New to this.....does this sound right??

[V4 Johnson]

I got to take my first boat out for the first time over the weekend. I think the prop setup seems right. But I guess I'm looking for a second (or more) opinion.

Boat: Four Winns Marquise 170
1170 lbs
220 lbs for the driver
315 lbs motor
+/- 25 gal fuel (not sure of capacity)
<100 lbs gear

Motor: 1984 Johnson 115 (+.030" with fresh rebuild)
13 1/4"x17 3-blade aluminum prop

At WOT the RPM's are 5500-5550 and speedo (GPS) at 40-41 mph. Trimming experiments only netted, at most, +/- 1/2 mph and really no change in RPM until the prop started to blow out.

The rig seemed to work very well. But, really, what do I know?? :redface:
Does this all sound right or wrong??

 

[cribber]

Re: New to this.....does this sound right??

Do you know what the gear ratio is? With that you can use a prop calculator to see where you are and what pitch adjustments will likely do for your setup. You may be in the sweet spot with what ya got.

 

[V4 Johnson]

Re: New to this.....does this sound right??

Do you know what the gear ratio is?

I do not.

I didn't get any kind of manuals for either the boat or the motor. So I'm pretty well lost as far as any of the specs go.

 

[bruce40]

Re: New to this.....does this sound right??

V-4,
My 115 Rude manual says "optimum rpm range 5500-5600" Id say your good to go.

 

[hwsiii]

Re: New to this.....does this sound right??

V4, If my information on your motor is correct, I show a maximum RPM range of between 4,500 and 5,500 RPM and a gear ratio of 2:1, please verify this. If this is correct then your prop slip is at 10% right now, and that is very good. One thing that might increase your speed a little bit would be if your motor could be raised a little higher on the transom, but you are in very good shape at this time, in my opinion.

You might try reading this for a better understanding of changing props for better performance, and for the major differences between aluminum props and stainless steel.

http://forums.iboats.com/showthread.php?t=369057



H