Prop Pitch Again

[Jon Thunda]

Sorry for the a repeat on this subject but, I'm not understanding prop pitch. I have a 35 hp Johnson with a four bladed adjustable pitch prop. The prop is "plastic"... how do you determine the pitch? The prop has positive and negative signs on the outside hub. What does this mean? Is positive more? And if it is what is the relative outcome?

.... more pitch does what and less does what?

Sorry for being a pain but I just don't get it.

 

[steelespike]

Re: Prop Pitch Again

Sorry for the a repeat on this subject but, I'm not understanding prop pitch. I have a 35 hp Johnson with a four bladed adjustable pitch prop. The prop is "plastic"... how do you determine the pitch? The prop has positive and negative signs on the outside hub. What does this mean? Is positive more? And if it is what is the relative outcome?

.... more pitch does what and less does what?

Sorry for being a pain but I just don't get it.

You should post in your original listing it is on page 2 and will come to the top when you post.I explained the effect of pitch change in the other listing.
I would assume the + on your prop is an increase in pitch and - is less.You shouldn't be changing pitch without a tach to follow your rpm changes.Extended operation outside the reccomended rpm range can lead to premature death of your motor.A tiny tach is an easy install and reasonable price.Have you attempted to solve the planing issue by trimming the motor in(prop closer to boat)possibly moving some weight forward? Are there any other markings on the prop perhaps indicating pitch range. perhaps 15/21 or similar?Perhaps markings indicating the pitch at each position.
Selecting the pitch is like trying to select a single gear on a car to do all things.low(low pitch number) gives excellent hole shot but not much speed high (high pitch number)gives good speed but poor hole shot.A prop is a comprimise for best hole shot and speed while staying within rpm range.
Sometimes you need to change to a prop specifically selected for skiing etc.
And you may have to be careful to operate within rpm range.

 

[MikDee]

Re: Prop Pitch Again

Steel is right, and has given you a lot of info. I just want to add this, the proper motor angle to start with, is to set your motor so that the cavitation plate (just above the prop) is paralell (flat) with the boat bottom, using a straight edge.

Next onto the prop, at the maximum + setting, this should be the most pitch, a lot of forward angle of the blades. Mostly good for speed, not power, less rpm = A bit like overdrive gear in a car.

Then at the maximum - setting this should be the least pitch, just a little forward angle of the blades. Mostly good for power not speed, most rpm
= A bit like being in 1st gear in a car.

You have to determine the happy medium setting for your boat, without overrevving the motor.