Saturday, November 13, 2010

Is lighter really faster? SUP weight experiment- by Robert Stehlik

This entry is kind of off topic for the Zen Waterman blog as it is a technical description of an experiment I conducted, although it does tie into paying attention and being focused.  If you are interested in the interplay of weight and acceleration/ speed/ momentum on stand up paddle boards you might find it interesting.

I was inspired to test the effect of weight on speed in Stand Up Paddle boards when I was reading a discussions on the Stand Up Zone forum titled "Heavier Boards Faster?".
You may want to read it to understand the discussion that let to this experiment.  I will use some of the things I wrote in the discussion and will try to add details and information here that were not covered in the forum discussion.

The setup:
The short video clip above is a test of the GoPro camera and shows the set up used for the test.
Board: 12'6" x 29 1/2" Amundson Touring/race board.  For more information on this board, please check out the Aquaglide brochure.  I chose this board because it is stable enough to handle 30 extra pounds without making it difficult to balance. It has 247 liters of volume, so it can float up to 247 kilos= 544 pounds.  It weighs just over 30 lbs, so adding 30 lbs roughly doubles the weight and should make a measurable difference in speed.  I was concerned that using less weight would make the speed difference too small to be significant and measurable.
In the video: GPS and Go Pro cam taped to board: to record the speed on the GPS with the camera to see how the weight affects acceleration/ deceleration and top speed.

The 12'6 Amundson has a sealed insert on the deck. I screwed in an old windsurfing unversal and used it to tie off the weights so I could not lose them.

My weight is just under 200 pounds, the board itself weighs just over 30 lbs, I added 30 pounds on the deck for testing.  Although the board weight is doubled by adding 30 pounds, if you consider the weight of the rider + board, the weight difference is 230 lbs vs. 260 lbs with the extra weight, or just 13% more, and I'm assuming results would be different with different rider weights.

Test Day #1:
Here are the results of the 400 ft sprint test:

with 30 pounds extra weight:
Run 1: 49 seconds
Run 2: 49 seconds
Run 3: 48 seconds

without extra weight:
Run 1: 45 seconds
Run 2: 45 seconds

The acceleration was noticeably faster with the lighter board and the 3-4 seconds difference is significant.

For the half mile test, the results were less pronounced but still significant- as follows (wind was light 2-5 knots):

with 30# extra: Upwind: 5:44, downwind: 5:29 
without extra weight: upwind: 5:32, downwind: 5:16

I calculated a 3.6% speed difference upwind and 5% downwind

Here is what I noticed watching the videos of the half mile tests:
With the 30# extra weight it took me 7 seconds and 8 strokes to accelerate to 5 mph
Without the extra weight only 5 seconds and 6 strokes.
I also noticed that the weighted board has more of a wake and turbulence behind the tail and seemed to make more noise over the water

Test Day #2
I re-did the sprint tests the next day as the speed readout on the GPS was not visible on the video of the sprints.
I did not think the weight distribution would matter for the speed test but was urged to try to spread out the weights over the length of the board by one of the commenters.
To my surprise, the board seemed to handle a little better with the weights spread out than with the weights in the center. I tried to figure out why and then it made sense- with the weight spread out over the length of the board it yaws less (meaning less side to side rotation per stroke) especially from a standstill.
I know you could turn this into another science project but here is the simple explanation I came up with: Think of doing a flip off a diving board: you can speed up the rotation by pulling in your arms and legs closer to the center of rotation, while spreading out arms and legs- weight away from center of rotation- slows down the rotation. Same thing on the SUP. If all the weights are at the center of the board, it will yaw more easily (center of rotation is center of board), while spreading the weights away from the center of rotation makes it yaw less- makes sense, right?
A takeaway from this is that if you pack gear on your board, placing it away from the center- towards the nose and tail- will make the board yaw less than mounting it in the center of the board.

On the second day, the results were as follows:

400 ft sprints:

with 30 pounds extra:
Run 1: 48 sec
Run 2: 48 sec
Run 3: 48 sec
Run 4: 49 sec

Without extra weight:
Run 1: 46 sec
Run 2: 46 sec

So results were a little less conclusive as the average results were almost a second faster with the weights and almost a second slower without than the day before. Still significant though.
You can watch the videos below of the sprints without and with extra weights and draw your own conclusions.
Run without the weights: 46 sec. top speed: 6.7 mph

Run with the 30 lbs weight: 48 sec. top speed 6.4 mph

I realize that putting the weights on top of the board is not the same as having a heavier board where the weight is spread out over the entire hull.  Nevertheless, I'll assume for the sake of this experiment that the effect of extra weight is similar.

I rounded the sprint results to 3 seconds slower with 30 pounds extra weights. For the 48 second time that is a difference of just over 6 %

I'm assuming that each additional pound has a proportional effect on speed, so 6% divided by 30 pounds= 0.2%

So, I'm assuming that a pound of weight added to the board makes it 0.2% slower.

So, you would expect 5 extra pounds to make it 1% slower and 15 extra pounds 3% slower

This sounds very minimal and if you are cruising or touring: who cares if you are going 1% slower, that's only 36 seconds per hour of paddling.

I just want to put it in perspective from a racing standpoint.
Imagine for a moment that you are Rob Rojas and just finished the BOP Elite race in 1:03:15
If you want to check the results:

So, you finished the Elite race in 15th place- a respectable finish against the world's top SUP athletes, but not top ten, no podium, trophy, prize money, shaking Jerry and Sparky's hands, pictures in the mags and on the web etc.

Matt Becker, on the other hand, finished in ninth place in 1:03:08. His time was 7 seconds (or 0.185%) faster and he makes the cut.

If you knew that making your board just one pound lighter would have made you 0.2% faster would you still say that weight does not matter?

I think not.

Another thought:
The speed difference might seem very small in the controlled flat water test but in downwind racing it's all about catching and connecting bumps. That slightly faster acceleration can be the difference between making and missing a bump, which can compound the effect. If you race in downwinders you know that connecting one good bump train can put you 50 yards ahead (or behind if you miss it) of you competition, and it does not really matter if you are at the front or in the middle of the pack.
If you are not racing, or want a board to train on, save yourself a bundle and get a solid, less expensive board, but in racing, light weight is KEY

Note: The test used weights on top of the board, not evenly distributed. Also, I used the sprint results to calculate the 0.2% effect per pound. Most likely the difference would have been smaller with even weight distribution and over a longer course. My estimate is that one extra pound, evenly distributed will make the board somewhere between 0.1% to 0.2% slower and maybe less than that in some circumstances.  Other factors are size, volume and design of board, rider weight, etc.  I'm thinking a displacement type board should be less sensitive to weight than a planing hull, which has to lift out of the water to plane and reduce wetted surface and drag.

This is just what I'm taking away from this experiment.  To read what others thought of it, or if you want to make a point or comment, please check out the discussion thread at:

Robert Stehlik

No comments:

Post a Comment

Thanks for posting a comment on Zen Waterman, your comment will show as soon as we have a chance to screen it for spam. Mahalo, we hope to see you on the water!