What size prop please help?

[bass1130]

I have a 1985 Champion 18 6 , with 150, that tops out at 4300 rpm. What size prop do I need, please help.

 

[dan02gt]

Re: What size prop please help?

What 150 do you have? I ask because the gear ratio matters when selecting a prop. If is a Mercury with the 1.87 ratio you would want something in the 21P range.

 

[steelespike]

Re: What size prop please help?

What is the prop size?(probably under the prop nut)wot gps speed at 4300? Its not unusual for a tach to not be accurate
or for that matter the speedo as well.Some cells have a gps app.

 

[bass1130]

Re: What size prop please help?

150 evinrude, 4300 rpm at 51 mph on GPS.

 

[bass1130]

Re: What size prop please help?

It's a 14 1/2 * 23 prop.

 

[steelespike]

Re: What size prop please help?

Ok, you can't go 51 @ 4300.
With 10% slip rpm would be about 4800.Motor is rated for 4500-5500 so while not ideal 4800 is acceptable.
If you want more pep a 21" should work well and put you at about 5100-5200.
You really should confirm if the tach is indeed off 500 rpm low.

 

[jestor68]

Re: What size prop please help?

How long have owned the boat? It's a 1985; what is the state of the motor? The kind of prop?

What is your pad to prop shaft measurement? A good starting point is 3.5 inches below the pad. A jack plate makes it easy to adjust.

The prop selector calls for a 23 pitch prop(1.86 ratio), and says it should be able to spin it to about 5000 rpm @ 55 mph( 7% slip).

Sounds like issue(s) with the motor(power is down), the set up, , the wrong prop type, or last but not least, the tach is wrong.