re: Any boat propeller experts on here? [update #3 Pg4]

That prop is definitely too small or otherwise not fitting right. As said, the prop should basically be a continuation of the lower unit not something that looks added on with that gap and different size.

Yeah it definitely looks like there is more paint rubbed off of that prop than there should be for 2 hours, but it does wear off quick initially so that's not a guarantee on anything. Given it doesn't appear right though, I wouldn't doubt someone threw the wrong prop on there.

Been too busy traveling for work to deal with the boat so the FiL was handling this for me while I was out of town. Dealer tells him we have a spun prop and normally Mercury doesn't cover that under warranty but he'll put a new prop on it for us for free. And since they are putting a new prop on it for us they are going to put a larger diameter prop on it at the same time to give it more "bite". Now I think they are either liars or incompetent and just trying to cover their asses or maybe a little of both. I debate calling them out on their bullshite but at this point I just want the prop on and back in the water and not have to deal with these guys ever again. FiL and BiL pick the boat up and get it back in the water. Say it's driving much better now.

Spent the weekend on the lake. Took the boat out by myself to measure the prop/engine performance at WOT and the stats are:

25mph
5200rpm

RPMs seem low to me for a completely unloaded boat. It's going to be way below the 5k-6k recommended rpm range once the pontoon is loaded up. Take a look at the Prop and they put a 15P on there instead of a 13P like it originally had.

Loaded 4 adults, 1 kid, couple of coolers, bimini top up towable shoved between the tow bar and rails acting as a parachute I came up with these numbers.

PROPELLER PITCH
15

GEAR RATIO
2.38

ENGINE RPM
4700

ACTUAL SPEED (MPH)
21

PROPELLER SLIP
25%

The speed seemed plenty fine. Would like to get the RPMs up into the correct range. If I add another 2 souls on board I would think the 13P would be over propped as well? Can I add RPM without significantly reducing the top speed? Mercury sells "XC" versions of their props which are supposed to be Pontoon specific with more cup but will adding cup just negate reduction in pitch so I'm back at the same RPM range? 4 blade reduce my top speed too much? Slip seem OK?

It's all a give an take, but more bite will obviously reduce RPM's as it puts more strain on the motor. Maybe you could have your prop vented a bit to fine tune. Hard to say if it's worth it on a pontoon boat. I do have to say, I think it's a little fishy to jump up prop sizes like that.

I've forgotten most of what I researched when looking into my prop a few years back (was trying to get as much as possible out of a 60hp). Ultimately, I went to a prop shop and just chatted with the guy. This guy was knowledgeable, but you could tell he was more like a fabricator. He knew what to do to make adjustments, but you'd have to go back and forth a few times to get it right. He gave me a number to powertech props in Shreveport. That guy was like an encyclopedia. He was familiar with my boat and engine size and could spout out what RPM's/top speed/etc. that I was seeing. Ultimately, I was getting the best I could, which was in line with every number I saw on the internet. Maybe giving them a call would help.

call these people

LINK

I think the OP will find that most dealers have a lot more experience with SS props. Eventually he will likely need/want to get a SS prop -- this might be the time to bite the bullet and upgrade.

You will love it.

Hope it works out for you. Let us know how she runs this weekend. On the bright side, you now have a spare prop to keep on board and that is never a bad thing.