is diameter a big deal?

[rhuntbach]

I want a better hole shot so I'm considering switching to a 4 blade prop. I currently run a 15.25X15 3 blade aluminum (which puts me in the right wot rpm range) and I'm thinking I'll switch to a 14.8X15 4 blade aluminum.

My question is, what will reducing my diameter by .45" do to my performance? I've heard that larger diameter=higher efficiency, so I'm a little nervous about reducing my diameter. Should I be concerned?


As background. My boat is a 1977 Glastron SSV-189, with 250 ci straight 6 that puts out 165 hp and about 260 foot pounds of torque.

Thanks in advance!

 

[steelespike]

Re: is diameter a big deal?

Generally diameter isn't considered when selecting a prop except to be sure it physically will fit.If a prop is intended for your application the diameter will follow.

 

[180Fisherman]

Re: is diameter a big deal?

I would think a larger prop would push more water at any given rpm

 

[dazk14]

Re: is diameter a big deal?

Regarding the original post...

Your kind of comparing apples to oranges.

The 3 blade has a bigger diameter, but the 4 blade will have more total blade area and that will often pull down rpm's 150/200. That's why most people drop an inch of pitch to keep rpm's equivalent.

If you compared nearly identical 3 blade props with an inch difference in diameter, there will be ~400 rpm difference (Lower rpm's for larger diameter).

Since we don't know the 2 different props you speak of, and don't know where your rpm's stand at this point - there isn't much more to say.

 

[Tail_Gunner]

Re: is diameter a big deal?

Always remeber to keep the diameter of the prop the same as the outdrives....If the prop does not align with the drive you will create a disturbance in water flow...very undesirable...I doubt very much if diameter has any other effect on a boat prop that is...