15 February 2011

Kayak length, speed and stability: observations

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Don't get too hung up on length and speed. Because, as you say, all other things aren't equal here. Longer hull at the same beam and hull shape also means increased wetted surface and more drag. It also requires more materials to build, so its heavier and that takes more energy to accelerate. 
Even ignoring that, the relationship between hull speed and length is proportional to the square root of the waterline length not the actual waterline length. Note: Waterline length not overall length. A long boat with less than it's design load sits up out of the water and has a shorter waterline length than the same boat loaded. The difference in hull speed between a 580 and a 530 would be less than a quarter of a knot or 0.5 km/h. For both boats it would be between 9 and 10 km/hr and thats a very fast pace to maintain cruising any distance. Unless you're racing you probably won't notice the difference.
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(10FEB11, John Anderson_SeaKayakForum.com )
 
John's comments are similar to my findings.
In paddling groups I have observed that paddlers left behind occasionally blame their shorter kayak for the lack of speed and them not being able to keep up. However the pace is usually around 6-7 Km/h at best.
Some paddlers are convinced that if they had a longer kayak they would be able move faster.
It would be interesting to see what would really happen if they tried the longer kayak. Chances are they would be actually slower, if they could not improve their paddling technique.
Obviously things are different if a paddler can bring his/her kayak to hull speed (maximum speed that their particular kayak can achieve). Most sea kayaks hit "the wall" at much higher speeds than at recreational paddling pace.
Club paddle_1_c
One must really push hard to eventually feel the kayak being unable to go any faster.
At slower speeds (Club outing pace) a shorter kayak will create less resistance and therefore be easier to paddle.
Here are some resistance stats for known sea kayaks hulls.
(Posted by: wilsoj2 on Nov-24-09 2:44 AM (EST) www.paddling.net )

Here are some drag figures for 7 boats from Sea Kayaker from 2 to 4.5 knots (2.3 to 5 mph) listed from most drag to least at each speed:
at 2 knots:
 Valley Rapier 20 = .97
Epic Edundrance 18 = .97
NDK Explorer = .94
Chatham 16 =.93
Foster Legend = .9
Avocet = .9
Nordkapp LV = .9

at 3 knots:
Valley Rapier 20 = 2.04
Epic Edundrance 18 = 2.03
Foster Legend = 2
NDK Explorer = 1.96
Chatham 16 = 1.93
Avocet = 1.92
Nordkapp LV = 1.88

 at 4 knots:
Chatham 16 = 3.89
Avocet = 3.74
Foster Legend = 3.7
NDK Explorer = 3.63
Epic Edundrance 18 = 3.55
Nordkapp LV = 3.52
Valley Rapier 20 = 3.45

 at 4.5 knots:
Chatham 16 = 5.58
Avocet = 5.4
NDK Explorer = 5.25
Nordkapp LV = 5.24
Foster Legend = 4.9
Epic Edundrance 18 = 4.73
Valley Rapier 20 = 4.45

The drag figures given are calculated assuming flat water.


It seems that the shorter kayaks have less resistance than the long ones, at recreational/Club speed.
 
I also find intriguing the emphasis put on  maneuverability and stability observations from paddlers' reports on a given kayak.
They vary incredibly.
I hear/read comments like: "the kayak is very tippy" or "the kayak is very stable" for the same very kayak.
 
So what gives? how can a person really find out what are the characteristics of a kayak?
 
I believe that stability is difficult to quantify.
Sure there are scientific measurements taken and published for most kayaks out there (Sea Kayaker Magazine being a great source) but those numbers are much harder to interpret and to come to a conclusion than the simple measurements of speed.
What one person finds stable other might find tender.
Las Chicas de Rio Mistico Kayaks
Photo: Rio Mistico Kayaks_used with permission
The biggest factor in objectively assessing a kayak's stability is the paddler's skill level.
A novice might find a narrow round hulled kayak very unstable while a proficient kayaker will pronounce it "rock solid". Needless to say that quality seat time in any kayak will increase one's skill level. It certainly did for me: here
Being able to roll also adds an incredible sense of security and a kayak that used to be regarded as tippy suddenly becomes OK. Before I could roll proficiently I would be very wary of narrow kayaks.
A paddler's weight is probably the other most deciding factor on a perceived kayak stability. I however find that more weight doesn't equate to more stable. Gear or ballast in a kayak will increase stability but a paddler's weight might not. There is a marked difference between the weight distribution between men and women; the latter being advantaged by a lower centre of gravity that in terms equates to a more stable kayak.
I notice girls having an easier time balance bracing a kayak than guys.
Balanced brace training (c)
Being top heavy and having broad muscly shoulders does actually make it more difficult.
Last but not least: the paddling conditions.
Some crafts are excellent in calm waters but become a bit of a handful in following seas.
Regular readers of this blog will also know that I find ruddered kayak less stable in following seas where the rudder no longer can function to aid directional stability. A kayak that can be controlled by the paddler's body and paddle stroke is usually a more stable kayak, in conditions.
 
