Pontoon prop?

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  • Pontoon prop?

    Will try and make this as TLDR friendly as possible. Both props tested same day, same conditions, same load. RPM confirmed via VesselView and speed via GPS. Would like to be able to hit max RPM(6300) or just above with this load as it is about as light as we're ever going to be. Also confused by top speed, research tells me this boat with this engine should be in the 30s.

    2018 22' pontoon(dual) with lifting strakes and under skinning.
    2018 Mercury 115 Pro XS 4 Stroke Command Thrust(2.38 gear ratio).

    Original prop - 14.5 x 17P Solas Rubex aluminum 4 blade = 4400 RPM at 19 MPH.

    New prop - 16 x 12P Mercury Black Max XC(Extra Cup for pontoons) aluminum 3 blade = 5500 RPM at 21 MPH.

    What would be recommended as the next prop I try? Budget does not allow for stainless. Merc prop calculator suggests their 14 x 12P SpitFire aluminum 4 blade.

  • #2
    Just a couple of comments. It is very difficult to get a 22’ bi toon with a 115 over 30mph. On 22’ bi toons with Honda 115’s we run 14x 11 props and get 5700+ rpm and just under 30 mph.
    same 22’ boat Tri toon same engine 33-34 mph.

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    • #3
      Originally posted by Shif View Post
      Just a couple of comments. It is very difficult to get a 22’ bi toon with a 115 over 30mph. On 22’ bi toons with Honda 115’s we run 14x 11 props and get 5700+ rpm and just under 30 mph.
      same 22’ boat Tri toon same engine 33-34 mph.
      I hear ya. However, I've read countless posts on various forums about people reaching low to mid 30s with the same engine and very similar boats.

      Boats.com and Boating Magazine both reviewed my exact boat, except that the test boats had the non ProXS/CT versions of the Mercury 115 4 stroke. They both reached a top speed 34+ MPH with 15P props on them.

      And, yes, I'm aware that those test sessions were done with minimal load, just the captain and whatever fuel they had on board. Still, I feel like I should be able to achieve roughly 30, and that's really all I want.

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      • #4
        What specific boat is it?

        by chance, does your motor give you your GPH while your running? if so, what is your GPH at wide open?

        Also, you can get a decent stainless Solas prop for about the same as you'd spend on a Spitfire aluminum.
        I'd buy a used stainless prop before bothering with aluminum.
        The odds of you gaining 30% on top end buy buying a 12 pitch spitfire is pretty slim. Not saying it can't happen, I get surprised sometimes, but I don't think just a prop is going to make that big of a difference.

        Going to need a 13 or 14 pitch prop to get to 30 at 6300 RPM mathematically.
        One that would be interesting is a Solas HR3 in 14 pitch.
        They are increasingly hard to find though. cost 280 from me and I'm sure you can shop around and find one cheaper.

        Ken Reeves
        [email protected]
        941-735-5808

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        • #5
          21 isn't in the same ball park as 30 MPH, something isn't right. I've done enough research on tons to know a 115 should reach at least 28 and some into the mid 30's.

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          • #6
            Originally posted by ken2 View Post
            What specific boat is it?

            by chance, does your motor give you your GPH while your running? if so, what is your GPH at wide open?

            Also, you can get a decent stainless Solas prop for about the same as you'd spend on a Spitfire aluminum.
            I'd buy a used stainless prop before bothering with aluminum.
            The odds of you gaining 30% on top end buy buying a 12 pitch spitfire is pretty slim. Not saying it can't happen, I get surprised sometimes, but I don't think just a prop is going to make that big of a difference.

            Going to need a 13 or 14 pitch prop to get to 30 at 6300 RPM mathematically.
            One that would be interesting is a Solas HR3 in 14 pitch.
            They are increasingly hard to find though. cost 280 from me and I'm sure you can shop around and find one cheaper.
            I keep reading there is no benefit to stainless on motors under 150HP. And, yes, I also have my doubts any prop will get me an additional +/- 10MPH at this point. The boat is a 2018 Princecraft Vectra 21. As for GPH, I think I can set that up with my MercMonitor gauge/gateway. I get all of the other parameters like engine temp, oil pressure, RPM... just haven't dug into fuel usage yet, I think I may need another harness to get that data.

