25hp on 15ft aluminum prop

[tomwsk]

Current setup
3 blade 10x13 aluminum prop, looks worn out a bit
Wide open throttle RPM 5400 at 21mph with 2 adults+tackle fuel should be about 400lb
2010 tracker pro guide v15 sc weighing 780 Lbs. with a 1997 25hp 3-cyl Evinrude 160lb?
total weight is about 1340lb. I realize that this is pretty heavy, but right now I cannot afford a larger engine. I am happy with 21mph.

The current prop is an aluminum prop, looks a bit worn out. I'm also looking at going camping with the family couple of times a year, loading the boat up with gear. Majority of the other time would be spent with 2 adults onboard fishing.
I'm essentially looking for a spare prop that I will switch for heavy loads. Is 4 blade a better choice for this application?

thanks.

 

[steelespike]

Re: 25hp on 15ft aluminum prop

Your slip seems to be really high at about 29%. I wonder if the prop is really bad or the tach is reading high.
Speed seems reasonable for the weight.I would like to see the wot rpm and speed lightly loaded.
A 13" prop seems a little on the high side for the weight.
I think a Solas Amita 4 blade in 11" should work well.May be a little light for light loads you may have to watch the rpm.

 

[tomwsk]

Re: 25hp on 15ft aluminum prop

I should have mentioned that the measured speed was not on calm water, maybe 2 foot waves. I'll repost results on smooth water and light load.

 

[tomwsk]

Re: 25hp on 15ft aluminum prop

Tried lightly loaded boat, it only went up to 23mph at about 5400rpm or so.

 

[tomwsk]

Re: 25hp on 15ft aluminum prop

2 adults, 2 kids with Solas Amita 4 blade in 11"
Got to about 20mph at 5250 rpm. Haven't got a chance to try it lightly loaded with that prop.

 

[steelespike]

Re: 25hp on 15ft aluminum prop

It seems that 13 really must have been worn.While the 4 blade could lose about 100 rpm, going to an 11" woiuld usually add 300 to 400 rpm.Expecting about 5600 rpm result.

 

[steelespike]

Re: 25hp on 15ft aluminum prop

It seems that 13 really must have been worn.While the 4 blade could lose about 100 rpm, going to an 11" would usually add 300 to 400 rpm.Expecting about 5600 rpm result.Assuming a 2.23 gear ratio 5600 with an 11", 18% slip (still high)= about 21 mph.
Your hole shot must have been better?Did you play with the trim. Is the antivent plate(just above the prop) about even with the bottom
of the transom.

 

[tomwsk]

Re: 25hp on 15ft aluminum prop

It seems that 13 really must have been worn.While the 4 blade could lose about 100 rpm, going to an 11" would usually add 300 to 400 rpm.Expecting about 5600 rpm result.Assuming a 2.23 gear ratio 5600 with an 11", 18% slip (still high)= about 21 mph.
Your hole shot must have been better?Did you play with the trim. Is the antivent plate(just above the prop) about even with the bottom
of the transom.

Yes, the hole shot was better. The antivent plate is about even, maybe 1/2" lower than the bottom of the transom. Next time I'm out I'll play with the trim a bit.