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What defines an Expedition Yacht?

Discussion in 'Popular Yacht Topics' started by YachtForums, Mar 18, 2013.

  1. Capt J

    Capt J Senior Member

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    I'm no Naval Architect, but I'm pretty sure that with a true displacement hull, there is no amount of horsepower that would get it to plane. I think an absorberant amount of horsepower would push the bow underwater and sink the boat.
  2. Opcn

    Opcn Senior Member

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    K1W1, do you mean any hull shape, or where you referring to a hull of any weight? Perhaps in response to what I said about there being D/L ratio limits on semi-displacent and planing hulls. To that I'll say that I totally agree, the ratio just comes in when determining what is practical.
  3. K1W1

    K1W1 Senior Member

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    Hi,

    It is a theoretical statement.

    There is a resistance to friction that can be overcome by a thrust in excess of it.

    It works out ok on paper but in practice there are a few technologies missing that are required to make it work not least of which is the prop.
  4. Capt J

    Capt J Senior Member

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    Forget the props, just mount some turbines off of an airbus on it!!!! :)
  5. K1W1

    K1W1 Senior Member

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    Not sure what the highlighted word is can you clarify?
  6. K1W1

    K1W1 Senior Member

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    Do you imagine an Airbus is driven by thrust out the exhaust?
  7. Capt J

    Capt J Senior Member

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    Yes, the energy from the combustion process turn the fan blades inside of the turbine pushing thrust out the exhaust portion of the engine and that is what propels the airplane. However, then you won't have to deal with any underwater drag you know if shafts and propellors in the water, trying to get your yacht onto plane.......LOLOLOL Similar to a waterjet in principle......such as a kawame

    exorbitant: exceeding the customary or appropriate limits in intensity, quality, amount, or size

    I must have mispelled the word.
  8. HTMO9

    HTMO9 Senior Member

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    hull speed

    As I thought, K1W1 was just provocating.

    As we all know, the hull speed of a full displacement hull is dependend on its waterline length (LWL). Any displacement hull produces its own wave system, concisting of bow and stern wave. If with increasing speed, the bow wave reaches the stern wave, the hull gets trapped in its own wave system. If you apply more power, the only thing that goes up is noice and fuel consumption, not speed. The theoretical hull speed of a full displacement measured in Kts and can easily be calculated by the formula 2.43 times the square root of the LWL.

    One of the biggest containerships of the world, the mighty Emma Maersk has a total length of 1302 feet and therefore a theoretical hull speed of 48,22 Kts. Her engine deliveres app. 80.000 KW. Her service speed is around 25.5 Kts with a clean hull. As the power requirement increases with the square with increasing speed, one can imaging the power required to reach 48 Kts.

    But there is a little trick to go faster with displacement hulls. If you design a very sleek hull with a very long sharpening part and a length to width ratio of app. 10:1 and add a very sharp tear-off edge at the stern, the stern wave stalls and the hull speed can be rased for a 25 Kts hull up to 40 Kts. This design is used for warships like destroyers or fregates. But this hulls are so unstable along its longitudinal axis, they start rolling virtually on a wet lawn. The yacht Rising Sun is a typicall example for this theory. Plus its brutal power of 4 times 9000 Kw MTU 20V 8000 it makes here a pretty fast boat.

    But this type of hulls are called meanwhile semi displacement hulls, but in reality they stil belong to the displacemnet hull breed.

    Cheers
  9. PacBlue

    PacBlue Senior Member

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    And you are no different J? You pretty much blanket any comment I have made on this forum, because the world is alright as long as it is according to the word of CaptJ.

    Sorry for the agravation, I'll try and keep the bar low.......
  10. YachtForums

    YachtForums Administrator

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    Let's all try to stay on subject, please. Splitting hairs will only leave the forum bald.
  11. Old Phart

    Old Phart Senior Member

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    I dunno
    Risking splitting hairs to only leave the forum bald, should that be 1.34?

    Square root of 1302 x 1.34 = 48.35 :rolleyes:

    Hull speed - Wikipedia, the free encyclopedia
  12. Opcn

    Opcn Senior Member

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    Moving back to the subject. Does anyone have any standards to propose about what we should consider to have made the cut? Is there a lower (or I guess upper too) limit on the vessel size?
  13. Capt J

    Capt J Senior Member

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    I don't know......I'd say the Nordhavn 46' would be an expedition yacht. It's just with the smaller the expedition yacht, the smaller the toys you'll be able to carry......but could still carry an appropriate sized dinghy and a scooter on one. They're proven transatlantic boats and rough weather boats. I would say that would be about the smallest of the breed.......
  14. Opcn

    Opcn Senior Member

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    Presumably some of what you would need a large tender for if you traveled around in a large yacht you could just do with your yacht if it were as small as the 46'
  15. 'RoundTheHorn

    'RoundTheHorn Senior Member

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    Lest we forget, the Nordhavn 40 (at 39 feet 9 inches) was the vessel that did the Around the World Voyage from November 3, 2001 to June 30, 2002.

    Nordhavn Around the World Voyage
  16. AMG

    AMG YF Moderator

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  17. HTMO9

    HTMO9 Senior Member

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    Hull speed

    Sorry gentleman my mistake, the formula for the theoretical hull speed in Kts is 2.43 times the square root of the LWL and the LWL measured in meters. I live in the metric world. And 1302 feet is the total length of Emma not the LWL. But I took the correct figures, 48,22 Kts is correct.

    Cheers
  18. HTMO9

    HTMO9 Senior Member

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    Expedition yachts

    In the course of this thread we have talked about size, range, seaworthyness, provision space and the space and usefull load capacity for tenders and toys.

    But what makes a boat a true expedition or explorer yacht, as far as type of hull, propulsion (type and number of engine, gear and prop, steering, electrics, hydraulics), redundancy, enviromental conciderations like type of exhaust (dry or whet), exhaust gas cleaning and wastwater treatment, etc. are concerned.

    Cheers
  19. Marmot

    Marmot Senior Member

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    What these guys decide to call it or what the buyer decides to do with it.

    Attached Files:

  20. HTMO9

    HTMO9 Senior Member

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    Sorry that I forgot the question mark, but it was a true question, in order to start a discussion obout these subjects. I am learning a lot from this thread.

    The combined knowledge of Yachtforums is unbelievable. I am glad that I joined the forum!

    Cheers