This article about kayak stability was first published years ago. Those times were different from now. Back then, stability wasn’t considered as important as it it now, and some people even argued that a fishing kayak doesn’t necessarily have to be stable, since anglers eventually get used to fishing out of an unstable platform. We blasted this notion for years, and now it’s gone.
Since then, the kayak world has changed, especially the fishing kayak part of it, and stability is king. This periodically leads to kayak manufacturers trying all kinds of solutions designed to increase the stability of the fishing kayaks they offer, and to some ridiculous claims being made about that alleged stability. The part in this article discussing tunnel hulls was added a few years later, as a response to a wave of such ridiculous claims, which came from a manufacturer who incorporated the tunnel hull design in their main fishing kayak brand. In hindsight, it was a tempest in a teacup, and people have learned not to trust such claims. A similar thing happened with a fishing kayak equipped with integrated folding outriggers.
The reason we republished this article on the W fishing kayaks blog is in order to enable people to comment on it, which was impossible in its first version tat was published as a static html page.
WHAT IS STABILITY?
Stability is defined as resistance to change, deterioration, or displacement, and it is synonym to reliability and dependability. In naval terms it means the ability of a watercraft to maintain equilibrium or resume its original, upright position after displacement, as by the sea or strong winds.
This article discusses lateral stability and not directional stability i.e. tracking, which is discussed in other articles on this website.
WHY IS LATERAL STABILITY SO IMPORTANT?
Lateral stability is a key factor in kayaking and kayak fishing since it enables prevention of accidents as well as increases the well being of kayakers and kayak fishermen.
This article explains the basic terms used in kayak design in the context of stability, and how the patented W kayak offers a degree of lateral stability previously thought to be unattainable in kayaks.
Before going further the author of this article would like to stress that in his opinion the idea of relying on the kayaker’s skills in performing the ‘Eskimo Roll’ as a primary resource in safety terms has largely failed since the overwhelming majority of people who paddle kayaks in recent decades has ignored it, and increasingly so. The reason for this is that rolling is basically a method of recovery and not a means of prevention. This explains why most manufacturers and kayakers apply common sense and prefer to prevent accidents rather than focus on unreliable recovery techniques.
Primary and Secondary Stability
Primary (Initial) stability refers to what the kayak feels like when used in flat water – Does the kayak convey a basic sense of ease and confidence as far as its stability goes?
Secondary stability refers to how easy it is to stabilize and control the kayak once it’s already heeled, or generally speaking in adverse conditions where it is either constantly and/or suddenly being tilted on its side – either because of an external force or because of something the kayaker did.
Both primary and secondary stability are important but while primary stability relates mainly to how the kayak passengers feels, secondary stability is what mostly affects their safety and performance in paddling and fishing.
Any further discussion about these terms would be futile without determining who’s inside the boat, since in most cases the passenger weighs several times more than the kayak itself, and they are the key factor that affects the way the boat reacts to destabilizing forces – whether external or internal.
Flat water racing kayaks can be as 18″ or 19″ narrow, while some fishing kayaks have a beam that’s over 40″. The first are designed for use by highly skilled and relatively small sized kayakers that can’t stabilize such kayaks without keeping their paddle in the water, while the latter are required to offer good stability mostly to bigger and less skilled paddlers that occasionally happen to be fighting big and strong fish, and often stand up in their kayak when paddling and fishing if they happen to be using W fishing kayaks.
Therefore, primary stability has much to do with comfort and secondary stability is what helps you from getting your kayak overturned in real life conditions – whether you’re surfing with it in five foot waves or struggling to pull a hundred pound bass on board.
HOW TO MAXIMIZE KAYAK STABILITY?
1. The first stabilizing method is not necessarily the most popular one, and it consists of minimizing the destabilizing effect of the kayaker’s weight on the kayak in traditional (monohull) kayaks, and making use of this weight and other attributes in W kayaks. In order for this method to be effective this weight needs to be applied as low as possible, preferably much lower than waterline.
In traditional, monohull, sit-in kayaks the designer who wants to apply this method would try to lower the kayaker’s center of gravity (CG) by designing a deeper hull and placing the kayaker’s lowest parts as closely as possible to the bottom of the kayak.
In this case the designer’s efforts will be limited by the fact that traditional kayaks must have a shallow draft or else they won’t offer sufficient free board, and by the modern kayaker’s need for a padded seat, which places them at about a couple of inches higher than the hull’s lowest point.
This approach is mostly passive and regards the kayaker as a load having certain physical properties such as height, width and weight.
Applying this method of stabilization in sit-on-top (SOT) kayaks, which have gained roughly one third of the kayak market today is not possible because the SOT kayaker must sit several inches above waterline in order to enable water to drain down from the deck through the scupper holes, and try to prevent the deck from being often flooded by water coming from below through those holes
The W kayak is not restricted with issues of free board and draft, and it enables the kayaker to apply their own weight directly to the lowest point of each hull through his feet, especially in the standing or riding positions where the legs carry most of the weight. This stabilizing method works less effectively in the sitting position, which is also less effective ergonomically and biomechanically – similarly to the traditional sitting position in kayaks.
