SEA KAYAKING - SPEED-DRAG-HP
by Les Berke (440) 572-0178

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The focus in our club is on white water kayaking and this article is for you only if you are developing a deeper interest in sea kayaking and have not yet read all the books about it, otherwise it will put you to sleep. Those of you who have been sea kayaking for some time know most of what I will discuss, but it still might contain some useful or interesting information.

In the last installment on kayak surfing in our KaNews, Apr. 98, I wrote about waves and how to get started in surfing. Playing in the surf zone not only builds kayaking skills but waves become friends instead of adversaries, and that is important for sea kayakers. Longer kayak trips with possibilities of encountering waves of various sizes over open water become interesting and enjoyable. Remember, Lake Erie weather is somewhat unpredictable.

When planing longer trips the question of drag, speed and what sustained paddling (horse) power is needed, are fundamental considerations. I will do some musing about kayak speed, drag and needed paddling power, but not about sea kayaking techniques. As a former downhill ski instructor I firmly believe in taking structured, formal courses in skill sports to avoid ingrained mistakes and bad habits that are later hard to break. In our geographic area Red Cross, and Red Cross certified instructors give courses, including safety aspects, so take those courses. The British Canoe Union has a very thorough set of courses available for example at the Annual Great Lakes Sea Kayaking Symposiums and in Canada.

As we all know kayaking started out a few thousand years ago for hunting and warfare (yes!) in arctic regions. One might say two distinct types evolved, stable wider ones for rougher waters in the Pacific North West, including the Aleutian Islands, and long narrow boats for the calmer waters around Greenland. There are other locations with their variations to fit the local conditions. To start with, the classic source book "The Bark Canoes and Skin Boats of North America" by Edwin Tappan Adney and Howard I. Chapelle is a must reading. It is available in the Cuyahoga Public Library system. The recently re-released very interesting cute three (note) books, "The Little Kayak Books, I, II, III" also have data, history on native boats. You should have them. You can order them from: John Winters, Redwing Designs, Box 263, Burk’s Falls, Ont, POA 1CO, Canada. . Technical Pages about Canoe and Kayak Designs: John Winters It was advertised in Sea Kayaker. He has a shortened version of it on his website: The Shape of the Canoe

You should also read the excellent book "Form and Function of the Baidarka" by George Dyson. He is producing beautiful replicas of a particular Aleutian style kayak characterized by a forked bow and transom stern as functional forms at the two ends, interacting to reduce drag. See Canoe and Kayak , March 98 for article and pictures on building one. I saw them in a shop in British Columbia. They are art pieces to hang in your living room uncovered, just the frame. His book is very interesting reading, and provides basic theoretical background to support claims about their speed and seaworthiness with its forked bow and transom stern. Dyson argues that Pacific Eskimos could push them into planing speeds, but I would question that. Olympic K-1 Sprint boats achieve the highest speeds of all kayaks, but they are in a dynamically lifted mode (semi planing?) with their round, slightly cambered, non-planing hulls (more on max. kayak speeds later). They are propelled by dedicated athletes like the legendary Greg Barton, and by Hungarian Arnold Swarzenegger clones I saw train on the Blue Danube around Margaret Island in the middle of beautiful Budapest. Olympic sprint is very much part of the kayaking culture there. They win a lot of medals.

The better known native type is the long and narrow graceful Greenland style boats discussed in the first two books mentioned above. They serve as the motivation for most commercially available sea kayaks. I have an exact copy of an original hunting kayak from the East Greenland village of Angmagssalik. It is an extreme sea kayak, 18 ft long with only 19 in. beam, unstable minimum wetted surface cross section, and is "stealth" with only an inch free-board to fool the seals, and me. It is the closest thing to a paddled submarine with the stern actually sucked under at higher speeds -- weird. It is a very frisky anthropological museum beauty of a boat. It has poor primary but fair secondary stability, hallmark of an advanced boat for advanced paddlers who make a living hunting seals. The proper technique is tilting from one secondary stability to the other shifting cheeks to sit on and pulling on the opposite side to also minimize yaw (tricky). Has a superb compromise between tracking and maneuverability. I’m into my third year of learning how to exploit its secret qualities but I have a long way yet to go. I’m a disaster with it in Lake Erie confused chop above 2 feet, but that is the challenge. I never finished a sandwich in it either, the fish get most of it, my Eskimo roll is heavily handicapped with a sandwich in one hand. Well, I did not grow up in one of these beauties.

