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1984 46 post fuel consumption estimates

Discussion in 'Post Yacht' started by Posterboy91, Dec 12, 2017.

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  1. Posterboy91, Dec 12, 2017
    #1
    Posterboy91

    Posterboy91 New Member

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    Hello everyone,

    I finally closed on my purchase of a 1984 46 with DD 450hp. i have gotten all the major systems up and running in the last week and now i am running the boat from new jersey to florida over the next few weeks before a real winter storm closes me out and i am forced to winterize the boat. i am new to Post and have been trying to determine what the burn rate will be. Some people i have met that own Posts have told me as low as 25GPH and i have heard as high as 45GPH. With this large of a gap i was hoping to get some input from the owners on the site here. Since i heard someone say 45GPH i have been very concerned with my range per day and figuring out ports to pull into on the way down
  2. Hermen Ferraz, Dec 12, 2017
    #2
    Hermen Ferraz

    Hermen Ferraz Member

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    Hello, welcome i am also new to post have some input for you. I have an 88 46 Post but i have the 6v92 with 550hp. I bought it in north St. Petersburg and drove hit home to Miami. I hold about 630 gallons of fuel and if my math was correct i wasted between 28-32 GPH on the trip home cruising at 20knots. Hope this helps and welcome you’re going to fall in love with the Post i have.
  3. Capt J, Dec 13, 2017
    #3
    Capt J

    Capt J Senior Member

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    What engines are in it? 6-71 TA's? 25 gph seems awefully hopeful. 30-35 GPH sounds about right for the pair. But I don't have a lot of experience with the 6-71's
  4. RT46, Dec 13, 2017
    #4
    RT46

    RT46 Senior Member

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    I attached a fuel graph for 671 TIs
    I understand if your engines are running correctly and you can get max load WOT your fuel burn is going to be really close if not exact.

    I have 671 TIBs and I follow this graph pretty closely.
    I don't have floscans.
    I always round up to 2 gallons per nautical mile at cruse when planning a trip.
    I burn less fuel, but I round up for math and safety margin.

    At the end of the trip I always seem to have left over fuel and
    fuel burn seems on or close to the below fuel burn graph.
    671.jpg
  5. mwwhit1, Dec 13, 2017
    #5
    mwwhit1

    mwwhit1 Senior Member

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    I have an 84 43, with the same engines. You will burn in the low 30's per hour at 2000-2100, matching the graph above. You can run 10-12 hour days, with your fuel tankage. A 200 mile day is probably a safe maximum. Keep your plans very tentative and flexible. Weather, this late in the year, is tougher and may force you inside if you have to keep moving. Congrats and best of luck with the trip!!
  6. Posterboy91, Jan 21, 2018
    #6
    Posterboy91

    Posterboy91 New Member

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    well the results of my trip from new jersey to florida have been good the boat averaged between 22-26 with the gen on and engines running at 2000-2100. some people I have talked to said this maybe the case because the props are to small and the engines are not operating at the proper load. I have averaged 16-17.5kts most of the trip with full tanks of fuel. what are some of your thoughts
  7. Capt J, Jan 21, 2018
    #7
    Capt J

    Capt J Senior Member

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    Yes, less load equal less HP demand (at a given rpm) and less fuel burn.
  8. Capt Ralph, Jan 21, 2018
    #8
    Capt Ralph

    Capt Ralph Senior Member

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    22-26 total ship?
    At 2100RPM, your under loaded.

    Think of this as stuck in second gear on a three speed.
    Lets double check your wheel sizes and reduction.
  9. Capt J, Jan 21, 2018
    #9
    Capt J

    Capt J Senior Member

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    Well what speed/rpm are you making at WOT with full fuel/full water and gear......let's start there.

    Also rcrapps, he has 6-71 TIB's and if memory serves me right (it's been a long time) cruise is 2400 and WOT is 2800 rpms.....so he's running under cruise rpms too. But the graph says 2500 rpms.......what is cruise rpms on these motors?
  10. Capt Ralph, Jan 21, 2018
    #10
    Capt Ralph

    Capt Ralph Senior Member

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    You know that sound of fingernails on a chalk board? Your back bones feel weak and you want to turn away?
    A 71 spinning toward 2800 RPM has the same effect on me.
    I think high idle @ 2500 and loaded @ 2450 should be the max numbers with a light boat.
    Fast cruise from 2100 to 2200 RPM.

    At 2100 RPM, I figure at least 350 maybe up to 375 HP if the wheels are correct. That should be around 35+GPH total boat (less gen-set).
    The above graph seems a lil conservative to my reasoning. However, the graph and I do agree, He should be consuming a lil more fuel at 2100RPM .

    Ah, but the rub; It's hard to do whole trips at speed. 6-71TIs or TIBs really don't consume mega gallons at lower RPMs.
    Posterboy91 just quotes average.
  11. Posterboy91, Jan 22, 2018
    #11
    Posterboy91

    Posterboy91 New Member

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    I did the average based on cruise speed times and made an adjustment based on Times I was idling but most of my trip was outside in the ocean so these are the numbers I got. The boat also had a full load of fuel water 4 guys and provisions for 2 weeks onboard. WOT the engines are hitting 2600 so I know I can pitch up a size in the blades.
  12. Capt J, Jan 22, 2018
    #12
    Capt J

    Capt J Senior Member

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    If you're hitting 2600 with full fuel, water, provisions, and 4 guys. Yeah you're underpropped. Each inch of pitch drops 50 rpms.
  13. Davidoc, Jan 22, 2018
    #13
    Davidoc

    Davidoc Senior Member

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    What were your RPM's at 20 knots? Genset running? Thanks
  14. Capt Ralph, Jan 22, 2018
    #14
    Capt Ralph

    Capt Ralph Senior Member

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    I remember this old BlackFin I purchased.
    The only set of props, probably original, were re-worked so many times they lost lots of blade area and diameter.
    I was impressed with the new & correct props, how much larger they were over the old ones.
    Oh, DaFin ran like a race horse. Finally able to apply HP to the water.

    Would you have a spare prop set on board? Readable numbers?
  15. Beau, Jan 22, 2018
    #15
    Beau

    Beau Senior Member

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    Did the OP get his answer on probable fuel burn so he can paln his trip to FL?
  16. Capt Ralph, Jan 23, 2018
    #16
    Capt Ralph

    Capt Ralph Senior Member

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    Based on post #6, I assume he is here.
  17. Beau, Jan 23, 2018
    #17
    Beau

    Beau Senior Member

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  18. RT46, Jan 25, 2018
    #18
    RT46

    RT46 Senior Member

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    671 TIB max WOT is 2550 RPM under load
  19. Capt Ralph, Jan 25, 2018
    #19
    Capt Ralph

    Capt Ralph Senior Member

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    You need more wheel.
  20. Capt J, Jan 25, 2018
    #20
    Capt J

    Capt J Senior Member

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    Then I'd just leave the wheels the way they are, a touch under propped is better than over propped.
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