[MHml] fuel efficiency and the 1500ft Catamaran

[Roy Mills]

  ----- Original Message ----- 
  From: Kerry Thomas 
  To: 'Informed discussion of multihull issues' 
  Sent: Sunday, January 04, 2009 7:03 PM
  Subject: Re: [MHml] fuel efficiency and the 1500ft Catamaran


  Hi

  If you go 8 to 1 you may as well have a monohull. 12 to 1 would be a starting point for a cruising boat. See Chris Whites book. Increasing length without increasing any other dimensions is a cheap and easy way to increase speed. There is a Gudgeon design which has taken this to the extreme, but Sundreamer is a good example.

   

  Kerry Thomas

  Master FG Ship. MNZIM. CMRINA.

  www.altairmarine.co.nz

   

      With respect Kerry I think yor views are somewhat extreme.  Cruising trimarans often have a main hull around 8 to 1 and they can often  show the way to cruising monos with their 3to 1 or 4 to1 hulls. My Tennant Turissimo10  had 12 to 1 hulls but was considered to be a coastal cruiser/racer, and raced quite well so I would not consider 12 to 1 as a beginning point for a cruiser at all.



          And answering two posts with one,  Yes Dave, I did not have those numbers but I did feel that several very fast boats were considerably finer than 16 to 1, I'm surprised that the common figure is as high as 30 to1. Maybe Bruce just felt from the curves that there was little point in going finer than 16 to 1, and maybe based on his figures he was close to being right. Considering the small size of his home made test tank and instruments it is a tribute to him that his figures pointed the way quite closely, though obviously not precisely. I don't suppose any of the people designing maxi racers would care to share the figures they use for ratios of 24 up to 30 to 1. As for 8 oar rowing shells, they are highly competitive and races are often won or lost by seconds or fractions of seconds. Bruce did not say do not go beyond 16 to 1, he indicated that above 16 to 1 was, he felt, well into the region of diminishing returns and he may still have been right, but any return at all to a competitive rowing 8 or multimillion dollar racing cat or tri is worth grabbing for.



          Roy Mills
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