Scientific Flatwater Board Testing 101

[PonoBill]

Wow, Larry's article is very interesting. I like the notion of stroke effectiveness, it encapsulates several elements of paddling that I've been thinking about lately which motivated me to buy both a vivoactive watch and a Speed Coach as well as dusting off all the bits for the Paddle Pod I built years ago. Absent direct measurement of power, a result-based number like distance per stroke time velocity gives a good measure of power applied in an efficient manner. The problem I see with direct power measurement is that it doesn't translate into performance without a measure of efficiency. However we go about deriving efficiency, the way to get to a useful power figure is measured power times efficiency. Stroke performance does that directly.

I think I'm barking up the wrong tree thinking about measuring hull performance with a winch dragging weighted boards across Nichols Boat Basin. I'd be measuring a very static characteristic that must change quite a bit in a dynamic environment. The first thing that came to mind about Larry's testing is that "well, that calm flat water is never encountered in a race". I should hold the same criteria to my own ideas. No one is racing paddleboards by dragging them across flatwater. My proposed method is probably an order of magnitude less relevant than Larry's test. I need to think of something else to do with my new high-torque stepper motor and arduino shield.

I haven't tested the accuracy of the speed coach, but from the specifications, it seems capable of either directly measuring or deriving all the factors in Larry's test. Speed is probably pretty good, and that's easy to calibrate. Record instantaneous speed, try to hold it constant for a measured distance. I can check stroke rate accuracy with video, as well as stroke distance, which is certainly a calculated value. Of course everything the Speed Coach displays is calculated from GPS data, so the accuracy of that data determines accuracy of everything else. Decoupling speed from GPS data with a dragged impeller might be worthwhile if any inaccuracies show up.

Anyway, very cool article. Food for thought for days.  I think a combination of UKGM's rigor and Larry's aim for results that correllate to actual performance would yield some excellent information. I'd like to read your full paper if you're comfortable with that, UK.

[ukgm]

Wow, Larry's article is very interesting. I like the notion of stroke effectiveness, it encapsulates several elements of paddling that I've been thinking about lately which motivated me to buy both a vivoactive watch and a Speed Coach as well as dusting off all the bits for the Paddle Pod I built years ago. Absent direct measurement of power, a result-based number like distance per stroke time velocity gives a good measure of power applied in an efficient manner. The problem I see with direct power measurement is that it doesn't translate into performance without a measure of efficiency. However we go about deriving efficiency, the way to get to a useful power figure is measured power times efficiency. Stroke performance does that directly.

I think I'm barking up the wrong tree thinking about measuring hull performance with a winch dragging weighted boards across Nichols Boat Basin. I'd be measuring a very static characteristic that must change quite a bit in a dynamic environment. The first thing that came to mind about Larry's testing is that "well, that calm flat water is never encountered in a race". I should hold the same criteria to my own ideas. No one is racing paddleboards by dragging them across flatwater. My proposed method is probably an order of magnitude less relevant than Larry's test. I need to think of something else to do with my new high-torque stepper motor and arduino shield.

I haven't tested the accuracy of the speed coach, but from the specifications, it seems capable of either directly measuring or deriving all the factors in Larry's test. Speed is probably pretty good, and that's easy to calibrate. Record instantaneous speed, try to hold it constant for a measured distance. I can check stroke rate accuracy with video, as well as stroke distance, which is certainly a calculated value. Of course everything the Speed Coach displays is calculated from GPS data, so the accuracy of that data determines accuracy of everything else. Decoupling speed from GPS data with a dragged impeller might be worthwhile if any inaccuracies show up.

Anyway, very cool article. Food for thought for days.  I think a combination of UKGM's rigor and Larry's aim for results that correllate to actual performance would yield some excellent information. I'd like to read your full paper if you're comfortable with that, UK.

I'm still doing some more data collection but I fully intend to put it in the public domain on an open access journal when its done. This might be a while yet though. In answer to your question though, the Speedcoach should do just fine. I also did my slowdown test which also loses some specificity of paddling like your idea of a drag test  but its important to try to separate board performance from paddling performance and the two would complement (but not replace) each other.

[PonoBill]

Well, I've got all the parts, might as well build it and try it.

