What prop do you have with Merc 90 4-stoke on 24'

[katoom]

Hello everyone,

Looking forward to do some reading on this forum as there seems to be lots of good topics.

My first question is..... We just recently purchased a 24' Tracker PB with a Mercury 90 4-stroke. The current 3 blade 14x13 aluminum prop was not damaged more than a little bump on one ear. Nothing I would give reason for any considerable running differences.

But my concerns pertains more with the engine RPM's than anything at this point. Cruising along on a decent plane the engine will need to run at about 5100 rpm, and will easily and quickly jump up to about 6100 under WOT. My understanding is that the prop is probably too light for the application. I've even talked to Mercury and the tech felt the same based on the information.

Therefore I've considered looking at getting a 15p to see if the overall rpm's will drop a little, but I cant seem to find any real definitive answers to what I should expect. Everyone seemingly has a different opinion, and thats not even accounting for the added variables when discussion a SS prop as well.

So that said, I'm more wondering if anyone has any data to supply if they happen to have a Merc 90 4-stroke with a similar boat and size and what you're experiences are. Thank you everyone.

[Rick McC.]

I had a similar sized 'toon (22 1/2' Crest, but they're built heavy) several years ago, with a 90 HP four stroke Suzuki engine.

I believe that I ran a 14 by 17 pitch three blade on it.

Seems like it came with a 19 pitch, and I dropped it to a 17.

I sold it over 10 years ago, but I'm pretty sure about the prop numbers.

[katoom]

Thank you. Do you remember what the lower end gear ratio was for that Suzuki motor? I'd think that "may" pose as a variable since I understand they're not all the same. I think the Merc 90 of my year (2006) was something like a 2:30. Thanks again.

[BobG]

6,100 at WOT says you have the right prop. That's where it SHOULD be at WOT (5,800 - 6,200)

[GXPWeasel]

A slightly different animal, as I have a 90hp 2-stroke, but I run a 13.25x17p 3 blade on ours. Works best with a group of people. If I'm light (less than 5 ppl, and a small cooler, then it's not enough prop for our boat. We're usually pretty loaded down though.

[katoom]

Thank you.

My concern is running at 5100 all day. Seems unnecessary, adding wear and tear, and using more fuel if the motor is capable of cruising with the same load at around 4000 rpm.....

The problem I'm facing, which I'm sure others do as well, is that the opinions and suggestions can be all over the map. And buying multiple props can prove to be financially stupid. Then only to know that SS and aluminum props will react different so similar pitch props can offer different results.

What I found odd is that these size props rarely come with a progressive pitch, but have more flat ears. Weird.....

[taylorjm]

I have a bentley 20' with a 2007 mercury 90hp 4 stroke. Says max rpm is 6000. I can't tell you how it runs because I haven't had it in the water yet, but it has a 14 x 11p. That's what was recommended when I checked the prop wizards as well for pulling a skier/tube.

[Jake_Daddy]

I will throw in my two cents as well. My 20' with a Mercury two stroke will soon have a 15P on it. I started with a stainless 16P that came with my boat and was 100-200rpm shy of recommended WOT went out and bought a 13P, aluminum turning point this time, and I am hitting 200rpm over my WOT now. Now just trying to decide on if I want another TP prop or try a newer Merc prop.

[mpilot]

Not sure of the year but looks like some of the newer applications are using the 15.3x14 pitch prop. If it'll fit that big of a prop that might be a good starting point. Most dealers will let you swap props as long as you don't damage them and let them know what you're doing.

[mzodarg]

I chased the rpm/performance game for an entire season. I have a 2015 22' Sun tracker with a 90merc Command thrust. Initially came with an aluminum 15x17p on it and at WOT it would spin 4900-5100 rpms (lugging the motor IMO) So I went on the hunt for a prop that would put me in the in the optimal range at WOT.

I purchased a used 15x15 enertia SS prop and had custom work done on it. Before the work, it would bump of the limiter and now It hits 5500 at WOT, not optimal but it'll have to do.

Also had the simonize tune added and didn't gain anything on the performance end. IMHO I could have spent that $600 on something else.

Not sure my experience help in your hunt, Good luck and be sure to share your results.

Mike

[Rick McC.]

[quote="katoom"]Thank you. Do you remember what the lower end gear ratio was for that Suzuki motor? I'd think that "may" pose as a variable since I understand they're not all the same. I think the Merc 90 of my year (2006) was something like a 2:30. Thanks again. [/quote]

I have no idea what it was, but an online search would probably work.

[katoom]

Great responses..... Especially pointing out the "larger" diameter props the pontoon boats are coming out with, because I had a prop repair shop just tell me that he's been noticing that people are finding that the propeller diameter is playing a huge role in these pontoon boats. They seemingly dont respond as well to the steeper pitch but smaller diameter. They apparently do better with more propeller surface area in the water. Which brings into question, I've been hearing some about the new Spitfire 4 blade props performing better than the common 3 blade applications. Tooooo many choices.

[mpilot]

You stated in your original post about your boat planing, but unless it has substantial lifting strakes it will never really plane as a displacement hull. That's why more water volume from a larger diameter helps pontoons vs more pitch. Even most tritoons run a bigger prop with lower pitch than they would run if they were a mono hull boat because it takes a lot to get them running and even when they are on plane they aren't as efficient as a mono hull boat. This does change a little when you get to some high HP applications though. I would find out your maximum diameter prop is and start there. Most are running a 15x15 or that 15.3x14 I mentioned before.

[ron nh]

I know you could play with this forever, But with strakes and underskin there's no reason you shouldn't run as fast as the boat in the video.

[katoom]

[quote="ron nh"]I know you could play with this forever, But with strakes and underskin there's no reason you shouldn't run as fast as the boat in the video.[/quote]

What video?