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How fast do you cruise your MY at?-gctid355566

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    How fast do you cruise your MY at?-gctid355566

    The question of the day is how fast do you typically cruise your Bayliner MY at?

    Our 4788 cruises quite nicely at hull speed and about 1200 RPM on the engines.

    We intend to operate it at hull speed most of the time.

    The captain I hired for docking training indicated that he likes to run the 4788's at around 10 knots. He says it is a good compromise of fuel economy and speed.

    Fast cruise is at 2400 rpm and 15 knots. We can do that, but the way I look at it is that if I wanted to go fast I would have kept our 2859.

    At what speed do you cruise your MY at most of the time?

    KEVIN SANDERS
    4788 LISAS WAY - SEWARD ALASKA
    www.transferswitch4less.com

    where are we right now?

    https://maps.findmespot.com/s/36S4

    #2
    Kevin

    Just curious what speed do you find hull speed to be with the 4788 ?
    Jim McNeely
    New Hope a 2004 Bayliner 305 Sunbridge Express Cruiser
    Twin 5.7s with Bravo2 drives
    Brighton, Michigan USA
    MMSI # 367393410

    Comment


      #3
      JimMc wrote:
      Kevin

      Just curious what speed do you find hull speed to be with the 4788 ?
      Jim, I want to say 7.5 knots, and I know thats close. I tried to search through my old posts looking for the sea trial information with the new engines but I did not post the hull speed cruise.

      I remember 7-8 knots as very peaceful, with little wake.

      I will tell you in 56 days I'll be able to answer that much better.

      KEVIN SANDERS
      4788 LISAS WAY - SEWARD ALASKA
      www.transferswitch4less.com

      where are we right now?

      https://maps.findmespot.com/s/36S4

      Comment


        #4
        Kevin... While my boat is closer to your 2859, I have been thinking about the very same question you are asking. If I may, I'd like to approach this issue from a slightly different angle. It will be a few weeks to a month before my repower is complete and my boat is ready for a sea trial, but the pressing question for me will be at what RPM range I should be operating my Diesel that will allow it to go 8000 hours prior to needing a rebuild. This is of course assuming I would be giving it proper care and maintenance, which I'm sure you will be very attentive to as well.

        The pair of Cummins you've had installed are very resilient and are well capable of taking a beating. However, they are also capable of lasting forever (in engine life years, that is) if you're able to find the load factor and RPM combination that will stress the engines out the least amount possible. If your turbo charger is configured to kick in at a certain RPM, you might consider running it at below the trigger point for as much as you are comfortable doing so.

        This is just my two cents; and I realize every individual has different cruising needs/goals. And this would be a personal choice in my book; but wanting to get the maximum number of hours out of the investment of two new engines is something I would give serious consideration to. It's not only due to the financial aspect (it's a low priority concern for me) but mainly due to the time, effort, and resources invested into a repower. It is something I only want to do once during the life of my boat and be done with.

        Besides, I'm finding myself in less and less of a hurry to get to places -- as enjoying the journey is just as important as enjoying the destination. I feel old saying this at 38...geesh.

        Comment


          #5
          I cruise my 3870 at about $32 an hour.

          Comment


            #6
            ksanders wrote:
            The question of the day is how fast do you typically cruise your Bayliner MY at?

            Our 4788 cruises quite nicely at hull speed and about 1200 RPM on the engines.

            We intend to operate it at hull speed most of the time.

            The captain I hired for docking training indicated that he likes to run the 4788's at around 10 knots. He says it is a good compromise of fuel economy and speed.

            Fast cruise is at 2400 rpm and 15 knots. We can do that, but the way I look at it is that if I wanted to go fast I would have kept our 2859.

            At what speed do you cruise your MY at most of the time?
            Kevin, we cruise our 4788 at 7.5-8.5kts (about 1.8-2 nmpg) 80% of the time, and 15-15.5kts (0.8-0.9 nmpg) the other 20%. We don't spend much time between the two. 1200 RPM will get you about 7.5kts.

            10kts would not be that efficient as you would be pushing a pretty big bow wave.
            Mike
            "Allante I" Rayburn 75
            Previous: '97 4788

            Comment


              #7
              Our logs show that we cruise at 7 knots near 1,100 rpm's about 20% of the time and above 2,400 about 60% of the time.

