Questions on what prop

[Redrig]

Hello, I have some general questions about what prop to use. It is my understanding that elevation has a big impact on your prop and I want to make sure that I am using the best prop for my upcoming trip.

1) Performance issue you are trying to correct.
I want to gain Max MPG,
I usually go to Lake Powell in which I can be 20-30 miles from the marina so max fuel economy would be great.

2) Current prop manufacturer, model, aluminum or stainless as a minimum.
OMC is manufacturor. I have several different pitches 14 - 18, all aluminum I beleive.

3) Current prop diameter and pitch (required).
14 x 14 through 14 x 18

4) Wide open throttle RPM and speed with an average load (very helpful)
I have some questions here, I do not know the WOT. or what RPM I should be shooting for, I have always just got the boat on plane and used the least amount of RPM to stay on plane (which is usually about 2800 RPM) Is that not the correct way ?

5) Engine/drive make, model, year, and HP
1977 OMC sterndrive electric shift with a ford 302 - 175 HP

6) Boat make model, year, length and weight
1977 Bell Boy 18 footer no idea on the seight, sorry.

I got this boat form my grandpa and he has several props with it, he usually went to mountain lakes elevation of 6000 to 7000 feet above sea level. I usually take this to lake powell which is 4000. I usually have a decent load in the boat 2-4 people with enough gear to camp for a week.

any thoughts on what prop I should be running ? and what the ideal range for RPMS are for my boat.

 

[Leardriver]

Re: Questions on what prop

I always use a wildly inaccurate rule of thumb of one inch of pitch per thousand feet of altitude.

If a boat ran great at sea level with a 21 pitch, then a 19 pitch at 2,000 feet, 17 at 4,000 feet, and 15 at 6,000 feet. That has always worked for a starting point.

So, for a hot 3660 lake elevation at Powell, 4 inches less than sea level. Maybe 3 inches less if you aren't pulling slalom skiers and are looking for max fuel economy.

 

[Redrig]

Re: Questions on what prop

I always use a wildly inaccurate rule of thumb of one inch of pitch per thousand feet of altitude.

If a boat ran great at sea level with a 21 pitch, then a 19 pitch at 2,000 feet, 17 at 4,000 feet, and 15 at 6,000 feet. That has always worked for a starting point.

So, for a hot 3660 lake elevation at Powell, 4 inches less than sea level. Maybe 3 inches less if you aren't pulling slalom skiers and are looking for max fuel economy.

Lear, thank you for the repsonse.

That makes alot of sense now, the first year I had the baot I used a 14 at Powell and my economy stunk, last time I tried a 17 and that seemed to help alot.

If my boat is loaded though with gear an people , would a 16 make sense ?

 

[Leardriver]

Re: Questions on what prop

A 16 would probably be right if around 20 was good at sea level. You want to be able to hit your recommended RPM range in order to have the best combination of hole shot and top end, and the fuel economy sort of is what it is.