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    #46
    Originally posted by Fishtank View Post

    I don't see how this could be true. Even if one engine is loaded up more than the other, as long it's near or lower than the optimal cruise rpm, it's simply not overloaded. Plus or minus a hundred rpms on the other engine would be insignificant. If the other engine was off by something like 500 rpm then sure, it would be an issue, but if the tachs are accurate and both engines were close, then no worries.
    Please share your results of turbo diesels and their resultant EGT and boost readings, which engines? Which boat? Are your EGT's post or pre turbo? What are the prop specs?
    It is absolutely accurate …

    When we vary rpm by even 25 the loads on the engine vary greatly.
    50 rpm and you can have a boost reading of say 6 on one side and 10 on the other.
    Pyro begins to drift up on loaded engine by 100-150 degrees - into the unsafe zone.

    We have seen where a couple of dozen barnacles on one prop can cause an engine imbalance even when the props are S1.
    Sometimes its just a few feet of poly rope tied around one prop hub 'unloading' that side - without boost and EGT how would you know?
    Please share your results of turbo diesels and their resultant EGT and boost readings, which engines? Which boat? Are your EGT's post or pre turbo? What are the prop specs?
    Northport NY

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      #47
      Here is a picture of the tachs, GPS, EGT's and boost gages on a typical run...
      Attached Files
      Northport NY

      Comment


        #48
        Where picture? I really wanted a thingy of Capt Jack asking Where Rum.....
        P/C Pete
        Edmonds Yacht Club (Commodore 1993)
        1988 3818 "GLAUBEN”
        Hino EH700 175 Onan MDKD Genset
        1980 Encounter Sunbridge "Misty Blue" (Sold)
        MMSI 367770440
        1972 Chevrolet Nova Frame off Resto-mod in the garage
        Boating on the Salish Sea since 1948

        Comment


        • smitty477
          smitty477 commented
          Editing a comment
          I can see the picture attached - can you?

        #49
        I have always understood if you are over propped at one speed, you are over propped at all speeds.
        I don't think tacks are any indicator until you get to wot. Its how hard you have to work the engine to get to the rpms.
        Started boating 1955
        Number of boats owned 32
        Bayliners
        2655
        2755
        2850
        3870 presently owned
        Favorite boat. Toss up. 46' Chris Craft, 3870 Bayliner

        Comment


          #50
          Big difference between a 6BT in a Dodge truck 250 HP and a boat 270 hp.
          Truck cruising on a flat at 70-75 mph, @2000 rpm, 4 psi boost, 500 F egt .
          Boat cruising at 1900-2000 rpm, 14 psi boost, 700 F egt.
          Joon, Kathy, Jaden & Tristan
          Uniflite 42 AC, DD 671N
          93 3058 sold
          92 2855 (day boat)
          91 Fourwinns 205 (lake boat)
          Longbranch WA
          Life is Good

          Comment


            #51
            Originally posted by Ruffryder View Post
            Big difference between a 6BT in a Dodge truck 250 HP and a boat 270 hp.
            Truck cruising on a flat at 70-75 mph, @2000 rpm, 4 psi boost, 500 F egt .
            Boat cruising at 1900-2000 rpm, 14 psi boost, 700 F egt.

            Many , many Cummins 6b owners on this site have installed EGTs as a result of reading posts such as this one - or due to engine failure.
            They would kill for an EGT reading in the 700 range or even to stay 200 above that number.
            Northport NY

            Comment


              #52
              Originally posted by smitty477 View Post


              Many , many Cummins 6b owners on this site have installed EGTs as a result of reading posts such as this one - or due to engine failure.
              They would kill for an EGT reading in the 700 range or even to stay 200 above that number.
              I'll research this more - thank you for your perspective. For the record, my Meridian 411 has 330 Diamond 6bta's. I have no pyrometer/EGT, and I've always operated it at an economical 2300rpm cruise w/ a 3850 WOT. I keep the engines synched with a synch tach.
              1995 Bayliner 2452 Mercruiser 5.7L Alpha 1 Gen 2

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                #53
                Umm Diamond 330 3850 RPM @ WOT?
                Targeted WOT RPM should be 2900-2950 for that engine ...
                Joon, Kathy, Jaden & Tristan
                Uniflite 42 AC, DD 671N
                93 3058 sold
                92 2855 (day boat)
                91 Fourwinns 205 (lake boat)
                Longbranch WA
                Life is Good

