Need analysis of rowing experiments reducing blade area while maintaining performance

Discussion in 'Hydrodynamics and Aerodynamics' started by lunatic, Jan 12, 2023.

  1. lunatic
    Joined: Jan 2008
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    lunatic Senior Member

    Oars01.jpg Oars03.jpg Oars04.jpg Oars05.jpg Oars07.jpg Oars08.jpg The amount of research on competitive rowing is overwhelming but little is applicable to utilitarian dinghy rowing. High aspect blade motion is horizontally rotational, out and in from boat, and vertical only down to blade immersion with much ventilation (Fig. 1); competitive rowing seems to move little water quickly with great effort by trained athletes in specialized craft. For a dinghy, high aspect blade has less rotational motion, speed, ventilation, but more vertical travel (Fig. 2, 3), and is user-friendly.

    To judge performance chose routine use over several days in various conditions switching, port to starboard, mismatched prototype oar with traditional 5” blade (Fig. 4B, 7A) as base comparison. Using boat rotation from line of travel had too many variables in open water, and the instinct to row straight, with its unconscious corrections, is very strong.

    Experimental prototypes, based on dubious theory, did surprisingly well, empirically leading to less area through chord reduction and the higher aspect thin blade. Thin oar (Fig. 4C, 7BCFG) matched base comparison oar (Fig. 4B, 7A) in general performance, even in first stroke and braking which others could not, and produced my first experience of flutter. Steel was quick and easy for prototypes but reached its limit with the pipe oar (Fig. 5); switched to wood for stiffness and more sectional variation (Fig. 6).

    Further research found the Greenland paddle, a precedent for maintaining performance with reduced area, but much discussion was of avoiding flutter, rather than theory. And Petros on this forum https://www.boatdesign.net/threads/what-is-the-propulsive-efficiency-of-oars.47468/ , page 4: his downward slice at an AOA (Fig. 8) seems a far better model for dinghy rowing than the racing research. My simplistic diagram (Fig. 3) looks possible but does not account for the persistence of flutter, high at startup and braking, less at sustainable speeds. Petros attributes this to lack of technique and Karman vortex street, clearly evident in braking; but no change of AOA or technique eliminated flutter in the thin blade, maybe a difference between oars and paddles.

    Although initially annoying, the extra travel per stroke and/or the turbulence of flutter seem beneficial. Again Petros’ “The forward facing surface is of course the low pressure side of the foil”, seems good condition for LEV with high lift and no back side drag penalty; but sharp edged flat side of Fig 7D had no flutter, less performance, more ventilation. With a simple 180 degree flip of the oar (Fig. 7C), there is flutter, better performance, less ventilation.

    I’ve been rowing with matched thin blades (Fig. 7G) through the fall and into the winter in various conditions with good results but with no insight or basic diagram as to what’s going on. Time for a more objective rower -- a reluctant friend expecting to be rowing in circles with mismatched oars (Fig. 7A, 7F), said upon return, “Now if I lose an oar, I know any old stick will do.” Need help in finding a better stick!
     
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  2. BlueBell
    Joined: May 2017
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    BlueBell . . . . .

    Isn't the point to move as little water as possible while moving the boat as much as possible?

    "Need analysis of rowing experiments reducing blade area while maintaining performance."
    Why? What is your objective?
     
  3. seasquirt
    Joined: Dec 2015
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    seasquirt In the beginning there were waters.

    Why not do your own practical research with an electric model rowing device, and a collection of paddle types, in your bath or pool. If you're only testing paddles, it won't matter if the row machine isn't 'anatomically correct' in its motions, because it's all relative to the conditions being identical for different paddles. Even a single oar position giving flow speed of fluid in a channel of water, or volume 'paddled' (pumped) over time, could inform you of any shape benefits. Whittle up as many model oars as you like, with standard or radical shapes. Try a hockey stick or cricket bat. You may find the next big thing, or the best marine store oar/paddle shape. Keep in mind that people have already been paddling for thousands of years, so probably everything has already been tried, right up until outboard motors. Leg oars aren't much different, sculling is a bit different, ancient Greek Tireme oars look modern, Pacific Island traditional oars are a bit different. Maybe modern materials may make a difference, eg. light weight hollow carbon fibre oars, or flexible sections distorting to benefit in different ways throughout the stroke. I'm sure some college or uni would have already done materials science study on rowing gear, since it is a prestige sport. Try searching in google scholar for research. Reduce the blade area with a long propeller shaft, electric motor, solar panel, battery, and a beverage of your choice, while towing a shiny lure. Unscientific but sometimes worthwhile.
     
  4. lunatic
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    lunatic Senior Member

    Point was trying to show the geometric difference between two distinct rowing systems. My objective was to satisfy my curiosity, after kayaking next to a fast swimming deer, that there might be other blade possibilities.
     
  5. lunatic
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    lunatic Senior Member

    Way too many suggestions for my limited capacities, but a tennis racket came to hand, lousy oar but good ventilator, "sometimes(not)worthwhile" but looked great in action.
     
  6. Hull Speed
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    Hull Speed New Member

    If you are interested in very narrow blades, you should check out the Irish curragh, which is rowed with oars often described as "bladeless".
     
  7. lunatic
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    lunatic Senior Member

    Thank you and the Irish, so any stick, even a deer's leg, might do, but why? Foil seems to be high aspect operating at low Reynolds numbers, with beneficial flutter, any clues here?
    Enjoying the ease and visuals of rowing with silly sticks, still looking for better ones.
     
  8. Kayakmarathon
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    Kayakmarathon Senior Member

    The blade is a foil, so the blade actually slips less due to lift generated as the blade moves away from the boat. This gives the appearance of moving little water when viewed perpendicularly from a fixed point on shore. More water actually moves over the blade as the stroke rate increases. Once the face of the blade starts to move toward the boat, the efficiency of the blade drops. In a kayak using a wing blade, I always keep the blade moving away from the hull to maintain lift. Once the blade starts to move toward the boat, the blade can dive quickly. When I used a flat bladed paddle, I didn't have to worry about the blade diving.
     

  9. lunatic
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    lunatic Senior Member

    Little experience with kayaks but there seems to be much more nuanced control than with oars. Fig 2 dinghy diagram shows little horizontal travel due to vertical sweep down, seems a very different geometry needing a different blade? Ever use a Greenland paddle? Suprised by its arctic origins; with a small area, it still has the force to right a kayak in critical conditions. Rough cold water seems to breed small, or even, no blades?
     
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