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Science Digest: Rowing Efficiency

 

I’m always jealous of other sports with the resources to conduct actual scientific research on the physics of performance.  Crew and sculling are among those sports.  The R&D is aimed to investigate and optimize every possible aspect of performance to hopefully yield multiple avenues for improvement.  Perhaps we will never see full carbon-Kevlar dragon boats weighing less than 250 lbs, but I love reading this stuff because it makes my wheels turn in hopes that some trickle-down truth can help us in our traditionalist sport.  After all, each of our sports utilize glorified sticks to push water in order to propel a hollowed-out log carrying people.

The Propulsive Efficiency of Rowing by Dr. Valery Kleshnev

The Digest

There are many potential areas where energy can be wasted, starting from the very chemistry that powers our cells into performing work.  This particular article takes a stab at investigating what factors signficantly influence rowing efficiency.

At one point in my life, the mathematics presented would have made much more sense and I may have had more thoughts on this, but for now, I’ll just say “duh” and move on.

Interestingly, the study found that blade efficiency increased as boat speed increased.  Based on the curves in Figure 2a, it would seem that there would be some point at which efficiency plateaus or perhaps even decreases as boat speed continues to climb.  I always felt that in dragon boat, getting “good pulls” in dragon boat was affected by boat speed.  When the boat is at a full stop, the water feels thick and I feel like I can apply a great amount of force to the water.  As the boat starts to pick up, those heavy pulls become lighter and lighter still, which would seem to me that my strokes are not as efficient at those higher hull speeds.  I would speculate that having better stroke technique designed for higher boat speed is important for improving blade efficiency.

Interestingly, Dr. Kleshnev notes a decrease in boat efficiency as stroke rate increases.  I thought this section was simply better written for my smooth brain to understand.  Decreasing the “drive/stroke ratio” would mean either decreasing time spent in drive phase (period where blade is in the water) or increasing time spent on the stroke (entire time spent between drive and recovery).  Decreasing drive time could mean exiting sooner, but that would also decrease total stroke time.  “Fast through the water” is another way to think about it and would be assisted by higher boat speed.  Increasing the time spent out of the water could also work to increase stroke time, but while it may be beneficial to “let the boat glide” spending an extreme amount of time not propelling the boat allows the boat to slow down between strokes.

Combining his 2 findings on boat efficiency, one might speculate that (at least in rowing) increasing stroke rate lead to a increase in drive/stroke ratio.  At higher rates, I’d think stroke time must decrease in order to fit in more strokes per minute.  If recovery were quickened to fit in a higher rate but boat speed did not allow for drive time to decrease (leaving a long drive time due to slow water), the ratio would be increased.  Indeed, the conclusive statements suggest shortening drive time as a way to increase efficiency at higher stroke rates.

Application to Dragon Boat Paddling (to be continued)

CDBA 2012 Sprint Results Online!

Results are up!  Congrats to all teams for some killer racing and a big thank you to CDBA for making it all happen.

View results online here

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Sprint Race 2012

Stay strong
Stay true
Stay passionate
Stay together.

Congratulations to a race well run, paddlers of SFL.  This is why I coach.

Rotation

The questions are: why is rotation important and how much should be emphasized?

      IF:  Rotate + Reach + Dig + Pull + Exit = Paddling
THEN:  Rotation is a critical component to paddling technique!

Why Rotate?

Rotation is a natural part of reaching your hand towards something.  It’s how we get our hand closer to the prize.    Back when we were apes, rotation was critical to reaching the next branch to escape predators.  As evolving hunter gatherers, rotation was critical for reaching that high branch of fruit.  Nowadays, it may seem that reach/rotation is largely tied with grabbing the TV remote control while sitting on the couch, but it also serves a critical role in dragon boat paddling.  Rotation is, quite simply, intended to extend the length of your reach and thus, length of your stroke.  With the increase in stroke length, there is the potential for greater power transmission to the water.

The Hand Bone’s Connected to The…

Your arm is connected to your trunk by the shoulder girdle.  The shoulder girdle is comprised of your shoulder blade and collar bone.  The shoulder girdle sits in contact with your rib cage and sternum, which provide the foundation for shoulder movement.  The shoulder blade is free to slide up, down, side to side, tip, and rotate along your barrel-shaped rib cage.  Since your rib cage is attached to your spine, its shape and position is altered depending on your posture.  At rest, the shoulder blade and the glenohumeral joint (ball/socket) face 30 degrees forward (more on this later).

If reaching effectively depends on max forward displacement of the hand, then we should try to make sure our shoulder blade positions our arm in a position of max reach.  Think about your wingspan.  How do you stretch your arms as wide as possible?  Out to the side.

