Need prop advice

[haskindm]

I have a 2005 Grady White 18' Center console (180 Sportsman) equipped with a 115 HP Yamaha 4-stroke. I am getting mixed messages on the prop. It is equipped with a 13X17 3-blade stainless prop. It will reach the recommended 6000 RPM WOT with a top speed just shy of 40 mph. Top speed is more than sufficient. The problem is that it struggles to get on plane, especially with 3 or more people on board. I talked to the factory and their response was that the boat really should have a 150 HP motor, in fact they no longer offer it with the 115. Thanks, but I am not ready to trade in a 3-year old motor.
I have been told that a 4-blade prop may help, but others say that a 4-blade has little effect on a boat less than 22 feet long.
I have been told that if I go to a 4-blade that I should keep the same pitch.
Others say that I should drop the pitch 2 inches (from 17 to 15" in my case).
One seller says that they will let me try the prop and if I have to exchange it for a different pitch, they will do so for $40 plus shipping.
There must be a more scientific way to determine if this is a good move than just experimenting with $300 to $400 props. My fear is that I spend $400 for new prop, find that the RPM is in the right range (or maybe exchange it once or twice to get in the right range, sending another $100 or so), but find little or no improvement in performance.
Any advice will be appreciated.

 

[haskindm]

Re: Need prop advice

bump

 

[K.P.]

Re: Need prop advice

Since you are already hitting Max RPM with the 17 pitch but your hole shot is suffering, reducing pitch for better hole shot may cause you to over rev the motor if you got to careless on the throttle.

Looking from the rear of the boat at the top portion of the motor mount, is your motor currently mounted all the way down on the transome or is it raised a couple bolt holes? With that poor of hole shot I'm assuming it is mounted all the way down. Raising the motor one or two holes should get you better hole shot, a little better top speed, and maybe only over rev the motor by 100 RPM. It would also help with any RPM reduction caused by a 4 blade prop.

Your boat may be a perfect candidate for a 4 blade. I am not familiar with any size restriction associated with them. They tend to help with hole shot as long as your RPM's are already in the upper end of the WOT range. However you may loose a little MPH.