While listening to reviews is often beneficial in the quest of selecting a new kayak, some reviews/observations are so terribly subjective that give the researcher little help. What most reviewers forget is to state their weight and height.  What really can not be quantified however is the skill level of the reviewer, to then be able to draw any conclusions from the review.


14 comments:

  1. Nice post Gnarly.
    Here's a short journey of mine over the last 2 years. Started the period as a dead-set sea kayak paddler, & bought a Rapier 20 (mentioned in the SK resistance tests above). Found it quite demanding in confused water but stuck with it for a year, by which time I was confident enough to take it out in anything.
    Had a go in an intermediate ski, the Epic V10S and figured I'd give that a crack, have now spent a year paddling it & despite being quite edgy to begin with would now take it anywhere.
    Recently got a V12, an elite racing ski, only 43cm wide & have been paddling it for 2 months. Found it as challenging to me now as the V10S was when I started with it last year. That was until I paddled a spec ski for a week last month when on holidays, which was set up for someone slightly shorter than me. I fell in 4 times in the first 300m on the spec ski, then wrestled with it for a week until I felt confident enough to get it out on small bar surf without capsizing. The problem was that my legs were too high, and the seat was too wide, so when I wobbled off line my arse slid off to one side & the whole thing went wobbly.
    Came back to Sydney, went for a paddle on the V12 which now feels like a stable barge in comparison to the speccy, & I'm now almost as confident in it, as I am in the much more stable V10S.
    My conclusion, as long as you have a modicum of fitness & core strength, stability is something that very quickly becomes relative. I don't think there is a single sea kayak out there that I would call tippy, so consequently I'm a lousy judge of stability to someone who is asking. My advice is always to challenge yourself, tippy is only temporary, & the more challenging the stability, the greater the rewards once you get the hang of it. I think that's the advice I gave you a couple of years ago!
    The caveat to that is that you shouldn't buy something that is REALLY challenging you, because you'll get sick of falling in & give up….

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  2. Nice post and nice comment - all in line with my experience with racing K1s an trainers. My own conclusion have been, that
    1. Tall, heavy men have a harder time finding balance than small, slim women
    2. Balance is relative. You can learn to paddle almost anything, if you are willing to invest the time and efford needed (and the displacement of the boat is large enough to keep you afloat).

    The displacement, by the way, can be very relevant. Too little weight in a sea kayak, and it may have a very lively primary stability. Too much weight (paddler, not cargo) may cost you secondary stability.

    Nice blog. Keep it coming :)

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  3. Once a person becomes skilled enough to appreciate and discern secondary stability then your comment about skill level becomes more relevant. But before they attain the skill, the paddler evaluates tippiness (sic.not a word) of a kayak based on perceived primary stability.
    At that point it is not difficult to see whether a kayak is tippy by examining the hull shape. At the most basic level conclude that round hull is tippier than hard chined or flat hull (as far as primary stability goes).

    And what matters most at these moments is something I have not seen you mention. FIT. How does the person fit into the kayak. A round hulled Nordkapp LV will feel very tippy to a person with a lot of weight in their upper body area but it might feel quite stable for a small person with light shoulders and a buttock of the size of a walnut. In fact they might have to try much harder to simply roll the kayak vs the heavy person who will plonk into the water like a freshly sharpened axe.

    Fit, I believe, is the primary indicator of tippiness when a person sits in a new and unknown boat.

    Fit includes seat height too. Lowering the seat for a top heavy person will do wonders to perceived primary stability.

    gotta go now. Enjoy the summer down there.

    SDP

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  4. I see the point about speed articulated many places, and yet, the myth 'longer kayak is faster no matter what' persists. To me the focus needs to shift from speed to efficiency or ease of paddling. Longer kayaks are easier to paddle at high speeds, shorter kayaks are more efficient at lower speeds.