There is controversy about which boats are more seaworthy the narrower or the wider boats. The narrower is easier to lean quickly to adopt to wiggle with the waves, but the wider is more stable to start with. It appears to me that the question is between adaptive dynamic stability versus static stability. The former is certainly more advanced, if so are your skills, having grown up hunting seals and dodging angry two ton walruses in your long and skinny among icebergs that did the Titanic in.

From these ancient hunting crafts (going back 4000 years or more by some archeologists) an almost infinite diversification evolved for various intended modern specialization. The various derivatives of the elegant Greenland kayaks appear dominant, but detuned for us amateurs as opposed to the native hunters, who had to have a superb swift vehicle. Theirs was a dangerous way to make a living. According to some records 1 in 10 native hunters died in kayaks every year, a huge unfriendly walrus could do major damage. Animals fought back or simply attacked, hunter became hunted. We only have to worry about our ineptness and bad decisions in critical situations. There are some stories though about a mama wale flipping a kayaker and a big white tasting a surfing kayak fortunately behind the cockpit, shaking it some then spitting it out. Santa Cruz surfing guys told me these stories, true or not. Supposedly a park ranger wanted to give the kayaker a ticket for interfering with marine life. The semicircular set of teeth marks convinced him that marine life interfered with the kayaker and he gracefully changed his mind.

What kind of boat fits your need depends on your intended user profile. Are you going to use the boat for a few hours of aerobic exercise after work a few times a week? for short or for long trips? at speeds in the 2-3-4 mph range most of the time? or attempts at more heroic speeds (6-8 mph) during extended trips? overnight camping? expeditions lasting weeks? etc. The applicable boats range from simple inexpensive plastic general purpose pointed bathtubs in the short 12-15 ft range for exploring wetlands or just poking around, all the way to top of the line expedition kayaks. Or is your thing a slim graphite speed machine of 19-20 ft length with 17 1/2 in. beam in which you part your hair in the middle not to upset its nonexistent stability. Cost ranges from $200 for plans and materials for a nice plywood garage project to over $4000. After that come the sails and the outriggers perhaps. Take your pick.

A typical performance kayak would be 18-19 ft long with 20 to 22 in beam requiring fair paddling skills. For all around kayaks 17-18 feet length and 24-26 in. beam is popular. The additional drag of a shorter/wider boat comes in at higher speeds and its drag might actually be less at lower speeds. The differences at lower speeds are hardly noticeable, but the more comfortable ride certainly is, especially after a few hours on the water. It’s just that advanced paddlers would not want to be caught in a wide boat, the narrow ones look much racier, but on a long trip the minor added speed can get defeated by a more relaxed and rested paddler in a wider boat. Think narrow only if you are athletically inclined to take advantage of it in the above 5-6 mph range, where it has it. Again, take your pick.

The designer’s compromise between speed, primary and secondary stability, tracking and ease of turning, are the important aspects to make you feel good in the boat. Narrow kayaks can be quite stable with a flat rectangular cross section, and cross sections that minimize wetted surface to reduce drag can be quite unstable even with wider beams. The variations are infinite. As we will see, looking at some numbers, there is not that much difference in drag between them at the usual low speeds, and other user requirements should dominate your choice. Rudder or no rudder is arguable. Ruder is often useful to reduce effort of keeping direction, but it is a vulnerable added clutter, and a little added drag. Some designers hate it, but marketing considerations offer you choices.

