Impossible boat fuel mileage, 50 footer goes 29 knots at 5.5 liters per nautical mile??

Discussion in 'Powerboats' started by sdowney717, Oct 16, 2021.

  1. sdowney717
    Joined: Nov 2010
    Posts: 1,175
    Likes: 85, Points: 58, Legacy Rep: 274
    Location: Newport News VA

    sdowney717 Senior Member

    nautical miles liters.PNG Fantastic Boat Trip to Skellig Michael with John Brennan - YouTube

    at 7:14 into video, he shows the screen with speed and fuel consumption. Has twin diesels.
    at 5 minutes in, he says it is a semi displacement hull?
    How can this large boat go almost 30 knots per hour in the ocean using such small amount of fuel?
    5.5 liters is 1.4 gallons per nautical mile and the boat is going almost 30 nautical miles per hour.

    That is better mileage than many large boats get.
    What am I missing here.
    There are couple videos on this boat, one shows the layout and engine room.
     
  2. Mr Efficiency
    Joined: Oct 2010
    Posts: 10,386
    Likes: 1,042, Points: 113, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    5+ litres per nautical mile I would say isn't that wonderful.
     
  3. philSweet
    Joined: May 2008
    Posts: 2,682
    Likes: 451, Points: 83, Legacy Rep: 1082
    Location: Beaufort, SC and H'ville, NC

    philSweet Senior Member

    It suggests around 450 hp at the shaft. Maybe a bit more if dead on the engine sweet spot. At about 45 pounds per hp at 30 knots, that's a 20,000 pound boat. A Sea Ray 500 weighs double that. It burns 47 gal/hour per engine at 28.6 knots. Maybe that's one engine? Or the 50'er isn't really a 50'er footer, and the tide is favorable.
     
    fallguy likes this.
  4. sdowney717
    Joined: Nov 2010
    Posts: 1,175
    Likes: 85, Points: 58, Legacy Rep: 274
    Location: Newport News VA

    sdowney717 Senior Member

    it is a 15 meter boat made by Redbay
    More detailed info and walk through on the boat at the dock.
    Meet The Owner : John Brennan - YouTube

    At 20 minutes in is the engine room. I think he says 3 Yanmar G70 engines?
     
  5. BlueBell
    Joined: May 2017
    Posts: 2,684
    Likes: 959, Points: 113
    Location: Victoria BC Canada

    BlueBell . . . _ _ _ . . . _ _ _

    That's ~160 litres per hour...
    Certainly not miraculous
    Also known as "knots".
    .
     
  6. philSweet
    Joined: May 2008
    Posts: 2,682
    Likes: 451, Points: 83, Legacy Rep: 1082
    Location: Beaufort, SC and H'ville, NC

    philSweet Senior Member


  7. cracked_ribs
    Joined: Nov 2018
    Posts: 160
    Likes: 146, Points: 43
    Location: Republic of Vancouver Island

    cracked_ribs Senior Member

    Seems reasonable, in the sense that I would have no problem with those numbers as long as it wasn't my visa we filled up on.

    Did you maybe get the units reversed in your head and think they were claiming 5.5litres per hour?

    Now that would be impressive!

    Although it could be done. I don't think with Yanmars but there's a Volvo product that could get you to 30 knots on a 20m boat, burning even less.


    Team-SCA-VO65.jpg
     
    DogCavalry likes this.
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.