High-Speed Pentamaran Yacht

Discussion in 'Boat Design' started by High Life, Jan 23, 2013.

  1. groper
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    groper Senior Member

    Ive run the program many times.... but its difficult to get anything meaningful when we dont know anything about the design in detail. All i can tell you is the minimum resistance of any high speed displacement hull, occurs when the length beam ratio is around 25:1, is of near semicircular round bilge type - ie its depth is as close to, or equal to, half its waterline beam and has an eliptical plan form. In general, if you stick to this arrangement, it contrains the hull form very tighly into an olympic rowing/skulling boat hull shape.

    As you deviate from the above ideals, resistance increases above what is minimum - doesnt matter where its the amas or main hull, the optimum form is the same regardless of size or the number of hulls. The intereference drag is about the only thing you can control beyond this ideal configuration ie. where you place the amas in relation to the main hull.

    All this is moot, however, as this boat is obviously not designed for best efficiency. Its designed for sheer opulence and show off factor... minimum resistance is clearly very low on the SOR list - you can tell by the installed power... If the displacement to length ratio (DLR) is favourable, then you can assume they actually care about efficiency... they havnt given a displacement as far as i can tell???
     
  2. groper
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    groper Senior Member

    heres one michlet godzilla run... i didnt let it run for very long, but you can generally see where things are heading... all the hulls are somewhere around 20:1 length beam ratio and the ships length was contrained to the main hull length. It went slightly better with the amas trailing behind the main hull, but this isnt allowed under the current arrangement of the ship in question here... many assumptions are of course in play here, the hulls displacement was constrained to 4:1 main hull to ama displacement... who knows what the ship in question ratios are...??? its all hypothetical, but it follows the general trends ive always seen for minimum resistance.

    [​IMG]

    Next on the list is to model a pentahull, with all hulls immersed and compare the 2...
     
  3. daiquiri
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    daiquiri Engineering and Design

    Hi Groper,
    Thanks for that effort. :)
    But, before you carry on with the pentamaran case, how about discussing a bit the goals and methods of the simulation? This is my two cents worth:

    The issue which you want to explore is:
    which one has a higher resistance - a trimaran with long shallow amas (such as that Austal's express ferry), or a trimaran with shorter (how much, half the length?) and deeper amas (such as the BMT when forward amas are out of water)? Because, as we have seen, BMG becomes hydrodynamically a pentamaran only when stability issues require it to do so. In normal operation, it is designed to operate as a trimaran.
    What you want to keep constant is, imo, the main hull's displacement, form and slenderness ratio. The shape of the hull section is (imo) of secondary importance, since you are making a comparative study of just different ama configurations. Hence, it is imo not necessary to undertake the long optimization runs for this purpose. Simple Wigley hull forms could do the job as well.

    So, imo, creating the pentamaran model is out of the scope of that analysis, and would be a waste of time for the purpose of this comparison.

    Cheers
     
  4. groper
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    groper Senior Member

    Yes you are correct, i realized this as i was configuring the next run...

    Ive noticed a few trends a few runs thus far;

    If the main hull is allowed to be close to ideal shape then godzilla optimizes the ship total total resistance to have very tiny amas with nearly all the displacement in the main hull.

    If the main hull is constrained to a more modest length beam ratio, i contrained it to 10:1, then it does the opposite and puts relatively more displacement in the amas.

    It makes sense in that, if a hull or ama is allowed to be an optimum shape, then it should carry as much displacement as that form allows. If one of the hulls is below optimum, then ideally it should carry less displacement and the ideal hulls should carry more of it. I think thats what conclusions i can draw anyway...

    So in response, i think the austal ferry has a more optimum configuration in term of resistance.
     
  5. daiquiri
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    daiquiri Engineering and Design

    While you were typing, I was typing too, and have added the remark about the hull form (just my opinion). Please check it out.

    Cheers
     
  6. groper
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    groper Senior Member

    The ship in question here, has an overall beam of 30m and LOA of 130m... looking at the rendering, i would say the main hull would be around 15m beam;

    [​IMG]

    This indicates a less than ideal slenderness ratio of 130/15:1. Knowing this, getting as much displacement into the amas whilst making each ama approx 20:1 LBR would be ideal. If each ama is 2m waterline beam, then each should be around 40m LWL... much longer than what is shown in the rendering...
     
