Minimum sized motor boat to round around non stop ?

Discussion in 'Boat Design' started by longcours62, Aug 22, 2013.

  1. Mr Efficiency
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    Mr Efficiency Senior Member

    I see great promise in this round-the-world motor boat exercise as a proving ground for seasickness remedies. I don't think too many will pass the test though !
     
  2. longcours62
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    longcours62 Junior Member

    May be, a good opportunity to lost the 20 pounds of fat than my doctor wanted I lost !:D

    But you are right a passagemaker is far less confortable than sailing boat .
    But paravanes cost in energie ( I thing remember Idelwild fit them after the journey Africa /Australia), actives fins is also a loss of efficiency , bilges keel also ...
    Tanks is a loss in stability
    Sails....may be the loss in windage is compensed by the gain in stability and some "power" aded when you are luky and get wind from the stern.( sometimes it could happen !:p)

    Our actual boat is a great platform for training resistance against seasickness !! with is (too?) big stability, and a roll period of roufly ,2,5 secondes, I already get a very good training
    for giving back my food to the fishs:p

    And, unfortunately for my ego, my wife (until now) never got seasickness !!:mad:
     
  3. Chuck Losness
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    Chuck Losness Senior Member

    Have you thought of a trimaran hull shape. There are only two of you on board so the accommodation needs are minimal. These could all be on one level. The two ama's could hold additional diesel and provide stability. The main hull could be long and very narrow for its length since it will only hold the diesel engine, tankage and stores and no living space. Should be very fuel efficient. Don't know how comfortable it would be. Just a thought.
     
  4. sharpii2
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    sharpii2 Senior Member

    When I read the crossing of Ideiwild from South Africa to Australia they wrott : Rolling 60° ! but I don't understand clearly if it is 60° each side or the total (30° starboard = 30° portside ) ?

    If thinks roll could be more gently :) or your stomacs is far stronger than mine :?:[/QUOTE]

    A deeper, narrower hull would most likely have a longer roll period, because the quickness of the roll is a function of a vessel's initial stability vs. it's roll dampening characteristics. This is why Robert Beebe had his much maligned A/B ratio, which compared the amount of hull profile above the WL with that below the W/L, in screening what would likely be a good ocean crossing powerboat. With a high 'B' portion, the boat was likely to have a lot of natural roll dampening, so would likely be more comfortable in a sea way.

    A boat with a high 'A' portion is likely to have a very quick roll period, or be plain dangerous, as its Center of Gravity would have to be quite high to get the longer roll period, and would not likely be able to recover from a wave induced knock down.

    A quick roll period is far more likely to induce sea sickness than a slow one. A slow roll period is also easier on the boat and gear.
     
  5. sharpii2
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    sharpii2 Senior Member

    I think such a vessel was built during the '80's or '90's, or at least designed.

    I wouldn't put any fuel in the floats and I would configure them so they barely touched the water when the vessel had full tanks.

    The vessel's main hull could be quite narrow, maybe 1.5m, and deep, maybe about 1.5m. It would require no ballast and would have little wave making characteristics. The main hull would be mostly one very long section, about say about 9.0m long, with a bow and a stern completing the length.

    This vessel would float at least half a meter higher when the tanks were exhausted.

    A mono version would probably have a Beam of 3.0m, a draft of 1.5m, and interspersed ballast tanks which would be filled as the fuel is exhausted. It would likely float 0.25 to 0.34m higher at such a time.

    The narrower double outrigger would likely have slightly more whetted area, but less wave making, and therefore likely have a faster cruising speed. The floats should have at least some rocker, to keep the portion of whetted area to initial righting moment within reason.

    The living accommodations of both vessels would best be right on top of the tanks, with little or no added Beam above the WL. This would make somewhat cramped living accommodations for a vessel this size.
     
  6. Tad
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    Tad Boat Designer

    First link in first post of the thread......;)
     
  7. JSL
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    JSL Senior Member

    Getting back to the range vs boat size matter, etc. The attached is my recently launched Ocean Packet 54 - long range cruiser and should give an idea comparison for range, speed, fuel capacity, etc. The owner has yet to hook up the main engine but on his back-up engine he reports 5 knots burning 1 gal (3.8L) per hour. So theoretically, with the capacity of 2100 gal (7938 L), no wind, or current, or growth, or reserve, he could squeeze out 10,000+ miles - about 40% of a circumnavigation. If the entire boat was built of aluminum you might offset weight saving with an increase in fuel capacity but this would still be short of your requirements.
    So, yes, for a small vessel, your objectives may be possible but the compromises could be very invasive. Free 'energy' you don't have to carry ( wind, solar, etc.) might be a more practical approach.
     

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  8. FAST FRED
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    FAST FRED Senior Member

    One problem you should plan on is the boat , at some point will need added ballast.

    25,000 miles even at 5mpg will be many 5000+gallons,many tons of fuel.

    The first burn off may lighten the boat , but after a while the fuel tanks will need to be filled with sea water to maintain even light ship trim.

    This must be planned for.

    I would contemplate flexible bladder tanks that could be removed after the stunt is over.

    The creation of a more normal type interior will help you sell the boat .

    Stunt boats have almost no resale (look at Idelwild) so a normal inside may recoupe some of the investment.

    A simple way to do this might be to find a sailboat of about 60-70 ft , and pull the rig and entire interior. This should remove a couple of tons.

    Install a right sized motor , the required bladder tanks and build a temporary light weight ply living space.

    Sailboat hulls are easier to operate in an overloaded condition , say with the water line a foot below designed.

    Good Luck,,
     
  9. longcours62
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    longcours62 Junior Member

    The "problem with a sailing boat converted in a motor boat is the too great stability, even our actual motor boat whit is stabilty (18476 m/kgs at 48°)she could be "uncomfortable" in some condition.
    With short period of roll (2,5 s)
     
  10. dskira

    dskira Previous Member

    The bicycle must help ;)
     
  11. longcours62
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    longcours62 Junior Member

    The exemple of the "solar planet " is not a good exemple
     
  12. FAST FRED
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    FAST FRED Senior Member

    >The "problem with a sailing boat converted in a motor boat is the too great stability,<

    Easily solved with the first empty fuel bladder filled with sea water and mounted on the PH rooftop.

    Many working sail schooners would hoist an anchor up the mast to slow the motion , which seemed to work well.

    This would simply be a modern variant.

    Unbolting the sail keel , and replacing it with a lighter unit would be too much work ,if the boat will be restored .
     
  13. longcours62
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    longcours62 Junior Member

    In this case we must "move" this weight" + the original ballast (of the sail boat) all the way...and increase the consomption
     
  14. JSL
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    JSL Senior Member

    Another downside in converting a sailboat is the lower efficiency of the propulsion system with the smaller propeller: You might only get 80% around the world.
     

  15. FAST FRED
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    Location: Conn in summers , Ortona FL in winter , with big d

    FAST FRED Senior Member

    A long range boat to be efficient must go slow on minimum power.

    The usual rule of thumb is 1 1/2 to 2 hp per ton , 2240lbs, probably less for extended range .

    The keel weight will be a couple of tons , but eventually the stability WILL be required as the boat gets lighter .

    No matter what the boat will be a slow rolling slug when down a foot on the water line at the start, and a floating cork (with out brought aboard ballast at the end of the voyage.

    Sail boats are built to be a rock awash , when needed , most motorboats are not built to have heavy water on the deck.

    <Another downside in converting a sailboat is the lower efficiency of the propulsion system with the smaller propeller>

    Not really the minimum power required for under SL1 operation does not require a huge propeller. A large diameter 2 blade , perhaps a CPP would be ideal.
     
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