Scientific Flatwater Board Testing 101

[Area 10]

That would be conventional wisdom, yes. But actually I am beginning to suspect that it isn't really like that. It's largely about pitch changes through the stroke, I suspect. If you wanted to revolutionise how we think about SUP designs maybe you'd work with a talented shaper like supuk to create boards with interchangeable noses and rails (like supuk is already doing) and then festoon the board with monitoring devices in order to model the movement of the board in all axes as it moves through the water at different parts of the stroke. I suspect you'd find the results surprising. It would be great to have people applying a bit of science to the "gut feel" of SUP shapers, and it could result in much better board designs.

[ukgm]

That would be conventional wisdom, yes. But actually I am beginning to suspect that it isn't really like that. It's largely about pitch changes through the stroke, I suspect. If you wanted to revolutionise how we think about SUP designs maybe you'd work with a talented shaper like supuk to create boards with interchangeable noses and rails (like supuk is already doing) and then festoon the board with monitoring devices in order to model the movement of the board in all axes as it moves through the water at different parts of the stroke. I suspect you'd find the results surprising. It would be great to have people applying a bit of science to the "gut feel" of SUP shapers, and it could result in much better board designs.

Yep, I like that !

[PonoBill]

You might recall the "schnozz" replaceable noses I made a few years back. My goal wasn't science. It was to make a dw board work in flatwater. Didnt work well. The nose needs a bottom profile that works with it. At leasr that was my conclusion. Might just have been some shitty fabrication.

[ukgm]

That would be conventional wisdom, yes. But actually I am beginning to suspect that it isn't really like that. It's largely about pitch changes through the stroke, I suspect. If you wanted to revolutionise how we think about SUP designs maybe you'd work with a talented shaper like supuk to create boards with interchangeable noses and rails (like supuk is already doing) and then festoon the board with monitoring devices in order to model the movement of the board in all axes as it moves through the water at different parts of the stroke. I suspect you'd find the results surprising. It would be great to have people applying a bit of science to the "gut feel" of SUP shapers, and it could result in much better board designs.

By the way, something I found as I trawled the literature the other week ties in with Larry's 'stroke effectiveness' metric is this paper here which you can all view. It's a little dry so be prepared to have to chew your way through it.

http://www.biorow.com/Papers_files/2006%20ISBS%20Rate-DPS-Speed.pdf

This 'stroke index' (SI) as such has been evaluated successfully in kayaking, canoeing, swimming and rowing.

[Kaihoe]

Interesting paper uk.  I think that measure has use, but I can see if being miss-used easily. 

The assumption that the unknown k factor is equal across 2 combinations of SR and SD needs to be carefully managed. What makes me uncomfortable is that it assumes that k doesn't change as the speed changes, this might be true for rowing skiff and flat water canoes which have a much more optimal hull shape. Even then the analysis they provided seems to indicate a tail off in the model as speed goes up.  I'd be really interested to see if this model has been cross checked across a wider range of data and boat types.

[UKRiverSurfers]

"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.

Simply put - the fin adds directional stability which could be called 'forward drive'

Similar to a centre board on a dinghy. It takes the energy from the sail and transmutes it into forward drive.

Of course - get a rudder on and all that crap goes out the window

[UKRiverSurfers]

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.

It's simple - not every part of the stroke adds forward thrust.. The fin helps by transmutting your energy into a straight line. Without the fin you'll need loads more correction stroke and even less forward direction.

[UKRiverSurfers]

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.

Moves for certain - seen it in my test pool

[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.

It's simple - not every part of the stroke adds forward thrust.. The fin helps by transmutting your energy into a straight line. Without the fin you'll need loads more correction stroke and even less forward direction.

You are talking about increased tracking. This is not what some fin manufacturers are claiming. They talk about increases in "lift", creating forward thrust. Quite different.

One possible link to what they mean might come from the effect of transferring weight from side to side on a windsurfer. I do not windsurf, but a friend of mine who does maintains that with certain fin setups in no wind he can generate some forward movement of the board by doing this. He reckons that this may be what the fin makers are talking about. I can't quite see how this relates to flat water speed on a SUP since conventional wisdom has it that it is fastest to keep an even keel. But I'm keeping an open mind on it. I just get suspicious when claims are made without any explanation of them at even the most basic level. Sometimes the fin brands will say that they don't explain because they don't want to give their secrets away to competitors. But there are other possible explanations for not explaining claims too...