Prop diameter question

[jsaylor]

1750 procomp with 1987 mariner 150, terrible hole shot, sometimes can't get on plane, currently using a turbo 14.25 X 22. Mounted on a 6 inch jack plate, WOT is 5000 rpm, at 55 mph. I'm thinking of going down to a 20, does diameter make a difference? also would I improve my hole shot by lowering my engine or raising?
What would you suggest?
Thanks in advance.

 

[jsaylor]

I'm more concerned with the height of the engine

 

[MikDee]

Diameter is usually in proportion to your prop application. Bigger diameter props usually 15" or bigger are used on bigger, heavier boats.

 

[steelespike]

If you check prop sizes you will find that usually as pitch goes up diameter goes down,pitch down diameter goes up.
It would help to know your gear ratio and is your speed by gps?
Assuming a 2.00 gear ratio at 5000 rpm and 13% slip speed would be 45.
It's obvious you are struggling the question... is your 27 year old motor a little tired?
Or is the 22" pitch too much.Perhaps a combination of both.
You do need to varify your tach is accurate or at least get a lightly loaded gps speed.
Hopefully you can find your gear ratio.
Gear ratioo is 1.87 numbers still don't add up

 

[Frank Acampora]

Is your current prop vented?

 

[jsaylor]

My gear ratio according to the manual is 2.00, prop is vented, haven't checked GPS, compression is 120 in all cylinders, Just checked on my jack plate engine sits 5 inches below pad, would raising the engine help?

 

[dazk14]

My gear ratio according to the manual is 2.00, prop is vented, haven't checked GPS, compression is 120 in all cylinders, Just checked on my jack plate engine sits 5 inches below pad, would raising the engine help?

If you are saying that your A/V plate is 5" BELOW the bottom of your boat...

Then raising the engine will certainly improve ALL aspects of your performance.

Can you trim out enough to get the prop to blow out (ventilate)?

 

[jsaylor]

Boat trim is usually tucked down all the way until I'm at around 3k or 30 mph otherwise it will porpoise. As far as my engine height, I measure from the center of my prop to ground, then measure from bottom of boat to ground, then I subtract the difference, 5 inches. I wouldn't have to trim much to blow out.