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    4788 actual fuel economy

    I’ve had my 4788 since 2011 but until now have never actually checked what the fuel economy at displacement speed is over a long trip. I have floscans but nothing tells the truth like filling up before and after a trip.

    I filled up and went on a adventure from seward Alaska to Cordova Alaska and back. The trip was 315 NM on the GPS. The seas varied from smooth, to pretty rough. The tides were with me and against me. I think it was a really good representative trip. The fuel used also included 5 days of generator running when needed which was 21 hours.

    The entire trip I ran the Cummins 330 HP engines at 1450 RPM which with my 21” pitched props pushed the boat at between 8 and 9 knots depending on sea state and tide. In smooth no current water it seemed like I was getting 8.3-8.5 knots. The boats bottom was clean as I had just had a diver scrub it a couple weeks prior.

    Total fuel used was port 108 gallons and stbd 114 gallons. The generator is on the stbd tank.

    So... My cruising fuel economy all told was 1.4 NMPG. Not great but not bad.

    If we take the 440 gallons of fuel, the run dry range would then be 616 NM and the 75% safe range would be 462 NM.

    The furthest distance needed for my planned 2021 voyage to La Paz is right at my safe cruising limit, so I’m happy!

    If you have measured actual fuel used (not with a floscan) over a significant voyage, please post the results. I am VERY curious as to how other 4788’s perform. Personally I think I can improve on that economy by dropping to 1350 RPM which would drop my speed to probably 7 knots, but the engines and the boat both feel “good” at 1450 and my Balmar alternator has a decent re-charge rate at that rpm.

    KEVIN SANDERS
    4788 LISAS WAY - SEWARD ALASKA
    where are we right now​​​​​​???​

    https://share.findmespot.com/shared/...j23OquWOj2N3Xe

    #2
    Kevin,
    i can't help you with displacement speeds but I can tell you coming up the coast late last summer we ran the motors 106 hours and the generator a bit but did not track it. We burned 1285 gallons of fuel. I calculated we ran 856 nm but the mileage is low because I did not turn on tracking into and out of ports. We also cruised a bit at slow speeds around the San Juan’s when we arrived. The hours and fuel are accurate and it equates out to a little over 12 gal per hour. We cruised mostly on plane to make bar crossings both leaving and entering, plus it was a bit more comfortable. Our offshore cruise speed varied between 11 to 15 knots. Our longest run was from Ft Bragg to Crescent City at 153nm around Cape Mendocino. Got our butts kicked on that one and that was after waiting four days for weather. We were against wind, current and waves of varying sizes almost the whole trip. I was very happy how the boat performed! Our boat does have underhulls and a swim step hull extension so our performance is going to be different than a stock hull. I also performed virtually every bit of maintenance and upgrades a person could do on the motors and running gear (short of replacing them) to make them as reliable as possible. A hiccup here and there but nothing at all serious. I am glad that I know the boat pretty well so that added to my confidence. We did not have a schedule. I said if we have to leave the boat for the winter, I was ok with that. I rate the trip a 10! It was fantastic. So.... back to fuel usage. You may want to plan to run at displacement speeds but I would also add some time on plane. One of the safety advantages of our boats is the ability to move fairly quickly if we are willing to pay the bill. You have more experience and know better than than me about long runs and rough seas boating where you boat and your delivery up the inside passage!
    Steve
    2000 4788 w Cummins 370's, underhulls, swim step hull extension
    12' Rendova center console with 40HP Yamaha
    MV Kia Orana
    Currently Alameda CA

    Comment


      #3
      We just did 10 days around Memorial Day weekend. I didn't record or export chartplotter data so the distances below are just from what I've drawn on Google Earth because I wanted to contribute to this discussion. Our trip:

      Anacortes to Sucia - Up Guemes Strait, north around Orcas Island: 24.5m
      Sucia to Stuart (Reid Harbor):18.2m 42.7 total
      Stuart to Roche: 5.8m 48.5 total
      Roche to MacKaye Harbor (south end of Lopez) via Cattle Pass: 24.6m 73.1 total
      MacKaye to Bowman Bay: 14.7m 87.8 total
      Bowman to Cornet Bay: 2.7m 90.5 total
      Cornet Bay to Anacortes via Swinomish Channel including some extra touring mileage: 35.7m 126.2 total

      We refueled at Cap Sante and put in 63 gallons.

      126.2 miles / 63 gallons = ~2 mpg, or 1.73 nm/gal

      The above figures include generator usage as well. Didn't log the hours but we used it whenever we wanted- which sounds extravagant but usually means only for the stove at breakfast and dinner.

      Happily for us, sea states were very pleasant and weather was innocuous. We planned our transits around slack tides for Swinomish Channel, Cattle Pass and Deception Pass, but traveled whenever we wanted to otherwise.

      I usually run between 1200 and 1500 RPM with 330's. I can't confess to know my prop pitch but these motor speeds generally net us a GPS speed of 8-9kts in neutral seas, although with currents we've run 10 and 11. The boat was hauled, stripped, and painted in Jan, so I am pretty sure the hull is clean.

