An article of news on the Skjold class

Discussion in 'Boat Design' started by BMcF, Sep 28, 2012.

  1. BMcF
    Joined: Mar 2007
    Posts: 967
    Likes: 45, Points: 28, Legacy Rep: 361
    Location: Maryland

    BMcF Senior Member

  2. Leo Lazauskas
    Joined: Jan 2002
    Posts: 2,696
    Likes: 146, Points: 63, Legacy Rep: 2229
    Location: Adelaide, South Australia

    Leo Lazauskas Senior Member

    Thanks, Bill.
    There's something very satisfying about the Skjold's compactness.

    You should also feel very proud of your 1/20th model for the SeaTrain.
    I'm impressed with any scale model that requires its own special
    trailer!

    Demihulls with L/B=90 fit thin-ship theory beautifully, which is
    why I can get excellent agreement with the tow tank results.

    Incidentally, my calculations show that the total resistance can be
    reduced by using higher pressures in Cars 2 and 3, and slightly
    lower pressures in Cars 1 and 4. Of course, it depnds on what
    pressure differences can be sustained, but it isn't difficult to
    reduce total drag by at least 10%.
     
  3. Ad Hoc
    Joined: Oct 2008
    Posts: 6,124
    Likes: 358, Points: 83, Legacy Rep: 2488
    Location: Japan

    Ad Hoc Naval Architect

    Hard not to be impressed!! :D
     
  4. BMcF
    Joined: Mar 2007
    Posts: 967
    Likes: 45, Points: 28, Legacy Rep: 361
    Location: Maryland

    BMcF Senior Member

    I saw some predictions like that. Taken to their limit, it was predicted that the 3rd "car" in a four-segment train would be getting a drag-free ride.

    I hope the concept sees the light of day again; I thought it held out great promise for coast-wise shipping.
     
  5. Leo Lazauskas
    Joined: Jan 2002
    Posts: 2,696
    Likes: 146, Points: 63, Legacy Rep: 2229
    Location: Adelaide, South Australia

    Leo Lazauskas Senior Member

    I'm surprised the reduction wasn't more than 25% of wave drag when "taken
    to the limit". Or maybe that study didn't use the spatial variation of pressure
    that (impractical) mathematicians are allowed. ;)

    So do I. But I can't see a 13800 t vessel being built without several smaller sizes
    first being trialled.
     
  6. BMcF
    Joined: Mar 2007
    Posts: 967
    Likes: 45, Points: 28, Legacy Rep: 361
    Location: Maryland

    BMcF Senior Member

    We took a hard look at the economics of a "half scale" diesel-powered version and it looked spectacular..if moving various forms of what is typically now "barge cargo" at 30-35 knots vice 6-8 knots makes economic sense. Frankly..I don't delve in to that side of it enough to know if it really does.

    Back in the "naive 80s", everyone was building fast ferries based on nothing more than the simple construct of a variation on Moore's Law: "If fast is good, faster is more gooder". That fallacy having been quite thoroughly wrecked on the reefs of economic reality....its very hard to get anyone excited about going fast on the water for commercial purposes these days.
     
  7. Ad Hoc
    Joined: Oct 2008
    Posts: 6,124
    Likes: 358, Points: 83, Legacy Rep: 2488
    Location: Japan

    Ad Hoc Naval Architect

    They are still pushing for "fast" in HK. Yet the harsh realities have reduced the shouting to a more audible chorus. If they can find a means without paying the penalties of cost/weight/maintenance etc etc..they'll still go for it. (The usual holy grail). They seem obsessed with speed in the waters of HK.

    It does seem the rest of the world is lowering that 45knot to 35knot aspiration. Price of fuel...money talks! :eek:
     
  8. Leo Lazauskas
    Joined: Jan 2002
    Posts: 2,696
    Likes: 146, Points: 63, Legacy Rep: 2229
    Location: Adelaide, South Australia

    Leo Lazauskas Senior Member

    Bill:
    I am in the throes of writing up some work on the "SeaTrain".

    The attached graphs show my predictions compared to the experiments
    reported in the FAST 2009 paper by Irvine et al. and your paper with Scher
    et al. As you can see, Flotilla does a reasonable job for both the 1/20th
    model and the full size vessel.

    Offhand, do you know why there is a largish gap in the experimental
    results between about 9.5 knots and 12 knots for the model scale?
    (I can imagine that it was a very expensive operation, which would
    have limited the number of runs.)

    Leo.
     

    Attached Files:

  9. BMcF
    Joined: Mar 2007
    Posts: 967
    Likes: 45, Points: 28, Legacy Rep: 361
    Location: Maryland

    BMcF Senior Member

    Leo;

    It was the free-running open-water tests that I was directly involved with (after building the whole mess, of course); I was not "close enough" to the model basin tests to answer your question.

    I'll query Dr. Bob and Marty though..and see what they might recall.

    Most excellent agreement, by the way...I'm impressed.

    -Bill
     
  10. Leo Lazauskas
    Joined: Jan 2002
    Posts: 2,696
    Likes: 146, Points: 63, Legacy Rep: 2229
    Location: Adelaide, South Australia

    Leo Lazauskas Senior Member

    Thanks, Bill.
    I'll be using it as an example when I release a slightly crippled version of
    Flotilla for SES, hopefully within the month. It's a real delight to have
    experimental results at decent Reynolds numbers!
     

  11. kach22i
    Joined: Feb 2005
    Posts: 2,398
    Likes: 106, Points: 63, Legacy Rep: 1222
    Location: Michigan

    kach22i Architect

Loading...
Similar Threads
  1. thenavalarch
    Replies:
    0
    Views:
    232
  2. thenavalarch
    Replies:
    0
    Views:
    174
  3. thenavalarch
    Replies:
    0
    Views:
    301
  4. thenavalarch
    Replies:
    2
    Views:
    454
  5. mustafaumu sarac
    Replies:
    2
    Views:
    981
  6. ckutlu
    Replies:
    9
    Views:
    943
  7. mustafaumu sarac
    Replies:
    3
    Views:
    952
  8. DCockey
    Replies:
    0
    Views:
    698
  9. thenavalarch
    Replies:
    0
    Views:
    808
  10. floating
    Replies:
    1
    Views:
    655
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.