skeg measurement trials

I paddled my Seda Ikkuma inside the bay, at about 4 kts, in a steady 10 kt cross wind and very light chop. The Ikkuma weather cocks very slightly, as a good design should, and is easy to control directionally with slight leans and slight sweeps.

However, my GPS indicated an increase in speed of 0.1 to 0.2 kts was achieved by deploying the skeg. Without the skeg slight sweeps and leans are required every 4 or 5 strokes, while with the skeg deployed even slighter corrections are required every 20 or 30 strokes. I repeated these skeg up and down trials multiple times with the same results.

The Ikkuma skeg is small, with high aspect ratio, but quite effective. Any drag increase due to the skeg is overwhelmed by the benefit of greater stroke efficiency.

YMMV. Don’t know if this applies to any boat and skeg.

sounds about right
I think the “debate” begins when people talk about using skegs NOT for wind, but to compensate for a hull that may be too loose, or for a paddler’s technique causing side-to-side veer. Or, in my case, just to coast in a straight line when not paddling – messing with a camera. Some of us have found that the skegs cause drag and impede speed. I often forget to put my skeg up, after taking photos. I soon notice that the boat feels sluggish.

low drag
Using my gps on calm water I have not been able to detect any drag/speed difference with the skeg deployed or not. Perhaps your skeg is very large or you are more attuned to small drag differences.

Faster/less effort with effective skeg
At least that is what I have found the few times I have paid attention. The times that I have it more than partially deployed, I am usually focused on other things. IMO, the skeg and drag thing is way overrated as an issue for anyone other than people racing. The keel on my first sea kayak was a lot more distracting than the skeg has ever been (which is not always healthy for a skeg when landing).

Really depends on the hull shape
Like most racing boats NEED the rudder, many standard kayaks perform better the skeg.

I like that you took the GPS and made your own discovery with it. I learn the most about my different boats by trying to pay attention to how it responds in different situations, but I’d do better if I kept notes.

Right now, my newest boat does not respond well to an outside edge but really turns with an inside edge which is opposite of what I do most of the time. It is really taking me a long time to adjust. I hope to become unconsciously competent with it, but then I wonder if I’ll be able to go back to a sea kayak and paddle using mostly the outside edge.

Design consideration…
Yes, it still goes to the designer’s intent. My first sea kayak really was intended to work with a rudder even in its stowed position - it was part of how that hull was planned to deal with wind. Since I found the rudder to be a PITA for my own purposes and always ended up taking it up again, that meant a different boat when I decided that I’d rather be living with a skeg. So I got a boat that was designed with a skeg in mind.

QCC tends to offer a choice of either on their boats, which can muddle the point for newbies that a given hull is often designed with an assumption about whether rudder or skeg. So we end up talking about these things artificially, as though you can take any hull and successfully pop one off and the other on. But for some boats that can be a fairly bad idea - if you want the hull to behave you really have to get the device that normally comes with it.

Which boat?
My first kayak turned towards the inside edge. It really messed me up because everyone was telling me it was supposed to turn away from the leaned (down) side. After paddling it hundreds of hours (weird thing named Kanoe Latvija), I concluded it had three turning positions, slight, medium, and heavy lean, which turned the boat in, out and in. It did mess me up. I got rid of it.

I am wondering what boat you have that is giving you the fit.


Sorry, your test proves nothing.
That small margin of difference could have easily been your mindset. Without doing a blind test, that 2.5%-5% difference means nothing. Not trying to be harsh, just looking at this scientifically.

I agree that nothing was proven. However, I tried it enough times to lead me to deploy the skeg in wind and chop if I want to go a bit faster or with less effort.

I agree about a blind test
and about the lack of definitive proof, but really…

…a skeg is usually used to counter the effects of the wind, such that fewer correcting strokes are required from a paddler to hold a straight course. Is it not inevitable that a boat covers a greater distance with less effort with its skeg deployed?

Accuracy of gps ?

– Last Updated: Jan-29-13 8:16 PM EST –

The GPS processes the incoming satellite signals
and calculates the difference in timing and
equates that to distance over time which equals speed.

I don't believe the equipment and conditions can
be set up or calibrated in a way to truly record
differences that can't be explained away by the
inaccuracies of measurement.

Try mowing your lawn and see if the GPS records
every turn, every variance, every nuance of your
moves in an extremely small area like a residential lot.
Handheld GPS units don't like slow speeds with small movements

I would tend to agree, and…
I would say that is a good hypothesis. I’m not sure the efficiency of a skeg has ever really been tested. It would take an incredible amount of resources to really prove the efficiency. There are simply so many variables (paddle style, stroke style, paddler size and ability, skeg shape, hull shape, water conditions, wind, etc). I guess it’s reasonable to go along with the experience of someone like Paul Caffyn who agrees that skegs over distance are better (and rudders are better yet), but I tend not to firmly believe anything without testing by scientific method. And even then, a theory is only correct until it’s proven wrong. My experience shows that a skeg is more efficient for beginners in high winds because they don’t have the skills to cope without an aid to prevent weathercocking, and some boats also have a strong need of an aid to prevent broaching. But when it comes to splitting hairs over 2.5%-5% efficiency, I really don’t know. Either way, it’s an interesting thing to think about.