      Coming from my 2855 with a 454 and B2 I/O, I am still laughing when I pay for fuel these days. This thing is awesome!
      Chris & Bethany
      Sleep Walk - 1999 4788 w/330 Cummins
      New to us in October 2017
      Moored in Anacortes, WA

      Sold: 1994 2855 Rosalita 7.4L B2 2013-2017

      Comment


        #4
        Originally posted by Sleepwalk View Post
        We just did 10 days around Memorial Day weekend. I didn't record or export chartplotter data so the distances below are just from what I've drawn on Google Earth because I wanted to contribute to this discussion. Our trip:

        Anacortes to Sucia - Up Guemes Strait, north around Orcas Island: 24.5m
        Sucia to Stuart (Reid Harbor):18.2m 42.7 total
        Stuart to Roche: 5.8m 48.5 total
        Roche to MacKaye Harbor (south end of Lopez) via Cattle Pass: 24.6m 73.1 total
        MacKaye to Bowman Bay: 14.7m 87.8 total
        Bowman to Cornet Bay: 2.7m 90.5 total
        Cornet Bay to Anacortes via Swinomish Channel including some extra touring mileage: 35.7m 126.2 total

        We refueled at Cap Sante and put in 63 gallons.

        126.2 miles / 63 gallons = ~2 mpg, or 1.73 nm/gal

        The above figures include generator usage as well. Didn't log the hours but we used it whenever we wanted- which sounds extravagant but usually means only for the stove at breakfast and dinner.

        Happily for us, sea states were very pleasant and weather was innocuous. We planned our transits around slack tides for Swinomish Channel, Cattle Pass and Deception Pass, but traveled whenever we wanted to otherwise.

        I usually run between 1200 and 1500 RPM with 330's. I can't confess to know my prop pitch but these motor speeds generally net us a GPS speed of 8-9kts in neutral seas, although with currents we've run 10 and 11. The boat was hauled, stripped, and painted in Jan, so I am pretty sure the hull is clean.

        Coming from my 2855 with a 454 and B2 I/O, I am still laughing when I pay for fuel these days. This thing is awesome!
        That is Really good economy, and more in line with what I have heard over the years regarding the 4788.

        I am wondering... you ended up with about 20% better fuel economy than I did. Same boat, same engines.

        Could this be sea state? I was in some fairly serious seas during a bunch of the trip.

        I’m going make another fuel economy test next week when i make a 330 NM voyage across the gulf of Alaska, and I’ll of course post those results.

        KEVIN SANDERS
        4788 LISAS WAY - SEWARD ALASKA
        where are we right now​​​​​​???​

        https://share.findmespot.com/shared/...j23OquWOj2N3Xe

        Comment


          #5
          IMHO the best FF (fuel flow) information is derived by the use of flow sensors and represented as GPH. You can then extrapolate into NMPG but that number should only be used as a general guide as sea state can, and will, dramatically change the range but it will not effect the amount of fuel consumed overtime, which remains constant. Pick an rpm, you’ll always get the same FF in GPH but the NMPG will definitely change as you head into a sea vs a following sea.
          Jim Gandee
          1989 3888
          Hino 175's
          Fire Escape
          [email protected]

          Comment


            #6
            Originally posted by Jim_Gandee View Post
            IMHO the best FF (fuel flow) information is derived by the use of flow sensors and represented as GPH. You can then extrapolate into NMPG but that number should only be used as a general guide as sea state can, and will, dramatically change the range but it will not effect the amount of fuel consumed overtime, which remains constant. Pick an rpm, you’ll always get the same FF in GPH but the NMPG will definitely change as you head into a sea vs a following sea.
            I agree completely!

            Thats why I am gathering trip based data Vs just using the data from my floscan units.

            KEVIN SANDERS
            4788 LISAS WAY - SEWARD ALASKA
            where are we right now​​​​​​???​

            https://share.findmespot.com/shared/...j23OquWOj2N3Xe

            Comment


              #7
              Originally posted by ksanders View Post
              I’ve had my 4788 since 2011 but until now have never actually checked what the fuel economy at displacement speed is over a long trip. I have floscans but nothing tells the truth like filling up before and after a trip.

              I filled up and went on a adventure from seward Alaska to Cordova Alaska and back. The trip was 315 NM on the GPS. The seas varied from smooth, to pretty rough. The tides were with me and against me. I think it was a really good representative trip. The fuel used also included 5 days of generator running when needed which was 21 hours.

              The entire trip I ran the Cummins 330 HP engines at 1450 RPM which with my 21” pitched props pushed the boat at between 8 and 9 knots depending on sea state and tide. In smooth no current water it seemed like I was getting 8.3-8.5 knots. The boats bottom was clean as I had just had a diver scrub it a couple weeks prior.

              Total fuel used was port 108 gallons and stbd 114 gallons. The generator is on the stbd tank.

