prop pitch vs gearing?

[Mac525]

Just wondering why the other thread was closed????
Any how the other big consideration is cavitation of the blades and blade tip speed, which will affect what gearing will work best. These factors might be why the one test with the two lower units resulted in a better option with the lower gearing higher pitch ie the prop is turning slower and being more effective

 

[Robbabob]

Re: prop pitch vs gearing?

Mac,

Not sure what you're getting at here.. obvious a different thread was closed, so I will only answer what I'm reading here.

Seems to me, you only change the gearing when a pitch change necessary exceeds practical application. This is typically found when over or under powering a boat; meaning, a motor change where HP rating is too high or lower than needed.

If this has to do with the vibration at 2/3 throttle and lack of additional speed or RPM, then I can't help... sorry.

Good luck!

 

[craze1cars]

Re: prop pitch vs gearing?

Just wondering why the other thread was closed????

Because the thread was created and discussed back in 2007...4 years old...and then was suddenly stirred back up from the dead yesterday. So the assumption here in 2011 is that the original poster is no longer monitoring a 4 year old discussion, and has likely had his/her question answered by now...

The moderators on this particular forum frown on bumping old topics, though it seems to be common practice on most other forums. But here on iboats the powers-that-be seem to prefer people start brand new threads instead of bumping up the antique ones...

 

[Mac525]

Re: prop pitch vs gearing?

sorry rob Im not going to re type the whole thing but the gest of it was some guys had tested a 1.80 with and 17p and a 2.0 with a 19p and found even thought they come out the same in the math that the 2.0 - 19p produced a better top speed and better mpg at cruise then some disscusion on why they make different gearing and why these test numbers came out the way the did. Thats where I come in on this thread basiclly lol

 

[Robbabob]

Re: prop pitch vs gearing?

sorry rob Im not going to re type the whole thing but the gest of it was some guys had tested a 1.80 with and 17p and a 2.0 with a 19p and found even thought they come out the same in the math that the 2.0 - 19p produced a better top speed and better mpg at cruise then some disscusion on why they make different gearing and why these test numbers came out the way the did. Thats where I come in on this thread basiclly lol

Yeah, I hunted it down. Moderator says to start a new thread if you want a discussion on it.

By the way, playing with gears is like playing with pitch. The ultimate goal is to have the engine near top rmp at wot (this you already know). Only time you typically change gears is when a re-power takes place and the necessary pitch is not available. Else, it's all the same to the engine... bottom line it's prop rotation/resistance keeping the motor at/near it's max rating at wot.

Now, to fend off anyone that is a math expert or performance boat person: my comments are the for casual boater to not worry about it. You TOP GEAR people know there could be a lot more to do with it than my simplification! :facepalm:

Not sure of the worth if you want to post a theoretical question/topic.

Enjoy!