On the relative power involved in fixed seat rowing races

Discussion in 'Hydrodynamics and Aerodynamics' started by JotM, Feb 22, 2014.

  1. JotM
    Joined: Jan 2009
    Posts: 94
    Likes: 8, Points: 8, Legacy Rep: 34
    Location: Leiden, the Netherlands

    JotM Junior Member

    Hi all,

    Over the last 20 years racing in fixed seat boats in the Netherlands, collectively called "sloepen" in Dutch (link to Wikipedia page in Dutch), has been based on an estimated average power per rower, or better, on the relative estimated power per rower on flat water without wind.

    For quite a long time this has been considered to be the best way to enable comparison between boats that at times differ hugely from one another.
    (as can be seen from the register of boats admitted to race: "sloepenregister 2013")
    Over the last years some serious doubts and discussions have arisen over the question whether some sub-types of boats have a systematic advantage because of properties in their design or not.
    In the coming weeks a working group, with support from an expert from the "ship hydromechanics and structures" group at Delft University of Technology, will therefor set out to evaluate the presently used methodology on one hand and possibly come up with recommendations for a structural change on the other.

    The drag of a boat used in calculations in the present system is based on open water towing tests, which every boat has to undergo every 5 years. The boats are towed on the side of a tug, pretty much like proposed by "petros" in the thread on the propulsive efficiency of oars, with a setup I posted earlier.
    [​IMG]

    One of the doubts in recent times is about the influence of cyclic loading (during the stroke) and the cyclic motion of pitching and heaving caused by the swinging motion of the upper bodies of fixed seat rowers.
    Does anybody on this forum know of available information on the impact (in terms of added "drag" / energy loss) of the resulting unsteady motion while rowing, in comparison to the "steady state" motion during towing tests?

    All hints and information will be much appreciated!

    Regards,

    Jaap
     
  2. JotM
    Joined: Jan 2009
    Posts: 94
    Likes: 8, Points: 8, Legacy Rep: 34
    Location: Leiden, the Netherlands

    JotM Junior Member

    Some additional information on the calculations supporting the NL handicap system

    I might add to my previous post that the relative average power per rower during a race is estimated on the basis of the power needed to propel a boat (without losses to wind and wind waves) at the average speed over the race (the relative average power is considered to equal the power needed at the average speed), by means of a spread sheet [link].

    Towing tests are used to estimate an overall drag coefficient curve, the drag coefficient being a function of speed v, which in turn is used to estimate the overall average power mentioned above.

    The drag coefficient curve is defined as Cw(v) = A/(1-(v/B)^2) when F_towing = Cw(v) * v^2 ; the results from the towing tests are used to establish the parameters “A” and “B”, which can be found in both the spread sheet linked above and the register of boats eligible for racing linked in my previous post.
    (If anyone reading this is aware of the origin of this formula, I would very much like to get a reference, as I have not been able to establish that origin in 2 years of sifting through books, articles and proceedings)

    To achieve that, the boats are towed in 6 runs: 2 at the average speed v_average (accomplished in the races over the last 1-3 seasons), 2 at 0.9*v_average and 2 at 1.1*v_average.
    Every run lasts for about 50 seconds, during which the towing force needed at the speed v through the water is recorded (by a load cell and 2 separate logs) alongside apparent wind speed and wind direction. Sensor readings are sampled at 1000 Hz.
    Per measurement the wind load is estimated from apparent wind speed and – direction and subsequently deducted from the towing force, yielding the drag force.
    (F_drag = F_towing - F_wind)

    The drag coefficient at the average speed of the run (kept constant to the maximum extent possible) is then averaged from the approximately 50,000 records per run.
    Based on the resulting 6 speed-drag coefficient pairs, the “A” and “B” parameters for a best fit of the overall drag curve are obtained through the “least squares” method.

    The average speeds - in terms of Froude number - of the various boats at the races cover quite a wide range, as can be seen from a histogram based on the 2013 boat register:
    [​IMG]

    And especially in the lower Fn-range, "B" as an estimate of "hull speed" (the 1ste peak in wave making resistance at v=B for which Fn = sqrt(2/(3*pi)) and total resistance is expected to be "infinitive" [link -> page 10]) is not as strong as the rating officer of the fixed seat rowing association has implied over the last decade:
    [​IMG]

    The big question remaining is:"how big is the influence of all estimates mentioned and is that influence the same for all boats?"
    (in other words, does the system described systematically favor some boats over others or not?)

    Regards,
    Jaap
     
    Last edited: Feb 22, 2014
  3. Leo Lazauskas
    Joined: Jan 2002
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    Location: Adelaide, South Australia

    Leo Lazauskas Senior Member

    You could try an added mass approach to estimate the effects of surge
    as a first approximation. For Olympic shells that quantity is very
    small and can usually be ignored. It might be more significant for
    your beamier boats.

    Doctors et al. and Day et al have conducted tests to determine the
    effect of unsteady flow on the resistance of rowing shells. Their
    computer model is in very good agreement with the wave resistance at
    low oscillation frequencies, however, at frequencies approaching those
    of real rowing shells, their model under-predicts the resistance by a
    very large (> 500\%) amount.

    Day et al estimate that unsteady effects can increase
    the total resistance by about 3%. Scragg and Nelson suggest that
    either surge or pitch increased the resistance by between 2% and 5%.

    I suggest that you search for Kleshnev's "Rowing Biomechanics Newsletter".
    His site is a treasure trove for rowing research.

    I appreciate that you are looking at fixed seat rowing, but you might
    find the following useful. (Sorry, but I don't have time to convert
    most of them from LaTeX biblio format). Also see my Rowing Science Notes:
    www.cyberiad.net/rowing.htm
    (I plan to release the rowing program "FIRM" later this year.)