    'Hull Speed' is not the "maximum speed that their particular kayak can achieve". It's just a speed at which the bow wave achieves the length of the kayak's waterline.

    There's absolutely nothing special about this number as it is but a point on an increasingly steep drag*speed curve. Unlike big ships, kayaks produce very small bow waves so hull speed has even less meaning for us. Most paddlers will be able to exceed the hull speed of sea kayaks for short sprints.

    With regard to stability, you make good points about experience and rolling ability. However, in sea kayaking stability should mean more than the ability to brace and roll. There are many situations where you want the kind of stability that can make you stay up without the use of the paddle. Photography, stretching the spray deck over the cockpit after a self-rescue, hand-pumping a swamped cockpit (yes, you need to have a foot/electric pump), reaching for your lunch in the day hatch are just a few examples. If your kayak is only stable when aided by the paddle blades, your sea kayaking range is restricted.

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  5. Had an article on the same topic some months ago. It is in Danish but there is a link to google translator to the right.
    http://www.kajakgal.dk/?p=1151

    My experience is like yours: Theoretical a long sea kayak is the fastest but there is a lot more to speed than that.

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  6. Thank you all for adding and elaborating some of my findings. There is so much that can be said about these subjects that probably I will come back to specific areas like fit, hull shape and seating arrangement in other posts.

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  7. Hi Gnarlydog,

    glad you liked my assessment with respect to length. I paddle a Nordkapp RM and find that for the most part the speed limitation is all with me. I rarely go anywhere near the boats limits.

    With respect to stability, I first paddled one coming straight from an Australis Gecko and with a low level of skill and poor core strength and stability. That test paddle was very challenging. I had to stop after a couple of kms and actually had to raft up with someone to rest. I like a challenge, so I bought one.

    Within a couple of weeks I was perfectly comfortable in it on flat water and on rough water the boat just gets better and better. This boat has made (and is still making) me a better paddler.

    I also wrote a short piece on why I bought a kayak with low primary stability in response to a question from a paddling buddy. In it I discuss interpretation of stability curves. I don't know if it would be of interest to your readers, but it can be found here.

    http://hunterpaddler.ning.com/profiles/blogs/of-swings-roundabouts-and

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  8. John, I checked the link and I have to say: well written little piece that is understandable by common mortals. Worth reading, indeed.

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  9. Your post is awesome! It clearly shows (at least in theory) that length of a kayak is not the only factor that determines how fast a kayak goes, as long as it's of a similar design.

    Perhaps the "Longer is Faster" saying holds true because some of us confuse length with design.

    River kayaks are generally shorter and more designed for turning, and sea kayaks are generally longer and designed for tracking. This might have given the impression that longer kayaks are faster.

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  10. Ahoy All,

    I'll chip into this post, because "observations" is a nice word, not widely used these days. (Gnarly, U R a gentelman!)
    I hope I do not offend anyone including Naval Architects but we all know that what comes out of a computer program has to do with the data loaded in the first place. What often is forgoten are those "little things" like rudders and skegs, not to mention hanging toggles draging like an anchor...
    When Matt Broze wrote his spreadsheets...GPS did not exist and all Mariner yaks had a clean stern for good reasons...
    For years, kayak manufacturers got away with designs dictated by their marketing departments and copying whatever was there to copy. What was good 30 years ago may be crap today, because for one, composites technology changes give more freedom when designing, the decks in particiular.
    It is not as difficult, but these days I can have a look at a new kayak design and can tell which program was used in designing it or if the plug was shaped by hand.
    Minimizing drag is only one small aspect of a good sea kayak design. Ergonomics and biomechanics should carry much more importance when searching for the "perfect boat".
    And if there would be such a thing, it would look very much like the HYBRiD 550! (LOL)

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  11. Nice post Gnarly. I do wonder if we as paddlers get a little too hung up on our boats' capabilities instead of concentrating on the "Joy of Being in One". The many scratches on my banged-up plastic boat no doubt have reduced its "hull speed", but I look at every scratch and dent lovingly knowing I put them there by having a heap of fun out on the water. Of course it'll be no surprise to anyone that I prefer fun over performance. ;)

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  12. Moulton Avery3/1/11, 2:33 PM

    Great post and comments Gnarls. Coming back into the sport I love after a long leave of absence - and sporting a fancy new hip, I might add, I've been frankly astonished by the tremendous range of products available - from boats to paddles to VHFs. But there's also a bit of a humorous side to all this. With some folks, (gentlemen folks) it almost seems like a mine-is-bigger-than-yours dance that I'm witnessing. I've met a number of lads sporting $3000+ boats with $900 Kevlar / Kryptonite / Molybdenum encrusted paddles who don't have a decent forward stroke and couldn't roll in a bathtub. Now maybe it's just sour grapes because I'm a wee bit short on cash at the moment, but it just seems like massive overkill at times. Yeah, buddy, you got an Olympic class paddle, but so what? Do you know how to use a paddle to begin with?

