{"id":2037,"date":"2017-12-01T11:37:00","date_gmt":"2017-12-01T11:37:00","guid":{"rendered":"https:\/\/www.gacooarlocks.com\/gaco\/?p=2037"},"modified":"2022-11-01T23:55:03","modified_gmt":"2022-11-01T23:55:03","slug":"the-turbo-oar","status":"publish","type":"post","link":"https:\/\/www.gacooarlocks.com\/gaco\/the-turbo-oar\/","title":{"rendered":"The Turbo Oar"},"content":{"rendered":"\n

Attacked for failing to discover a light filament after 1000 tries Thomas Edison famously replied; \u201cBut now I know 1000 materials that don\u2019t work.\u201d I\u2019m in a similar boat. I have tried two known oar theories, and have now come up with a third which works, but may not be the complete answer.<\/p>\n\n\n\n

The simplest theory according to William of Ockham of Ockham\u2019s razor fame is most likely the correct one. In this case it happens to be; \u201cTo every action there is an equal and opposite reaction.\u201d (Newton\u2019s third law). That is, as the oar blade pushes on the water the water pushes back. This theory has been elaborated in a scientific paper that excited me some years ago; \u2018The force from the blade on the water is generally normal (at right angles) to the blade surface at all times. The only exceptions to this are at the catch and the release. This force can be broken down into the following two components: 1) parallel to the direction of the boat, and 2) lateral to the direction of the boat. The lateral force does not contribute to the forward motion of the boat. Between 70 and 110 degrees, the oar\u2019s angle with the boat\u2019s direction provides the greatest forward force on the boat. Ideally the rower\u2019s force should be highest when the oar is in this position.\u201d (Virginia Technical Institute, Mechanical Engineering, Tidwell 1998)<\/p>\n\n\n\n

Well: \u201cThe lateral force does not contribute to the forward motion of the boat.\u201d It seemed logical, so I made an oar that is always at right angles to the boat to eliminate the lateral (sideways) force.<\/p>\n\n\n\n

The articulated oar blade (Take in photo A)<\/p>\n\n\n\n

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The blade swivels at right angles to travel. Its angle is controlled by a lanyard attached to the gunwale.<\/figcaption><\/figure>\n\n\n\n
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A failed experiment<\/figcaption><\/figure>\n\n\n\n

What a disappointment! It was very easy to pull at the catch and release and not very efficient mid stroke. However it was a bit like going nowhere and moved the boat less than a conventional oar. I dumped the project, but gradually figured out why it didn\u2019t work. Of course, at the catch the blade was going two-thirds sideways, and only one-third aft. Although it was easy to pull, two-thirds of my action was being wasted. How then was the conventional oar so much more effective at other than right angles, when most of its energy was being wasted because \u201cthe lateral force does not contribute to the forward motion of the boat?\u201d I have come to the following conclusions about this, especially for low load conditions.<\/p>\n\n\n\n

  1. For a well designed curved blade on a boat in motion, the water will flow over the blade at the catch, as the boat moves forward, in the same way as the wind blows over a sail and drives a boat to windward. As a matter of interest the area of a normal oar blade is equivalent to a wind-sail of 70 m2 or 760 square feet when the difference in density between air and water, is taken into account.<\/li><\/ol>\n\n\n\n
    \"\"
    At the catch the motion of the boat induces the water flow as shown.The angle of flow over the blade corresponds to the angle of the oar in the water.<\/figcaption><\/figure>\n\n\n\n
    \"\"
    At the release the reverse occurs.<\/figcaption><\/figure>\n\n\n\n

    This does not apply to a boat getting under way as the blade will stall. This explains why starting strokes are short and close to right angles with the boat. Further readings on \u201cHydrodynamic lift\u201d in relation to rowing confirm my conclusion. They disclose the counterintuitive fact that the oar moves forward in the water by around 4 inches (10 cm.) during the rowing stroke. The following diagram based on actual photos taken during a rowing stroke, illustrates this.<\/p>\n\n\n\n

    <\/p>\n\n\n\n

    \"\"
    The rowing stroke.<\/figcaption><\/figure>\n\n\n\n

    The above diagram shows the rower at the three stages of the same stroke (the catch is the start, the drive is the middle, the release is the final part). The dots represent the position of the blade in the water about every 5 degrees of stroke. Notice especially that that the blade has sailed forward in the water. This \u201csailing\u201d occurs for 60 degrees of catch and release while stalling or moving back in the water occurs for 40 degrees of drive. It must be borne in mind that even a flat blade will appear to sail forward at the catch because of the forward motion of the boat. The aim is to make a blade that will sail better. (Data from \u201cHydrodynamic Lift in the rowing strike.\u201d Ken Young, University of Washington, 5 June 1997)<\/p>\n\n\n\n

    1. The lateral motion of the oar will now induce the water to flow over the blade rearward creating a forward thrust in return.<\/li>
    2. Greater efficiency is offered at the catch, as the oar is moving sideways into clean water. The parallel to this is the greater efficiency of a sailing boat on a reach (catch) than a run (drive).<\/li>
    3. When the oar is at right angles to the boat it loses energy through slippage. This slippage amounts to about 30% at the tip, which travels furthest. This argues for a shorter wider blade, but for reasons of balance, and clearance on the return stroke, this is not practical beyond a certain point.<\/li><\/ol>\n\n\n\n

      Years ago I was interested to observe the native use of canoes on the remote island Tagula in New Guinea, where I had been shipwrecked. Although they had efficient paddles they would always use a pole to propel the canoes when the water was shallow enough.<\/p>\n\n\n\n

      The pole had no slippage of cvourse, and gave close to 100% efficiency (in contrast to estimated efficiencies of 70%-80% for racing oars and probably less for their paddles). They would allow their weight to fall backwards off the canoe while poling and push themselves upright, at the last, in the most skillful manner.<\/p>\n\n\n\n

      Excited about the interesting and counterintuitive theory of the sailing oar, I made a prototype oar that is shaped more like a sail to improve its performance. The leading edge is curved aft at 45 degrees to the line of the shaft and the blade is curved length ways and sideways to encourage non turbulent flow.<\/p>\n\n\n\n

      Testing with a hose showed the water attaching much better to the rear of the prototype.<\/p>\n\n\n\n

      \"\"
      The water does not attach to the rear of a more conventional blade.<\/figcaption><\/figure>\n\n\n\n
      \"\"
      The water attaches to the rear of the prototype for at least part of its length.<\/figcaption><\/figure>\n\n\n\n

      Now for the acid test, how would it work? Had I wasted my time again? I chose a calm day to test the oar down on the Hawkesbury River and opposed the prototype \u201csailing oar\u201d against a more conventional blade of the same area, in which the blade curves evenly through 15 degrees. The test had to be done under calm conditions. If the boat was carefully rowed with equal force on each oar, prototype one side, it should turn away from the prototype if more efficient, and towards it if less efficient. After twenty careful test runs, eyes closed, eyes open, the dory consistently turned away from the prototype. It was even more effective when a long catch was used. The feel at the catch is of a quite refined performance, with a pull propelling the boat further than expected.<\/p>\n\n\n\n

      Sometimes the laws of physics work against you. In this case not so, the prototype is very much stiffer because of its more compound shape. This enables a lighter blade that has the important effect of reducing outboard weight where such a reduction will have most effect.<\/p>\n\n\n\n

      Where to from here? Well of course even more radical shapes are to be tested until the shape becomes too extreme. 
      End of part 1<\/strong><\/p>\n\n\n\n

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