DESIGN FOR BETTER KAYAK STABILITY: WHY AND HOW
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 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 it 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.
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 he/she is 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 closer to 40". The first are
designed for use by highly skilled and relatively small 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 (that is 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 onboard.
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 freeboard, and by the modern kayaker's need for a padded
seat, which places him/her at about a couple of inches distance 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 as restricted with issues of freeboard and draft,
and it enables the kayaker to apply his own weight directly to the
lowest point of each hull through his feet, especially in the standing
or riding positions (see user manual)
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 his/her physiological
attributes namely his/her natural propensity and obvious capability to
balance himself/herself through the use of the legs, feet etc.
For a clearer understanding of this point we recommend that the reader ask himslef/herself 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 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 among the worst imaginable. |
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Figure 1
This figure shows a cross section of a W Kayak and its 5.5" (14 cm) draft when loaded with a 200 lb (90 kg) passenger.
The red arrows show where the kayaker applies his weight with his feet at the lowest point in each hull's bottom - in this case 5.5 inches below waterline.
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2. The most common solution for increasing kayak
stability is widening its beam, although the wider the kayak the less
efficient 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 regular (monohull) kayaks this is
achieved through a wider beam, but even the widest traditional kayak still has most
of its buoyancy concentrated along its longitudinal axis - as demonstrated in Figure 2:
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Figure 2
This
figure shows a traditional kayak (left) and a new, W kayak (right) of
identical length and width - Both kayaks are viewed from the top.
The
vertical, interrupted lines represent the longitudinal axes of each
kayak, respectively.
The yellow colored areas represent those parts in the kayak that are
sufficiently distant from its longitudinal axis to effectively
contribute buoyancy that may counteract its heeling.
Although the traditional kayak on the left is very wide for
its size these areas still make just a small part of its overall volume.
In contrast, the yellow areas in the W kayak on the right represent
100% of its total buoyancy, and are several times bigger than those in
the traditional kayak.
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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.
Figure 3: Comparison Of Three Kayaks' Cross Sections
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 W
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.
Hyper Stability: Demonstration of Principles
-Click to watch video
The W technology is protected by U.S. utility patent #6871608, and it is patent pending in Canada.
