Yamaha Prop Questions

[SWAMPFOX]

I have a 40 hp, 1986 Yamaha outboard. I've been running a 10 1/4" x 14G prop. But I have found that this motor will also accommodate a 10 3/8" x 13G prop. ( I don't know what the G stands for).

The top end RPM on the engine is 4500-5500 and I am planing at about 25-30 mph at top speed with the 10 1/4" x 14G prop.

My question is what, if anything, would I gain by switching to the 10 3/8" x 13G prop?

Thanks.

 

[Railroader]

The 14 and 13 are the pitch of the blades, in inches forward per revolution.

With the diameters being so close, the only thing you MIGHT gain is topping out a little closer to max rpm.

This would be because the prop is "loading" the engine a bit less, allowing for higher RPMs.

With the 13, you MIGHT see a small increase in top speed, IF your engine actually spins closer to maximum rpm.

The trade off is, that it will take a touch longer to get out of the hole and onto full plane.

In reality, you probably won't notice any real difference without a GPS, and a tachometer. In most cases, you gotta change at least 2" of pitch for anything really noticable to happen.

You just gotta try it and see...

 

[ribber]

I have a 40 hp, 1986 Yamaha outboard. I've been running a 10 1/4" x 14G prop. But I have found that this motor will also accommodate a 10 3/8" x 13G prop. ( I don't know what the G stands for).

The top end RPM on the engine is 4500-5500 and I am planing at about 25-30 mph at top speed with the 10 1/4" x 14G prop.

My question is what, if anything, would I gain by switching to the 10 3/8" x 13G prop?

Thanks.

Assuming you have the motor on a 15-16 ft boat, you would see very little difference. Lots of variables with props, but going down 1 inch in pitch wouldn't do much on a 40hp. You might jump on plane slightly quicker.
Props won't make huge differences in small to midrange motors (2,3,&4 cyl). Where cup, diameter, pitch, shape, etc. really shine is in the larger V6 and above motors. The faster the prop spins, the more things like pitch and cup make a difference.