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Jeff(39)s repower update-gctid381761

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    Jeff(39)s repower update-gctid381761

    Some of you wanted me to post results on repowering my 3218 from 225 hp 305's to 280 hp 350's, last fall, so here goes. I now have about 7 hrs. of break in time on new engines, (the manufacturer recomends 10 ). Cruise speed on old engines was 17mph to 19mph at 3550 rpm depending on fuel load. New engines are 19.5 to 20 mph at 3450 to 3500 rpm with full fuel, water, and 3 adults on board. Now don't ask me why speed would increase when considering prop pitch is the same, and rpm is slightly less, because I have no idea. But I'm not complaining. W.O.T. on old motors was 22mph to 24 mph. Now with only 7 hrs of break in time on new motors, I'm not supposed to fire wall the throttles for another 3 hrs, but gee my hand slipped! This little "accident" for a period of not more than 5 to 10 seconds, got me 27.4 mph on the GPS. That's what I would consider WARP speed for the old tub! As for fuel economy, it's way to early to tell yet, but I will let you guys know by the end of the season. Other than that they really sound smooth with roller rockers, and so far I am pleased with the results. Oh by the way, that W.O.T. thing was at a tach reading of 4400 rpm. The manufacturers recomended W.O.T. is 5000rpm. see you all later, Jeff.

    #2
    Great news Jeff, thanks for the update. I'm sure small boats look surprised when they see all that boat doing warp speed

    Comment


      #3
      Sounds like a great improvement.

      Jeff, you need to do something about the wot. If you can't reach the suggested rpms, you are lugging your engines.

      And you are lugging them at every speed, not just wot.

      It will shorten their life.

      And yes you might lose a little top end but your engines will like you for it.

      Doug
      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


        #4
        Doug,

        What is your definition of "lugging", and can you please explain to me how he will be "lugging them at every speed, not just wot"?

        Comment


          #5
          An alternate school of thought is that you are overloading the engines at higher speeds. If WOT is supposed to be 5000 rpm, and your plan is to cruise at no more than 80 percent of WOT, and you can only reach 4000 rpm, 80 percent would be a max cruise of 3200 rpm. 80 percent is a good rule of thumb for gas engines. In this example any prolonged speed over 3200 rpm would harm the engines. Best solution, verify tachs are accurate and if OK, then lower pitch or diam of props to achieve the recommended max WOT.
          Started boating 1965
          Bayliners owned: 26 Victoria, 28 Bounty, 32, 38, and 47 since 1996

          Comment


            #6
            RJH wrote:
            Doug,

            What is your definition of "lugging", and can you please explain to me how he will be "lugging them at every speed, not just wot"?
            I'll chime in here.

            Marine engines are properly loaded when they will reach full rated RPM in a fully loaded boat.

            If you cannot reach your full rated RPM then you are applying more load to the engines than the manufacturer intended.

            You are overloading, or lugging your engines.

            This is the most common cause of premature engine failure in marine engines.

            When we repower a vessel (I've done this several times now), one of the most important things to do is to adjust the loading on the engines so that they can reach rull rated RPM or more. This is done by adjusting the pitch you are running on your props.

            If you have too much pitch you'll be overloading your engines.

            If you have too little pitch you'll not be getting all of the speed you can out of your boat. You'll be underloading your engines. This is not generally problematic unless the underloading is severe, but its best to start out your new engines life properly loaded.

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

            where are we right now?

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

            Comment


              #7
              If you guys read the results again, you will notice that W.O.T. was held for only a few seconds because of lack of break in time. It would not have had time to reach anything close to top rpm, so lets not repitch or worry about overloaded engines quite yet ok?

              Comment


                #8
                Kevin,

                Do you know what a propeller power curve is and how it relates to the torque and horsepower curves of an engine?

                Comment


                  #9
                  I dont rhink I would change a thing until I had say around 20 hrs on the engines.