“Twist until your chest faces your partner”

How many coaches use this as a verbal cue?  How much rotation is really needed to get good reach?   Building from the above, if you are sitting on a boat with your arms stretched out to the sides like a “T,” you would have to twist your trunk close to 80 degrees to reach your hand forward.  Pushing that kind of rotation range stresses your spine and, especially in sitting, your intervertebral discs.  Minimizing spinal stress while still getting reach is a compromise.

Earlier, I wrote that the shoulder blade and glenohumeral joint already face 30 degrees forwards.  This sets up what is called “scapular plane.”  Raising our arm to the side 90 degrees and then moving it forwards at shoulder height by ~30 degrees will put your hand in scapular plane.  Now we need to get the hand up front and your trunk rotation can make up the difference.  Keep your arm 30 degrees forwards in relation to your body at shoulder height, now twist at the waist to bring the hand to proper reach position (depending on where you sit on the boat, how the gunnel flares, where your coach wants you to reach).  Instead of rotating 80 degrees at the waist, now you only need to rotate 40-50 degrees, causing less stress to your spine and still giving you good reach.

More On Reach

Of course, leaning forward at the trunk is another method to increase reach, but ultimately a paddler who performs well has an efficient stroke length, which depends on the geometry of the paddle and paddler in relation to the water and boat.  I’d recommend incorporating this notion of rotation with those topics written earlier here.

Posture Perfect

Did you know that slouching causes you to have decreased shoulder flexibility?  Try slumping in your chair and raising your arm overhead.  How far can you reach up?  Now sit up tall and raise your arm.  There you go!

Not only does slouching alter your shoulder’s ability to move through its potential range, but can also cause a decrease in muscle strength and increase in stress and risk of injury to sensitive tissues.  Part of efficient reaching and power delivery comes from trying to keep a neutral spine during the stroke.  For this topic, I’d recommend reading this previous article.

May Race 2012 Results Online

Photo & Video Sharing by SmugMug

Photo & Video Sharing by SmugMug

Photo & Video Sharing by SmugMug

Official racing results are now online courtesy of CDBA.

Check them out here!

Back from the Dead

Back from the brink of complete loss.  

No lights at the end of tunnels.  

Every race being the Last Stand.Image

Sixth on the Fifth

May Race is over and with it, the official start of the mixed dragon boat team season in the Bay Area.  In a series of heats true to form, the SFL Dragon Boat Team once again demonstrated itself to be a team not to be ignored.  With a single crew comprised of 75% SFL paddlers and 25% Lightwave paddlers, the team managed some of the most competitive race starts in the field.  Credit goes to the Lightwave paddlers for quickly adapting to the SFL starting count with just a single practice start prior to the Seeding heat.  Our token Cardinal paddler, Brendan, also did a great job at meshing in with the crew for our later races and showed us how much more in shape we could be if we could only reverse the sands of time.

Special thanks goes out to Katherine, Jeannie, Rebecca, Ashes, and Hon for helping to carry the SFL crew into A-Division 6th place.

A big thank you also must go out to those SFL paddlers who made the commitment to keep the team racing this year at May Race: Huy, Erica, Cory, Megan, Christine, Marissa, Will Huang, Will Lam, Jerome, Henley, Jacky, Allen, Jon, Marissa, Solongo, Shelley, and Derek.  Thank you to short-haired Bonita for offering to paddle when we were in need.

The team of “Smooth Wind Dragons” breathes again!

Paddle Length and You

A quick search online will reveal several published resources making general recommendations for choosing a paddle length.  These resources often quote paddler height, level of experience, or bench placement in guiding buyers towards choosing a paddle size.  While these rationales are reasonable, there are several factors in choosing a paddle size that, when thoroughly understood, can help determine how to find a paddle that works best for you.

Background

The International Dragon Boat Federation (IDBF) has established a general schematic for all dragon boat paddles approved for use in IDBF competitions world wide.  This helps minimize any disparities between teams racing in an IDBF event due to equipment considerations.  The current standard is known as Specification 202a, which specifies that paddle length (from blade tip to top of handle) is between 105cm and 130cm.  Dealer websites may measure this in terms of inches, but the standards are the same.

The Business End

What part of the paddle matters the most?  The blade.  It’s the part of the paddle that serves as the interface between you and the water.  When choosing a paddle length, the ultimate goal is to get the blade into the water where it works best.  Generally, this means AT LEAST submerged below the surface of the water.

Shaft, can you dig it?

Since Spec 202a paddles all have specific dimensions for the blade, the one effective variable in paddle itself is the shaft length (spanning between the top of the blade and the handle).  This makes choosing a paddle length about facilitating the best leverage for a paddler to apply force to a fully buried blade.

