1987 four winns 245 vista with merc 260

[timw51]

I just got this boat and it had a 14.25 x 15 pitch prop on it and ran at 5000 rpm the motor says Wot should be 4200 to 4600 it runs 29mph according to gps I bought a 15 x 17 pitch prop and it runs 32mph at 5000 rpm I thought my rpms would drop I have an se106 outdrive with 1.47 gearing. Im just trying to figure out what prop I should be running I also tried a 14.5 x 19 pitch prop and it ran 30mph at 3900rpm ? I Dont get it

 

[alldodge]

Re: 1987 four winns 245 vista with merc 260

Welcome aboard

For your speed to drop after increasing your pitch I'm thinking you either have something else going on, bad tach, bad speed-o, engine coupler slip, or incorrect usage of trim and the prop is cavatating.

What are you using for RPM and speed? This is a loaded question, the tech and speed-o on a boat are usually not that accurate.

 

[steelespike]

Re: 1987 four winns 245 vista with merc 260

Something is screwy. slip with the 15 is 39%,the 17 is 41% and the 19 is 33%
A heavy boat will have higher slip but 41% is off the chart.
You have the same rpm with a 2" pitch change and then you lose 1100 rpm with a 2" pitch change .
I suspect your tach.
Could be other than the tach but the tach is easiest to verify.

 

[timw51]

Re: 1987 four winns 245 vista with merc 260

Welcome aboard

For your speed to drop after increasing your pitch I'm thinking you either have something else going on, bad tach, bad speed-o, engine coupler slip, or incorrect usage of trim and the prop is cavatating.

What are you using for RPM and speed? This is a loaded question, the tech and speed-o on a boat are usually not that accurate.

I used the factory gauge for tach and my gps on my phone for speed

 

[timw51]

Re: 1987 four winns 245 vista with merc 260

Something is screwy. slip with the 15 is 39%,the 17 is 41% and the 19 is 33%
A heavy boat will have higher slip but 41% is off the chart.
You have the same rpm with a 2" pitch change and then you lose 1100 rpm with a 2" pitch change .
I suspect your tach.
Could be other than the tach but the tach is easiest to verify.

What difference does the size of prop make the 15 is 14.25 and the 17 is 15 and the 19 is 14.50

 

[steelespike]

Re: 1987 four winns 245 vista with merc 260

I would still suspect your 26 year old tach.You may be able to borrow a shop tach to check the rpm.
Diameter is a secondary consideration Generally as pitch goes up diameter goes down.obviously there are exceptions.
The 15 X 17 might lose a little more rpm than the 150- 200 per inch rule of thumb.Another reason to suspect your tach.
The 19" should act like a 19" Going from a 15 to a 19 would normally lose 600 to 800 rpm.Still another reason to suspect the tach.