Help with prop question please

[emilime75]

OK. We have a 2003 Crest 22' Family DL pontoon boat with a 2003 Suzuki DF60 outboard. We have 2 props...

Prop (A) is 3 blade aluminum 13.75 in diameter with a 15 pitch. It does have a chip in one of the blades, about .25 by 1 inch in size, roughly. With this prop the engine RPM maxes out at 4600 with a GPS confirmed 16mph top speed.

Prop (B) is also a 3 blade aluminum prop but it has no markings as to diameter and pitch. With this prop, the max rpm reached at wot is 4400 with a top speed of about the same, 15 to 17 mph with a similar weight load.

According to the engine's manual, the top operating range for this motor should be 4700-5300 rpm.

Can anyone suggest a properly sized/pitched prop for this configuration with the info provided? We'd like to stick with aluminum due to cost. Thanks.

 

[steelespike]

Re: Help with prop question please

It appears you need about 700 rpm And based on your gear ratio a 15 does seem high thus your low rpm. A Solas Amita 4 blade in 11" pitch should do well.
A 4" pitch change could net about 800 rpm but I think the 4 blade will result in slightly less.
The 4 blade will be less likely to vent(cavitate) and should handle better at the dock.

 

[emilime75]

Re: Help with prop question please

Hey steelespike, please excuse my ignorance here but I am a bit confused by your reply. I understand you're suggesting a 4 blade prop, but I'm not sure what you're suggesting as far as diameter and pitch are concerned.

 

[craze1cars]

Re: Help with prop question please

I'm certain he just misspoke when he recommended a 11" diameter 4 blade.

He meant to say 11" pitch. Diameter will be whatever the prop happens to be...

 

[steelespike]

Re: Help with prop question please

Boy I guess i had a brain fart. See what happens when you don't proof read.
Sorry for any confusion.

 

[emilime75]

Re: Help with prop question please

OK, so a 4 blade prop with an 11p. How does the diameter thing work, are you guys saying the diameter doesn't matter?
I always thought diameter and pitch were both important, but this statement from craze1cars "Diameter will be whatever the prop happens to be..." has me thinking now that it might not matter as much.
It looks like finding a 4 blade prop in my area will be difficult, if I had to go with a 3 blade, what size and pitch would you guys recommend then?
Thanks.

 

[steelespike]

Re: Help with prop question please

Diameter is a function of the design different manufacturers might have slightly different diameters
for the same prop application.Generally as pitch increases diameter decreases and viceversa.
A 4 blade would be worth the struggle in my opinion. Solas makes a good prop that has an excellent record for predictable results.