Lower Triangle

Triangles are an efficient shape for transferring force.  By this rationale, our bodies will theoretically transfer force efficiently to the paddle and water when our back and outside arm are straight.  Different paddling styles aside, after burying the blade, the goal becomes pulling the blade back (or yourself up to an “anchored” blade) while it is at a set depth.  This means that as we pull back, our outside hand remains at a somewhat consistent distance to the water’s surface.  This creates a triangle between our body and the plane of the water.  This triangle is our foundation, the basic requirement to getting the blade buried during our reach.  Paddle length has little to nothing to do with this triangle as it depends primarily on the physical size of the paddler.

Fig 1

Upper Triangle

Adding the top arm and paddle shaft into the picture, we see an upper triangle formed.  The efficiency of this triangle is highly dependent upon paddle length and paddler technique.  In Figure 2, increasing trunk rotation on the reach has the functional effect of lengthening our outer arm and shortening our top arm.  This affects angle of paddle at entry, influencing the vectors (direction) of force applied by the paddle to the water.  It also serves to increase the horizontal displacement of our paddle during the pull, which is a good thing!

In Figure 3 B) and C), we see how increasing paddle length affects our body position and efficiency.  Leaving the bottom hand the same in B), a longer shaft forces our top arm higher which can cause more strain to our top shoulder’s joint and potentially lead to increased risk of rotator cuff or labral injuries.  Choking up at the bottom hand in C) to preserve top arm angle forces the paddler to bury the blade deeper in the water.  Because the blade is farther from the bottom hand, the force of the water against the blade (or vice versa depending on the relative physics) is applied farther away from the bottom hand.  This increases the torque that a paddler fights during the pull, making each stroke feel more difficult despite the same amount of power being put into the water.  In other words, choking up due to a paddle being too long puts the paddler at a mechanical disadvantage, wasting energy.

Having an excessively long paddle also forces you to compensate during recovery just to clear the blade from the water.  Having an excessively short paddle will decrease the horizontal displacement of your blade during the pull, which decreases paddling efficiency.  A short paddle may also force you to flex more at the trunk during the reach to get the blade buried, which compromises 1 side of the Lower Triangle and may increase your risk for spine injuries (not pictured).

Fig 2

Fig 3

Choosing the “Right” Length

After all that theory and physics, it requires trial/error and close assessment with your coach to determine the paddle size that gives you the best fit.  Depending on how skilled you are with paddling, your fitness level, where you sit, and how your coach would like you to paddle, you should choose a paddle length that allows you to get the blade fully buried while allowing you to pull with an Upper and Lower Triangle that is most efficient for you.

Recommendations

1.  Continuously refine your paddling technique.

2.  Get regular 1 on 1 feedback from your coach about your paddling technique.

3.  Try a variety of paddle sizes from teammates to see how it meshes with your paddling technique.

4.  Consider changing your paddle length if your technique is strongly compromised, it forces you to work beyond your level of fitness, or you have noticed it contribute to painful symptoms.

What To Do If the Boat Starts to Sink

I remember taking a mandatory safety class through the CDBA as a requirement to sit for the steering certification test and there was a topic that came up on what to do should your dragon boat start to take on water (eg sink) while you are away from dry land.  The official recommendation (and subsequently the correct answer on the exam, ahem) was to have several paddlers bail water, have other paddlers paddling back to shore ASAP, and have another group of paddlers jump overboard and hang on to reduce the amount of weight in the boat.  It was clarified that, to be fair, those people who jumped in could rotate in/out of the water with other paddlers if the journey to shore would be too long for comfort.

Yea, that clip pretty much sums up my feelings, so here we go!

Top 3 Reasons Why That Plan Sucks:

1.  The boat is sinking but not sunk yet, you have some time before it ceases to become water-worthy and your crew is effectively stranded off shore.  Thus, it behooves everyone to get to shore as fast is flippin’ possible.  Faster travel requires more paddlers.  Why on Earth would you drag people through the water?  Ever pulled a tire behind the boat, it’s hard right?  Pulling a tire doesn’t allow much speed even with a crew of buff paddlers, right?  Losing able bodied paddlers while dragging them through the water will slow your return to shore.  I will say having folks stop paddling occasionally to bail could be helpful if water is rushing in quickly.

2.  The additional weight of having 2 paddlers in the boat will not affect the rate of sinking very much compared to the time lost from the effects in #1.

3.  The water’s probably going to be colder than the human body.  Hypothermia is a life threatening condition that you’re actually considering having people volunteer for when they don’t need to?  Having paddlers rotate being in/out of the water is even more dumb.  Hypothermia can still occur after you get out of the water.  Plus, you now have 2 freezing people back in the boat and 2 people about to freeze in the water.  Nice going.  Did I mention that freezing people don’t paddle very fast?

Just don’t make that question the one that causes you to fail the test, ok?  Also, after passing the test, please don’t kill people unnecessarily by actually following the recommended answer you used to pass the test.  Thanks.