Effect of Crew Movement on Dragon Boat Speed

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Dragon Analytics - race start

In rowing, the mass of the crew is much more than the mass of the shell. Therefore, any movements by the crew affects the momentum of the boat. Because of this, much research has been done to minimize the detrimental momentum changes and maximize the positive momentum changes caused by body movement.

Dragon boating has the same situation, with some fundamental differences.

  1. A dragon boat crew has up to 20 paddlers, a drummer, a sweep, paddles and the boat itself.
  2. The crew faces the way they wish to travel.
  3. The paddle blade and our body movement are in the same direction.

A fully loaded dragon boat is not just a 2000kg solid body – it contains two separate components:

  1. Crew with paddles, representing 70-80% of the total mass; and
  2. Boat (drummer and sweep), representing 20-30% of the total mass

During a stroke the individual components of the dragon boat move relative to each other. Sometimes the crew is pivoting backwards while the boat is moving forward. Other times the crew is pivoting forwards while the boat is moving forward.

Unlike rowing, pivoting backwards and forwards is not moving your whole body. In dragon boating, only some of the total mass of the crew is moving in a way to affect the momentum.

How much crew mass is moving backwards and forwards? Let’s find out how much each part of the body weighs and which parts are moving.

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6 COMMENTS

  1. I enjoyed the article Mark. Would it not be more appropriate to consider the studies that have been done for the Sprint Canoe Stroke (Kneeling)? There is information on the Journal of Human Kinetics site that may be worth a nod as the Dragon boat stroke is much closer to the sprint canoe stroke than it is to rowing or canoeing. The ability to move forward fluidly without generating that backward impulse is key to minimising the drop in speed during the recovery. I believe it can be trained just like every other part of the stroke.

    • Hi Alan. You are right. The Sprint Canoe Stroke is much closer to the dragon boat stroke than rowing is. My main aim in the post was to show that the phenomenon does exist in other sports with differing effects. I also agree that moving forward fluidly may be the answer to minimising the backwards impulse. I will definitely look into the Sprint Canoe studies. Thanks for your feedback.

  2. If you isolate your system and assume no external forces present, the net effect of any finite motion internal to the system cannot change the momentum of the system. This is true and something you state right off the bat. The problem with your argument at the end is that you start thinking of v_b (dead weight velocity) as v_t (total system velocity – which according to the momentum conservation cannot change due to internal forces). So although v_b may change throughout the phases of your stroke, v_t should not.

    The second issue is that you must look at this momentum problem with respect to time. So a more appropriate approach would be to integrate your momentum during each stroke phase where each incremental sum is dp = m*(dv/dt). At the end of each phase (pull and recovery), v_c must reach zero before turning around and going the opposite direction. There is an acceleration then deceleration forward during recovery and then the opposite direction on the pull. So it might be true that v_b will oscillate during the recovery and pull phase, but at the end of each phase, both v_c and v_b will go to zero.

    The real crux of the problem is moreso a) whether or not drag forces increase due to crew movement and b) whether those drag forces cause the boat to slow more than it can gain by having the crew twist and lean forward for a longer and possibly stronger pull due to physiological advantages. But in an isolated system where we assume drag forces and external forces don’t come into play (basically assuming a frictionless environment), the net effect of any finite internal movement will be zero.

  3. I’m curious to see what you think about the effects of the vertical shift in the center of balance throughout the stroke. When I watch videos of races, and I watch the nose of the boat as the paddlers pivot back during the compression phase of the stroke, I’ve noticed that the nose dives down. Conversely, when they the recover and pivot forward, the nose of the boat rises. I’m guessing that when pivoting back and compressing, the nose dives down due to the center of gravity of each paddler going up, and that would have an equal force going down on the boat. Wouldn’t that increase drag? Does that sound accurate?

    • Hi Alan. The rise and fall of the nose of the boat could be due to the phenomenon mentioned in the post making it “look” like the boat is diving down a bit, or it could be due to other factors. The centre of mass of the 20 paddlers is moving forwards during the recovery and backwards during the drive but simultaneously down during the recovery and up during the drive. So the reactive forces on the boat could be in the opposite direction – i.e. up during the recovery then down during the drive. The same up and down movement could also be caused by the power on the blades – especially if the angle of the blade goes negative (i.e. pulls the boat down). Get only one side of a dragon boat to do a power stroke and invariably the boat will dip on that side. So more research on any vertical movement of a dragon boat is obviously required. If the nose and the rest of hull is diving down, then most certainly the drag on the hull would increase. The aim of this site is not to speculate and present it as fact (we already have enough dragon boat “experts” in the world doing this). So in order to answer your question properly, let me take this on board and knock out a post to explain what is happening during a stroke and its effect on the vertical movement of the boat. A great question.

      • What made me look at the nose was thinking about the positive angle and how it should lift and accelerate the boat. I starting checking youtube videos and I was trying to see what I expected, which was the nose to rise, and a wake to come off from the increase in speed. What I actually saw was the nose drop and a larger wake from the force of the downward motion. If you look at this video, you’ll see two teams using two different strokes. The scaled boat in the back uses the “A-frame” stroke with the front/back pivot. you’ll see the larger wake, and a slight dip with each compression. The boat in front does not rock front/back, but rotates left/right for reach. https://youtu.be/RPdX_tjF9AM?t=164

        It does not seem like the scaled boat is lifting enough water at the exit to say that the downward motion of the boat is caused by a negative blade angle. That’s when I started thinking about whether or not the center of mass motion had a large effect on bouncing the boat up and down.

        Yes, as of now, it’s just speculation. I would love to see a more applied study and analysis.

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