sail drive vs in-line diesel, opinions please.

Discussion in 'Boat Design' started by gow153, Nov 12, 2008.

  1. gow153
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    gow153 Junior Member

    Hello all, this is my first post here, but I have been lurking for a while. I will be building a small displacement hull cruiser to do the Great Loop on. The design will be a 27' St. Pierre Dory, something like this. http://www.spirainternational.com/hp_newf.html
    My top 3 priorities are seaworthiness, ease of construction and fuel efficiency.
    This design is centered around a typical in-board engine design. I know that this is the simplest most efficient design but it also comes along with some down sides;
    - Engine compartment takes up valuable floor space in a small boat.
    - Puts engine noise and heat right in the cabin.
    - Access to engine is limited.

    So I would like to get your opinion on using a sail drive, which eliminates some of these problems. Of course it creates it's own set of problems:
    - Puts engine weigh far back.
    - Drive-train is more complex / less efficient.

    http://www.yanmarmarine.com/uploads/products/pdf/GM_YM/1GM10_TechData.pdf

    Here are the engine choices, what's your opinion?

    Thanks, Greg
     
  2. Eric Sponberg
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    Eric Sponberg Senior Member

    Actually, the Yanmar installation is very simple, goes into the boat with ease. I have specified it a number of times for sailboats--comes in at least three different sizes for larger engines than the one you show. You'd be happy with it.

    Eric
     
  3. gow153
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    gow153 Junior Member

    Eric, I'm assuming your talking about the sail drive. I was not referring to the installation as complex, that part seems simpler that the in-line version. I'm referring to the out-drive, it has to change direction twice. I'm not sure of it's reliability for continuous use. In sailboats it's used on occasion, but in this boat it would be about 1100 hours / year.
     
  4. Eric Sponberg
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    Eric Sponberg Senior Member

    Gow153, In my experience Yanmar has been very reliable, although I do have to admit it is primarily with sailboats. If you would like to discuss this further with someone in the know, the people who manage my mooring in Newport, RI, Oldport marine, are agents for Yanmar, and they have installed a lot of these units. You can give them a call at 401-847-9109, talk with Mike Muessel. They can give you advice and point you in the right direction.

    Eric
     
  5. Tad
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    Tad Boat Designer

    gow,

    A lightly loaded Dory will not be the most comfortable sea boat, but it probably won't kill you. You need to pay attention to centering weights in such a small waterplane.

    The 1GM is not a great engine, a 2 cyl Kubota block marineized by Beta is a far nicer engine to live with for less money including parts at farm price.

    The saildrive is an expensive collection of Yanmar parts not intended for continuous duty. Boatbuilders love them because they can be installed by a guy with a saber saw and some glass tape. No running around finding parts, no fitting and aligning bearings, engine, & shaft. But prop size is limited, and a properly sized prop (for your speed & load) is the key to fuel efficiency. For a displacement cruising boat you want the biggest reduction ratio available. As you will be traveling at about 5-6 knots, ideal prop speed will be 5-600 RPM.

    Depending on your plans, an electric drive system may make some sense.
     
  6. gow153
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    gow153 Junior Member

    Thanks for responding, it's funny because the other boat design that I have been waiting to get a better look at is one of your designs, timbercoast 22, http://bartenderboats.com/images/TimberCoast info 10-08.pdf I'm assuming you are the designer.

    Again, the same things concern me about an inboard taking up valuable floor space right where I need it most. This just may be one of the compromises that must be made. Can you elaborate on the Timbercoast design and also an electric drive. I'm assuming you are talking about a diesel / electric or some kind of hybrid system?
     
  7. TeddyDiver
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    TeddyDiver Gollywobbler

  8. haybayian
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    haybayian Junior Member

     
  9. harlemriverman
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    harlemriverman Senior Member


    in-board, in-line with a honda generator that you can refit in most any sea state as a secondary source of power to the drive train, which in terms of comfort puts you closer to 32' in my humble judgement.

    for some reason the dory is coffin of choice for adventurous sojourners. if i were so inclined, and safety my first priority, i would be looking at a design more along the lines of http://www.turbosquid.com/FullPreview/Index.cfm/ID/168497
     
  10. gow153
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    gow153 Junior Member

    I think a little clarification is needed based on the responses. This is the great loop http://www.starsongcruising.com/id6.html (not a circumnavigation). It has open water areas in the Great Lakes, Gulf of Mexico, a few runs along the east coast and Island hopping to the Bahamas. I will be in no hurry so waiting for the right weather window will be the rule.
     
  11. harlemriverman
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    harlemriverman Senior Member

    ah...

    dory's fine. reversing myself, go with the sail drive. the complication factor will be more than compensated by your savings in replacement screws. sounds like a fund voyage.
     
  12. Tad
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    Tad Boat Designer

    This is a coastwise and protected water cruise, no (or very little) open ocean voyaging. Moderate draft and full prop protection will be a huge advantage.

    Without a ton of fish aboard the dory sits on top of the water, the flat bottom means CB shifts very quickly as the boat heels, this means quick righting and quick (tiring) motion. In a deeper hull CB shifts more slowly, she will roll farther and slower, with more gradual increase of righting arms. This is the concept behind the Timbercoast Troller. The deep-vee double-ended hull has fine ends which flare above waterline. She is efficient at low speed, 7.5 knots being max. She also does not change shape much with loading. Full propeller protection behind a deep keel means the boat won't blow all over the ocean at low speed.

    For your intended cruise electric propulsion would necessarily be a hybrid system with a substantial diesel charger. Whether such a system made any sense will depend on the specifics of the particular system, and on your individual style of use. If you plan on many longer non-stop hops and anchoring out every night it may not work. But if you intend short daily hops with marina (plugged in) stops of several days the electric solution may be an interesting idea. In my experience these systems are expensive, but for some the convenience pays off. Especially when sneaking up on ducks!
     
  13. gow153
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    gow153 Junior Member

    I had Beta marine size my system and this is was they say:

    "Thanks for contacting us.

    I ran a prop calc, and for boat with a displacement hull, and LWL of
    20.17', displacement of 4,600, and transmission ratio of 2.6:1, here
    is the performance info:
    Beta 14, approximate hull speed = 6.5 knots with 15 x 9 RH three
    blade prop

    The Beta 14 can run at 3600 RPM all day. So 80% will be about 2880
    RPM. That is a nice fuel efficient point to operate the boat. You
    should consume something between a pint and a quart of fuel per hour.
    The largest gear reduction we have for that engine is 2.6:1. With a
    15" three blade prop, your have very nice blade loading and efficiency,
    with minimal slip."

    That would be a 15" prop. at 1100 rpms. To run at 5-600 rpms I would need a 22-24" prop. and run the engine in an inefficient part of it's power curve. Also a prop. that size becomes hard to deal with physically. I'll see what they say about the V-Drive and sail drive.
     

  14. FAST FRED
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    FAST FRED Senior Member

    My top 3 priorities are seaworthiness, ease of construction and fuel efficiency.

    For the trip intend , seaworthyness would be at the bottom of the list.

    Frankly I would consider an outboard 20hp Honda or similar.

    The inital cost will be far lower than any added fuel cost on a 1500 hour trip.

    The advantage in running aground (lots of rocks in much of the Canadian portion) or of simple engine replacement ot repair would be al, to the OB , and a handicap with any diesel.

    Sometimes the simplest way IS the better way.

    FF
     
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