This approach in W kayaks takes into account the kayaker’s physical attributes such as size and weight, as well as their physiological attributes namely their natural propensity and obvious capability to balance themselves through the use of the legs, feet etc.
One Simple Question
For a clearer understanding of this point we recommend that the readers ask themselves the following:
-“Would I consider sitting in the traditional, L kayaking position when surfing, riding a horse, riding a snowmobile, an all-terrain vehicle (ATV), a jet ski etc.?”
The correct answer would obviously be “Definitely not!”, and this is because all these sporting activities require active and efficient balancing, which is best achieved through the use of our legs, and for this purpose the L kayaking position is probably the worst imaginable.
This figure shows a cross section of a W500 Kayak and its 4″ (10 cm) draft when loaded with a 200 lb (90 kg) passenger.
The red arrows show where the kayaker applies their weight with his feet at the lowest point in each hull’s bottom – in this case 4 inches below waterline.
2. The most common solution for increasing kayak stability is widening its beam, although the wider the kayak the less efficient for paddling it becomes. Very wide kayaks are practically impossible to paddle for any reasonable distance.
Improving initial lateral stability is achieved by placing maximum buoyancy as far as possible from the kayak’s longitudinal axis. In monohull kayaks (both regular and ‘tunnel’ hulled) this is achieved through a wider beam, but even the widest monohull kayak still has most of its buoyancy concentrated along its longitudinal axis – as shown in Figure 2:
This figure shows a monohull kayak (left) and a new, W500 kayak (right) of identical length and width – Both kayaks are viewed from the bottom.
The vertical, interrupted lines represent the center line of each of the two kayak forms. The white colored areas represent those buoyant parts in the kayak that are sufficiently distant from its longitudinal axis to effectively contribute to its stability.
Although the monohull kayak on the left is wide for its length, the white areas in it still make just a small part of its overall volume.
In contrast, the white areas in the W kayak on the right represent 100% of its total volume, and they are several times bigger than the white areas in the traditional kayak.
In sum, all monohull kayak designs (SIK, SOT and Tunnel hull) use just a small part of their buoyancy for effective stabilization, while the W design uses all its buoyancy for this purpose.
This is how the W kayak is capable of offering its unmatched initial stability and some of its legendary secondary stability.
3. Another common solution for increasing lateral stability is through minimizing the kayak’s propensity for rolling and overturning by increasing resistance to rotary motion: This can be achieved by giving the kayak a form that generates resistance from the water through the need to displace water when the kayak is tilting on its way to roll. This method is useful mainly in dealing with primary stability.
Figure 3: Comparison Of Three Kayaks’ Cross Sections
A. B. C.
Kayak A: The bottom part of this traditional kayak’s cross section is round, and such a kayak would be called ’round bottom’ (think of a virtual wheel, or a barrel). Such kayak offers practically no resistance to rotary motion, and therefore is particularly unstable.
Kayak B: The bottom part of this traditional kayak’s cross section is angular, and such a kayak would be described as having ‘hard chines’. The chine is the nautical term for the line where the side and bottom of the hull intersect. Such kayak would have to displace some water when in lateral rotary motion and thus offer more resistance than kayak A, and therefore would be more stable than kayak A.
Kayak C is a W300 Kayak: The bottom part of this kayak must displace big quantities of water when heeling (tilting) and forced into rotary motion, and thus it offers maximal resistance to rotary forces.
A tunnel hull is a name given to a monohull with usually one ‘tunnel’ going along its longitudinal axis – from bow to stern. The tunnel is submerged, including its ‘ceiling’ (top side).
Tunnel hull kayaks are not stabler than other monohull kayaks (I.E. common SIK and SOT) of similar size and proportions, as will be explained here. Tunnel hulls have been in use since the late part of the 1870s, and the concept has already been implemented and tested in various canoe and kayak designs over the years.A tunnel hull kayak is another form of monohull kayak – It is not a multihull kayak (see figure 2), so unlike a multihull the tunnel hull does not distribute more buoyancy on its external sides than a regular monohull does (see figure 2).
In other words, most of the tunneled hull’s buoyancy is wasted when it comes using it to increase lateral stability, which is also the problem in other monohull designs (E.G. SIK and SOT).
Primary (Initial) and Secondary Stability
It’s easy to see that with its sides considerably less buoyant than the sides of a multihull kayak a tunnel hull kayak cannot possibly be as stable. Interestingly, the tunnel hull kayak is less buoyant than the hull of common monohull kayaks (SIK, SOT). In other words, the tunnel reduces the kayak’s load capacity, which decreases both its primary and secondary stability.
Primary (Initial) Stability:
If the monohull kayak’s tunnel is made deep and wide enough, and its vertical sides have the right form (see example in figure 4) they can act as additional ‘hard chines’ and thus add some initial resistance to rotational motion. This is far from being comparable to such effect in a catamaran kayak because the tunnel’s sides are shorter than the boat’s overall length while in a catamaran kayak (E.G. W kayak) the hulls’ length is equal to the boat’s overall length.
