What difference does diameter make?

[southtexas]

Thanks to this forum, I understand what pitch does for performance of a prop. However, I don't know what a change in diameter does to performance?? Anyone care to enlighten me? Thanks

 

[Dhadley]

Re: What difference does diameter make?

It's not simply the diameter but rather what they do with the added blade area or less blade area. Different diameter props are usually meant to do different things. Sometimes more diameter means you can run the prop higher. Basically they change more than simply adding a little material to the blades.

In the "early days" of ss props it was common for props to lose diameter as they gained pitch in the same model of prop. You don't see that too much any more. Today we see the diameter stay the same in a given brand & model of prop. Different models may have very different diameters from the same manufacturer but they are aimed at different markets.

A 14 1/4 x 23 Turbo is not designed to do the same thing as a 14 3/4 x 23 Lightning or a 14 3/8 x 23 SQX or even a 14 1/2 x 23 Vector.

 

[dontask]

Re: What difference does diameter make?

Allot of difference.

 

[Boss Hawg]

Re: What difference does diameter make?

Allot of difference.

Very informitive answer

 

[southtexas]

Re: What difference does diameter make?

OK, here's why I'm asking. I run a 2005 115 four stroke yamaha on a 20' everglades 200cc (flatbottom) with a jack plate. I currently have a 13x15 cupped Power Tech. I want good hole shot and am willing to give up some top end for it.

My rpms can run off the tach, especially when I jack up the motor; therefore, I need a prop with more pitch. I am looking for a 13x17 and was wondering, while I am at it, if 13.25x17 would make a difference. I figured it would, I just don't know what kind of difference??

 

[Dhadley]

Re: What difference does diameter make?

OK, if you are staying with PT then your results may be different than if you go to something like a Stiletto. Stiletto makes 4 stroke specific props and application specific props. PT may do so also.

 

[southtexas]

Re: What difference does diameter make?

I don't have a brand preference (yet), so I'll definitely look at Stiletto props' website. However, I still don't know what a change in diameter will do to me. I've been reading other threads where mention is made of certain props performing better higher on the transom (they seemed to say a smaller diameter performs better as the blade gets higher on the back). Obviously, this is the application I now need since I have added the jack plate.

Does a smaller diameter prop perform better than a larger one the higher on the transom you raise it? I did notice on iboats prop guide that it says changing a diameter up to 1/2" will not make a discernable difference on performance.

Hadley, I also noticed on iboats store that it seems stiletto doesn't offer a 4 blade 17pitch; but they do have an 18pitch. Do you know if stil makes a 4 bl 17p?

 

[junior1113]

Re: What difference does diameter make?

all different brands of props make their props differently to do different things.

dont let this diameter thing mess with you. in most cases were talking 1/4-1/2inch which is 1/8-1/4 difference in blade length

most lessen diameter to add rake, cup, and aggresivenes. which really throws the water it gets a hold of and still keeping it in that pitch range. some keep diameter large to grab more water with little cup ect.

imoa i would run a prop that has characteristics of running close to the surface this will give you the best performace especially with a jack

hope this helps

 

[Dhadley]

Re: What difference does diameter make?

The newest 4 blade props from Stiletto for your motor are in even number pitches starting at 16.

 

[southtexas]

Re: What difference does diameter make?

Well, that figures. To review:

My 13x15 SS 4 blade cupped allows me to WOT over 6000rpm (with engine all the way down). When I jact the motor up, I can spin over 5000rpm but not go more than 15 mph (gps). Motor's suggested range is 5000-6000.

My 13x19 alum 3 blade WOT at 5200.

Do I get the 16 pitch and cup it? Or get the 18 and leave it as is, and hope it won't lug?

 

[southtexas]

Re: What difference does diameter make?

??bump??

 

[junior1113]

Re: What difference does diameter make?

right now you are lugging your motor at 5200 i would want to see 5600-6000

dhadley has it with that 4x16.

turbo makes some awsome props also check them out

you need 4x16 or 3x17

 

[southtexas]

Re: What difference does diameter make?

thanks for all of the advice. sounds like a 4bl 16pitch is the way to go...
appreciate it everyone!

 

[junior1113]

Re: What difference does diameter make?

check back with the new numbers