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            • #7
              Originally posted by LFBB View Post
              21 isn't in the same ball park as 30 MPH, something isn't right. I've done enough research on tons to know a 115 should reach at least 28 and some into the mid 30's.
              I agree, and the reason I'm feeling lost on this one. I know I went up on the diameter, but I really thought dropping 5" in pitch would've maxed out my RPM, yet I'm still 800 away from the 6300 max.

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              • #8
                Originally posted by emilime75 View Post

                I agree, and the reason I'm feeling lost on this one. I know I went up on the diameter, but I really thought dropping 5" in pitch would've maxed out my RPM, yet I'm still 800 away from the 6300 max.
                Here's an online review of your boat hitting 33+ per the video w 115 Merc.

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                • #9
                  Originally posted by LFBB View Post

                  Here's an online review of your boat hitting 33+ per the video w 115 Merc.
                  I've seen a coupe already - can you post a link in case it's one I didn't see?

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                  • #10
                    Originally posted by emilime75 View Post

                    I've seen a coupe already - can you post a link in case it's one I didn't see?
                    2015 Princecraft Vectra 21 | On the Water Boat Review - YouTube

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                    • #11
                      Thanks, I actually hadn't seen that one. That's now 3 different independent reviews all reporting 33-34 MPH on the exact same boat with a 115, except that all 3 are the non CT versions, meaning I can't use the same props as them as the CT is a different gear ratio.

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                      • #12
                        What is CT??

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                        • #13
                          I don't prop pontoons, but do sell that motor a lot in both versions.
                          I,m propping aluminum Lund's and have found that they use the same pitch prop.
                          so if a 13p works on the small gearcase, a 13p will be right on a big foot.
                          They are different bore sizes so they won't interchange.

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                          • #14
                            CT is Command thrust, which is basically a motor that has a larger then normal gearcase for its HP.
                            All motor manufacturers offer it, as its helpful in certain setups.

                            OK, now we know what boat it is, and we expect it to run low 30's.
                            your barely getting 20.

                            Is there any growth on the toons? a little green slime can take a surprising amount of speed and RPM off.

                            When is the last time you drained the toons? and the center pod if it has one? I know its a newer boat, but you have to check everything.

                            How are you trimming the motor at wide open? what happens if you trim higher?

                            How many people do you have on the boat for these numbers ? got coolers, and gear for everyone I assume?

                            Ken Reeves
                            [email protected]
                            941-735-5808

                            Comment


                            • #15
                              Originally posted by ken2 View Post
                              CT is Command thrust, which is basically a motor that has a larger then normal gearcase for its HP.
                              All motor manufacturers offer it, as its helpful in certain setups.

                              OK, now we know what boat it is, and we expect it to run low 30's.
                              your barely getting 20.

                              Is there any growth on the toons? a little green slime can take a surprising amount of speed and RPM off.
                              By now there is, but the day I took it out and recorded the before/after new prop performance in the original post, it was clean with no algae growth. Next time I swap props I'll pull it out again and clean the logs again.

                              When is the last time you drained the toons? and the center pod if it has one? I know its a newer boat, but you have to check everything.
                              I've never drained the logs. Last time we had it out, I had the GF move the truck back and forth while I tried to listen for water sloshing around in the logs - didn't hear anything. Also not seeing it sit any lower in the water than normal, based on the water line stain on the logs. It doesn't have drains down low, but it does have inspection caps up on top of the logs, I'll stick my inspection cam down there next time we have it out. The engine pod is self draining.

                              How are you trimming the motor at wide open? what happens if you trim higher?
                              Once I start accelerating, and get to WOT, I'll trim up incrementally and watch my RPM and speed. I'll keep going up as long as I see speed increase. I can usually take it to a little above the center point on the gauge(analog gauge, not sure how accurate it is). If I go beyond that, RPM and speed both start to drop off more and more the higher I go. Haven't tried taking it to the point to where the prop starts to cavitate/ventilate. I'll also add that trimming up also does a good job of raising the front of the boat up nicely.

                              How many people do you have on the boat for these numbers ? got coolers, and gear for everyone I assume?
                              On the day of the prop swap test in the original post, we were about as light as we'd ever be. Just me and my GF and minimal gear. We went out solely to test the prop, so we didn't bring a cooler and/or our dog who usually comes out with us and we didn't bring some of the usual toys like our Lily pad. Before I bought the new prop I did a light load test as well, in order to be able to compare the 2 as fairly as possible.
                              Thanks.

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