Dragon Boat Paddle Length

My last "physics 101" post was wildly popular, so I thought that I would do an analysis on another issue that I think plagues many paddlers: choosing the right paddle length.  While this usually comes down to personal preference and trial-and-error, people are usually choose a paddle length without much thought into what is right for them.  Many paddle manufacturers will over-simplify the process down to your height and experience level, which might give you a vague idea of the appropriate size paddle but has flaws.  First of all, why is your overall height important in a sport where you are sitting down?  Simple answer: it isn't.  So if not height, then what is important?  And what is the criteria for experience?  Is it just years of paddling experience?  If so, then every year you continue in the sport you should be buying a new longer paddle.  I'm sure the paddle manufacturers would like that, but if you're like me, then you're more concerned about what the right choice is for the long-term; not an interim paddle that you will "grow out of".

Background

To start off a little background information.  According to the IDBF paddle specification 202a, a dragon boat paddle must be at minimum 105cm (~41 inches) and at maximum 130cm (~51 inches) in length.  This specification refers to the overall length of the paddle from the top of the handle to the bottom of the blade.  All paddle manufacturers keep the blade at a constant length and adjust the overall length of the paddle by lengthening the shaft.

What does a longer paddle do?

It is usually a general consensus that a longer paddle is better, but what exactly is the effect of having a longer paddle?  It's safe to assume that your arm length will remain constant, regardless of what paddle length you use.  Also, it's safe to assume that your bottom hand height is constant at the catch since the blade length is constant and your hand should be placed just above the blade (you are doing that right?).  So when you go with a longer paddle, what's moving is your top arm.

Longer paddle length vs. top arm angle.

As you increase the paddle length, the effect on the catch is that you get a more positive blade angle, and effectively increasing the length of your stroke.  The counter effect is that your top arm position is at a higher angle.  As you increase this angle, your ability to apply force at the catch becomes sub-optimal.  In the image above, you will see that in figure 2 the paddler has his top arm in a full 90 degree overhead position.  This is what I would consider to be the optimal case since the shoulder is stable in that position.  In figure 3 the arm is over extended, which may cause injury due to the way the pressure is applied to the shoulder.  Your top arm angle will be limited by your top arm mobility (overhead position mobility), so you need to consider this when choosing your paddle length.

Longer paddle length at limited shoulder mobility

When your shoulder mobility is limited, the overall effect of a longer paddle is detrimental.  What will happen is that the catch angle of your body will decrease because you will hit the water sooner.  As your catch angle becomes more and more upright, your ability to reach your bottom arm forward is reduced and your stroke becomes shorter.  If you find yourself padding with a very upright torso, it may be because your paddle is too long for you.  But, conversely, what happens when you go too short?

Paddling with a short paddle

In the above image, you see that with a shorter paddle, the paddle is still in the air at the paddler's fully extended "catch" position (fig 1) and the paddle only hits the water once the arms drive down (fig 2).  This makes the paddle catch less positive (in fig 2 it's almost perpendicular with the water) and the length of the stroke is reduced.  The fully extended catch position stated above is determined by your ability to rotate your torso and the angle of your torso at the catch (limited by oblique/lats mobility).

Conclusion

Your optimal paddle length will depend on your top arm's overhead mobility, your torso's rotation and oblique/lats mobility.  This is the "experience" level stated by paddle manufacturers.  So now let's address their other measurement: your height.  Well your overall height is actually not a good metric for paddle length, however what does have an effect is the length of your torso and your arms.  So if you want to good way to ballpark an appropriate paddle length, sit down on the bench and stand your paddle next to you (blade on the bench, and top arm over the handle).  If you can barely reach the top of your paddle, then the paddle is probably too long for you.  If you can reach the top and your elbow is extremely bent, then the paddle is probably too short for you.  Ideally, you should have a slight bend to your elbow while being able to comfortably grab the handle of the paddle.  From there, check your catch angle and adjust accordingly with a longer or shorter paddle.

This is a blog post I found last week that I thought was interesting. The author - Kevin, Assistant Coach for the Dragon Boat Club of Boston - is stating what we show in this video.  Though we are discussing how to size an outrigger paddle, we use this same system for sizing dragon boat paddles.