                Comment


                  #54
                  Originally posted by smitty477 View Post


                  Many , many Cummins 6b owners on this site have installed EGTs as a result of reading posts such as this one - or due to engine failure.
                  They would kill for an EGT reading in the 700 range or even to stay 200 above that number.
                  I remember reading Tony @ Seaboard saying the normal range is more like 350-750, manual says 905 @ WOT.
                  Many Cummins are still over propped ... killing their engine I'm assuming.
                  Joon, Kathy, Jaden & Tristan
                  Uniflite 42 AC, DD 671N
                  93 3058 sold
                  92 2855 (day boat)
                  91 Fourwinns 205 (lake boat)
                  Longbranch WA
                  Life is Good

                  Comment


                    #55
                    Originally posted by Ruffryder View Post
                    Umm Diamond 330 3850 RPM @ WOT?
                    Targeted WOT RPM should be 2900-2950 for that engine ...
                    Typo! Meant 2850... which is a little lower than I'd like.
                    1995 Bayliner 2452 Mercruiser 5.7L Alpha 1 Gen 2

                    Comment


                      #56
                      Originally posted by Ruffryder View Post

                      I remember reading Tony @ Seaboard saying the normal range is more like 350-750, manual says 905 @ WOT.
                      Many Cummins are still over propped ... killing their engine I'm assuming.
                      Hardly any of the Cummins marine owners I know can get as low as 900 when at higher cruising speeds.
                      I guess it would surprise you then to hear that a number of BOC members (over a dozen) have seen temps above 1000 and even up to 1400 when they install EGT's.
                      Then they know for sure why they need to cut down the props and monitor the EGT's so they do not lose another engine.

                      Northport NY

                      Comment


                        #57
                        Originally posted by Fishtank View Post

                        I'll research this more - thank you for your perspective. For the record, my Meridian 411 has 330 Diamond 6bta's. I have no pyrometer/EGT, and I've always operated it at an economical 2300rpm cruise w/ a 3850 WOT. I keep the engines synched with a synch tach.
                        So the question for the general public is what does synchronizing the rpm actually do?
                        Its just arbitrary.
                        Folks believe that they will balance the loads between engines by syncing them.
                        Question - what do your prop scans tell you? Are they within 5% or less of one another?
                        If they have not been scanned and balanced then likely not m, even when balanced they will be out enough to make rpm matching quite arbitrary.

                        One real life story, when cruising with a group of boats over a 65 mile leg....
                        - following a 46 Sea Ray with 8.3 Cummins for near 40 miles with no issues
                        - within a couple of miles he start showing heavy black smoke on pt engine
                        - he does not notice anything on his autosync or gauges
                        - sees no engine temp changes at all
                        - I call on the radio and we agree to stop at a marina nearby
                        - get in engine room and detect an overheat in progress (engine color on various parts)
                        - upon closer inspection detect the rubber hose between the turbo and intake manifold is split right along the hose clamp edge
                        - cannot really see it at all but under load it is spilling out all the boost and over fueling the engine

                        These unbalanced loads can come on slowly or quickly by engine issue such as these or by partially wrapping a prop with rope or debri or by slight dings in the prop taken on by partially floating objects.
                        Your temp gauge will not help you, neither your oil gauge or tachs.
                        Boost will tell you instantaneously and EGT will tell you within a few dozen seconds. We fitted boost and pyro gages on each boat we owned for maybe $500 total for both engines.
                        If you are going to run these 5.9 Cummins above hull speed they are really a low cost insurance policy.


                        Northport NY

                        Comment


                          #58
                          Originally posted by Fishtank View Post

                          Typo! Meant 2850... which is a little lower than I'd like.
                          - 2,850 on both? Exactly?
                          - are your tachs strobed?
                          - What do you get at high idle? (no load WOT)
                          Northport NY

                          Comment


                            #59
                            Worth repeating from post #11 above...


                            Cummins 5.9 - 3 rules you must follow:
                            1. Prop them carefully and always to reach at least WOT +3-5%
                            2. Run them at less than 66% of load (use pyro ,boost, and/or fuel flow gages)
                            3. Maintain them by the book without exception (read shop book and SBMAR site)
                            In return they will give you a long life.
                            Northport NY

                            Comment


                              #60
                              Originally posted by Fishtank View Post

                              I don't see how this could be true. Even if one engine is loaded up more than the other, as long it's near or lower than the optimal cruise rpm, it's simply not overloaded. Plus or minus a hundred rpms on the other engine would be insignificant. If the other engine was off by something like 500 rpm then sure, it would be an issue, but if the tachs are accurate and both engines were close, then no worries.
                              100rpm would be roughly an extra 90' that the faster engine would be dragging the slower engine along every single minute. If you look at the HP required to move your boat about .9kn (90'/min) at your cruise speed that is the differential of power between your two engines. It wont be that small of a number.

                              Boost is predictive (useful but lots of things can change before HP is made) EGT is the most valuable if you are looking at/comparing how hard each engine is working.
                              1989 3888
                              Nobody gets out alive.

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