Best Prop for Evinrude 140hp (1980's) on a 5m fiberglass ski boat...

[Jesterarts]

Hi,

I recently purchased by first boat. It was a second hand Pride Panther ski boat with a 140hp Evinrude on the back.

The dealer also gave me 2 props, a 17" and a 19".

Now, the boat lauches and gets on plan pretty easy even with 3 people in it so I was wondering if I should change props as I'm currently maxing out at 35mph according to the speedo.

Ideally, I want a prop that I can used to tow someone on a ski or towtube but that I can also use for top speed jetting about from beach to beach.

Any recommendations?

Thanks,

 

[smokeonthewater]

Re: Best Prop for Evinrude 140hp (1980's) on a 5m fiberglass ski boat...

welcome

go to the top of the page and the "read this first" thread.... come back to this thread with that info

 

[Jesterarts]

Re: Best Prop for Evinrude 140hp (1980's) on a 5m fiberglass ski boat...

1) Performance issue you are trying to correct.
From what I have heard, this hull and motor have the potential to go faster. I just recently got into boating as my background is cars. My daily drive is a 600hp HSV (Australian make) so I'm a fan of things that go fast. The boat feels "zippy" but doesn't feel fast. I have watched various video's and ready articles that suggest the motor and hull have alot more to give than 35mph.

2) Current prop manufacturer, model, aluminum or stainless as a minimum.
No idea on manufacturer or model. I know it's stainless steel and has 3 blades.

3) Current prop diameter and pitch (required).
13x19" from what I remember. I also have a 13x19" but that will be even worst than the 19.

4) Wide open throttle RPM and speed with an average load (very helpful)
When the engine is at 6000rpm I am cruising at 35mph on fairly flat water.

5) Engine/drive make, model, year, and HP
Engine is a Evinrude 140hp. Not sure what specific module but it's a 2 stroke and from the 1980's I think (1988 specifically). Boat is stored not at my house during the week so can't check plates on it until the weekend.

6) Boat make model, year, length and weight
Boat is a 1980's Pride Panther. It's 5m long but I have no idea about the weight. On the particular day I was out and noticed the speed I had 40L of fuel, 3 people (92kg, 60kg and 82kg) plus basic gear no more than 50kg I would say.

 

[steelespike]

Re: Best Prop for Evinrude 140hp (1980's) on a 5m fiberglass ski boat...

first thing it seems to me without looking too hard that that setup should run 50-60 mph. probably with a 21`-23" prop
should be really overeving with a 19".
Prop calculator says your slip is 27% Slip measure the actual movement of the prop through a liquid.
The higher the slip the worse the performance.A good slip number would be about 6%
Youre numbers don't add up.Is your speed by gps?
Does the boat get up and run on about the rear 1/4 to 1/3 of the bottom?
Does it respond when you trim up?
You need to varify your tach I think your motor is actually turning about 4600 rpm. 27% slip is off the chart so to speak.

 

[Frank Acampora]

Re: Best Prop for Evinrude 140hp (1980's) on a 5m fiberglass ski boat...



I agree with steelspike that your top speed is too low. You should be up around 50 MPH--of course. depending upon hull style. Speed on water is deceptive and the only way to accurately measure it is by GPS. You also need to have a functioning tachometer.

As a comparison, the first two photos show a 4.5 meter (14 feet) flat bottom that tops out at 60 with an admittedly weaker Force 125 (than your 140). The last photo shows a 5 meter (15 feet, 9 inches) deep vee that tops out at 45 with an old Chrysler 105. Yeah, yeah, I know: The photo shows a Chrysler 75. The same boat is in the avatar with the 105 (Which really only delivers 90 HP at the prop.).

So, yes, your top speed is low.

Oh, OK! here it is with the 105 and an older 3 cylinder 90. Both drive it at 45 mph top speed.

NOW: ANY prop has a parasitic drag. This is the power it absorbs just to turn it through the water. A low pitched prop turning real fast takes more power to turn through the water than a high pitched prop, thus reducing the available engine horsepower to drive the boat through the water. Additionally, the engine develops its maximum horsepower at a given RPM. Exceed this RPM and horsepower goes down.

SO: Your objective is to prop the boat at wide open throttle to keep the engine near the rpm at which it develops its rated horsepower.

Without an accurate tach and accurated speed measuring, this will not be possible. Now, of course, I understand that I have not really answered your question. However, hopefully I have pointed out to you the need for correct measurements if you hope to acheive the hull's speed potential without a lot of experimentation and money spent on props.

 

[Jesterarts]

Re: Best Prop for Evinrude 140hp (1980's) on a 5m fiberglass ski boat...

Wow... that is a lot of information for me to digest. Thanks guys.

The comment about the RPM not being accurate got me reading and I feel I might have screwed up my tacho setting.

Basically, coming from cars... you have a 8 cylinder and you set it to 8 cylinder on the tacho. The boat engine is a v4 so I set it to 4 on the tacho

BUT, after some reading I noted that the alterator on my engine is likely to be a 6 pole or 12 pole, and thus the tacho should be set to 6.

This would go some what to explain the inaccurate RPM and low speed.

Thanks for the information so far guys. I'm learning... slowly!

I've also gotten in contact with the dealer who sold me the boat and he said he is happy to swap the 17" pitch prop me gave me as a spare with the boat for a 21".

 

[steelespike]

Re: Best Prop for Evinrude 140hp (1980's) on a 5m fiberglass ski boat...

Before making a deal on a different prop wait for the final results on your setup.I suspect there are other things going on besides a tach adjustment.

 

[Jesterarts]

Re: Best Prop for Evinrude 140hp (1980's) on a 5m fiberglass ski boat...

Just thought I would post a quick update.

Turns out the prop on the boat was the 17" and not the 19".

So, went and put the 19", adjusted the tacho correctly I had on the boat and when out today.

Much better. @ WOT the engine was reving about 5700rpm and we were cruising alone happily at 45-47mph.

Very happy with that.

 

[steelespike]

Re: Best Prop for Evinrude 140hp (1980's) on a 5m fiberglass ski boat...

Thanks for the update
Previously I was guessing the year of the motor.Now I feel its likely a 85 with a 2.00 gear ratio.
The numbers make more sense indicating about 8% slip.
With that relatively small 15 foot boat I still feel the motor should be running a 21 or 23" prop at about that 5700.
A 21 would produce 52 mph.If the motor is a little weak your wasting a little fuel
because its slower at a given throttle setting and its wasting fuel because it's not 100%.
Probably no big deal and it likely would be difficult to measure the difference in fuel use.
You may want to check compression and be sure its in proper tune and the throttle opens all the way.If you do the compression check note the position of the plugs and their condition.
Could be your setup; be sure the antivent plate(just above the prop) is even with or slightly above the bottom of the boat.