In stability terms it means that on still, flat water certain tunnel hulled kayaks could feel more stable than comparable common monohull kayaks, that is offer a little more primary (initial) stability than a traditional SIK or SOT design. However, this potential advantage is likely not to be perceptible since it would be offset by the tunnel hull’s deficiency in buoyancy.
A tunnel hull kayak may not provide additional stability for significant weight displacement of its passengers, and it wouldn’t be useful in moving water, waves and other adverse conditions: The secondary stability of a tunnel hull kayak does not exceed that of a regular monohull kayak of the same size and proportions, I.E. it’s considerably less stable than a twin hull kayak.
Figure 4: Cross Sections of Regular and Tunnel Monohulls
Regular Mono Hull Tunnel Mono Hull
Ergonomics as a stability factor
In a tunnel hull kayak the paddler or fisherman sits with their legs stretched forward and the trunk only a few inches higher than the ankles. This position hardly differs from the notoriously non ergonomic L kayaking position, and therefore hardly offers any improvement as far as the ability to use the legs for balancing, control and power generation while it still forces the passenger to rely on a back rest for support, consequently causing fatigue and discomfort, which are additional destabilizing factors.
What is a tunnel really good for?
Incorporating a tunnel in a monohull can be an effective means for improving tracking as the tunnel enables water to flow in a straight line (I.E. not deflected or ‘curved’) along the hull, in parallel to the direction of the boat.
This can be helpful in very wide monohull canoes and kayaks (E.G. fishing kayaks) that track poorly.
Similarly to a rudder, the tunnel has a negative effect on speed.
In motorized boats the tunnel can help the hull plane but this is irrelevant in low speed boats, especially human powered ones such as canoes and kayaks, which are the slowest.
‘What if’ – a quick reality check
Introducing a tunnel in a monohull kayak places the passengers higher than in a regular monohull kayak without having them benefit either from significant increase in stability or significant improvement in their paddling or fishing position.
If the tunnel hull kayak design offered any real advantage in terms of stability it would enable producing narrower (I.E. faster) yet stabler monohull canoes and kayaks. Since in reality the tunnel does not produce such effect the various tunnel hull canoes, kayaks and hybrids are among the widest designs on the market.
In comparison, the W kayak design offers both increased initial and secondary stability as well as improved ergonomics resulting in Hyper Stability: The ability to perform things that are impossible with any other form of kayak, and an overall better user experience than that offered by any other kayak, including the widest and most stable ones. Such Hyper Stability was initially achieved with a hull that was only 25″ wide, which is the width of some fast sea kayaks. Being wider, and featuring wider hulls, the W500 is even stabler.
Food For Thought About Truth In Advertising
Well, it’s more of a snack really, but the following anecdote may shed some light on this subject from a different angle – that of ‘marketing hype':
The tunnel hull design for small, paddle powered watercraft has gained some new life in recent years with one company that promotes it quite energetically.
We found that company’s website describing the tunnel hull as being ‘extraordinarily stable for a single hull boat’, while the same website claims that another small watercraft that company offers ‘incorporates a V hull design to provide stability…’
It doesn’t take a boat designer to realize intuitively that a kayak hull whose cross section is shaped like a deep V is in fact unstable, and the only reason one would incorporate such a form into a hull design is to try and improve its tracking capability.
More Food For Thought About Truth In Advertising
Advertisers often cross the line between fact and fiction, and sometimes they cross the line between true and false.
For example, a well known fishing kayaks store has recently advertised on its website that one of the brands it offers for sale (a sit-on-top kayak equipped with integrated folding outriggers) is (quote): “The only kayak to truly let you stand & fish with 100% confidence”.
By doing so that store made a number of significant mistakes:
First, they openly admitted that all the other brands they have advertised for years as being suitable for stand up fishing in fact do not offer to stand and fish with 100% confidence. This is exactly what what Wavewalk has been saying all the time.
Second, that store is misleading the public to think that particular kayak is safe, while it is far from being so since its outriggers are positioned at the stern, and therefore leave the standing kayak fisherman with no extra buoyancy at all to support him on the sides of his kayak’s middle and front parts, where he’s likely to tilt his boat when fishing. Anyone can see that.
Third, if a kayak fisherman standing on that SOT loses balance, as he’s expected to do sooner or later, he has a metal frame to hold on to, but nothing to fall down on – Assuming that fisherman is holding his fishing rod with both hands (common practice…) he’s likely to fall overboard, as he would from any other SOT or sit-in kayak. In fact, holding on to the metal frame increases leverage on the hull and makes it easier to tilt sideways and overturn.
And last but not least, that store’s statement is obviously false since the only fishing kayak that really offers fishermen to stand up and fish with 100% confidence and safety is the Wavewalk, as anyone can see by watching this movie:
More reading about kayak stability:
What Makes The W Kayak The Stablest Fishing Kayak?
How Effective Can Fishing Kayaks’ Outriggers Be?