Lets say a boat with a 1.5 geared bravo was switched to a 1.36 ratio AND the correct pitch prop to obtain the same output.

Will the engine have to work harder with a 1.36 ratio to achieve the same results as the 1.5 ratio?

Thanks

not if the prop is changed to achieve the same speed at same rpm, which may not be possible

50mph at 4000 rpm is still 50mph at 4000rpm regardless of ratio to achieve that.

Unless prop slip changes.

Would there be more resistance on the smaller prop having to turn more rpm to achieve the same output?

I am not saying you are wrong. I am just trying to get all sides. I have been hearing conflicting theories.

I understand what everyone is posting and that it should be the same.
However, most people I know would rather have the lower gear ratio which multiplies your torque.
Also there is some advantage to turning the props faster as far as lift goes.

Also think of it lt like a screw with fine vs course pitch, a course pitch screw will take more HP to turn thru the water then a finer pitch spinning faster.

Atleast thats how I was told and makes sense in my head.

How does spinning the props faster affect lift? Would it increase stern lift?

I am asking because I am looking at a boat with 1.24 drives and it needs as much stern lift as possible.

BTW, Mercury only recommends gear changes when there are no available prop pitches left.

To me, it seems more efficient to turn a more aggressive pitch propeller slower to achieve the same speed.

This was my original understanding but it seems there are differing views. I have never tested it but will be shopping next season and I see there are many different power/drive combos out there.

This is what I have been told as well. However, I have heard that higher pitched props can be less efficient.

I bet if you asked 10 "prop experts", 5 would say one answer and 5 would say the other.