  7. Number4

    Number4 Previous Member

    Applications of the Pentamaran Hull Form for Fast Sealift and Freight Applications
    http://media.bmt.org/bmt_media/resources/112/Paper41-NSRPPresentation03-03-05.pdf

    Stabilised Monohulls – Trimarans and Pentamarans
    History – Evolution and the Future
    http://media.bmt.org/bmt_media/resources/112/Paper45-StabilisedMonohulls.pdf

    Pentamaran central hull design
    http://www.fsopt.com/downloads/2005_PaperDudsonHarriesFinal.pdf

    BMT Frigate
    http://www.bmtdsl.co.uk/BMT/bmt_media/bmt_media/33/2007-09-26Concept-F5DataSheet.pdf


    http://www.boatdesign.net/forums/boat-design/pentamaran-ferry-20606.html
    "However I'm now puzzled on why the thin side wall sponsons are broken up in the middle like that?

    'Cos it would only be a trimaran otherwise . Seriously though, the idea is that the centre hull is quite narrow (for less drag) and the aft sponsons are just submergerged at the design waterline. The forward sponsons are above the static waterline and only sumberge (and hence provide stability) when the ship rolls/lists. This reduces the wetted surface area of the (upright) hull form and hence reduces drag. Its all about not having any more ship in the water than you need. Of course, you could have 3, 4 or 20 sponsons each side, each stepped slightly higher above the waterline than the previous one. Taking this to its logical extreme, you would have a single continuos sponson which raked up as it went forward. But that's a trimaran..."

    There are other advantages, such as good survivability charecteristics.

    Pentamaran concept sailing cruise ship
    http://www.ship-technology.com/projects/eoseas-concept-cruise-ship/
     
  8. Stumble
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    Stumble Senior Member

    The thing I can't figure out is why having two additional hulls is preferable over having a flare sided sponsons, or have a stepped sponson so that as the boat heels you get the same advantage.

    I can see the advantage to some extent in a military vessel where combat damage makes completely redundant flotation desirable, but I don't get it for private use.
     
  9. myark
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    myark Senior Member

    http://www.youtube.com/watch?v=UF5b2MRu3NA

    I worked in Perth on this floating dock several times with the company that built the dock and has an Austal ship on top.
    I enjoyed watching Austal testing their ships speed that was also next to the work shop I was based.
     

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  10. groper
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    groper Senior Member

    The military doesnt think so, all the ships theyve built in this configuration are trimarans, no special pentamarans with airborne hulls as yet... austal has built several high speed tris for the military already...
     
  11. Number4

    Number4 Previous Member

    Austal build some amazing ships.
    The USS Independence is revolutionary, I did not realise it was theirs.
    It again has very similar dimensions, but also an extra gas turbine over the Veloce.
    After watching a video of the Benchijigua Express, it is incredible that anybody could even consider a private yacht so big, just the fuel bill would melt a wallet full of platinum credit cards.
    It must be a marketing ploy to bump their pentamaran idea back into media circulation.

    Here is another pentamaran, this time real, with five parallel hulls.
    M80 Stiletto
    http://www.mshipco.com/military_m80.html
    http://en.wikipedia.org/wiki/M80_Stiletto
     

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  12. El_Guero

    El_Guero Previous Member

    Well the Stiletto with 6 plus years of service indicates the penta-hull form works good for what the Navy is using her for.
     
  13. FAST FRED
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    FAST FRED Senior Member

    I have no idea why an opulent boat is such red flag to so many.

    A boat of this size gives pay for thousands of man hours , raising the std of living for perhaps hundreds of working folks.

    A wealthy person purchasing a basket of stock , gives zero jobs.

    Why the hate for boat builders??
     
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  14. El_Guero

    El_Guero Previous Member

    After looking over this pentamaran, I think the reason this one is so odd looking was to get around patent issues that won't be given up before 2016 ....

    http://www.boatdesign.net/forums/boat-design/pentamaran-ferry-20606.html

    From there http://www.bmtdsl.com/BMT/bmt_media/bmt_media/33/2007-09-26Concept-F5DataSheet.pdf

    And The attached PDF.

    It would seem they hold the 'pentamaran' patent for a pentamaran that works better until 2016. In their model, they point out the difference between acting like a large trimaran with additional wetted surface, and acting like smaller trimaran amas until needing the larger amas.
     

    Attached Files:


  15. El_Guero

    El_Guero Previous Member

    I would not say I hate boat builders.

    But, I would say I appreciate beauty. And that there boat lacked a lot in the beauty department. And her functionality seemed less than comparable boats .... all IMHO of course.
     
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