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350 MAG Bravo 1 Performance Issue?

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  • 350 MAG Bravo 1 Performance Issue?

    I'm looking for opinions on what the expected performance should be with a 2009 350 MAG 300 HP. 1.5 gear ratio, 17P prop. I installed a complete SeaCore package into a Bayliner 2252 Hardtop (22.5 ft and approx 5000 lbs) a few years ago and have been underwhelmed by the performance and it seems that something is not right when I compare it to many other boats with similar size and power. Its max speed is about 44 MPH at 5100 RPM (target RPM is 5000-5200) and it gets about 2.2 - 2.3 MPG at best cruise ~30 MPH @ 3500 RPM. The hull is clean and I haven't found anything obvious. No one has a prop shaft dyno near here and I have asked two different Mercruiser Techs to look at it and they came up blank. This boat has a lot of frontal area with the hardtop but I still would expect about 50 MPH top speed and a much coarser prop than 17". Thoughts???

  • #2
    welcome aboard

    your boat weighs too much and you dont have enough power to hit 50 with that hull

    Cheesehead boating the Gulf Coast of FLA 27.51° N, 82.53° W

    1988 Cruisers Rogue 2420 -VP 290 DP now powered by custom 468 - https://forums.iboats.com/forum/owner...988-rogue-2420

    Past Boats
    1970 Wooster Hellion - Merc 9.8
    2002 SeaRay 190BR - 5.0 - A1G2 - "Cheeseheads in Paradise"
    1984 Avanti 170DLI -3.0 stringer- "Ship Happens"

    What’s behind you doesn’t matter.Enzo Ferrari

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    • #3
      Maybe, it could be that is all I can expect from this hull. Steep deadrise probably doesn't help. I'm just asking for opinions because I have seen larger, heavier boats with the same power perform equally or better.

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      • #4
        IMO your about rite on the expected #'s... my buddys 1997 bayliner 2352 trophy with a 2009 350 mag MPI with an alpha 1 with 1.62:1 and a 17p prop is about the same as your #'s... remember these hulls are not built for speed

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        • #5
          Yes, it's probably just the nature of the beast. I'm not concerned so much about the top speed except as a reference. I was hoping for a lower rpm mid range cruise and better gas mileage. I believe there is about 21-23 % prop slip through the rpm range so it may be time to try a 4 blade prop. With a kicker, downriggers and other fishing gear, it is probably heavier than I think. The extra 200ish lbs of the Bravo setup over the Alpha probably doesn't help either.

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          • #6
            Check your prop's slip. If it is ok, then there is nothing you can't do because your boat is heavy. 5100 rpm @wot is perfect for engine's health. But you really have 20-22% prop slip. With normal prop slip you should not reach 5100rpm...
            by the way, my 20ft (22deg v) wellcraft nova with 2009 350mag mpi with 1.48alpha and 18p enertia hits 59mph@gps @5200rpm. My boat is heavy for it's length as well...this performance is reach ed with about 3600-3700lb weight and 80f ambient temp. If for any reason have to load the boat so to weight 5000lb and push it to wot, it definately will not hit 5200rpm!!! I hope you understand what I mean.

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            • #7
              Hardtop
              The hardtop is nice but also will slow it down from the increased drag. You have 20% slip or so but 2+ mpg isn't bad
              94 Formula 27PC Custom 509MPI MEFI3 , B3 XR
              95 Rinker 232 w/ 7.4L Carb 0F425011 B1 0F486471
              07 Seadoo GTX
              Merc Adults Only VP Adults Only
              G-Dad always said "First Liar doesn't stand a chance"

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              • #8
                You could to with a 19 pitch prop to get the RPM down a tad and pick up a little on the top end. That should also get your cruise RPM down a little.
                83 Sunrunner 16.5 120 merc Alpha 1 drive SOLD 8/1/13

                1996 Crownline 202BR
                5.7l EFI 0f791070
                Bravo I drive

                GMC Yukon tow rig

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                • #9
                  I tried a 19" Prop some time ago but found the top rpm would not quite make it not the target range with a heavy load. I don't want to stress the engine too much.
                  What kind of prop slip #s do you guys get?

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                  • #10
                    Heres a V6 doing 32 mph https://www.youtube.com/watch?v=4Ag58OzgibU Is your performance comparable?
                    NO PERSONAL QUESTIONS, THIS IS WHAT THE FORUM IS FOR.

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                    • #11
                      Originally posted by Bt Doctur View Post
                      Heres a V6 doing 32 mph https://www.youtube.com/watch?v=4Ag58OzgibU Is your performance comparable?
                      Hey BT. Thanks for that video... That was a non-vortec (180hp) V6 in a 22-1/2' boat. For so long we've been seeing some posters saying that size boat without a v8 is under power, and I've been saying no it isn't... Hopefully this video is enough to shut them up!

                      Cheers

                      Chris...
                      xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
                      The world takes on a whole new perspective when viewed from 100’ below.
                      1972 Bertram ‘Bahia Mar’ 20
                      2006 Mercruiser 4.3MPI (0W617679) w/Alpha One Gen II (0W829301)
                      (Original - 1972 '165' In-line 6. Previous - 1994 4.3LX)


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                      • #12
                        That's using the boat speed-o
                        94 Formula 27PC Custom 509MPI MEFI3 , B3 XR
                        95 Rinker 232 w/ 7.4L Carb 0F425011 B1 0F486471
                        07 Seadoo GTX
                        Merc Adults Only VP Adults Only
                        G-Dad always said "First Liar doesn't stand a chance"

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                        • #13
                          My boat is the same as the one in the video, give or take a year. I have a kicker and downriggers but that barely adds 200lbs. It came with the same engine (4.3/Alpha) and could barely make 25-26 mph (gps) top speed. Cruise was at 20 mph plowing. That's why I went big with the repower. I haven't seen any sign of hidden weight, ie. waterlogging or any concealed gold bars anywhere so I don't know.

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                          • #14
                            I was looking at props and see there are 16" diameter (vs15 1/2) available. I'll give that a try, or a 4 blade to try to get the prop slip down.

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                            • #15
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                              Originally posted by Joesolta View Post
                              I was looking at props and see there are 16" diameter (vs15 1/2) available. I'll give that a try, or a 4 blade to try to get the prop slip down.
                              Agree your prop slip is up, but if the skip is reduced then the rpm's are going down. Your getting 44 mph WOT at 5100 rpm, and I think your doing good for a 5K lb boat. If your drive ratio was higher you may have a better chance of getting a tad more IMO, swapping drives is expensive.
                              94 Formula 27PC Custom 509MPI MEFI3 , B3 XR
                              95 Rinker 232 w/ 7.4L Carb 0F425011 B1 0F486471
                              07 Seadoo GTX
                              Merc Adults Only VP Adults Only
                              G-Dad always said "First Liar doesn't stand a chance"

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