You should learn about kayak theory in a little more depth to add to your enjoyment. I will discuss a few aspects of it . For a deeper view the easiest place to start is John Winters’ web sites. His book, the "Shape of the Canoe", is an exceptionally illuminating discussion on kayak theory. You can order it from his address mentioned earlier. John Winters is a much respected Canadian designer (canoe and kayak are more or less synonymous words in UK derived usage) and the developer of the code KAPER used in Sea Kayaker for drag prediction in their kayak reviews. Visit his web sites, you’ll learn a lot: SHAPE, and KAPER

"The Kayak Shop" by Chris Kulczycki, the owner of Chesapeake Light Craft, Inc., a plywood boat kit company, is delightful reading about designing and building (plywood) kayaks. For equipment and how to, perhaps the best book is "Sea Kayaking" by John Dowd. You can also surf the web starting with SEA KAYAKING It is a California kayakers bulletin board, including the Tsunami Rangers, and also has accident reports. The Sea Kayaker magazine with it archival articles is a must if you are serious about sea kayaking.

Now lets get back to kayaks. Looking at the top view a kayak can be symmetric or asymmetric, the later then being fish form if it is widest ahead of the cockpit or Swede form if it is widest behind it. Swede form appears to be more popular although some say fish form has less drag. Less drag is true for submerged water craft (submarines and fish), but according to the Navy, slight Swede form is better for surface piercing craft. So there you are.

The tables that follow give you an idea for comparison between short/wide and long/narrow boats. In what conditions do you intend to kayak should influence your choice for a boat that is best for flat water, for waves, or perhaps a sit-on-top without fear of closed cockpit, are deciding factors. Glass boats are better than plastic boats, that is obvious. The drag of a plastic boat is higher with everything the same, and it gets worse with easy scratching influencing friction, the source of around 90% of the total drag (see next). The price difference tells you all about that.

In the April issue of Sea Kayaker you’ll find two boats reviewed that gives us a good opportunity to compare short and wide with long and narrow, plastic and glass. Two sets of drag values are given for both boats. One set is calculated by KAPER mentioned above. The other set is by Matt Broz of Mariner Kayaks using data from the classical Taylor Standard Series of actual boat (model) tests in the Navy’s David Taylor Tow Channel facility. I calculated a third set that compares drag at various speeds of boats of different lengths but of the same beam to show the effect of length only. Those numbers were calculated based on an approximate theory by Prof. Alan Adler, the inventor of those red flying rings you see in stores that hold (held?) the World record for furthest thrown object.

The needed horse power (hp) is indicated with the third set and also what percent of the total drag comes from friction -- most of it at low speeds. You will find that all the numbers are close regardless of what boat it is. The shorter boat has less drag at low speeds, the longer at higher speeds, as expected. The difference at low speeds can easily be washed out by raising the hull friction coefficient by dirt, deposits, scratches, etc. These differences count only when a 10 hr trip becomes 10 1/2 hr. because of difference in friction drag. The trouble is that the additional 1/2 hour comes after the ten that got you already exhausted. The 5% linear drag increase becomes a nonlinear increase in pain in the muscles and in an other place. You can also loose a race by 0.001 % difference. So you decide if small differences are worth the attention influencing your choice. The short boat reviewed is plastic and a higher friction coefficient is applied for it in KAPER.

Look at these numbers and make your own conclusion. You might notice that paddling hp needed doubles from 5 to 6 knots (long/narrow boat), and that in that speed range you want to be in the long/narrow boat.

Drag is made up of friction between the hull and the water and many other complex fluid dynamics effects usually lumped into "residual drag". Main contributors to that are wave making at higher speeds and form drag. Friction is a liner function of wetted surface which in turn grows with the square root of boat length. Shorter boats have less friction at low speeds, longer boats have less residual drag at higher speeds, theoretically combination of the two defines an optimum length for a given speed, but as shown above not by much, unless, as mentioned earlier, becomes important on long trips or races. Wave making grows to the fourth power of the beam-to-length ratio and starts to be important after around 5-6 mph, hence the love of narrower boats for speed oriented kayakers.