[Foilman]

I was reading this test and have to say it's at best semi scientific. The biggest variable, the paddler is not taken out of this test. Not only do you have the conditions as a variable but also the paddler. You can do as many test runs as you wish and then average them out but you still are nowhere close to a real test result. Since I'm playing around with making my own fins I kept thinking about how to scientifically testing them. Nowadays you see many board or fin manufacturers telling you "my fin's / board's tracking is a 9/10 and the stability is a 7/10 but what does that really mean? 9/10 in comparison to what? Here a couple of thoughts I had for testing boards or fins
First off I would take the paddler out of the equation and use a electric motor with a propeller or even a RC boat. Something that gets the board with either weights or the paddler sitting on it (center of gravity at the position of the handle) to around 6mph
Board speed:
Install the motor on the back of the board and see which board reaches the highest speed using the same fin and the same weight on the board
Drag:
Bring the board up to 5 or 5.5mph and measure the current on the motor. This way you'll see with which board the motor uses the most juice to keep the preset speed
Glide:
Bring the board to a preset speed, turn the propulsion off and measure the time till the board slows down to let's say 3 or 4 mph. You can also measure the distance from the point you're turning off the motor
Tracking:
Mount the propulsion to the middle on either side of the board. When you turn on the motor you'll go in circles. Use a GPS tracker on your phone and see which board or fin creates the biggest radius circles.
Stability:
This one is really difficult to measure. The ideal situation for this would be a wave pool. Even there you can't really simulate all conditions you'd encounter. I do have a couple other ideas on how to measure stability but that would get very technical and very expensive very fast.

You could also get fancy in these tests and use a frequency generator to simulate paddle strokes with cycling the engine on and off.

I'd also love if manufacturers would give you a value for the amount if rocker a board has. Just take the radius of the rocker for example. Different topic though.

Rob

[ukgm]

I was reading this test and have to say it's at best semi scientific. The biggest variable, the paddler is not taken out of this test. Not only do you have the conditions as a variable but also the paddler. You can do as many test runs as you wish and then average them out but you still are nowhere close to a real test result. Since I'm playing around with making my own fins I kept thinking about how to scientifically testing them. Nowadays you see many board or fin manufacturers telling you "my fin's / board's tracking is a 9/10 and the stability is a 7/10 but what does that really mean? 9/10 in comparison to what? Here a couple of thoughts I had for testing boards or fins
First off I would take the paddler out of the equation and use a electric motor with a propeller or even a RC boat. Something that gets the board with either weights or the paddler sitting on it (center of gravity at the position of the handle) to around 6mph
Board speed:
Install the motor on the back of the board and see which board reaches the highest speed using the same fin and the same weight on the board
Drag:
Bring the board up to 5 or 5.5mph and measure the current on the motor. This way you'll see with which board the motor uses the most juice to keep the preset speed
Glide:
Bring the board to a preset speed, turn the propulsion off and measure the time till the board slows down to let's say 3 or 4 mph. You can also measure the distance from the point you're turning off the motor
Tracking:
Mount the propulsion to the middle on either side of the board. When you turn on the motor you'll go in circles. Use a GPS tracker on your phone and see which board or fin creates the biggest radius circles.
Stability:
This one is really difficult to measure. The ideal situation for this would be a wave pool. Even there you can't really simulate all conditions you'd encounter. I do have a couple other ideas on how to measure stability but that would get very technical and very expensive very fast.

You could also get fancy in these tests and use a frequency generator to simulate paddle strokes with cycling the engine on and off.

I'd also love if manufacturers would give you a value for the amount if rocker a board has. Just take the radius of the rocker for example. Different topic though.

Rob

I'm not sure whether you are talking about what I did or what Larry did. However, I personlly included one test which did isolate the board from the paddler. However I have talked about this with Larry (and others) and there is a pretty good argument why you would want a paddler involved (as both technique and bodymass are integral to a boards performance). There is also a good argument why you need someone paddling as a board pitches, yaws and rolls and testing the board alone without considering that is not actually a true reflection of the board itself when placed in actual context.

To suggest something is or is not scientific really comes to to whether any test follows the scientific method.

1) Is the data repeatable ?
2) Does the data have accuracy and precision ?
2) Is the study repeatable by others ?
3) Are the limitations discussed and stated ?
4) Is the study design relevant to what is being asked or what is intended to be found out ?