              The balance of the time is manuevering and at the dock type stuff.

              When above planning speed (2,400) we run at varied speeds between 15 -18 knots dependent upon load and sea states.

              Anytime we are running at cruising speed we make it a point to stay at or below 'using' approx. 180 hp per engine which is 2 cubic inches per hp produced.

              So the way that we view your questions result in these thoughts:

              - make sure the boat is propped for 103-105% max rpms in gear as a test (worst case loading)

              - Always run at or below approx. 1/2 hp per cubic inch of engine displacment

              - Run either below or above transition speeds

              - Avoid lengthy trasition speed runs as they load most engine/trans/prop combinations at the wrong rpm's

              Kevin - with your pyro and turbo gages you will see a non linear readout from them within the transition range. As an example your turbo boost number vs speed will be much higher in the 11-14 knot range than at any other speeds. So we either go below 7 knots for fuel & engine savings or above somwhere near 14.5 knots for the same reasons.

              Hope this helps
              Northport NY

              Comment


                #8
                Running by myself usually about 2500-2550 ~15kn

                Running with brother usually about 2650-2700 ~16.5kn

                His dingy really doesn't tow well at 15kn but the other thing we often would do to make up for slight differences is the slower one gets out of marina first and gets a bit of a head start then the faster will catch up, pass, and get to destination a bit ahead of the other. I was the faster one for a few years in the old boat, now with the 38 he has me by a bit.

                I know it costs me to run faster but most trips are weekends and you only have so much time before you have to be back to work.
                1999 Sandpiper Pilothouse - Current
                1989 3888 - 2011-2019, 1985 Contessa - 2005-2011, 1986 21' Trophy 1998-2005
                Nobody gets out alive.

                Comment


                  #9
                  Kevin based on the last 2 yrs of data we cruise around 10 knots (1.20 g/nm). The rpm is between 1800-2000rpm (tides/wind vary my data) on our 4588.

                  Comment


                    #10
                    I generally run at either 7-8KN or about 24KN. These are my most 'economical' speeds. 7KN saves fuel. 24KN saves time.

                    We have a number of friends with whom we cruise. Many are ragbaggers (5-6KN max), so traveling slowly keeps us fairly close together. Traveling at hull speed is nice; we enjoy the trip as much as the destination.

                    Comment


                      #11
                      Hull Speed is a theoretical number. Hull Speed (in knots) equals 1.34 X the square root of the waterline length (in feet).

                      I don't know what the actual waterline length of a 47MY is but lets assume about 42 feet. Then hull speed is 8.68 knots. Run above this speed and you really start to push, with a building bow wave.

                      This is not the most economical speed however - something less, often suggested as about 3/4 of hull speed. That would be about 6.5 knots. This might come close to a zero wake speed.

                      It would seem that running at 10 knots would put you well into the "transition zone" that Smitty referred to.

                      I run my Avanti 40 with 370 Cummins at 8 knots, 1300 RPM - about 2 mpg, OR at 20 knots, 2400 RPM - about 1 mpg. My engines turn to 3050 RPM at WOT.

                      Think of it this way - coming home from a weekend outing 20 miles away, if I run at 8 knots instead of 20, with diesel about $4 a gallon, I save enough for dinner with my wife - $40 bucks - no drinks of course.......

                      Walt

                      Comment


                        #12
                        I'm not sure my info will help you.

                        We either run at 6-8 or 15-17, anything between is just digging a hole and throwing a big wake.

                        Comment


                          #13
                          I have been told for engine longevity to cruise no less the 1500 rpm with my Volvo diesels, something about keeping the turbos spinning.

                          Comment


                            #14
                            Kevin:

                            Cruised at about 2600 rpm/15 kts from Anacortes to Whittier and crusie about 2000 rpm 9 kts around the Sound. Trip Whittier/Eshamy/Jackpot/Lower Bainbridge/Procession Rocks and return takes 200 - 225 gallons of diesel (6 days) with furnace running most if not all the time and generator about 3 hours a day.

                            Darby

                            Comment


                              #15
                              usually about 16 knots as I hate going slow.
                              www.boatyardgm.com
                              www.pacificyachtimports.net
                              2002 Carver Voyager 57
                              "Making Waves"
                              3988 250 Hinos
                              "The Dark Side"
                              Alameda, California

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