Canoe Sprints

Discussion in 'Hydrodynamics and Aerodynamics' started by DCockey, Aug 10, 2012.

  1. DCockey
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    DCockey Senior Member

    During coverage of the Olympic 200 m canoe sprints a commentator mentioned that the boats are designed to "lift" at speed. Good times for the K1 and C1 men were well under 40 seconds for the 200m. The maximum allowed length of the C1 and K1 boats is 5.2 m. The boats are very narrow. One builder's website shows beams of 40 cm for their K1 boats and less for their C1 boats.

    200 m in 40 secs means an average speed of 5 m/s. Combined with a length of 5.2 m the Froude Number is 0.7 which is well above "displacement" speed. There is no restriction on beam and the boats are very narrow. At speed the bows of the C1 boats rose above the water. The K1 boats pitched considerably with the paddling and the bows were alternately above the water and then immersed.

    The only other restrictions on the hull size and shape other than length I could find in the rules are "Section and longitudinal lines of the hull of the kayak and canoe shall not be concave (Only horizontally and vertically)" and for "Canoes", ie C1, C2 and C4, "The canoe must be built symmetrically upon the axis of its length". Beam restrictions were removed in 2003. There is also a clause in the rules that significant innovations have to approved by the ICF Canoe Sprint Committee. http://www.canoeicf.com/dms/icf/doc...-Sprint-Rules-2011/ICF Canoe Sprint 2011 .pdf

    This document includes an undated paper on Hydrodynamics for Development of Sprint Canoes for Olympic Games which has a reference to Leo's work. Unfortunately the details of the references were not included. http://www.google.com/url?sa=t&rct=...nkgcgH&usg=AFQjCNFyQJvHgEssYvj7-YJNDJqsl84dYg
     
    Last edited: Aug 10, 2012
  2. PI Design
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    PI Design Senior Member

    The GBR team have been practising the 200m canoe sprints in the tow tank at QinetiQ (aka admiralty research). Controlled environment and all that.
     
  3. Leo Lazauskas
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    Leo Lazauskas Senior Member

    Thanks, David. I removed my early papers because they were written
    when the rules restricted minimum beam. Under current rules length
    is restricted, but beam is not.

    Note how the CFD paper you linked to contains beautiful coloured
    graphics, but no comparisons of predictions with experiments? I'm
    certain that if the predictions were good the author would have
    highlighted the success.

    I'm not sure that there is much lift there. As is often done, people
    claim substantial lift, or even planing, when the weight supported
    by dynamic forces is actually quite small, of the order of 1% at
    most. At lower speeds the hulls sink and trim, rather than lift and
    trim.

    I have put up some short non-mathematical "Rowing Science Notes" and
    "Kayak Science Notes" at:
    http://www.cyberiad.net/rowing.htm
    and
    http://www.cyberiad.net/kayak.htm

    I now have very good experimental data and predictions for 16 classes
    of rowing and 9 kayak classes. I'll try to post some more non-technical
    notes and mathematical papers after the Olympics and when I recover
    from "couch sores".
     
  4. latestarter
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    latestarter Senior Member

    What surprised me was when some of the men stepped out of the C1 canoes on to the dock the canoes keeled over onto their sides.
     
  5. Leo Lazauskas
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    Leo Lazauskas Senior Member

    They are quite unstable, even without a 90+kg paddler.
    There are foam knee pads and other arrangements inside the boat and these
    are not necessarily placed on the centreline.
     
  6. SamSam
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    SamSam Senior Member

    I don't know much about it but I think the Froude Number, when applied to boats, is more like a rule of thumb thing than a law of physics, and only applies in a general way to a generic 'boat shape' displacement hull.
    http://en.wikipedia.org/wiki/Hull_speed

    I'm thinking the rule
    means from end point to end point on the boats, looking down from above (horizontal), the shape must always be flat or bulge outward. If you put a straightedge from either end to the beamiest part, there can be no space. Section wise (vertical), tumblehome is OK but flare is not.

    I'm wondering if there are rules about asymmetry? I remember reading, back in the early 1980s, rules for racing canoes where it said asymmetry was allowed, but the widest beam had to be aft of the center line and could not be forward of the cl. It seems counter intuitive to have it forward of the cl, but that's the way most fish are arranged, whales, dorados, bass etc. also the bulbs on ship bows somehow increase efficiency. A simple breakthrough, something like finned keels, seems to be due.
     
  7. Leo Lazauskas
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    Leo Lazauskas Senior Member

    Yes, but those fish don't swim close to the surface where wave resistance is
    important.
    There are some interesting arguments regarding the effect of squat on wave
    resistance that can provide insights...

    A "fish form" planform hull has the widest part closer to the bow. When the
    hull trims bow up slightly, the hull planform becomes more symmetric and
    therefore the wave resistance is reduced.

    A "swede form" hull has its widest part aft. When it trims bow up the hull
    planform becomes more asymmetric and wave resistance increases.

