New 21" prop on 140HP Evinrude - Ventilation or cavitation?

[Jesterarts]

Hey all,

I installed a new 21" SS prop on my 16 foot, Pride Panther boat that is powered by an 1987 Evinrude.

I took the boat out the other day and discovered that if I try to take off any much more that about 1/2 throttle, The revs jump up high and the boat doesn't gain much speed.

If on the other hand, I accelerate at a lower throttle until I get to about 20mph and then floor it, the acceleration is brutal and she shoots up to 45-50mph in slightly choppy water.

Once thing I did notice, is this prop doesn't seen to be sitting as deep in the gearcase sleeve as my last one. So I am thinking the thrust washer might be too thick and the result is exhaust escaping between the prop and the gearcase causing ventilation?

I had a 19" prop on the boat before and I did not experience the issue.

The motor is mounted correctly, with the cavitation plate just a whisper lower than the keel.

Please let me know your thoughts.

Thanks in advance.

 

[Bifflefan]

Re: New 21" prop on 140HP Evinrude - Ventilation or cavitation?

Sounds like you have the wrong style of hub installed in that prop.
Likely that you either grabbed the wrong one or it was miss boxed.
Pull it off and make sure.

 

[Jesterarts]

Re: New 21" prop on 140HP Evinrude - Ventilation or cavitation?

Sounds like you have the wrong style of hub installed in that prop.
Likely that you either grabbed the wrong one or it was miss boxed.
Pull it off and make sure.

Hey, when you say the "wrong type of hub", are you able to expand on this.

I probably should have mentioned that I purchased this prop from a boat dealer, 2nd hand but basically brand new.

I traded in an old prop and they guy said this one was the same set up.

Not sure if this helps, but both props had/have the rubber press in hub.

Thanks.

 

[V153]

Re: New 21" prop on 140HP Evinrude - Ventilation or cavitation?

Sounds more to me like the prop's blowing out comin outa the hole. If that's so it ain't no big deal. Watch the tach/feather the throttle so's it don't over rev. And wait a couple seconds til it hooks up. Then it's off to the races.

Please post pics of your boat/motor set up?

 

[jestor68]

Re: New 21" prop on 140HP Evinrude - Ventilation or cavitation?

Hey all,

I installed a new 21" SS prop on my 16 foot, Pride Panther boat that is powered by an 1987 Evinrude.

Once thing I did notice, is this prop doesn't seen to be sitting as deep in the gearcase sleeve as my last one. So I am thinking the thrust washer might be too thick and the result is exhaust escaping between the prop and the gearcase causing ventilation?

I had a 19" prop on the boat before and I did not experience the issue.

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If the prop does not fit into the gear housing like it's supposed to, any gap will allow exhaust gas to enter the prop and cause just what you are describing.

The 21 should work just like the old 19; IF it's the correct prop for your motor. It won't be the first time that a shop sold the wrong prop to a person.

The correct prop will fit on there the same as the old prop using the same thrust washer. It appears that the guy sold you the wrong prop.

 

[Jesterarts]

Re: New 21" prop on 140HP Evinrude - Ventilation or cavitation?

Hey all,

I installed a new 21" SS prop on my 16 foot, Pride Panther boat that is powered by an 1987 Evinrude.

Once thing I did notice, is this prop doesn't seen to be sitting as deep in the gearcase sleeve as my last one. So I am thinking the thrust washer might be too thick and the result is exhaust escaping between the prop and the gearcase causing ventilation?

I had a 19" prop on the boat before and I did not experience the issue.

-----------------------------------------------------------------------------------------------------------------------

If the prop does not fit into the gear housing like it's supposed to, any gap will allow exhaust gas to enter the prop and cause just what you are describing.

The 21 should work just like the old 19; IF it's the correct prop for your motor. It won't be the first time that a shop sold the wrong prop to a person.

The correct prop will fit on there the same as the old prop using the same thrust washer. It appears that the guy sold you the wrong prop.

Hmm... I will have to wait and see on the weekend as my boat is stored off site.

In the mean time, if we assume it is the correct prop. Is there anything I should be looking at to try and identify the cause?

Or is it simply a case that I need to ease on the throttle rather than trying to floor it from standing?

 

[steelespike]

Re: New 21" prop on 140HP Evinrude - Ventilation or cavitation?

If you post some pictures of the prop in relation to the gear case it may help identify if there is a problem.
Why the prop change? Were you having over rev issues? What is the wot rpm and gps speed now?

 

[Jesterarts]

Re: New 21" prop on 140HP Evinrude - Ventilation or cavitation?

If you post some pictures of the prop in relation to the gear case it may help identify if there is a problem.
Why the prop change? Were you having over rev issues? What is the wot rpm and gps speed now?

I will have some pictures this weekend.

The reason for changing the prop was that I wasn't able to go WOT with the 19".

I was getting up to 5800+ rpm and not yet at WOT.

Didn't get to check the GPS speed when I was out last weekend (stupid I know), but at WOT the RPM was sitting around 5600-5700rpm so right in the range it should be.

Based on the vacuum speedo in the boat, I gained about 10mph going from the 19" to the 21"

 

[Jesterarts]

Re: New 21" prop on 140HP Evinrude - Ventilation or cavitation?

Ok,

Naturally I forgot to take pictures this weekend. But on the plus site the issue of the prop not being nested in the gear as as far as I would like it is resolved!

Went out yesterday on the water yesterday, floored it and it griped well.... for the first 3 hours.

It decided to start slipping again after we had been out on the water for a while and while I was behind the boat knee boarding.

We limped back to shore keeping it under 3000rpm and went home.

Inspected the prop and everything looked fine so not sure why is started after running fine all day.

I suspect a spun prop? So I've marked the prop hub and will see if this is the issue next time.

 

[Texasmark]

Re: New 21" prop on 140HP Evinrude - Ventilation or cavitation?

Where do you set the trim on the hole shot? Is there a gap between the prop barrel and the LU casting? Is the thrust washer positioned on the prop shaft correctly, wedge to wedge? Is the new prop ported? Is it cupped?

You have more than adequate hp for that boat regardless of hull design. With the higher pitch prop and adequate hp you can romp on it and it can move water faster than the boat can accelerate which can suck in ambient air and ventilate, even with your engine sitting a couple inches too low.

When you get through playing, jack your engine up so that your AV plate is above the bottom of the boat as measured with a straight edge extended from the bottom. I like the number 1" with no setback......jack plate and all. You would be literally amazed at what getting the LU out of the water can do for your MPH.

Personally, I stomp on my little 90 on my 17' tin lizzie in the hole with the trim set about mid point. The engine blows out but in doing so, the rpms come up real good. When it catches, on it's own, I have my HP [(torque x rpm)/5252] or whatever the constant of proportionality is. When it bites again, the boat lurches forward and blows out again. After about 3 of these in just a few seconds, the wake looks like my Avatar and I am gone bye bye. But I'm over 70 as is my girlfriend and we shouldn't be doing this.....but this is our Harley!!!!!!!!!!!!!!! and she sits next to me rather than behind me.....................

Mark