twin-fins-or-more-on-a-race-board/so it begins

[Luc Benac]

On a different note, I am very curious to try the effect of hollow fins for both the central and ventral fins on my Whiplash i.e. Aercor center and Abuelo ventral

[Subber]

Just to be clear with everyone, let me state what the specification and limitations of my testing involves.

- 8 randomised runs of each fin set up.
- Board was 2017 Starboard Allstar, 14ft in a 24.5 width.

Is it the same board with the different fin setups?
I always wonder how much drag open fin boxes create?

(I used to tape over my FCS sidebite openings if not being used)

[ukgm]

Just to be clear with everyone, let me state what the specification and limitations of my testing involves.

- 8 randomised runs of each fin set up.
- Board was 2017 Starboard Allstar, 14ft in a 24.5 width.

Is it the same board with the different fin setups?
I always wonder how much drag open fin boxes create?

(I used to tape over my FCS sidebite openings if not being used)

Yep, I taped mine up between runs using black electrical tape.

[ukgm]

My points instead relate to the conclusions that we can draw from ukgm’s data. Ukgm has, to his credit, spelt these out. But I know very well that people will probably just ignore these critical caveats and jump to conclusions that are not logically justified. And then science (or more probably in this instance, technology) becomes marketing. This is not ukgm’s fault.

....... and to be fair, both Area 10 and I are in the same industry subject to this same kind of scrutiny daily. For those that don't know, publishing anything in a scientific journal is a arduous and rigorous process designed to make sure that what we say is what we mean and that what we mean is actually what was done. Ultimately, I don't see this kind of probing on here as negative at all and its not something anyone should take personally but moreso as a way of keeping me or this kind of work honest.

[Larry Allison]

Just to be clear with everyone, let me state what the specification and limitations of my testing involves.

- 8 randomised runs of each fin set up.
- Board was 2017 Starboard Allstar, 14ft in a 24.5 width.

Is it the same board with the different fin setups?
I always wonder how much drag open fin boxes create?

(I used to tape over my FCS sidebite openings if not being used)

at these slow speeds water does not notice fin box slots until you reach speed great then12 miles a hour and hold it like windsurfing thats double that. Notice the air bubbles from the paddling goes over the fin box.

[Larry Allison]

Burchas, I think you misunderstand my intent here.

I am certainly not suggesting that ukgm is wrong. I am completely open-minded on the issue. In fact, if anything I am ready to be convinced: I installed a 3-fin system on my UL board, and found it a tad faster in flat water than the same design but narrower board that has only one fin. I put this down to better tracking while reducing deeper water drag. Nothing more complex than that.

My points instead relate to the conclusions that we can draw from ukgm’s data. Ukgm has, to his credit, spelt these out. But I know very well that people will probably just ignore these critical caveats and jump to conclusions that are not logically justified. And then science (or more probably in this instance, technology) becomes marketing. This is not ukgm’s fault.

Incidentally, I would like to see ukgm rerun his tests on a course that requires “weaving”, or even a circular course. If you install more fins in a board and so it tracks better and is therefore faster in a straight line, this is pretty unremarkable. But the downside of increased tracking can be problems in cross-wind, and increased drag when not going in a straight line. These downsides can easily outweigh the advantages of increased tracking in real-world conditions.

WOW!!! Did you say you installed a 3 fin setup. Great my friend would enjoy seeing and helping you get the placement and fin choices right to get the correct end result. Stoked Area-10!

[ukgm]

Here's some of my preliminary data from my hydrodynamic 'coast down' tests. This removes a lot of the placebo concerns as this involves the rate of which the board slows down to rest. I obtained a pretty good data repeatability of these (surprisingly I thought - as a board can wobble a lot at low speeds).

Limitations.

6 runs of each set up.
Smooth glassy water.
Measures the rate of deceleration from a targeted top speed.
Fixed time sample of each decelerating run.
Paddler is 88.9kg.
A data precision of 5% is still very good but its plausible that even with this low level of variation may mean the protocol isn't sensitive enough to detect differences beyond the extreme ones regarding fins. I'd like to try it between boards instead.

I am busy intentionally hazy on some of the specifics here as I'm still working on stuff with this and playing around with the protocol.

The results showed that the Allison system had a fractionally higher level of likely drag (but its so small, its not considered statistically significant). I would argue that an extra level of drag of 3cm per second may still be seen as a lot but the margin of error (illustrated using standard deviation with error bars here in the graph) swamps this. In my case (and my case alone !) this might suggest to me that any benefits of the 4 fin system on flatwater are purely to do with how it may improve balance (reducing roll induced drag) and possibly tracking (yaw based efficiency - as per Area 10's thoughts). This said, this is using a relatively standard set up - if I'd tried Ponobills 'fence' set up or gone for a really small racing fin like a Black Project Tiger, this might have been very different.

[burchas]

Just for good measures, take single fin with the same SQI area of the 4 fins combined, (not sure
it exist but take the largest you can find) and compare deceleration.

Going the other way around trying to go down to the smallest 4 fin setup may give you
same or better deceleration but I suspect it won't give you better speeds on your board.

[ukgm]

Just for good measures, take single fin with the same SQI area of the 4 fins combined, (not sure
it exist but take the largest you can find) and compare deceleration.

Going the other way around trying to go down to the smallest 4 fin setup may give you
same or better deceleration but I suspect it won't give you better speeds on your board.

Thanks for the useful idea. I'm more likely to try something with a likely larger difference between them first and recheck my testing protocol. Probably boards first and then go from there.

[Luc Benac]

You could also "invert" ( from a zero to a 8 degree) the insert for the twins thus putting the twins as far as possible from vertical and creating a lot more drag for the same setup and compare the two to check the margin of error.

[yugi]

For bar charts, the numerical axis (often the y axis) must start at zero. Otherwise you are distorting.

for example:
https://guides.library.duke.edu/datavis/topten

[ukgm]

For bar charts, the numerical axis (often the y axis) must start at zero. Otherwise you are distorting.

for example:
https://guides.library.duke.edu/datavis/topten

That’s wrong. It doesn’t always make sense to start at zero if you’re trying to stress other aspects of the data such as overlapping (or the raw value) of error bars which might be a small percentage of the absolute value (in this case trying to demonstrate that the precision is very good).

It’s just a question of designing the bar chart intelligently with what you trying to show. My graph also states the P value in this case to minimise such concerns so that nothing is excluded and no bias is being promoted.

[yugi]

Playfair my friend.

[ukgm]

Playfair my friend.

As I say, you're wrong on this and I've given you the reasons why behind the decisions. The wording on the graph clearly states "no significant difference between them" in large letters. I'm not sure what you're trying to suggest but if you're trying to infer something more disingenuous is going on, actually say so and we can debate it. I don't like the tone with the reply you've given.

[PonoBill]

UKGM, I think you and Yugi are writing about two different things. From a data perspective, starting Y at an arbitrary value to provide clear visualization of the difference is proper, though it magnifies the difference. From a marketing perspective setting the origin at 0 minimizes the visual impact of the small difference. One of the many ways sleazy marketers like me lie with data. People will automatically look at the bar chart and see that the multi-fin set drags "much more" even with the caveat of the small P value (which no audience other than academic would immediately grasp or correctly interpret).

Yugi, graphical data representation is inherently "dishonest". If the graph started at 0 and used larger Y intervals the difference in the resultant stubby bars would be imperceptible. You could argue either side of that issue, it's not set in stone and not really a fairness issue, no matter what Duke U says. It's simply a question of what the author wants to display. In this case, the fact that the test is sensitive enough to repeatably show small variations.