Help me make the decision ... twin or single diesel?

Discussion in 'Diesel Engines' started by piperca, Apr 1, 2009.

  1. Stumble
    Joined: Oct 2008
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    Stumble Senior Member

    Personally for any offshore work I demand two engines. I have been caught out enough times when one craps out that the safety factor of a second means of propulsion is worth it to me. But if you are set on going with a single, then I would highly recommend an outboard kicker, with enough fuel to get you home, just in case.
  2. u4ea32
    Joined: Nov 2005
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    u4ea32 Senior Member

    I think the single six cylinder Yanmar diesel is the way to go. IMHO!

    I've run tens of thousands of miles in single diesel boats and never had a problem that would have been better with twins. Sure, sometimes one needs to mess with filters, but fuel is the single point failure on twins -- if a single dies due to clogged filters, both engines in a twin would also die. A lightly loaded diesel, like a single 315 in a 10K boat going 18 knots, will be tough.

    In fact, my own boat, also narrow beam (8.3 feet wide) with twin gas (in my case, twin big blocks) is going to need a re-power: both engines have failed. My boat weighs the same as yours. While my boat could top out at 70, in fact I also cruised around at about 22, as that's how fast the Pacific allows small boats to go!

    So I'm in the same place as you, a year later.

    My options:

    1) Just sell it now as a project boat: as-is.

    2) Get rebuilt engines and just sell the boat. I really am fed up with twin gas, so I would not want to keep her with twin gas I/O engines.

    3) Put small twin diesels in there. But as you have discovered, that's expensive. And still twin engine maintenance, and lousy service access.

    4) Fill in the transom holes, and change the stringers, and put in a single diesel, like a yanmar six as you've selected.

    As with your boat, I think only the single diesel option makes sense of the above.

    However, one more:

    5) Twin outboards! Twin Optimax 150 or 200s will work for Pacific Ocean speeds.

    The outboard option, like the single diesel option, requires some fiberglass work to the transom. But the outboards would allow all the structural stuff inside the hull to remain the same, so that should be cheaper. On a Skipjack 28 you've already got a flat cockpit floor, but in my boat, this would make my cockpit big and flat. Nice! But of course, some expense for the new cockpit sole.

    Installing outboards is MUCH MUCH easier than any I/O or inboard, and certified pre-owned can be less than $10K each, perhaps much less.

    And the huge weight savings -- 2500 lbs less weight, and the weight further aft which is better for a planing boat -- should really help fuel economy. And from what people say, these "orbital charge" Optimax are more fuel efficient than EFI 4 cycle engines. Light+efficient might make a noticeable dent in my fuel bill.

    For those of you not from Southern California: around here, its pretty typical to run 100 miles, and not unusual to run 200 miles in a weekend. On four day weekends I usually run about 500 miles. The islands are out there, they are big, and the interesting cruising places and good fishing places are way the hell out there.

    Hopefully my wife won't read this, but we run an average of 200 hours per year, and have been burning 20 gallons per hour at our Pacific cruising speed of 22 knots, so that's 4000 gallons per year at $3.50 or $14000 per year. And if I had to buy fuel at a gas dock instead of gas station on land, then the fuel cost would be $20K per year! So in California, the cost of fuel really has become the biggest cost of ownership, by a good margin.
  3. capt littlelegs
    Joined: Apr 2010
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    capt littlelegs New Member

    Twin engines means you have twin main or day tanks and change over filters for each engine so twin diesels are four times more reliable than one diesel with only one filter and diesel is far more reliable and economical than gas. Normal service maintenance shouldn't be anymore difficult with twins. Outboards are expensive to buy and maintain with a much shorter life.
  4. apex1

    apex1 Guest

    What a utter nonsense. How can twin engines be 4 times more reliable? Who is mad enough to have only one filter on a single engine?

    Are all the fishermen, is all the commercial shipping world just mad to choose only one engine for propulsion?
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    FAST FRED Senior Member

    one engine for propulsion?

    Really big difference between an industrial engine and a marinised car take out.

  6. Easy Rider
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    Easy Rider Senior Member

    I remember real marine engines. There aren't any anymore. They had flywheels on the fwd end, updraft carbs and some had cast iron oil pans that were common to engine and gearbox. Lathrop, Hercules, Red Wing, Palmer, Chrysler, Gray, Nordberg, Kermath, even Owens and Chris + Craft. One of the best engines of the 50s still exists today ..Universal.
    Where do they get 350 GM engines? Must be car engines. Never heard of a 350 Chev industrial engine. Diesel marine engines basically all come from industrial stock that not true Fred?
    Oh .. about the question. Twins are better. Like most things better ..more expensive.

