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GEAR BOX

B

becktc2004

Well-known member
I RUN A 2.68 GEAR BOX AND A NEW 3 BLADE SEN.SUPERWIDE.THE PROP IS SET AT A 3 ON THE BLADES AND I'M TURNING 5000 MAX RPM.HERE IS THE QUESTION THIS WK END I PASS A FRIEND WHO SAID MY BOAT WAS MAKING A CHOP SOUND LIKE A HELICOPTER.IS THIS THE CAVITATING I READ ABOUT OR NORMAL.SHOULD I DROP BACK TO A 2.38 AND LESS PITCH?BBC ABOUT 600 HP.18' BOAT.
 
I heard a three-blade powershift sound like that once and it turned out one blade had more pitch than the other two. I have heard that the marks on some Sensenich blades aren't all the same so maybe that could be the case with you too?
 
YOUR ONLY TURNING 5,000 rpms MAX TAKE A TAD OF PITCH OUT IT WILL RUN A LITTLE BETTER ALSO IF YOU GO TO 2.38 YOU WILL NOT BE ABLE TO SWING THAT MUCH PITCH. How does the boat run????????
 
You need 2 C-clamps --a carpenters square and a ruler.. Bring your blade down so you can clamp the carpenters square to the transom close to the prop -- Leaving room so you can turn the prop.. now measure from the tip of the square to the TRAILING EDGE OF YOUR PROP --- write it down and move to the next blade and do the same... If their is more than 1/16" difference you could get vibration at a short RPM range (say 1000 to 14000 rpm) or the whopping sound... Also make sure all of the hub bolts are torque exactly the same in the cross check method..
 
Thanks for the reply.The boat runs about 40mph top.I will try and check the pitch like
Ron said this wkend and get back with you.I had it on about 2.5 and it run slower seems to run good at current setting just have the wopping sound.
 
Finally got around to check the pitch of my prop with a gauge. Only one blade was off by less than one degree so I did not ajust them.So I dont know where the noise is coming from?
 
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