You are probably correct regarding
GPS accuracy if the original poster is talking about measurements of “instantaneous” speed, but not if the average speeds were calculated over sufficiently longer distances.

I don’t know which is the case here.

Side to side movement
GPS simply won’t pick up that very minimal ziggy-zag

motion that actually increases total distance.

A 1 meter gps accuracy = 3 foot of sloppiness in data

But there’s no need to measure that.

– Last Updated: Jan-30-13 5:13 PM EST –

All you really want to know is how long it took your boat to get from Point A to Point B, while paddling as straight as practical.

If two cars drove the same course in exactly the same amount of time but one of them had a bent wheel (thus it wobbled a little the whole time), would you say that the car with the bent wheel had traveled faster? Why bother? Each car covered the same distance in the same time, and delivered its passengers in the same amount of time, so by any definition that matters, they both went the same speed. Same goes for a boat for which every last bit of wig-wag can't be eliminated. Just worry about how long it took the boat make the trip and be done with it.

If the little wig-wags are due to poor technique, the paddler can effectively go a little faster by learning to go straighter (or in this case, deploying the skeg in windy conditions might make you faster for the same reason). After all, in a race that's what would matter. You couldn't take second place and then argue that you really should be awarded with first place because you unintentionally zig-zagged slightly more than the other guy.

Everything has limits

– Last Updated: Jan-30-13 4:03 PM EST –

Handheld GPS can't account for everything
- there are caveats and exclusions.

A receiver compares the bit sequence received from the satellite
with an internally generated version.
By comparing the rising and trailing edges of the bit transitions,
modern electronics can measure signal offset to within
about one percent of a bit pulse width.

Since GPS signals propagate at the speed of light,
this represents an error of about 1 to 3 meters.

I doubt few people could ""accurately"" measure
skeg_up vs skeg_down over a set distance and
get repeatable results.

A measured course on water is tough to set-up.
Bouys move and each gps will measure just
a bit differently from another one.

Tooo many variables in human, nature, equipment combo

agree, results will vary…

– Last Updated: Jan-30-13 4:40 PM EST –

If one really cared you may need to do say a one mile course ten times alternating between using the skeg and not. Be careful you don't make wind direction skew your results. Your speed would vary each lap but if the difference was big then one would win by a bit most times. If the difference was small you may see either skeg or no skeg win at any time but perhaps one wins a bit more often.

The part of about a fixed course though is easy. You just pick some pier, point, home, etc. and measure with the GPS or map. It's nice to know the approximate distance but you don't need to know the distance at all. You care that one trial takes say 4% less time than the other.
Time should be measured carefully on some fixed distance and that's pretty easy to do. You could also use a fixed time and measure the distance but it's easier to accurately measure time.

Sure enough. All I did was point out …

– Last Updated: Jan-30-13 5:37 PM EST –

... how totally pointless it is to worry about trying to measure non-contributary movements when doing so serves no purpose related to the desired outcome. Bringing up an entirely new way of saying that no method of measurement is perfect in all ways doesn't change the fact that being unable to measure extremely minute course deviations is totally irrelevant with respect to determining the time needed to cover the distance between two points.

Of course, the biggest issue of all is figuring out a way to insure that you actually exert the same degree of effort during comparative trials. Measuring speed accurately enough is easy compared to this part.

Correct, but it’s even easier than that

– Last Updated: Jan-30-13 5:19 PM EST –

The GPS may not be accurate enough to indicate very minor speed difference across very small distances, but the amount of error it introduces in measuring the length of a fixed course of substantial distance is very small. For example, fairly large error in location determination, such as being off by 50 feet at times, hardly matters at all when measuring the distance between two points that are one or two miles apart. Even that much error over a one-mile distance will allow calculation of overall course speed with a precision that is well within 0.1 mph of the actual figure, which should be good enough for most of us (in fact except for extreme errors in opposite direction, thus being additive, precision will be not far off from 0.001 mph, which is MUCH more precise than average people would care about). The greater the distance, the less this kind of error matters.

Also, don't forget that these kinds of errors are not instantaneous random events. If they were, a stationary GPS would indicate sporadic high-speed movements, but that never happens. The error is more like a slow drift, with the error changing slowly enough that a stationary GPS always knows that it is not moving, and by the same token, one that IS moving at a steady speed will not suddenly indicate drastic speed variation (except perhaps when reception has been obstructed for a little while, but that's another issue entirely). Anyway, none of that even matters for overall speed calculations over great distance, and I only mention it to put Willi's earlier complaint in perspective.

There is a reason it hasn’t been done

– Last Updated: Jan-30-13 7:27 PM EST –

Skegs and gps have been around for 2 decades,
no one has done the experiment "well enough" to publish.