I can't speak for Larry but my own tests cover 1-3. Whether my tests satisfy no.4 is always up for debate. 

As I've said, my focus was to ensure the testing was robust (the boards themselves was not relevant). Larry's testing was different and I've added some more robustness to what he did on his facebook page but he acknowledged he needed more runs and I think that would help.

[ukgm]

I was reading this test and have to say it's at best semi scientific. The biggest variable, the paddler is not taken out of this test. Not only do you have the conditions as a variable but also the paddler. You can do as many test runs as you wish and then average them out but you still are nowhere close to a real test result. Since I'm playing around with making my own fins I kept thinking about how to scientifically testing them. Nowadays you see many board or fin manufacturers telling you "my fin's / board's tracking is a 9/10 and the stability is a 7/10 but what does that really mean? 9/10 in comparison to what? Here a couple of thoughts I had for testing boards or fins
First off I would take the paddler out of the equation and use a electric motor with a propeller or even a RC boat. Something that gets the board with either weights or the paddler sitting on it (center of gravity at the position of the handle) to around 6mph
Board speed:
Install the motor on the back of the board and see which board reaches the highest speed using the same fin and the same weight on the board
Drag:
Bring the board up to 5 or 5.5mph and measure the current on the motor. This way you'll see with which board the motor uses the most juice to keep the preset speed
Glide:
Bring the board to a preset speed, turn the propulsion off and measure the time till the board slows down to let's say 3 or 4 mph. You can also measure the distance from the point you're turning off the motor
Tracking:
Mount the propulsion to the middle on either side of the board. When you turn on the motor you'll go in circles. Use a GPS tracker on your phone and see which board or fin creates the biggest radius circles.
Stability:
This one is really difficult to measure. The ideal situation for this would be a wave pool. Even there you can't really simulate all conditions you'd encounter. I do have a couple other ideas on how to measure stability but that would get very technical and very expensive very fast.

As I've already mentioned, there had been a study which towed kayaks off a beam towed from a speedboat. A load cell measures the difference in force between them. That should work but you need to ensure the board would be positioned out of its wake or either wave and it doesn't account for board roll, yaw or pitch. You could argue that this has isolated the board but not the full extent of its behavior in use.

To test fins though (and its on my own list itself) you have to think whats important and design a test or tests from that. I'd suggest:

- Test to identify hydrodynamic drag (with or without the paddler). I did a slow down test which is similar to what you describe above but I would do tests too that involve paddling.
- Stability (I pulled off an app last week that allows you to use the iPhones accelermetors. Mount the phone on a deck and then record the exact level of roll and compare the data over a set number of test intervals.
- I think its also worth talking about how to identify the effect of forward drive of a fin (a large fin for stronger paddlers might be advantageous - even if the drag is greater than a small one).

[Area 10]

"Forward drive"? Can you explain the physics of what you mean here? The concept of "drive" in respect of fins is usually associated with wave-riding not flat water paddling.

[ukgm]

"Forward drive"? Can you explain the physics of what you mean here? The concept of "drive" in respect of fins is usually associated with wave-riding not flat water paddling.

Any resulting force that then helps forward motion. I'm assuming this is the same as lift from the foil.

Ignore the older date and obvious sales pitch from Becker but he touches on it here: http://www.ridingbumps.com/2013/10/08/guide-to-sup-race-fin-selection/

[supuk]

I don't quite understand the drive thing on flat water??? I have never done any testing but I would think the amount of lift created from a standard style fin would be very small indeed. I would be interested to see if they do or not. It wouldn't be too hard to do test but at the moment I don't have time.

[ukgm]

I don't quite understand the drive thing on flat water??? I have never done any testing but I would think the amount of lift created from a standard style fin would be very small indeed. I would be interested to see if they do or not. It wouldn't be too hard to do test but at the moment I don't have time.

How would you suggest you test for it ?

[Area 10]

You want to be careful there ukgm: fins are a topic where discussions often require a suspension of disbelief, and there are a lot of people around making money out of people's willingness to do so IMO. It's one thing to discuss fin matters in relation to movement on a wave face, but something else altogether to talk about flat water, beyond some basics which are pretty straightforward. Unless someone can explain to me the physics (at even a rudimentary level) of an effect that is being attributed to a fin, my BS detector starts to show interest. The article you give a link to provides no plausible explanation.

