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Single Diesel vs Twin Gas Inboards

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  • Single Diesel vs Twin Gas Inboards

    I am a great lakes sailor who is just moving downeast close to Wilmington North Carolina. My commercially registered diesel sailboat is too far away, draws too much water and goes too slow for my new location.

    I am changing to a motorboat but I am not thrilled about the cost of fuel or the reliability of a single engine. I can't afford Twin Diesel engines. The Towboats I worked on as a kid had 2 or 3 diesel locomotive engines.

    I am located in an area that has strong currents and turbulent bar crossings. So what would the members of the forum recommend for this area:
    Single diesel (cheap to run, shuts down with dirty or foamy fuel)
    Twin gas inboards (expensive to run, may not run well at low RPM, Plenty of power if you need it, Redundancy)

    Thanks,

    Capt Jim

  • #2
    Depends on the type of boating you plan to do.

    A single engine boat has enough power to move it so long as it works correctly, even in high seas

    A twin motor boat does the same as the single, but will not be able to move it correctly with one engine down.

    If things get rough, loose an motor and your in trouble

    Go to a 3 motor boat and stand a better chance if loose one
    94 Formula 27PC Custom 509MPI MEFI3 , B3 XR
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    G-Dad always said "First Liar doesn't stand a chance"

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    • #3
      Dollar per nautical mile is about the same between a diesel and a spark ignited motor

      BSFC for a diesel is 0333 #/hp/hr
      BSFC for a spark ignited motor is 0.4#/hp/hr

      Diesel fuel is about 20% more per gallon

      Result is about same dollar per mile

      Not sure how you get cheep to run

      The benefit of a diesel is a longer MBTF, and a longer service life. However that is only with proper maintenance.
      Cheesehead boating the Gulf Coast of FLA 27.51° N, 82.53° W

      1988 Cruisers Rogue 2420 -VP 290 DP now powered by custom 468 - https://forums.iboats.com/forum/owner...988-rogue-2420

      Past Boats
      1970 Wooster Hellion - Merc 9.8
      2002 SeaRay 190BR - 5.0 - A1G2 - "Cheeseheads in Paradise"
      1984 Avanti 170DLI -3.0 stringer- "Ship Happens"

      What’s behind you doesn’t matter.Enzo Ferrari

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      • #4
        Really depends on what you plan on doing with the boat.

        We fish a King (mackerel) tournament out of Morehead every fall. The Sounds are shallow with highly variable water levels. What was navigable in the morning may not be navigable in the afternoon. Something with minimal draft has a distinct advantage.

        On top of that you have saltwater to deal with. Anything Inboard would require freshwater cooling or keep you very busy doing maintenance.

        Diesels are very reliable but slow. A Shamrock (diesel) made it to my short list last time, but too slow for the distances I travel, or my patience.

        My recommendation for that area is outboard power. Shallow drafts. Ability to trim the engine out of the water. No closed loop cooling systems to deal with.

        Its my understanding that the fuel efficiency of new high HP outboards (300-350 HP) rivals that of diesels.

        Unless your headed out to sea or the boat requires a multi-engine setup because of its size, a tow boat membership is a lot less hassle than dealing with a multi-engine setups.

        Another bit of advise...there is a reason why all the Carolina built boats have huge (Carolina) bow flares. It comes with the territory

        ....

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        • #5
          A short block V8 MPi will rival and diesel on the market for fuel consumption that has the same power.
          the diesel will be cheaper, but any diesel that can rival the power of an MPi v8 will cost twice as much to buy and service. Also be twice as noisy too.
          if I was in the US, a diesel wouldn’t really come into my thinking unless it was a serious boat or a commercial one.

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          • #6
            There are a few companies now making larger Diesel out boards also. There were some on display at the New Orleans Work Boat Show last November.
            The latest version of the 2 and 4 stroke gas outboards are hard to beat with the direct injection and supercharging. Needless to say the less room taken up in the boat.
            Kenner, Louisiana 1980 Donzi 18'. 2+3 6.2 MPI Alpha 1

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            • #7
              Originally posted by Scott Danforth View Post
              Diesel fuel is about 20% more per gallon
              This is not a real current thread, but where is diesel fuel more expensive than gas at what marina? We've been to most of 'em on the Great Lakes and it's either the same price or cheaper than gas. At at our home marina it is 50 cents cheaper than gas. Some places like Hatteras they either don't sell gas at all, or diesel is $1.18 less per gallon than gasonline.

              And most marinas will knock off some on the price, depending on how much you take on. When we take on 1,000 gallons we've gotten up to 35 cents off the published price.

              As far as number of engines, twin-screw are no better than single if you lose an engine because steerage is severely compromised on a twin-screw with one shut down. Quite a few trawlers like the Nordhavn, built for ocean passages, are single John Deere (Lugger) engine with aux "get home" engine if the main fails.

              A twin-screw with one down is ok in calm seas, but is a bear in current or heavy seas because of the steerage issue. When conditions are really nice, however, we do shut down one (depending on wind) and cruise on the other. Our boat is 72 tons, steel, 3406 Cats (repowered from 12V71's).

              Twin screw does have an advantage in docking, too, if the boat is not equipped with bow and stern thrusters.

              I really cannot imagine anything but a small boat without diesel power. While 850hp is easily economical with diesel power, it would be prohibitively expensive with gasoline for cruising in a displacement boat. Even running our 20kW generator on the hook would not be practical on gasoline.

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              • #8
                diesel is still 20% higher than gasoline at the pumps here. then again, if you are operating a larger boat, you wont pay the pump price, you have the distribution truck back up and pump. usually 1000 gallons or more.

                and if your boat is big enough, you have 4 or 5 trucks back up. (yes, talking between 4000 gallons and some close to 55,000 gallons)

                still doesnt change the fact that $ per mile for fuel is same between diesel and gas. (cant argue BSFC)

                if you want fuel economy in a boat, get one with slaves with oars or a sail.
                Cheesehead boating the Gulf Coast of FLA 27.51° N, 82.53° W

                1988 Cruisers Rogue 2420 -VP 290 DP now powered by custom 468 - https://forums.iboats.com/forum/owner...988-rogue-2420

                Past Boats
                1970 Wooster Hellion - Merc 9.8
                2002 SeaRay 190BR - 5.0 - A1G2 - "Cheeseheads in Paradise"
                1984 Avanti 170DLI -3.0 stringer- "Ship Happens"

                What’s behind you doesn’t matter.Enzo Ferrari

                Comment


                • #9
                  Sign up today
                  This:
                  Originally posted by chris.olson View Post
                  This is not a real current thread, but ....
                  Closed
                  Money spent @ Boat Restoration should be measured in Smiles & Pride SHOP IBOATS-BOAT SPECS-FORUM HELP-REPAIR/RESTO

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