Talking about 2 applications
1 Arnesons drives with 1.1 or a 1.5 gear ratio

Or Mercury #6 drive with 1.2 or 1.5 gear ratio

What is the difference you will experience with a smaller 1.1 ratio compared to a 1.5

The 1.5 should have higher top end speed right?

The drive ratio is only half the equation. You need a prop to finish it.

1:1 vs 1.5:1 is about like the difference in a 2-3 or 3-4 shift in a 4 speed transmission. You need to know what prop your will need with either drive ratio to determine availability. That will drive the gear choice. I am guessing many more options with a 1.5 gear.

I saw one drive I dont remember which one but it said it was a 1.1 also but it was a diesel drive.This 1.1 means the boat turns the propeller about one time for each revolution of the drive shaft right, and a 1.5 would turn it 1.5 times for the same revolution.So it seems like the 1.5 would be faster but maybe the way to work around that is to put a bigger propeller
Yes? Thoughts anyone?

A larger num gear ratio turns the prop slower which requires a larger prop given same engine ....other words you turn a larger prop slower.
A smaller num gear turns the prop faster which requires a smaller prop given same engine...other words you turn a smaller prop faster.


A diesel motor itself turns less rpm than a gas motor....this pretty much instantly determines using a lower num gear ratio than a gas motor so you can try to turn same size prop at same propshaft rpm as the gas motor,,,assuming you have enough torque to do so.

Other side of spectrum, a small V6 gas engine will use a higher num gear ratio to swing a bigger prop than it would with a typical gear ratio which if used would result in too small of a prop to really do much.


I'm not a good typer of thoughts....but that will give you the basics.

A certain size prop (pitch + diameter +...) will be best for your boat for a desired speed....you need to match the right motor with the right gearing for that.....have fun

turbos230 clear your PMs. I tried to answer your questions but your box is full.

Mercury only recommends changing gear ratio when there is no more available prop pitch. You can run a 1.35 ratio with a 32 pitch or a 1.5 ratio with a 36 pitch and they will run about the same.

he is talking large power and large props. at the bravo diameters it is one thing, but when you are talking 20 to 30 inch diameter props, prop rpm to boat speed is a bigger factor. that is why you see arnies with ratios from 1 to 1 up to 1.5 to 1 some with 1,1, 1,2, 1,3 options in between. I don't know the math, I only know each prop is worth more than any 1 of my boats...