Prop Swap

[ohana34]

Just splashed "Ohana" after new bottom job, new packing, wax, exc.
Also changed the prop.  Had 15x10 two blade, put on 15x9 three blade.
Now have less speed at same RPM but can turn up higher and get more speed than before. Engine runs smoother and has less walk in reverse, but I was looking for more motoring speed.  Tack shows 4000+ at full boar and 7knots on the GPS in slack water. Have calibrated the tach but realize it is still off, as idle is 1100.  
So, all this being said, think I'm turning around 3700 RPM at around 7knots but around 2800 I'm down to 5 or 5.4.
I'm looking for 6 or 6.4 at around 2800 is this unrealistic???
Boat is Mark 1 1991 Wing, with XP25. and fresh bottom.
Should I change the pitch of the 3 blade to 10?? Go back to the 2 blade or buy a new prop altogether??
Note: weight according to travel lift at splash 17000 lbs.
Help
JIm

[Ed Shankle]

Jim,
Yes you should repitch to 10. That's been the recommendation from the experts on the message board. I've got the 3 blade pitched at 10 and at the beginning of the season will get 6 kts at @ 2800 rpm. Once the bottom gets soft slimed I lose a half knot or more.

Ed

[Ron Hill]

Jim : If your new 3 bladed is a "Sailor" style prop repitch up to 10 inches.  You might also check the dip switch settings in the back of your tac.  
If you went to an alternator with a different pulley than the Motorola OEM alternator you'll need to recalculate which dip switch settings to use.
Look in the Mainsheet tech notes in your CD (or on line) - I wrote 2 articles on this very topic.