Wave-cancellation using side hull expansions

Discussion in 'Boat Design' started by Mani Kandasa, Mar 25, 2016.

  1. Mani Kandasa
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    Mani Kandasa Junior Member

    During a study on increasing payload capacity of a navy destroyer using retrofitted side-hull expansions, we discovered a nice wave cancellation mechanism akin to the bulbous bow. The side hull expansions modified the wave profile along the hull such that the wave-energy was reduced with a better pressure recovery at the stern. This effect applies to displacement vessels operating at length Froude number range of 0.1 to 0.3. Has anyone seen/used this effect in a boat?

    Link to paper:
    http://www.flowcfd.com/uploads/5/3/4/0/53401797/_fast-2015-hybrid-ship-updated2.pdf
     

    Attached Files:

  2. Ad Hoc
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    Ad Hoc Naval Architect

    You would need to validate the CFD first.

    Many small/minor appendages or changes to hull shape locally can each have their own influences, but as you note, usually at a given narrowly defined Fn range. And, as you note in the paper, you may gain in one location but lose in another, this case roll period! Nothing in life is for free...thus the best boat is a good compromise of all the conflicting requirements. There is no such thing as "the best" or "the most optimal" hull. Just "the best" for THAT design requirement, no more no less.
     
  3. messabout
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    messabout Senior Member

    From a simplistic first impression I would refer to one of Newton's famous laws: F=Ma. A body that initiates a wave uses energy, a body or other mechanism that cancels or diminishes such a wave also requires energy..........or for Newton's sake, Force.

    I would be pleased to learn how a wave cancelation system can result in a reduction in the net input force. Please note above that I said "simplistic first impression".
     
  4. SukiSolo
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    SukiSolo Senior Member

    I think you'll find some small racing dinghies have been using something similar to absorb wave energy for a while. Things like Finn dinghies have a very light layup above the w/l in the bow sections to present a narrower wedge angle and smooth wave impact. These are pretty heavy boats for the size and a 1mm thick skin in certain places suggests someone has been looking at this principle....;)

    Exactly how the energy is transferred and where, is a different matter after all it is not destroyed....;)
     
  5. philSweet
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    philSweet Senior Member

  6. wet feet
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    wet feet Senior Member

    I think the example of the Finn may be a bit of a red herring,it was through his thorough investigation of weight distribution in Finn hulls that Gilbert Lamboley's gyration test was added to the certification process for the class.
     
  7. SukiSolo
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    SukiSolo Senior Member

    I'm sure these boats pas the Lamboley test but the example given is a pretty modern build - 2010, so unless the test has changed quite a bit.....;)

    It was an 'interesting' repair - port/stbd and right through gunwhale in transparent blue gelcoat......;) that'a how I got rather familiar with the layup!.
     
  8. DMacPherson
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    DMacPherson Senior Member

  9. Mani Kandasa
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    Mani Kandasa Junior Member

    PhilSweet, Many thanks for the link! The boats in fig 29,30 look very similar to what we got. Chi-Chao's book looks very interesting indeed. That too from 1972! wonder why we don't see too many of those funny looking boats around yet.
    DMac, no deflation worries :) I am happy to learn. Looks like the old news is older than you thought.
    Ad Hoc, There is some chatter from the powers that be about model testing for validation; keeping my fingers crossed. In the meantime, I am thinking of modifying my kayak with styrofoam and paddling around in the summer.
    Messa, yes, the blistering eye sore would also require force to generate the second wave, but the resulting destructive interference modifies the overall pressure distribution around the hull that the wave resistance is reduced with a better pressure recovery at the aft. A simplistic analogy would be a bunch of surfer dudes carrying some of the payload surfing the bow waves and the rooster tail, thereby recovering some of the wave energy.
    Suki, wetfeet, thanks for the info. Time to read up on Finn Dingies.
     
  10. Leo Lazauskas
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    Leo Lazauskas Senior Member

    There was a lot of work on this in the 1960's by Lawrence Ward, and earlier by
    Wehausen, Weinblum and others in the late 1950's. Ada Gotman also did some similar
    work in the 1990's and 2000's.

