mercruiser 220Hp motors.
something is not right, too much cavitation, too hard to get up on plain.
to much viabration and working too hard.
Mike
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Old 05-24-2011, 04:39 AM   #2
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then I'd go try a set of 22p's..but you really need to watch what your wot range is...

so..the question is 2 fold....1)do you use your trim tabs to help you get up on step??..and 2) what is your wot rpm???...if you drop down...you may exceed your wot range on both engines...


although I have the 24p b3 drives..5.7mpi engines...my wot is about 5500rpm....I can hit 50 with those 24p props...

SP
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Old 05-24-2011, 04:48 AM   #3
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hey thanks for the nice comments.
Yes I have trim tabs and try to use them often to get up.
Problem is that when I do, it seems to make the problem worse in some cases by making things feel like there is a large amount of viabration.
When its fully up and at WOT and trimmed out, it runs 4600 rms @ 39mph by GPS.
But its hard to get up and in the middle of the rpm range the drives vibrate and it sounds just like cavitation.
Once up on top of the water, it runs sweet and effortlessly.
Low rpms while pushing through the water its not a proble either.
Now, if I am up and running along, I can duplicate the sound and feel and problem by pushing the tabs down or, by trimming up the drives a bit too much.
Its the identical feel and sound as the motors make while routinglyi trying to get up on the water.
If I ease through it or baby it through it, it will be fine,
Your thoughts??
ps by the way, I have 220HP Mercs x2 and bravo 3's
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Old 05-24-2011, 05:02 AM   #4
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ok..the other thing that might be happening...and I had this changed on mine cuz they cavitated easily and all I had to do was bump the drives up just once..and it would cavitate..
there is this part on the drive pivot shaft called the celery stick...it prevents the drives from coming in too close to the transom and maybe causing the bow to hook in a tight turn...I can tell you mine never hooked...it would cavitate in a new york second if I tried to mod the drive positions...all the way down was the best I could get...
to change that..the drive has to come off and the celery sticks changed out to a smaller one or rotated ..(can't remember which..)....I'll try and contact my mechanic to see how he does that...anyway...
my thoughts are that if you change the pitch of the drives you maybe underpropped....which will cause the wot to exceed limits...

try this though next time out...drives down...tabs down 25degs(roughly 1/4 down angle)....from a stop...or moving slowly...hit the throttles to 4k rpm....as you come up on plane...bump the drives up and slowly bump the tabs up...tabs first....then the drives...see how many bumps the drives takes...


SP
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Old 05-24-2011, 01:49 PM   #5
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ok cool, never heard of that but I will try that this weekend.
the prop people tell me that if I go to a 22P, it will increase my rmps at WOT by 400.
The engine specs for the 220Hp I think call for a range of up to 4800 rmp and on the 260 Hp version, 5,000rpm.
I guess at WOT I'd technically be at 5,000 but hopefully would not run at that speed too frequently if I were to go the re-prop route.
Problem is, that may not fix the problem either.
I'll keep you posted on what happenes this weekend when I try your sugestions, thanks, buddy, mike
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