              So... My cruising fuel economy all told was 1.4 NMPG. Not great but not bad.

              If we take the 440 gallons of fuel, the run dry range would then be 616 NM and the 75% safe range would be 462 NM.

              The furthest distance needed for my planned 2021 voyage to La Paz is right at my safe cruising limit, so I’m happy!

              If you have measured actual fuel used (not with a floscan) over a significant voyage, please post the results. I am VERY curious as to how other 4788’s perform. Personally I think I can improve on that economy by dropping to 1350 RPM which would drop my speed to probably 7 knots, but the engines and the boat both feel “good” at 1450 and my Balmar alternator has a decent re-charge rate at that rpm.
              Why don't you think the floscan gives accurate numbers? I was thinking of installing these on my 411 but the cost is a little ridiculous.
              1995 Bayliner 2452 Mercruiser 5.7L Alpha 1 Gen 2

              Comment


                #8
                And Floscan is out of business. There are certainly other solutions out there however.
                Patti & Gordon Lewandowski
                Sammamish WA
                1998 4788 (April 2018)
                ”Knot Home”

                Comment


                  #9
                  Originally posted by Fishtank View Post

                  Why don't you think the floscan gives accurate numbers? I was thinking of installing these on my 411 but the cost is a little ridiculous.
                  You can get floscans close, and mine are relatively close, but i want to get very accurate databased on hull speed travel in order to plan my future exploration plans.

                  KEVIN SANDERS
                  4788 LISAS WAY - SEWARD ALASKA
                  where are we right now​​​​​​???​

                  https://share.findmespot.com/shared/...j23OquWOj2N3Xe

                  Comment


                    #10
                    Carefully plot the flowscan data vs the fuel used at the pump over a period of hundreds of miles, multiple fuel fills and genny use. The flowscan K factor can be adjusted so that the flowscans are extremely accurate. As an example on my Cessna if I fill 70 gals at the pump my FF gauge is normally within 1 gal.
                    Jim Gandee
                    1989 3888
                    Hino 175's
                    Fire Escape
                    [email protected]

                    Comment


                      #11
                      Kevin,

                      We bought our 2001 4788 from Cape Fear NC to Venice, FL, (across Lake Okechobee) on the ICW in winter of 2017/2018. Temps were cool so both our fuel and air were denser than summer. Almost no generator hours. This was our first long trip, we started out topped off and our last fill up was in Cape Coral.

                      On the ICW I run slow, averaging ~8mph at about 1,400 rpm -- I try to leave little or no wake behind me whenever possible. I have the 370B engines with 24"x24" props. ICW is mostly very smooth running but on any given day we'd encounter tidal currents up to 2 mph either with us or against us - I think it mostly balances out so can probably ignore it. Days in January are short and on the ICW you can run out of daylight before you arrive in the next port, so there were at least 4 days (of the 20 total days) where I had to crank up to 1,600-1800rpm to make the next port on the ICW before sunset.

                      I wasn't being meticulous about recording the fuel numbers but it looked like we got about 2.3 statute mpg.

                      (Ok, all you PAC NW boaters...yes, on the ICW and the inland waterways we measure our lives in STATUTE miles. Nautical miles are for offshore blow-boats and ocean crossings... ;-)

                      Coming from a single-engine semi displacement trawler, I honestly did not expect to see anything close to this.

                      When we were looking for our 4788 we were told to try to find one with the 370B engines vs the 330B's. The 'scoop' was that (a) most of the 4788's with 330B engines were overpropped/underpowered and could expect pre-mature engine replacement and (b) that the 370B engines were actually way more efficient.

                      I do see you have pitched down to 21" (good move), so I doubt you are overloading your engines. I think I also saw you installed EGT gauges -- nice! But I think your fuel burn is pretty high compared to mine.

                      Anyway, when I looked into the claim that the 370B engines were more efficient I pulled up the Cummins data sheets and did some math. Sure enough, at 1,600 RPM the 370B's are making way more power and burning way less fuel.

                      So...I'm scratching my head. I cannot make sense of why the 370Bs would be so much more efficient than the 330Bs, especially at low-middle RPM ranges.

                      Or did I mess up my analysis? Anybody else seeing (pleasant) surprises in fuel burn with the 370B's?


                      Comment


                        #12
                        Kevin,

                        Ok I get that you believe that exact measurements of miles traveled and actual fuel used are much more accurate than using a fuel flow gage. It's the practical application of "real world" results. The difficulty is that throughout that period of time between the fuel fill and the re fill there are a tremendous number of variables that might effect the fuel usage. I believe you would be much better served trying to calibrate your fuel flow meters as accurately as possible. At every fill make note of conditions etc. that might have effected usage and not differences between actual usage and FF meter indicated usage. Adjust whatever factor necessary to make the reading more accurate. This will make the readings of your FF more accurate for your boat without having to rely on anecdotal data from others.

                        Now if you didn't already have the FF meters installed then that is a totally different scenario.

                        RB Cooper

                        Comment

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