Displacemente Pahi 63: how is this possible?

Discussion in 'Multihulls' started by eiasu, Jun 6, 2012.

  1. eiasu
    Joined: Nov 2011
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    eiasu Junior Member

    I read
    on the Wharram website Pahi 63 :
    Weight 8 tons
    Loading Capacity 4,5 tons
    Draft 0,9 - 1,5 m

    And on their websites:

    Chris White Atlantic 57
    Displacement 26,500lbs (12 ton)

    Gunboat 60
    Displacement Lightship16,200 kg 35,715 lbs Displacement Max Load19,000 kg 41,887 lbs

    How is possible that the Pahi is so light? Built with Ply wood and Epoxy and the other two use much more expensive, sophisticated and light materials?
    Can't understand !!!
    Must be something missing ...
    ciao
    eiasu
     
  2. Corley
    Joined: Oct 2009
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    Corley epoxy coated

    Theres lies, damn lies and boat weights they all fit into the same category. I'd want to have the boat craned out or weighed on a load cell before I believed a word of it. Also in what state? Lightship and whats defined by lightship varies from designer to designer some even weigh without essentials. Now there is an argument due to the lack of bridgedeck structure you save some weight but that much? I dont think so.
     
  3. Angélique
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    Angélique aka Angel (only by name)

    Pahi 63 plans call as standard for 2 outboards. (2 x 9.9 Hp high trust ?)

    The Atlantic 57 has 2 inboard diesels with saildrives. (2 x 55 Hp Volvo's)

    There you might have what, a ton ? *
    • Edit: Likely to be more than a ton, taking into account the starting batteries, engine controls and the 757 L diesel tankage for the bigger engines of the Atlantic. -- The Pahi standard starts with a pull rope and is likely to carry less fuel.
    Eiasu: ‘‘Chris White Atlantic 57 Displacement 26,500lbs (12 ton)’’

    12 tons what? Empty or Lightship or Max Displacement ?

    If it's Max Displacement then that's ½ a ton lighter than the Pahi 63.

    Cheers,
    Angel

    P.S.

    Gunboat 60: Motors + Gensets + Solar System + Battery Bank + Some Equipment
    Only thing the Pahi 63 has for that in the plans is 2 outboards, so goes for everything on board . . . . ;)

    Defferent boats, different weights....
     
    Last edited: Jun 7, 2012
  4. cavalier mk2
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    cavalier mk2 Senior Member

    And different interiors, the Pahi 63 is flexi space meaning there is nothing there but compartments with footwells. This eliminates the cabinetry weight. Owners are supposed to furnish with hangings, galley boxes etc....
     
  5. MikeJohns
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    MikeJohns Senior Member

    Weighing works for small boats but becomes rapidly very expensive then on to impossible as the size goes up. Also never believe the travel lift weight indication they are often out by anything up to 30% and usually well over what the boat weighs.

    Just check your measurements against the plans then if you have a 3D CAD model the displacement is really easy and accurate from measuring for and aft waterline to deck edge. With ships and larger boats sans plans we take the lines off the boat to find the displacement. It's just as accurate.
     
  6. sabahcat
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    sabahcat Senior Member

    You do realise weight and displacement are two different things?

    I read it as the boat weighs 8t
    Has a displacement of 12.5t
    allowing it to carry 4.5t

    It will have a different displacement in fresh water vs salt and a different one again if in a sea of mercury
     
  7. Alik
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    Alik Senior Member

    Many catamaran designers give very optimistic numbers for weight to keep the design attractive. Say, there would be weight without structural overweight margin, no genset, no teak, no air-conditioning system, no liferaft... At the end, boat is 2+ tons heavier then it was in the specs!

    When it comes to standard definitions, ISO8666 defines clearly what is meant by LCC (light craft condition) and LDC (loaded displacement condition). We usually show either LCC or both LCC and LDC to avoid confusion.
     
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  8. eiasu
    Joined: Nov 2011
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    eiasu Junior Member

    Thank you everybody for your answers,
    sorry for my ignorance, there is something i do not follow:

    i do not know the difference between weight and displacement,
    I thought:confused: it was the same, the mass of the fluid moved,
    but seemingly it is not so!
     
  9. champ0815
    Joined: Apr 2008
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    champ0815 Senior Member

    Well, I think your are not so wrong!
    The mentioned displacement is the weight of the loaded ship to the designed water line. The weight is the mass of the more or less empty ship depending on definitions.
    But maybe I'm also wrong?
     
  10. Steve W
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    Steve W Senior Member

    You cant really compare displacements of full blown bridgedeck cats like the Gunboat and Atlantic with a minimalist open bridgedeck cat like the Pahi just because they are a similar length, they are completly different animals, there is hugely more surface area with the bridgedeck boats and all this weighs something regardless of what it is built from, plus of course all the systems that just dont exist with the Pahi.


    Steve.
     
  11. sabahcat
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    sabahcat Senior Member

    Lets make some numbers up for demonstration purposes.

    If we have a 50 ft catamaran that displaces 10,000kg meaning when it is on its waterline, it has pushed (displaced) 10,000kg of water aside or if you lifted it out of the water, the two holes where the hulls were would take 10,000kg of water to fill.

    Person A builds the boat out of steel and on land that boat weighs 9,900kg.
    When he puts it in the water it will float slightly high, pushing aside (displaced) 9,900kg of water.
    He could then load 4 friends on board, several hundred litres of water, several months supply of food, beer etc etc etc and it would sink way past its design water line and perform poorly.



    Person B build's the same boat from foam/kevlar/epoxy and on land it weigh's 4000kg.
    When he put's it in the water it would float very high showing lots of antifoul and it would displace 4000kg of water aside.
    He could then load 4 friends on board, several hundred litres of water, several months supply of food, beer etc etc etc and it would still probably only "displace" 5500kg of water, still floating very high and perform very well.

    Does that help?
     
  12. DGreenwood
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    DGreenwood Senior Member

    Maybe you could explain this??
     
  13. sabahcat
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    sabahcat Senior Member

    Salt, fresh, mercury all have different densities so a vessel of the same weight will sit at different waterlines in that fluid.

    Go one step further and have a sea of set concrete, where will the boat be sitting then?

    This may help Buoyancy Archimedes Principle
     
  14. Mr Efficiency
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    Mr Efficiency Senior Member

    That sea of mercury was the dream of Carl Keikhafer ! Displacement will only be different in terms of volume, not weight.
     

  15. Steve W
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    Steve W Senior Member

    Displacement is derived from the cubic volume of the hull(s) below the designed waterline, seawater = 64 lbs/cubic ft while fresh = 62.5 lbs so the boat will float diferently as Sabahcat pointed out.
    Steve.
     
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