    Filter, Klaus B.,
    ``The system crew--boat",
    FISA juniors' coaches conference, Naples, Italy, 15--18 Oct. 2009.

    Barrow, J.D.,
    ``Rowing and the same-sum problem have their moments",
    DAMTP Report, Centre for Mathematical Sciences,
    Cambridge Uni., UK, 18 Dec. 2009.
    (This is also available on-line at arxiv.org).

    Brearley, Maurice and de Mestre, Neville J.,
    ``Modelling the rowing stroke and increasing its efficiency",
    3rd Conf. on Mathematics and Computers in Sport,
    Bond University, Quensland, Australia,
    30 Sept - 2 Oct. 1996, pp.\ 35--46.

    Cabrera, D., Ruina, A. and Kleshnev, V.,
    ``A simple $1^{+}$ dimensional model of rowing mimics observed forces and motions"
    Human Movement Science\/,
    Vol. 25, No. 2, 2006, pp.\ 192--220.

    Caplan, Nicholas and Gardner, Trevor,
    ``Modeling the influence of crew movement on boat velocity fluctuations during the rowing stroke"
    Int. Journal of Sports Science and Engineering\/,
    Vol. 1, No. 3, 2007, pp.\ 165--176.

    Day, Alexander H., Campbell, Ian, Clelland, David, Doctors, Lawrence J. and Cichowicz, Jakub,
    ``Realistic evaluation of hull performance for rowing shells, canoes, and kayaks in unsteady flow",
    J. Sport Sciences, Vol. 29, No. 10, July 2011,
    pp.\ 1059--1069.

    Dudhia, Anu,
    ``Physics of Rowing: Effects of weight in rowing",\\
    $www.atm.ox.ac.uk/rowing/physics/weight.html$,
    Last accessed: 28 June 2012.

    Findlay, M. and Turnock, S.R.,
    ``Mechanics of a rowing stroke: surge speed variations of a single scull",
    Proc. IMechE, Vol. 224, Part P: J. Sports Engineering and Technology, 2010,
    pp.\ 89--100.
     
    Last edited: Feb 23, 2014
  4. JotM
    Joined: Jan 2009
    Posts: 94
    Likes: 8, Points: 8, Legacy Rep: 34
    Location: Leiden, the Netherlands

    JotM Junior Member

    Dear Leo,
    Thank you very much for all the suggestions! I will scour all of the sources. :)

    I think the working group seems to be lucky getting dr. Keuning "on board".
    Besides whatever I can find in all new material you pointed out (a lot of which I had already come across, but there are certainly new leads) I will ask him whether he thinks we might be able to extract some information from the combination of Wu, J.-S., and J.-J. Sheu, "An exact solution for a simplified model of the heave and pitch motions of a ship hull due to a moving load and a comparison with some experimental results", Journal of Sound and Vibration, Vol 192(2), 495-520, 1996 and several of the articles on the Delft Systematic Yacht Hull Series (DSYHS) he has been involved in over ~40 years.
    From first glance it seems to be possible to tie the work of Wu and Sheu into Keuning e.a.'s work on the added resistance due to waves.

    And now the DSYHS has been made publicly available under a creative commons license [dsyhs.tudelft.nl], we might even be able to get some estimations of what to expect later, either from full size testing - if and when we're able to organize that - or from a (coupled multi-body &) CFD simulation.

    It are going to be busy but interesting times. :)

    Regards,

    Jaap
     
  5. JotM
    Joined: Jan 2009
    Posts: 94
    Likes: 8, Points: 8, Legacy Rep: 34
    Location: Leiden, the Netherlands

    JotM Junior Member

    And then, how to compare them?

    Once we have enhanced our knowledge about the energy expenditure during a race with this kind of boats, the *really big* challenge might very well be in designing a handicap-rule though. One that facilitates all the boats eligible for racing (http://www.sloeproeien.info/sloependatabase/sloependatabase/), ranging from

    [​IMG]
    to
    [​IMG]

    under circumstances ranging from

    [​IMG]
    (Grachtenrace Amsterdam [link] -> [images] : 23 km through the canals of Amsterdam )

    to

    [​IMG] [click to enlarge]
    [HT 2005]
    (HT-race: about 18 nm , from the port of Harlingen to the island Terschelling, across the Wadden Sea)

    in a way that every well trained and prepared team - on average, over a whole season - has an equal change of winning The Cup, regardless of the type of boat rowed.

    As said, up til now this has been done by calculating race results by means of an estimate of the (partial) power needed to tow (steady state) the boat at the average speed attained over a race, taking neither wind nor waves (incl swell) into account. But just how fair is that? Can we do better?
     

  6. JotM
    Joined: Jan 2009
    Posts: 94
    Likes: 8, Points: 8, Legacy Rep: 34
    Location: Leiden, the Netherlands

    JotM Junior Member

    Monitoring dynamics

    Following a lecture by gig rowing team "De Toekomst" this winter, we have been playing around with the Android app "Talos rowing" this week, in a whale boat like "Kaag 1" (pictured in posting #5) and in a Cornish Pilot Gig.

    As expected there is *a lot more* going on than just longitudinal accelerations. :cool:

    With 5 men rowing a boat meant for 8 here's an example of the speed changes relative to a mean speed at some moment last week:
    [​IMG]

    (How shall I put it? "There seems to be room for improvement too"? ;) )

    I'll try to extract some more general information on the accelerations in fixed seat rowing from the data also. But that might also require data collection from monitoring our better teams (in terms of championship results in the near past) and other types of boats too.
     
    Last edited: Mar 1, 2014
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