An other consideration is the human endurance aspect of maintaining a level of effort. There have been tons of studies on that for various sports, but not that much using kayaks where the upper body works with minimum help from the strong leg muscles. To give you some numbers, at 3-4 knots speed range (3.5-4.6 mph) the hp required is indicated at 0.02-0.05 HP. That effort can be maintained by a healthy human all day long, being in the range of walking. At higher speeds, the tantalizing 5-6 knots range, requiring 0.1-0.2 hp, is an athletic challenge to maintain for hours.

World class marathon racers maintain speeds slightly above 8 mph at a level of effort around 0.3 HP for 3-4 hours in their racing machines. It is a contest of will power and pain tolerance, like the Indian sun dance ceremony hanging on hooks through your flesh from a pole to see who is the bravest. The Finlandia Clear Water Challenge racers do they daily thirty some miles in around 4 hours keeping above 8 mph. Olympic bikers can maintain 2/3 hp. The peak human power output is by Olympic weight lifters, or panicked grandmothers lifting a car off their granddaughter at four horse power, but maintained only for a second. The above hp numbers for kayaking have to be reconciled with paddle and paddler efficiency. I have some numbers from one of the rare studies and tests -- but I can not find it, sorry. It was done at SUNY at Buffalo.

Human power, endurance, and calories burnt, are important subjects. Plugging the hp needed to paddle at 4 mph into a metabolic equation tells you that you’ll burn 400 cal/hour, depending somewhat on your weight. In a 10 hr trip at that speed you would burn off 4000 calories crossing Lake Erie around the Islands, a weight watcher’s dream. I’m at my correct weight so I don’t need to do it... Take my numbers not with a pinch but with a table spoon of salt, I did not scrutinize them much.

Talking about speed and effort we also have to mention two special type of boats. The sit-on-tops made their appearance both as entry level short and fat very stable slow boats, and as beautiful long and narrow speed machines mentioned above. There are two motivations for sit-on-tops at the two opposing end of users. Beginners take to it to avoid the fear of closed cockpit and the need for Eskimo rolling skills. You just fall in the water and clime back avoiding the need to roll, or just go for a swim. Expert speed and atrocious condition lovers, like the ease of the quick in and out it allows. The kevlar/graphite bullet proof sit-on-tops of the Tsunami Rangers (extreme coastal kayakers around San Francisco) provide safety surfing 10-15 footers in coastal "rock gardens" by quick bailouts before smashed against cliffs. On long risky trips, like a recent one from Alaska to California, a similar advanced Tsunami sit-on-top was used again for easy getting in and out when needed. I have a dependable combat roll, but if I want to chance a solo crossing of Lake Erie I would consider a performance sit-on-top (16’ x 21" for minimum drag at 4 mph ?) just for added safety of getting back easily with burning muscles, or whatever that would mess up my rolls. Refreshing dips every so often along the way would also point to a high performance sit-on-top.

The other class of boats one also has to mention are the Olympic K-1 (and K-2 and K-4) sprint boats, the most refined kayaks for acceleration and speed. They have to be not longer than 5.2 meters (17 ft) and at leas 0.51 m beam (20 in.) someplace. The top view is a diamond with the widest 20 in. just behind the cockpit. Their ultra refined hull shape is the product of many decades of even Navy assisted research. They are the fastest of all kayaks but only on mirror smooth water. Sit-on-top narrow surf skis are the fastest in waves, K-1-s are too unstable under any but ideal conditions. These two types, the surf skis and the K-1 are also used as aerobic fitness machines by performance enthusiasts. They are usually propelled with super efficient "wing" paddles by the skilled paddlers. Graphite is the material for these top line racing machines.

