wrong pitch on inboard = ?

[tgissel]

I recently purchased another boat. It was bought on a different lake and driven by water to the lake where I dock. My question is the boat is supposed to have a 14 x 9 three blade prop on it, but it has a 13 x 12 prop instead. There is no working tachometer on board I noticed no ill affects from the prop on it the four barrell opens correctly and the boat got fairly good gas mileage at cruise speed. Am I not pulling full RPM's? or over revving the engine.

Thanks, Thad

 

[Don S]

Re: wrong pitch on inboard = ?

There is no working tachometer on board

Am I not pulling full RPM's?

Who knows if you are pulling full rpm's or not. No one here with a working crystal ball.
Get a tach and find out.

 

[oops!]

Re: wrong pitch on inboard = ?

ditto.....a tach is a must have.......without it ....your guessing

 

[tgissel]

Re: wrong pitch on inboard = ?

Yeah I understand all the benefits of a working tach, I was asking what the difference between a 12" pitch versus the 9" pitch stated in the question, does it effect how many RPMs the engine will produce and in which way?

Thanks

 

[Don S]

Re: wrong pitch on inboard = ?

Moving to the prop forum.

 

[Haut Medoc]

Re: wrong pitch on inboard = ?

The lower the pitch # the more rpm's......
IE>, the 9"pitch will give higher rpm than the 12....
Better hole shot, less top end.....​

 

[tgissel]

Re: wrong pitch on inboard = ?

If I changed over to the 9" pitch is that going to improve the gph/mpg?
Thanks, Thad

 

[beanstyle]

Re: wrong pitch on inboard = ?

you definately need to get a tach, but if you had a 14x9 three blade and a 13x12 three blade with the same blade area, they are almost interchangeble as far as engine rpm's are concerned. efficency and speed though are going to be different

 

[tgissel]

Re: wrong pitch on inboard = ?

I understand about the tachometer, the boat is an older project cabin cruiser I just bought and drove roughly 50 miles by water w/ my other cruiser as tow just in case. The new project boat has a 302 w/ 1:1 velvet while my previous has a 318 w/ a 1:1 trans also. They both performed very well, the mileage is better on the 318 but it has a 1 foot wider beam and two foot longer, the 318 also had better holeshot. Both boats are supposed to have the same prop 14 x 9 3 blade cupped. Same manufacturer, 318 is 1200 lbs. heavier @ 7000, aluminum hulled Marinettes

Here are pics of the two
http://i25.tinypic.com/29lju5t.jpg project 302
http://i26.tinypic.com/2mpgd3t.jpg 318 chrysler

 

[beanstyle]

Re: wrong pitch on inboard = ?

could be your new boat needs a tune-up if your other boat with more horsepower and LWL gets better hole-shot and fuel efficency. but thats why it's a project
my thoughts are that you should try having everything running smothly before trying to adjust the prop around, might save you from having to change props again. also, try having the prop size calculated (once you get a tach) to know the correct size needed. and the prop tuned to ISO specs. but again these are things that have the best effects on a perfectly operating engine