Col. Steve Austin said:

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Gunny, no luck with the new prop. Sent you a PM with details.

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Did you confirm mounting height was right? Are you sure you have the correct shaft length? Surprising how many boats get rigged incorrectly at the factory/ dealer.

Some pictures might help also.

Already on all that. Motor is all the way down. He and I have been communicating almost daily. I confirmed the recommended prop from factory. His model number confirms a long shaft (20"). Crestliner specs say the boat should have a 20". Although a dealer could have ordered a 25" motor pod as special order. Or slight possibility that someone installed a short shaft on his ELPT power head…..that would be a long shot imho.
I told him today to get the dealer to measure the lower unit.
We also confirmed there is nothing sticking down in the water that would be causing disruption to the water flow foil to the prop intrusion water cone causing cavitation.
Crestliner is owned by Mercury (Brunswick) and ships the boats packaged with engine installed.

CS78 said:

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Col. Steve Austin said:

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Gunny, no luck with the new prop. Sent you a PM with details.

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Did you confirm mounting height was right? Are you sure you have the correct shaft length? Surprising how many boats get rigged incorrectly at the factory/ dealer.

Some pictures might help also.

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Boat is currently at the dealer waiting delivery of yet another prop to try. It's a third party prop they selected on their own. Gunny is highly skeptical that a non-Mercury prop would be needed to resolve this issue. I asked the service dept to verify height of the cavitation plate WRT to the waterline the next time they drop the boat in the lake.

Gunny and I have gone back and forth quite a bit with him trying to get a handle on this issue and provide guidance. Our PM string is currently at 32 messages (and counting LOL).

Theres a reason mercury props are ran on all kinds of boats and motors. Be surprised if another brand solves it.

Just throwing some ideas out but might try a mercury bravo 1 4 blade. They tend to hold grip when other props cavitate.

Id ditch the aluminum idea until you solve your issue.

If you can safely, have someone video or take pics of your motor while running. Ideally, you'll be able to see the cavitation plate right at/ above the surface of the water while on plane.

Where are you? And where do you boat? Ill come check it out with you ....

I've spoken with some industry colleagues and a dealer that has sold a number of 22' Crestliners with 115 Command Thrust engines on them.
The recommended prop has been either the Black Max 16"x 13" P XC ( for extra cup) or the SS Enertia prop in a 15.6"x 13"P if the customer wants a stainless prop. Both manufactured by Mercury.
They use the Command Thrust ( the Command Thrust lower unit is actually the 150HP V-6 lower unit..so it can accommodate those large diameter props) 115's on them specifically so they can use those large diameter 16" or 15.6". These large diameter props are specifically designed for pontoon boats and heavy hulls because they have such large blade surface area for lift and prevent cavitation tendencies.

He has now tried three props and they all cavitate.

The idea of using a Bravo 1 four blade is a good idea but I wouldn't suspect it will work for him because it has very high rake, is a performance based design, and it's specified for hulls that can run from 40-50 mph + and it's also only available down to 22" pitch …which no way that little 115 can turn that high of a pitch to the suggested rpm range on that 22' pontoon boat.

The Rev 4 prop is very similar design to the Bravo 1 but is still for performance applications and has high rake and smaller blade area and was not recommended in this application.

I have seen some success using the Mercury 4-blade stainless Spitfire propeller on smaller engines on Pontoon boats. It is low rake and has a large blade surface area….which lends itself to pontoon/small engine applications.

We have confirmed that the engine is mounted as far down as possible on the motor mounting pod.

We have confirmed by his dealer that there is nothing sticking down from the boat into the water that might be causing water flow foil disruption to the prop water intrusion cone which could cause cavitation.

Smaller engines like the 115 can not be trimmed out much or it will cause cavitation tendencies. I have made the OP aware of that.

Crestliner/Mercury specs show that the OP's boat model was built as a 20" transom length.
His model number of his engine is ELPT. Which is Electric Start, Long Shaft (20"), Power Trim.
So unless someone changed the lower unit in its past history, it is a 20" shaft, which should be correct for his boat specs.
However there is some information out in the industry that some dealers would in fact order The OP's model Crestliner with a 25" motor pod…..therefore needing a 25" or XL designated shaft length.
As of right now he is waiting for his dealer to measure to see if that might be the case with his boat.

The other possible scenario is that perhaps the original owner trashed the original lower unit and a 15" or short shaft lower unit was installed on it in error.
Lots of dealers confuse short shaft, long shaft, and extra long shaft actual lengths and wrongly call long shaft's short shafts and extra long shafts as long shafts….when they order them.
OP has asked the dealer to measure the shaft to confirm what length is actually on the engine. We don't have verification of that measurement yet.

I also told OP to have them measure from the water surface to the cavitation plate with the engine trimmed down and the boat sitting level in the water. We don't have verification of that measurement yet.

I go back to the fact that three props have now been tried on the boat and they all cavitate. The dealer already told him they put the correct prop on the boat once and OP had to take the boat back…and that is when he started this thread.

One of the props ( the Mercury 16x13 XC aluminum ) that my marine industry colleagues recommended, was the most recent prop tested….and according to the dealer didn't perform correctly.

So now the dealer is ordering an after market prop that they say " should work"…..

But it has not yet been confirmed if the motor actually has the correct shaft length lower unit for the boat….or if the boat has a 20" or 25" motor mounting pod.

So now you and Grem, if you guys read all of the above, (and I'm sorry it's so long but I felt you guys should have all the facts) know what's been done by myself and the OP so far.
I also offered for OP to bring the boat to me, I'd put him up here at the ranch, we could go run the boat, and I would work on it for him to help him out. Won't cost him a dime.

Steve. Read my above post to CS78. Sorry it's so lengthy but it covers what the OP and I have done over the last 14 days in regards to his problem and all the facts.

It would be cool if you indeed could get a look at it and run it. Wish I wasn't so far away. I'm going to email you with some thoughts. I'm just at the point that I don't believe it's a prop issue. Things don't add up.
I mean damn, it's a 22' pontoon with a 115 on it. I have set up lots like it. We aren't talking a 120 mph Allison here. It's not rocket science.
I feel for Col. Steve.


Not to derail. How did your charters go?

Depends on the application. Lots of Yamaha marine products have been tested with Mercury props with no appreciable gain in performance.
There is also high performance applications that some high end custom props excel over Mercury props and Yamaha props.
The point that was being made was that most boat companies, like the aforementioned Crestliner, that are owned by engine companies, like Mercury or Yamaha, design and engineer their products to perform really well with their own props.
That way they make money selling their own brand of prop on the boats they build.

Gunny456 said:

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I'm just at the point that I don't believe it's a prop issue. Things don't add up.

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Thats been my suspicion. Either wrong mounting location and if that didnt fix it, then wrong shaft length. Unfortunately, I have very low respect for most boat shops. Their top priority is always to just "get it out the door". Which results in all kinds of messes.

I just pulled a set of enertia 15Ps with hubs off my cat if OP wants to test one out before buying. But I agree, I kinda doubt that will fix the issue.

Yes sir. I had to do business for 40 years with 30-40 of them a year as dealers for our boats. There are some really good ones...like the guy I sent you to and a few others. Sadly between Texas, Louisiana, Oklahoma, Arkansas and Missouri....there is maybe 10 total I would trust my own boats with.

Appreciate your input on this thread. Will give you a call sometime this week.
Have a blessed Sunday.

SGrem said:

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Where are you? And where do you boat? Ill come check it out with you ....

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We live and boat on Lake Livingston.