Talking about the fastest kayaks, let me discuss in closing, in simple terms, kayak speed potentials as distinct from drag at some speed and horse power needed to maintain the various speed regimes. The question of which is a faster boat misses the point. Faster at what speed regime?, what is its top speed with your intended paddle power?, are correct questions. As we saw earlier, boats designed for top speed have higher drag at low speeds where most of the every day paddling is performed. So which is the faster boat, and for whom?

Sea kayaks operate mostly as displacement hulls, displaced water providing most of the lift. This does not seem like a great revelation, but it puts kayaks in the category of heavy sailboats, battle ships, ore carriers, and the like, whose top speed potential is determined by their water line length, as will be discussed next. The longer the boat, the higher the achievable top speed, but only if lift remains to be provided by displacing water.

There is a bad and a good side to lift by displacing water. The bad side is that displacement hulls have a (mushy) speed limitation called "hull speed" which in knots is equal to 1.34 times the square root of the water line length in feet. The good side is that displacement hulls have a constant lift (almost) at all speeds, with drag starting at zero at zero speed, giving an infinite lift to drag ratio (L/D in fluid dynamics terms) at rest. Starting from that advantage drag increases quite slowly up to the customary slow cruising range of around 3-4 mph, as the numbers earlier indicated. This is what makes sea kayaks efficient long range touring vehicles. Drag starts to rise more sharply as speed is approaching the theoretical hull speed, then levels off some once the kayak is pushed into semi planing, provided it is the right design and the right paddler. As discussed earlier, drag at low speeds is due mostly to friction of water against the wetted surface, at higher speeds other complex effects become more dominant. Keep your hull mirror smooth, it can make a very large difference in drag. Some suggest cultivate some slimy organism on it...

Wetted surface is a function of boat design, mostly cross section, and tends to increase in proportion to the square root of water line length, and, unfortunately, with cross sections with increasing stability. Flow around a hull is quite complex and is way outside the scope of these musings, and proving to be quite obstinate even against supercomputer efforts by various high powered Navy and private research groups engaged in Computational Fluid Dynamics.

No, they are not interested in kayaks, but there is a similarity number, the nondimensional Froud number, and its simplified but dimensional version, the speed to length ratio, or Taylor quotient (Tq), that are very close for kayaks, short and slow, and larger vessels, long and fast. Tq is equal to the speed over the square root of water line length. Because it is dimensional, speed is taken usually in knots and the water line length in feet. For a 16 ft kayak at 4 knots Tq=4/4=1, same as for a 900 ft ship at 30 knots Tq=30/30=1, so the kayak is a small model to study the flow around the big ship, thus the benign attitude of the Navy towards kayak research.

Because of the flow similarity, the Navy’s famous David Taylor facility has been cooperating with kayak designers in its long tow tank looking at them as useful models for flow studies. This is specially true for continuously refining Olympic K-1-2-4 sprint kayak designs. Because of the similarity of flow, kayak designers have been benefiting from Navy data and research in developing their simplified codes to predict kayak behavior, but enriching it with their own observations and experience. The recently developed code KAPER, mentioned earlier, is an example. Matt Broz’s code uses a drag prediction method derived from a classical set of Navy model test data, called the Standard Taylor Series after Admiral Taylor. Keep this in mind when you read the boat reviews in Sea Kayaker using these two approximate codes, there is a lot behind them.

Exact computations are difficult because drag is a complicated function of speed. The boat’s position in the water is changing from first being submerged at lower speeds slightly more than its load would dictate due to water pressure drop under the boat due to slightly faster flow there, then rising out of the water at higher speeds by emerging dynamic lift, if designed to do that, changing the submerged shape. This is very apparent when a kayak rises to plane as it surfs a big fast wave. To be a theoretical purist one would have to deal with a slightly different boat at each speed.

