Prop advice - 17' crestliner with 130 HP

[Frayed_Knot]

Greetings,
I am looking for advice on a prop purchase. I have a dinged up prop that I would like to replace and want to make sure I am purchasing the correct prop for replacement. Also, the top end speed with the current set up seems low compared to others with the same boat and smaller motor so I am wondering if the current prop is even the best option. I tried to answer all of the questions from the sticky thread for background info. Any suggestions would be appreciated. Thanks in advance.

Performance issue you are trying to correct.
Replace damaged prop. Also wondering if I have the correct prop on the boat from when it was purchased. The current top end at WOT seems slow for what I expected so I am wondering if its has best prop or not. I won’t be running at wide open but would like the boat to be as efficient as possible at cruise speed.


2) Current prop manufacturer, model, aluminum or stainless as a minimum.
Michigan Wheel company - 992004 aluminum


3) Current prop diameter and pitch (required).
14.5 x 19

4) Wide open throttle RPM and speed with an average load (very helpful)
WOT RPM = 4800
WOT Speed = 42

5) Engine/drive make, model, year, and HP
Evinrude 130HP V4 looper, 1996

6) Boat make model, year, length and weight
Crestliner Sportfish 1750 (17’1”) ~1300 lbs.

 

[steelespike]

Couldn't find specs for a 130.Do you know the gear ratio? RPM range? Using 2.00, 4800 at 42 I get about 2% slip a very low unlikely number.
Is the speed by gps? A tach is always suspect As is the speedometer.
On the tach perhaps you can borrow a shop tach.
​ There is a switch on the back of the tach note the position,operate it a few times to clean the contacts
Otherwise how is the performance? Strong hole shot? Does it react well to added weight?

 

[Frayed_Knot]

I think the gear ratio is 2.25:1 however, its possible that its 2.0:1 because I have read that OMC put both gear sets in the 2.0L V4 engines during that time period. I can check on that when I get back home (any advice on how to determine). I don't have any manuals for the specific motor and haven't been able to find any.

Speed was with GPS but the RPMs were from the boat tach. I will see what I can do about better RPM readings.

Performance -
Hole shot is great - sock you back in your seat kind of great!
I haven't put much weight in it yet - just two people + fishing gear and it seems to handle it fine.
At top end is where I wonder about the prop. Based on what I have read I am getting the same top end speed as guys running 90 HP loopers. Also I think the RPMs are supposed to be up around 5500 at WOT - again based on what I have been able to dig up from the boating forums (hear and elsewhere). Likely the only time I will run this thing WOT is when testing out props and tuning. I don't plan to run that hard normally but I figure I should get it set up right so its running at peak efficiency in the midrange - Am I thinking about that correctly?? I am probably going to run quite a bit on big water so I want something that gives me a lot of bite for control in the waves. I was starting to look at 4 blade props for that reason and quickly realized I need some advice from the experts...

Thanks!

 

[jestor68]

It appears likely that your tach is wrong(reading low).

Using a 2.0 gear ratio and 10% slip, it works out to a little over 5200 rpm.

Using a 2.25 gear ratio and 10% slip, it works out to a little over 5800 rpm.

 

[steelespike]

It's kind of a pain but you can check the ratio by removing the plugs and turning the motor by hand. Mark the flywheel and the prop so you can count accurately 2 or 2 and 1/4 turns for one turn of the prop. While the plugs are out check the compression.Note the condition of the plugs and their location.
Its possible the motor is a little tired but you can check that the throttle opens all the way,that the timing is set right and advancing as it should.

 

[Frayed_Knot]

Just checked and the gear ratio is 2.25:1. Also did some more digging and it seems the max RPM range for this motor is 5500-6000 which falls right in line with Jestor's calculation. So what does this mean? Am I running the correct prop and my tach is just wrong? Any thoughts on top end speed? I just assume it should be higher than a 90 HP sitting on the same boat, but maybe I am wrong?

compression seems great on all cylinders and throttle appears to open just fine. I will have to work on getting better tach numbers and check timing when I get time.
Thanks!

 

[dazk14]

I agree, the boats running slow. I would expect to see high 40's set up well and running a stainless prop. Is it possible you're carrying extra weight (wet foam).

Are you trimming out until just prior to ventilation? Your WOT range is 5-6000rpm max.

You could live with less diameter as well.

 

[Frayed_Knot]

Steele, Jestor, Dazk - Thanks for all the advice! The foam was dry during the test runs. The whole boat has been rebuilt since but the weight should be really similar now. The current prop is aluminum and a bit dinged up - a couple small bites missing which is why I was looking into replacing it.... and I have been wondering if I have the correct setup. I have a family emergency that needs to be attended to right now - much more important than working on the boat so I will be a little slow to respond. I will work on the numbers you asked for when I am back on the water. Thanks.