    You should get hold of:
    "The Wave Resistance of Ships"
    John V. Wehausen
    and read Chapter H.3:
    Ships of minimum resistance.

    A few other references that might be useful...

    "Ships of Minimum Total Resistance"
    Lin, Wen-Chin, Webster, W.C. and Wehausen, J.V.,
    College of Engineering,
    Uni. of California, Berkeley,
    Report No. NA-63-7
    Aug. 1963.

    "Optimal Ship Forms of Minimum Wave Resistance"
    Chi-Chao Hsiung
    College of Engineering,
    Uni. of California, Berkeley,
    Report No. NA 72-1
    Aug. 1972.
     
  11. Mani Kandasa
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    Mani Kandasa Junior Member

    Many thanks for the info Leo.
     
  12. daiquiri
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    daiquiri Engineering and Design

    When I first approached the boat design 20 yrs ago, CFD was used almost exclusively by the aeronautical industry. The theory, the turbulence models the numerical techniques were in a quite advanced stage of development, but the required hardware was still slow and costly. It was absolutely out of reach of an average boat designer, let alone a poor student like I was.

    So I had to learn from books. :D
    Many of them were about the history of yacht design, dealing with designs from big caliber names like Robert Stevens, Colin Archer, Dixon Kemp, Uffa Fox and others.

    And as soon as I read the subject of this thread, I have recalled the story about the schooner yacht Sappho, designed by William Townsen. After she was built, she had started attending the regattas. There was a considerable money circulating in the betting industry, hence so many regattas were held for big yachts at that time. But she had lost all the races she attended, so the owner took her to England with intention too try making her compete for the America's Cup. It was supposed to be an easy task, because American boats were routinely winning against the British fleet in AC of the time. Sappho raced the Isle of Wight race but she lost even that one, ending up last. The first place was won by the schooner Cambria.

    After getting back to the US, she was sold and the new owner ordered a rebuild of the hull. The central part of the hull was stripped of the planks, new wood was added to the outer edge of her ribs in order to increase the waterline beam of the hull, and was re-planked again. In other words, she has been "hipped" - that's the term used by Dixon Kemp to describe this kind of refit (the on-line version of Kemp's dictionary can be found here: http://www.thecheappages.com/kemp/).

    After the refit was over, she was taken back to racing fields. The first race of the "hipped" Sappho was again Cambria, previous year's winner. Three races, three large victories by Sappho. And she kept winning after that.

    What's the point of this story? Well, I guess there are two of them:
    1) The technique of "hipping" of the hull as a way for increasing the speed of the boat was well-known by experienced yacht designers and builders back in 19 century.
    2) Studying the history of ship and yacht design, even the anecdotal one, can be as important as studying the modern ship technology. It gives a good insight into what has been done in the past and which direction can one go in search for new solutions. :)

    Cheers

    P.S.
    Sorry for the poor quality of attached pictures. I don't have a scanner at home, so have scanned them from one of my old books with a smartphone.
     

    Attached Files:

  13. Jamie Kennedy
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    Jamie Kennedy Senior Member

    Did they keep prismatic coefficient constant when they did the study?
    This effect seems related to the way optimal prismatic coefficient varies with Froude number.
     
  14. Mani Kandasa
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    Mani Kandasa Junior Member

    No, the bow and stern remain unmodified. The extra displacement is added only in the midsection, and that too only below the waterline so that the waterplane area is not modified for roll period considerations. It would be neat if we could design a boat with inflatable chambers that can be inflated in sections depending on the speed of operation.
     

  15. Mani Kandasa
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    Mani Kandasa Junior Member

    Nice story! Thanks for sharing.

    Yep, when I first started with CFD as a student 15 years back we were using the DoD supercomputing machines to run simulations that can now be done using a high-end desktop.

    Btw, we just opened up a new CFD service for boat designers with pretty affordable and flexible pricing. Give me a shout if you ever need any CFD work done.
     
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