Propellers

[Dave Blaber]

Hi , I have a 60hp yamaha 4stroke high thrust 2007, it has a 13 1/2 X 15-K prop, I am looking for more speed with lower rpm, I want to purchase Stiletto s/steel props, do I get 13 1/4 X 15 or 13 1/4 X 17 ?

[rodbolt17]

you get the one that allows that motor to turn 5800-6000 RPM WITH THAT DAYS LOAD.
one day I need to post some pics of a 4yr old F150 with 3 detonated pistons.
we propped it at 5900 RPM with 2 people and a tank of fuel on a 24 Carolina skiff.
when it came back blown up and out of warrenty it had seating for 16 and a ski pole.
was still running the same prop.

if the engine had a knock sensor we may have caught it before the customer destroyed the powerhead.

overpropping can and will destroy a powerhead.
does not matter that it was propped for 2 people a small cooler and the dog.
once you add a few more coolers and 6 more people its now most likely over propped.

[boscoe99]

You don't select a propeller to get more speed. You select a propeller to meet an objective. That objective being that the motor can reach at or near its red line RPM, when the throttle is wide open, with the engine trimmed to the most efficient trim angle, with the boat loaded. As Rodbolt notes, 5800 - 6000 in your case.

If you are operating lightly loaded, on a cold day, running down wind in a 30 mph breeze, and the motor will go over 6000 RPM then it is your job to back out of the throttle. Most users are not going to have three, four, maybe five different propellers to change around depending upon load in the boat and ambient operation conditions. So, you go with what gives optimum all around performance and which enhances the life of the motor.

If you want more speed you need more horse power. Not a different propeller.

As noted, being over propped is lugging the motor. Lugging can and will kill it. Being properly propped, or slightly under propped won't hurt a thing.

But if you are willing to trade some life of the motor for maybe a mile or two an hour of more top end speed, then you can do that.

[boscoe99]

you get the one that allows that motor to turn 5800-6000 RPM WITH THAT DAYS LOAD.
one day I need to post some pics of a 4yr old F150 with 3 detonated pistons.
we propped it at 5900 RPM with 2 people and a tank of fuel on a 24 Carolina skiff.
when it came back blown up and out of warrenty it had seating for 16 and a ski pole.
was still running the same prop.

if the engine had a knock sensor we may have caught it before the customer destroyed the powerhead.

overpropping can and will destroy a powerhead.
does not matter that it was propped for 2 people a small cooler and the dog.
once you add a few more coolers and 6 more people its now most likely over propped.

I wish you would post those photos please. I am in a bit of a debate at a bass boating forum where folks are refusing to believe detonation damage. I need some evidence to convince them. Photos of blown F150 pistons (usually number two and three) will do the trick.