[ukgm]

You want to be careful there ukgm: fins are a topic where discussions often require a suspension of disbelief, and there are a lot of people around making money out of people's willingness to do so IMO. It's one thing to discuss fin matters in relation to movement on a wave face, but something else altogether to talk about flat water, beyond some basics which are pretty straightforward. Unless someone can explain to me the physics (at even a rudimentary level) of an effect that is being attributed to a fin, my BS detector starts to show interest. The article you give a link to provides no plausible explanation.

Yep, agreed. I knew of forward drive back in my sailing days from foils and whilst aerodynamic lift is a factor (and equally turbulent discussion in sports aerodynamics in actual practice), I have no idea how large the hydrodynamic effect would be and how I would test for it. I would ask questions whether the stochastic and low speed nature of SUP paddling could generate it when compared to something more steady state but since I prioritise stability over drag when it comes to fin choice, my musings might all be a moot point.

[supuk]

I don't quite understand the drive thing on flat water??? I have never done any testing but I would think the amount of lift created from a standard style fin would be very small indeed. I would be interested to see if they do or not. It wouldn't be too hard to do test but at the moment I don't have time.

How would you suggest you test for it ?

just need to have the fin in some sort of box with a force gauge or maybe I micrometer just to see if it moves at all.

[Area 10]

You want to be careful there ukgm: fins are a topic where discussions often require a suspension of disbelief, and there are a lot of people around making money out of people's willingness to do so IMO. It's one thing to discuss fin matters in relation to movement on a wave face, but something else altogether to talk about flat water, beyond some basics which are pretty straightforward. Unless someone can explain to me the physics (at even a rudimentary level) of an effect that is being attributed to a fin, my BS detector starts to show interest. The article you give a link to provides no plausible explanation.

Yep, agreed. I knew of forward drive back in my sailing days from foils and whilst aerodynamic lift is a factor (and equally turbulent discussion in sports aerodynamics in actual practice), I have no idea how large the hydrodynamic effect would be and how I would test for it. I would ask questions whether the stochastic and low speed nature of SUP paddling could generate it when compared to something more steady state but since I prioritise stability over drag when it comes to fin choice, my musings might all be a moot point.

If this is the situation you are facing then you will probably find that you are faster on a more stable board with a low drag fin than a theoretically faster (but less stable) board with a big fin to compensate for the loss of stability.

Incidentally, it is interesting to look at the variance in speed through the stroke according to board design. For instance, hybrid-type (prone paddleboard nose) designs tend - I think - not to achieve the same peak speed, but they also tend not to slow down as much through the recovery. This may suggest that different strokes may work for different boards. It's an interesting area for enquiry that has been noted by some shapers but never to my knowledge properly investigated for SUP.

[ukgm]

Incidentally, it is interesting to look at the variance in speed through the stroke according to board design. For instance, hybrid-type (prone paddleboard nose) designs tend - I think - not to achieve the same peak speed, but they also tend not to slow down as much through the recovery. This may suggest that different strokes may work for different boards. It's an interesting area for enquiry that has been noted by some shapers but never to my knowledge properly investigated for SUP.

Yes I have heard that too from some paddlers as well. I know of one sponsored rider who moved from a Starboard to a Fanatic and had to modify his cadence to get the best from the new board. I suspect a lot of this could be purely accounted for by finding out how good the glide is between boards and then realising that a board with poorer glide needs a higher stroke cadence to keep its speed 'topped up'. If you use a slower heavier stroke, the board will be compounded by its higher drag and drop too much in speed between strokes and wastes energy to get it going again (as we ll as the time loss). That makes sense to me and if seen notably in cycling such as mtb XC or high speed riding when the cubed effect of air resistance is working against you so much that even dropping your torque an inch really hurts your speed or when over rough ground you have momentum or rolling resistance hurting your steady state attempt at power output.

You could map a boards decceleration and see at what speeds this drag is greatest and then that also might mean not only does the board generally require a different cadence to what you're used to but might only be an issue with certain paddlers at certain speeds.