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  13. Moulton Avery3/1/11, 2:50 PM

    The interesting thing about the "Tippy Death Boat of The Novice", (a pejorative nickname occasionally hurled at Nordkapps back in the day) is that this business of stability turns out to be relative to personal experience - to what you've been accustomed to paddling.

    When my kayak partner Brian Price and I bought our Nordkapp HM boats from Ken Fink in 1984, we knew absolutely nothing about sea kayaks, and neither of us had ever paddled a river kayak. Canoes, yes, kayaks, no. We really had no idea what to expect. I first put mine it in the water on the Potomac River at the Washington Canoe Club dock, and when I got into the boat, I thought: "Damn, this thing feels really tippy and unstable." Same with Brian and his boat.

    But we thought - well, I guess that's just the way these sea kayaks are (the way all kayaks were as far as we knew) and it looked like it was just going to be a little bit harder to learn to paddle them than we thought. Compared to the initial stability of a canoe, it was a major transition.

    So I'm sitting there at the edge of the dock, feeling tippy, and along come a couple of guys at the club who raced those hard chine canoes that you paddle with one knee up. "How's the boat", they say. I allow that it's a nice boat but that I found it kinda tippy. They're looking at it, and one says "No way".

    So we switch and he gets in. Says it's like a barge, stable as a rock. He gets out and then crams himself back into the cockpit with one foot stuck behind the seat and his knee on a dry sponge to level it out - a half-baked imitation of his racing canoe stance. "Like a rock" he says, and proceeds to paddle it around with his canoe paddle, his center of gravity about 2+ feet off the deck. Then he lets me try his boat. It was OK for me as long as I kept the paddle firmly braced on the dock. Couldn't do anything else because there was no way in hell I was going to be able to keep it upright for more than 1/3 of a second. Sold me. His boat was the tippy one.

    So Brian and I thought, well, maybe these Nordkapps really aren't that tippy after all, we just need to learn how to paddle them. We did, and I'm glad it went that way, because it forced us to become more proficient paddlers a lot faster than I think we would have in a more forgiving boat.

    Those of you who've paddled the older Nordkapps in (forgive me) gnarly water know what I mean when I say "the rougher it gets, the more that boat settles down". It's fabulous in pushy conditions as long as you're comfortable in the saddle. It just takes a little longer to get to that point of "feeling" stable. Of course, I can still go over in an instant if I'm spacing out and catch a blade, so it does demand a bit of attention, and encourages one to learn to roll ASAP. Granted, it's not a picnic to use as a photography platform, but it will always be a far better boat than I am a paddler.

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  14. This is a great string Gnarly Dog and others. Thanks for sharing.

    I have been on the journey myself from 80+ cm wide sit-on fishing kayaks to K1s/2s racing in Div 1 and now back to sea kayaks. I also run a weekly beginners course which invariably brings up questions about hull design versus speed, stability etc. I do love all the physics behind the scene but my approach these days is to try and educate the folks asking the questions with higher level information they can contextualise. I show them (by putting them in the different craft if possible) about the different behaviours of chined hulls versus U-shaped, shallow versus deep profiles, thigh braces vs open cockpit, etc. If they're following the racing angle I also introduce the concept of stability through control, responsiveness, refined forward strokes etc. which is often at odds with basic hull design arguments. If they're more interested in the rougher water we talk about the effects of length on close inland waves versus more spread out ocean waves. We also talk about hull weight and composition and how that behaves in varying conditions. The advantage I find in working with people who are newcomers to the paddling fraternity, is they're not yet absorbed in emotive arguments of rudder vs skeg, chine versus U, long versus short, flat vs wing etc. and they're more willing to consider the relationship between boat design, paddler capability, intended use and environmental conditions as a holistic equation. Of course the downside is they want the perfect boat that does it ALL and we all know that doesn't exist or we wouldn't have garages full of kayaks ;-) Have a wonderful weekend!!!!

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