Prop Question

[agarabaghi]

All things equal (heavily weighted boat).

Would a 15x13 spin higher or lower rpms than a 15x12 prop?

The 15x13 would have a bit more top speed, but the 15x12 would have more torque / hole shot?

[88 PS190]

Its a smidge harder than that.
Imagine the prop isn't in water, its in jello, for one turn the 15x13 prop wants to move forwards 13" the 12" prop wants to move forwards 12".
That means that it is more work to move the 15x13, but the boat may have either a higher top speed or lower RPMs or even lower top speed with lower RPMs just depending on how much power the boat has. Prop designers get to work with more than just the Diameter and the Pitch, the impact of the cup of the blade, the volume of the blade, rake and progressive pitching means that they can work on how a prop does at hole shot and top end somewhat separately. So you should reach out to the manufacturers for specific recommendations in order to get a good outcome.

The example that I use with people is climbing a hill on a fixed gear bicycle. Your boat doesn't get to coast so its constant load in the very same way. You can make it easier to pedal and spin more RPM, you can make it harder to pedal and slow your pedaling down, you can add or remove weight from your system. But if you make it too hard to pedal you'll run out of power, and if you make it too easy to pedal you'll run out of RPM and you can't shift.

[Miss Rita]

Would a 15x13 spin higher or lower rpms than a 15x12 prop? a 13" prop would have lower RPM at WOT

The 15x13 would have a bit more top speed not necessarily, but the 15x12 would have more torque / hole shot? probably

My 13 x 11.5" CNC prop has better holeshot and top speed then the 27 year-old OEM 13x13 cast prop, but CNC props and cast props are two different animals.

The example that I use with people is climbing a hill on a fixed gear bicycle. Your boat doesn't get to coast so its constant load in the very same way. You can make it easier to pedal and spin more RPM, you can make it harder to pedal and slow your pedaling down, you can add or remove weight from your system. But if you make it too hard to pedal you'll run out of power, and if you make it too easy to pedal you'll run out of RPM and you can't shift.

^ I like this analogy.

[Ski-me]

For my 94' LT1, OJ gave me a 13 x 11 LC 1" XMP CNC 3 blade. I have a better hole shot and gained another MPH or two over stock.

This was for my elevation at 6000'.

At 2500' elevation it's a rocket and a blast to drive! Quicker and Faster!

[MC25]

Yes you are correct

[agarabaghi]

lol.

i am not sure its a justifiable cost for $550

[Ski-me]

It does help...just a big price to take for sure!