    Late edit...
    Attached are some slides for a non-technical talk on that perspective.
     

    Attached Files:

  8. DCockey
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    DCockey Senior Member

    Which paper in the link are you refering to?

    The one I mentioned, Hydrodynamics for Development of Sprint Canoes for Olympic Games by Tomaz Bugalski of the Ship Design and Research Centre in Gadansk, Poland and the work was done in conjunction with Plastex Composite PPH. The paper provides the history of the development of the Plastex line rather than being a CFD paper. It does include some illustrations of CFD results and discusses how the CFD results were used to complement the tow tank tests. Nothing it it suggested to me that the intent was to compare CFD to tow tank tests.

    I don't read into the lack of comparison between CFD and experimental results anything about the quality of agreement between them. Other than the color illustrations no graphical or quantitative results were shown in the paper, either experiemental or CFD. My guess is the results are proprietary and there are signficant limitations for competitive reasons on what can be published.

    The paper does describe a complementary approach to the use of CFD and experimental results in developing new designs. From the bottom of page 5 of the paper in a discussion of the investigation of existing designs prior to the development of new designs Bugalski states:

    "Although such experiments provide a large amount of reliable data in a short timescale, they do not always illuminate the physice mechanisms that affect the performance of the hull. For this reason, the experimental research was widely supported with extensive CFD simulation, which is more suited to a detailed comparison of the influence of flow parameters such as the wave elevation and the pressure distribution on the hull for different designs."

    Apparently the correlation of the experiemental and CFD results were sufficiently close that:

    "After testing the existing boats, the best design was chosen based on analyis results and works on new designs began. By implementing CFD into the design process, timescales and costs have been significantly reduced." p 7

    "The viability of each new design was first tested numerically, so that only a small number of optimized designs were selected for manufacturing and testing in the model basin. Final tests were carried out in the real conditions - with the professional competitor rowing along the basin." p 9

    The link also contains a two page article from Marine Report briefly describing the CFD work with lots of color graphics. Marine Report is a publication of CD-Adapco which is a developer and seller of CFD codes, presumably the ones used for the analysis.

    I don't have any idea how much lift there is nor what the commentator's comment was based on. Based on what I could see on the TV there didn't appear to be much sinkage.

    Thanks! That will be some interesting and informative reading.
     
  9. DCockey
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    DCockey Senior Member

    My reading is that there cannot be a hollow when a straight edge in any horizontal plane is placed against the hull at any location, nor when a straight edge in any vertical, transverse plane is placed against the hull at any location.

    The complete rules are available at the link I provided in the first post.

    Prior to 2003 there were rules about minimum beam and where it was measured, etc. Those rules influenced the hull shapes. Today there are no rule limitations on beam. The only restriction on asymmetry of the hull, which I forgot to include above, is for "Canoes", ie C1, C2 and C4, "The canoe must be built symmetrically upon the axis of its length". Presumably this is because the C1 boats are paddled on one side only and there might be an advantage to a transversely asymmetric hull. There are also restrictions on the deck and cockpit openings.

    I wonder if anyone has experimented with hull shapes that have a transom stern, particularly for the 200 m sprint boats? There doesn't appear to be any requirement that the boats have to be "pointed" on both ends but presumably the ICF could prohibit transom sterns or other "radical" shapes if they desired under the rule that significant innovations have to be approved. Or they could just change the rules.
     
  10. Ad Hoc
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    Ad Hoc Naval Architect

    I think that's a case of the commentator getting overzealous with his superlatives to sound knowledgeable. These are ostensibly 'displacement' boats and are there is very little if any lift. Either the boat goes through the water or on top, in general terms.

    Having designed many multihulls in the running the in 0.7-1.5 Fn range, all displacement, none obtained any lift. Regardless of shape.
     
  11. Leo Lazauskas
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    Leo Lazauskas Senior Member

    I have been doing some numerical work on this. It is worthwhile looking at
    because the speeds are relatively constant during the stroke. I don't think that
    transoms are of much use on rowing shells where the speed variation is much
    greater.
     
  12. Leo Lazauskas
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    Leo Lazauskas Senior Member

    At best, the "sinkage force" which tends to increase draft gets less as Fr
    increases. Around Fr=1 that sinkage force is equal to zero or sometimes
    slightly positive so that a small amount of weight is supported by dynamic
    forces. That's a very long way from planing, but enough for commentators,
    coaches and athletes to think that something magical has occurred :)
     
  13. Ad Hoc
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    Ad Hoc Naval Architect

    The "sweet spot" is very narrow for canoe type hulls:

    Family of Hulls.jpg
     
  14. Leo Lazauskas
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    Leo Lazauskas Senior Member

    The same paper has appeared in several guises, including conferences.

    I agree, though, that proprietary interests could be restricting what he
    discloses.
     

  15. Ad Hoc
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    Ad Hoc Naval Architect

    Indeed, the excellent systematic series of test by Karafiath & Carrico on the Series 64 hull form demonstrated this very well :)
     
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