Hollow Sections aft on ULTIME Trimaran Amas

Discussion in 'Multihulls' started by Doug Lord, Mar 28, 2018.

  1. Doug Lord
    Joined: May 2009
    Posts: 16,580
    Likes: 298, Points: 93, Legacy Rep: 1362
    Location: Cocoa, Florida

    Doug Lord Flight Ready

    I curious about the rationale for the hollow "rocker" on these two trimaran amas:
    CLARIFICATION: In the title I said "hollow sections" aft when what I meant was hollow rocker---sorry......


    Banque Populaire
    Banque Pop uptip foil.jpg

    Gitana 17
    gitana-17-vue-arric3a8re-photo-2-f-monsonnec-04-04-17.jpg
     
    Last edited: Mar 28, 2018
  2. Gary Baigent
    Joined: Jul 2005
    Posts: 2,959
    Likes: 102, Points: 63, Legacy Rep: 509
    Location: auckland nz

    Gary Baigent Senior Member

    Nothing new about this: Paul Whiting did hollow after sections in the late 1970s on Magic Bus, Newspaper Taxi and Smackwater Jack, in fact a number of New Zealand designers did the same on their planing IOR boats of that period. Okay, may have been for rule gains and other compromises but still, hollow is hollow.
     

    Attached Files:

    Last edited: Mar 30, 2018
  3. Corley
    Joined: Oct 2009
    Posts: 3,740
    Likes: 172, Points: 63, Legacy Rep: 826
    Location: Melbourne, Australia

    Corley epoxy coated

    The Multi50 trimarans Arkema and to a lesser extent the former Actual (now named Reaute Chocolat) have gone down a similar path with their ama hull forms, seems to work well from the results they have achieved.
     
  4. luff tension
    Joined: Aug 2010
    Posts: 64
    Likes: 5, Points: 8, Legacy Rep: 10
    Location: auckland

    luff tension Junior Member

    While they may look hollow the sight lines and various curves of the hard turn in the topsides can be deceptive, I would suspect they are just straight rather than slightly hollow.
     
    rwatson likes this.
  5. cavalier mk2
    Joined: Mar 2010
    Posts: 2,086
    Likes: 40, Points: 48, Legacy Rep: 214
    Location: Pacific NW North America

    cavalier mk2 Senior Member

    Designed to work on the wave at speed as a planing/semi planing hull form.
     
  6. Richard Woods
    Joined: Jun 2006
    Posts: 2,179
    Likes: 145, Points: 63, Legacy Rep: 1244
    Location: UK, USA and Canada

    Richard Woods Woods Designs

    Adds hull depth in way of the main beam and foils. So makes the hull much stronger where the loads are higher. I suspect the SAC is still quite smooth as the hull becomes chined aft so the WSA increase relative o a rounder hull

    Lots of designers have added bustle aft on multihulls, even I have. So too did Lock Crowther



    Richard Woods
     
    Last edited: Mar 30, 2018
  7. Gary Baigent
    Joined: Jul 2005
    Posts: 2,959
    Likes: 102, Points: 63, Legacy Rep: 509
    Location: auckland nz

    Gary Baigent Senior Member

    Hollow in after sections profile, not multihull top sides strakes and chines viewed from ahead or astern. Here is hollow stern profile on Laurie Davidson's Fun.
     

    Attached Files:

  8. patzefran
    Joined: Feb 2011
    Posts: 179
    Likes: 10, Points: 18, Legacy Rep: 10
    Location: france

    patzefran patzefran

    These shapes were first originated / tested as Serie 64 High speed semi displacement hulls at David Taylor Basin...........
     
  9. Manfred.pech
    Joined: Apr 2010
    Posts: 588
    Likes: 74, Points: 28, Legacy Rep: 319
    Location: EU

    Manfred.pech Senior Member

  10. Erwan
    Joined: Oct 2005
    Posts: 353
    Likes: 12, Points: 18, Legacy Rep: 97
    Location: France

    Erwan Senior Member

    As reorted by a famous beach cat navan architect who was involved in the C-Cat program Groupama C

    When asked : Why thekeel line of your C -Cat is flat at the bow and at the stern ?

    This september 2013 answer was :
    The flat at the bow aims to minimize the downward sucking forces of the waves train in the floating mode and create some little dynamic lift to help offsetting this downward force.

    The flat / concave / hollow keel line at the stern was supposed to minimize wetted area .

    Regards

    Erwan
     
  11. Richard Woods
    Joined: Jun 2006
    Posts: 2,179
    Likes: 145, Points: 63, Legacy Rep: 1244
    Location: UK, USA and Canada

    Richard Woods Woods Designs

    Not sure you can really compare the hull of a catamaran sailed in flat water inshore with the outrigger of an ocean going trimaran. Inshore boats tend to have more rounded/flatter forward sections, offshore boats tend to be more V'eed. A trimaran main hull tends to have a lot of rocker, an outrigger tends to have a very flat run these days and most now have square sections aft

    The old IOR boats were partly drawn that way for rating advantage and to plane, something multihulls don't do

    Richard Woods
     
  12. fastsailing
    Joined: Sep 2017
    Posts: 73
    Likes: 7, Points: 8
    Location: Finland

    fastsailing Junior Member

    What does SAC mean?
    How about CSA?
    Is there any online nautical abbreviation website someone can give me a link?
    Should there be one in this site?
     
  13. TANSL
    Joined: Sep 2011
    Posts: 5,690
    Likes: 172, Points: 73, Legacy Rep: 300
    Location: Spain

    TANSL Senior Member

    It would be interesting to know, in addition to "a trimaran main hull tends to have ....., an outrigger tends to have......", the why of those "tends to". Would someone be so kind to give explanations about it?. Something similar to what Erwan explains in his post # 10, which is very interesting. Thank you
     
  14. Doug Lord
    Joined: May 2009
    Posts: 16,580
    Likes: 298, Points: 93, Legacy Rep: 1362
    Location: Cocoa, Florida

    Doug Lord Flight Ready

    ==============================
    From Guillaume Verdier on Gitana 17:
    Flat-bottomed hull and floats: As is the case on the America's Cup craft, the Maxi Edmond de Rothschild is equipped with three planing hulls with inverted bows and flat bottoms, so as to increase the ability to fly and provide excellent stability in heavy seas. The central hull and floats have a high freeboard for improved protection at sea.
     
    Last edited: Mar 29, 2018

  15. TANSL
    Joined: Sep 2011
    Posts: 5,690
    Likes: 172, Points: 73, Legacy Rep: 300
    Location: Spain

    TANSL Senior Member

    There are still no technical reasons that explain the "why" of things. In any case, those foilers start flying very quickly so I do not think flat bottoms, high freeboards, etc. improve the conditions of their flights. The "improvements" in the hull seem more appropriate while the ship does not fly. I think that in this, in addition to showing amazement for everything that seems new (and in many cases it is not), would require some technical explanation at the elementary level.
     
Loading...
Similar Threads
  1. nzdavo
    Replies:
    29
    Views:
    3,412
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.