Prop id

[MEI]

I am attempting to find my prop pitchto look at improving performance. 90hp yamaha 2 stroke on a 21 ft pontoon boat.
the numbers on the side of the prop dont make sense to me. I bought this boat from someone else.

one side of the prop has numbers 6591
other side has 8843.
neither number would indicate pitch or size of the prop.
any ideas?
thanks.

 

[racerone]

Often times a prop repair shop will stamp the repair invoice # on a prop.------Do they look neat and factory stamped ?

 

[jimmbo]

In what way are you trying to improve Performance?
How long have you owned it?
What RPMs are you getting at WOT with the current Prop?
Do you know what your engines WOT RPM range is?

The Diameter and Pitch are somewhere on the prop, often on the inner hub where the prop nut is, or on the Outer Hub, or on one of the blades

 

[QBhoy]

On some Yamaha props like the k series, the diameter and pitch numbers are stamped on the inner hub casting. Not on the side.

 

[MEI]

In what way are you trying to improve Performance?
How long have you owned it?
What RPMs are you getting at WOT with the current Prop?
Do you know what your engines WOT RPM range is?

The Diameter and Pitch are somewhere on the prop, often on the inner hub where the prop nut is, or on the Outer Hub, or on one of the blades

Trying to keep a long story short. WOT is 6k which is a little high for this motor. The manual says 4500 to 5500 wot operating range.

Ultimately what I a trying to solve for is to tow a 2 person tube and get them outside the wake. Last season I could not do it. Tows fine but tube stays right behind the boat.
I am thinking a little more top end speed might help. It runs at 18mph top end. When i tried the yamaha prop selector it asked for existing pitch. The hub has some corrosion so not able to read anything. All I can find are the stamped numbers mentioned above.
boat is a 2001 21 foot odessy pontoon with a 90hp Yamaha 2 stroke.
other solution could be installing a tow bar to get the rope up higher. Currently have the harness attached to the rear of the pontoons.

 

[MEI]

Often times a prop repair shop will stamp the repair invoice # on a prop.------Do they look neat and factory stamped ?

Yes they are stamped.

 

[racerone]

I do not believe those have anything to do with identifying the prop !

 

[jimmbo]

If the prop has been rebuilt, and the Numbers support that theory, then maybe the repainting covered up the numbers.Check it over very closely. off of the engine if not so already. A prop rebuilder might have a Pitch Block, that might be a way to figure out what Pitch it is

 

[QBhoy]

Not sure if you saw my earlier post ? The numbers are on the inner hub casting on OEM Yamaha props, usually.

 

[MEI]

Not sure if you saw my earlier post ? The numbers are on the inner hub casting on OEM Yamaha props, usually.

Yes. Will need to remove the prop and clean of that area. Too much corrosion/ build up currently to see anything. Thank you.

 

[MEI]

Finally had the time to dig into this. The size and pitch were on the inside of the hub (towards the outdrive) so had to remove the prop to see it. Current prop is 13-5/8 x 13. Yamaha prop selector suggests a range of 13.5 x 15 to 14 x 16.

 

[MEI]

Ok. So I purchased 13.5 x 15 pitch prop. Installed it this weekend. RPM maxed out at 5000 which is more in line with what the manual says.
I thought the top end speed would improve but it's the same at 17-18 mph. Speedometer is not working so have been measuring using a gps app on my phone.
Should I have expected a speed increase?