[MHml] tons

[rb3232 at gmail.com]

try this thread:
http://www.steamboats.org/forum/steamboats-history/160-old-registry-tonnage.html
  ----- Original Message ----- 
  From: Roger Strube 
  To: Informed discussion of multihull issues 
  Sent: Tuesday, January 06, 2009 11:59 AM
  Subject: Re: [MHml] tons


        Bill,

        Do you know off hand how "Tons" relates to the designation of US Coast Guard vessels?  Documentation papers I have had on my boats have designated "Tons" but I understood this had something to do with the number of barrels that the boat could transport in time of war and dates back well over 100 years.  Is there an actual "pounds" correlation to "Tons" as used in USCG documentation?


        Roger


        --- On Mon, 1/5/09, Bill Gibbs <BillG at GibbsCAM.com> wrote:

          From: Bill Gibbs <BillG at GibbsCAM.com>
          Subject: [MHml] tons
          To: "'Informed discussion of multihull issues'" <multihulls at steamradio.com>
          Date: Monday, January 5, 2009, 10:16 PM


          Imperial  (long) ton = 2240 pounds

          Ton (in US, aka short ton) = 2,000 pounds

          Metric ton = 1,000kg = 2205 pounds





          From: multihulls-bounces at steamradio.com [mailto:multihulls-bounces at steamradio.com] On Behalf Of Rob Denney
          Sent: Monday, January 05, 2009 7:07 PM
          To: Informed discussion of multihull issues
          Subject: Re: [MHml] L/B ratios




          G'day,

          Not much help for container shipping (I can't see multihulls ever working for this, but agree that more efficient handling is possible), but my 2c worth on hull shapes follows.

          I agree with Derek that weight is the killer, not L/B.   L/B is just one part of the hull shape equation. Stern shape, D/B, prismatic and rocker are others.  Rocker's importance is under reported as most multihulls need it to tack, and for reduction of wetted surface.  However, if the boat is light enough, then wetted surface is not a problem.   Zero rocker also allows a high prismatic which reduces pitching and nosediving tendencies, both of which are speed limiters on conventional cats.

           As evidence, the video at http://www.youtube.com/watch?v=8chR6DAFjGA  shows a heavy 15m/50' harry with poor sails and a crew not paying much attention to trim on it's maiden voyage.  It is sailing at wind speed (10 knots in the first part, 15 towards the end) under working sails, a feat that is very rare in similar length cruisers.  The lee hull on this boat has static L/B of 21:1 and the ww hull of 10:1, respectively  a little less and a little more under the slightly heeled conditions in the video.   No rocker, semi circular hulls becoming U shaped at the ends. 

          In cruising trim, this boat weighs a bit over 3 tonnes, far less than a cruising cat of the same space or length.

          Dave,
          Surely the static waterline  is meaningless on hulls that are not vertical sided above and below the waterline on multis at speed, which invariably have one hull depressed and one raised.

          Tim, 
          I am also impressed with your efforts, but consider that your speed analysis is flawed.  On your boat, you are dragging around 2 relatively inefficient fixed keels, props, shafts and supports which have not been taken into consideration in the formula.   Your boat  weighs 16 tons (35,000 lbs). There are few, if any stripped out (5-6 tonnes) racing 60' cats and tris that get to 30 knots on flat water.  

          Roger,
          As a big fan of form following function, I also like bulldozers.  Your formula divides pounds by 2,000 to get tons.  Is this an American thing?  We divide by 2,200.  Not a big deal, just curious.  

          Regards,

          Rob







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