                  Also the part that determins the wot# is the cam. Now if you had a cam that calls for max power to be at 5000rpm verses a cam that calls for a 4400 rpm wot I have dont think you would be over loading the engine if you could only get 4400 out of the 5000 rpm cam. How ever your economy and performance could ultimately suffer. I would think that with more hp you would need to prop up but the it really matters where the hp is being made. If all the extra hp is in high rpm range then maybe you need to prop down. You wont really know until your engines are well broke in every thing is checked and timing is readjusted and all is good. Then do a wot test and prop accordingly. Other wise you may be waisting your money if you change it now.

                  Now if you can only get to 3500 to 4000rpm then you need to do some thing now because you are overloading the engines.
                  1989 Avanti 3450 Sunbridge
                  twin 454's
                  MV Mar-Y-Sol
                  1979 Bayliner Conquest 3150 hardtop ocean express.
                  Twin chevy 350's inboard
                  Ben- Jamin
                  spokane Washington

                  Comment


                    #10
                    RJH wrote:
                    Kevin,

                    Do you know what a propeller power curve is and how it relates to the torque and horsepower curves of an engine?
                    I do not to need to know every bit of science behind prop curves to know that if you cannot reach wot you are overloading your engines.

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

                    where are we right now?

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

                    Comment


                      #11
                      ksanders wrote:
                      LI do not to need to know every bit of science behind prop curves to know that if you cannot reach wot you are overloading your engines.
                      Overloading your engines at what speed. Lets say your props are set to miss WOT RPM spec by a couple hundred RPM because of a temporary overweight condition. If you are running your boat at displacement speeds, I see no way you would be overloading your engine(s). Would you be overloading your engines at 50% of the achieved WOT RPM?
                      Started boating 1965
                      Bayliners owned: 26 Victoria, 28 Bounty, 32, 38, and 47 since 1996

                      Comment


                        #12
                        mmichellich wrote:
                        Overloading your engines at what speed. Lets say your props are set to miss WOT RPM spec by a couple hundred RPM because of a temporary overweight condition. If you are running your boat at displacement speeds, I see no way you would be overloading your engine(s). Would you be overloading your engines at 50% of the achieved WOT RPM?
                        I would tend to agree with you. Possibly I'm not understanding but I do not believe that your doing long term harm when you run your moderately over propped boat at hull speed.

                        I think that the real life history of the 4788 supports that theory. I've seen boats that have engine issues after what seems like relatively few hours. I think these boats were run at a high rpm cruise and were over propped.

                        I've seen other 4788s with lots of hours and the engines are fine. I think these boats were run at displacement speeds.

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

                        where are we right now?

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

                        Comment


                          #13
                          I mean no offense, but let's not muddy the waters by bringing diesel engines into the conversation. Diesels operate differently than gas engines. There are a lot of similarities, but some very significant differences. The original topic concerns the engines in Jeff's boat. If we are to discuss Doug's post then we should try keep things relative to Jeff's boat.

                          Knowing what a propeller power curve is is hardly "every bit of science", but it is essential to understand if you want to know how any marine engine is being loaded. I disagree completely with Doug's statement and am quite willing to debate it with anyone who feels they can support it.

                          Comment


                            #14
                            RJH wrote:
                            I mean no offense, but let's not muddy the waters by bringing diesel engines into the conversation. Diesels operate differently than gas engines. There are a lot of similarities, but some very significant differences. The original topic concerns the engines in Jeff's boat. If we are to discuss Doug's post then we should try keep things relative to Jeff's boat.

                            Knowing what a propeller power curve is is hardly "every bit of science", but it is essential to understand if you want to know how any marine engine is being loaded. I disagree completely with Doug's statement and am quite willing to debate it with anyone who feels they can support it.
                            You are completely correct but we can only relate our discussion to what we know about. We have a long documented track record of understanding overloading issues with diesel engines.

                            Gas engines are another story. For the most part all we know is that you should be it would reach wide-open throttle rpm.

                            you clearly have some specific knowledge of gas engines and overloading. Instead of debating the issue how about if you share what you know and we can all learn?

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

                            where are we right now?

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

                            Comment


                              #15
                              Gas marine engines usually are specified with a 400-500 RPM range on WOT RPM. The diesels in our Bayliners mostly have a single target for the WOT RPM. I see that as one difference.
                              Started boating 1965
                              Bayliners owned: 26 Victoria, 28 Bounty, 32, 38, and 47 since 1996

                              Comment

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