    Easy Rider
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    FAST FRED Senior Member

    Never heard of a 350 Chev industrial engine. Diesel marine engines basically all come from industrial stock that not true Fred?

    The Chebbies come from a long supply line , both truck stuff (salt cooled valves) and racing stuff Forged crankshaft is off the shelf and cheap.The camshaft of your choice and the matching intake will put the HP at whatever rpm you desire.

    Crusaider does a good parts selection , would be worth researching and copying , or just by a Crusaider.

    In the more modest 250 to 500 Hp range most boat diesels are either from earth moving machines , ( CAT or John Deere ).

    Many will come from the generator or trucking industry , Detroit .Cummins.

    Dedicated marine engines are only in really large sizes as the 4000+hp EMd is actually a train engine .

    Once the cruise rpm is about 100rpm , its a modern marine engine.

  8. apex1

    apex1 Guest

    No that is not true, at least not for all brands. It would be as valid in several cases to say the industrial engines are derived from marine engines. Some Deutz, MAN, MTU, Detroit for example.

    There are still some of the "good old" diesels around, though not the brands you named, but Bukh and Sabb are alive.

    Have no comment on the chevy┬┤s, because the questoin was single or twin DIESEL.

  9. girvin
    Joined: Dec 2009
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    girvin Junior Member

    just please don't get the vovlo penta. They have alot of problems like impeller shafts shatter time and time again. We have gone through 3 engines, one of which only got 1800 hours. I am trying to get my boss to change on the next go around.
  10. girvin
    Joined: Dec 2009
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    girvin Junior Member

    Ohh and go single with a outboard kicker and its own gas tank. Its a good proven combination that the west coast whale watchers use and for use its all about being able to be safe in some serious waters and still make the best profit we can. We put about 40 - 50 hours a week on each boat for 4-6 months a year.
  11. mark775

    mark775 Guest

    I have tried to stay out of this because I already weighed in and I thought the thread would atrophy soon but "please don't get the vovlo penta" ? made me come back. Any engine one finds will have opinions "Yea" and "Nay". More than what color the engine is, the quality of service shud be one's deciding factor, IMO. I have a Volvo I trust my life to but that is not why I'm writing - It could be a Cummins or Scania or several others, I could sort out its idiosyncrasies and be happy for decades. With a diesel engine, run slow to run long. Getting a load on the engine is critical but too much of a load is worse than too little. If the boat is not to have CP, prop it so that it gets all of its rated RPM +, FULLY LOADED, back off at least to the recommended cruise RPM, find a "sweet spot" and watch your pyrometer and boost gauge for changes from the norm. Change your oil often, have a temperature sensor installed on your exhaust mixing elbow, change zincs on schedule, have the thing perfectly aligned, lots of dry air to the engine space, a shaft with a safety factor of at least five, feed it CLEAN, DRY FUEL and have a healthy electrical system. If one does these things, he will find satisfaction in his boat and almost never lose independence. In today's world, wonder why big "battlewagons" sell for so little relative to new? Why there are NO big Bertrams under construction at this time? Because unless there is a SPECIFIC AND QUANTIFIABLE NEED, twin engine boats are so much more expensive, LESS reliable than a well loved single, and less economical that they are an anachronism. Get one cheap and live aboard. To go to sea, get a single engine boat.
    Notice, too, that the most experienced mariners agree. Tho consensus does not make right, it's a damn fine place to start.
    None of this advice applies if one is the type to run it hard and put it away wet - for those, two, three, four engines are more appropriate. In fact, if in that category, I have to question a person going to sea at all under his own responsibility. Just charter a good boat and allow a pro to take care.
  12. girvin
    Joined: Dec 2009
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    girvin Junior Member

    I don't mean to bag on volvo maybe just the 330 and 310 I have thousands of hours in them and just think there are better alternative. THe bigger volvos I thinks are better. WE ran ours at 2700 rpm to 2800 never ran more than that and we have excelent mechanics and never missed a service. Just my experience, not law. Not trying to say they are all bad but every charte company here has had issues. 7 boats running them total. I am still a single engine kinda guy though.
  13. mark775

    mark775 Guest

    Out of curiosity, what is the model that has problems and what are the specific problems? I think this applies to the intent of the thread...
  14. girvin
    Joined: Dec 2009
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    girvin Junior Member

    the 310 and 330 have impeller shafts that shatter and the engine overheats and burns up. It has happened to every boat here running this engine at least once and we all have impeccable maintenance. we only got 1800 hours out of our last one and the guys next to use got 4000. Volvo says they will last 5,000 I have yet to see one get there out here. We don't have a choice though only one mechanic shop in town and 8 tour companies with alot of boats.

  15. mark775

    mark775 Guest

    I am not familiar with those models. Are they similar to the 40 series or D6?
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