As speed increases bow and stern waves are produced that in turn produce wave drag in a complicated fashion. The bow wave can interfere with the stern wave increasing or diminishing each other increasing or reducing drag at various speeds. Wave speed depends on wave size. As displacement hull boats go faster and faster, they generate larger and faster waves and eventually the speed of the generated wave will be equal to the speed of the boat, with a single wave traveling along the hull with the boat caught in it. That speed is called the hull speed . A simple derivation involving wave speed and wave length results in a simple formula indicating that hull speed in knots equals 1.34 times the square root of the water line length in feet. For a 16 ft kayak hull speed is 1.34x4x1.15 = 6.164 mph (1 knot is around 1.15 mph). A $100.000 dollar 36 ft Lake Erie luxury yacht hustling in a 30 knots gale at its breath taking hull speed of 9 mph signifies sailing as a "sophisticated way of getting wet while slowly going nowhere at great expense". Same was true even for the $80 million America Cup racers before they changed rules allowing fast light planing boats. Length is the reason why big Lake Erie ore boats are deceptively fast. Don't try to cross ahead of them, you might not make it. Once I had a very close call making that mistake and barely got across on my windsurfer. Crossing their giant bow towering over you is a very frightening sight when only a hundred yards away hustling at 25 knots towards you.

Hull speed can be exceeded a number of ways. The most obvious is by overwhelming power like in motor boats that get up on their hull to "plane" leaving their hull speed wave behind. Very light sailboats with large sails, and designed with "planing hulls", can also get into planing at some sufficient wind speed and overcome their theoretical hull speed operating like skipping stones over the surface of the water. Surfing is at planing speeds, so is wind surfing in strong winds. Narrow knife edge hulls of light catamarans with their large and powerful sails never notice hull speed. I pulled a water skier with my Hobie 18 at around 25 knots in 25 knots wind (hull speed would be a mere 6.5 mph). The boat never even felt the water skier behind it once he was up planing on his skies. So there you are about hull speed.. Now what does that mean for kayaks?

With paddle power you can not push your boat into the lower drag total planing mode. With appropriate hull design, like that of the Olympic K-1 sprint kayaks, the hull speed is a soft limit and is surpassed considerably, if you can supply the muscle power. For the short 200 m sprint 34 seconds is world champion class time moving at 13 mph achieved by one of those Hungarian clones of Arnold Schwarzenegger sticking out of these kayaks. That is twice the 6.35 mph theoretical hull speed of the around 17 ft K-1 kayaks. So why can’t you go that fast in your long 18 footer? Difference is in the kayak design and in the training. I was in Hungary last September and watched dozens of young boys and girls around the ripe age of 12 training for hours every day after school in their Olympic K-1-s on the Danube with their wing paddles. All of Cleveland has about six wing paddles and I have not seen a single Olympic K-1 sprint boat here. Well, it is a different, medals oriented, kayaking culture there, they even beat Greg Barton. They don’t just "boof" off.... Those interested in the mathematics of Low Drag Boats, explore:: Hydrodynamic Drag of Small Sea Kayaks. Good Luck!

So there you are with lot of confusing considerations, but that is what makes sea kayaking both a brain and a brawn sport. Most members of the Keel-Hauler’s are focused on white water, but many lake surf. Interest in flat water sea kayaking is also growing. Trips have yet to be properly organized within the club. There are many opportunities in Ohio. Sandusky Bay, the Islands in Lake Erie, wetlands, rivers, inland lakes, and many Lake Erie beaches provide ample opportunities. We can start to meet for after work short trips say Wednesdays at Bradstreet Landing on the border of Bay Village and Rocky river, weather permitting. It has the easiest put-in. Lake Erie water gets enjoyable around June, but kayaks were developed for arctic conditions, so it depends on you what is your comfort zone. If you are a river kayaker you enjoy snow melt ice water already, in your sea kayak you can roll among Lake Erie ice sheets. Andy Gross has his house rule: "if water and air temperature add up to at least 100, it is comfortable to kayak". Eskimos have a different rule, they say: "water is cold only if you think it is cold".

Les Berke

440 572 0178