The purpose of this article is to elucidate the general principles of
kayak stability, and to explain what enabled us create the world's most
stable kayak for fishing and paddling, based on the invention described
in US utility patent number 6871608 entitled 'Twin Hull Personal
Before going further, we'd like to recommend you watch this short demo video:
WHAT IS STABILITY?
defined as resistance to change, deterioration, or displacement, and it
is synonym to reliability and dependability. In naval terms it means
ability of a watercraft to maintain equilibrium or resume its original,
upright position after displacement, as by the sea or strong winds.
discusses lateral stability and not directional
stability i.e. tracking, which is discussed in other articles on this
WHY IS LATERAL STABILITY
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.
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.
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
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 (INITIAL) AND SECONDARY STABILITY
(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?
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.
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.
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.
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 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
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.
TO MAXIMIZE KAYAK STABILITY?
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
to be effective this weight needs to be applied as low as possible,
preferably much lower than waterline.
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.
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 him/her at about a couple of inches distance higher
than the hull's lowest point.
approach is mostly passive and regards the kayaker as a load having
certain physical properties such as height, width and weight.
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.
W kayak is
not restricted with issues of free board 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
where the legs carry most of the weight. This stabilizing
works less effectively in the sitting position, which is also less
effective ergonomically and biomechanically - similarly to the
traditional sitting position in kayaks.
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.
One Simple Question to Ask Yourself
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
these sporting activities require active and efficient balancing, which
is best achieved through the use of our legs, and for this purpose the
kayaking position is among 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 his weight with his feet
at the lowest point in each hull's bottom - in this case 4
inches below waterline.
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.
initial lateral stability is
achieved by placing maximum buoyancy as far as possible from the
kayak's longitudinal axis. In monohull kayaks (both regular
'tunnel' hulled) this is
achieved through a wider beam, but even the widest monohull kayak still
of its buoyancy concentrated along its longitudinal axis - as shown in
Monohull W500 Twinhull
figure shows a monohull kayak (left) and a new, W500 kayak (right) of
identical length and width - Both kayaks are viewed from the bottom.
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
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
In contrast, the white areas in the W kayak on the right
100% of its total volume, and they are several times bigger
than the white areas in
the traditional kayak.
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 unrivaled initial
stability and some of its legendary secondary stability.
Another common solution for increasing lateral
stability is through minimizing the kayak's propensity for rolling and
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.
Comparison Of Three Kayaks'
The bottom part of this traditional kayak's cross section is round, and
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
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
water when heeling (tilting) and forced into rotary motion,
thus it offers maximal resistance
to rotary forces.
tunnel hull is a
name given to a monohull with usually one 'tunnel' going along its
longitudinal axis - from bow to stern. The
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
Tunnel hulls have been in use since the late part of the 1870s, and the
already been implemented and tested in various canoe and kayak designs
over the years.
A tunnel hull kayak is another
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
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
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
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
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
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
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
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 multihull kayak.
Regular and Tunnel Monohulls
Tunnel Mono Hull
as a stability factor
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
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
consequently causing fatigue and discomfort, which are additional
What can a
tunnel really do to a kayak?
a tunnel in a monohull can be an
effective means for improving tracking as
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
a tunnel in a
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.
the tunnel hull kayak design
real advantage in terms of stability
it would enable producing narrower (I.E. faster) yet stabler monohull
kayaks. Since in reality the tunnel does not produce such
the various tunnel hull canoes,
kayaks and hybrids are among the widest designs on the market.
comparison, the W kayak design offers both
increased initial and secondary
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, and kayak outfitted with outriggers.
Such Hyper Stability is currently achieved with a hull
that's only 29" wide, which is the width
some touring kayaks.
Thought About Truth In Advertising
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.
company's website describing the
tunnel hull as being 'extraordinarily
stable for a single hull boat', while the same website
that another small watercraft that company offers 'incorporates a V hull design to
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.
Truth In Advertising
About Add-On Kayak Outriggers and Integrated Outriggers
often cross the line between fact and fiction, and sometimes they cross
the line between true and false.
For example, the owner of a company offering a fishing kayak featuring
folding outriggers at its rear end has claimed on a promotional video
that his product (quote) : "...offers the equivalence in stability of an
eight foot wide boat" (I.E. it's as stable as a bass boat...)
Such claim is so disconnected from reality that anyone can easily understand that it's false, of course.
But generally, crafty marketing hype is everywhere, and too many people
are fall for it, and them fall out of their kayak, unfortunately.
What's the real effect of small outriggers attached to the kayak's stern?
Generally, small outriggers offer some initial stability but too little
secondary stability. This means they give the kayak user some sense of
security on flat water and when the kayak is not tilting on its side,
but this sense of security is misleading, since a small outrigger is not
sufficiently buoyant to support the heavy weight applied on it when the
kayak is tilted on its side, and therefore such outrigger may not prevent an accident.
Practically speaking, as soon as the kayak user seriously loses balance,
for example in case they're attempting to stand up, or if the kayak is
hit by a motorboat's wake, they cannot rely on extra lateral stability
that's enough to prevent their kayak from tilting further. This problem
is particularly acute in SOT kayaks, since their user is already seated
or attempting to stand on a deck that's several inches above waterline,
and therefore they're insecure and less stable to begin with.
The folding outriggers in that fallacious promotional video are
integrated with the hull itself, and therefore offer less stability than
outriggers added on the kayak's sides.
Why is that? -
The reason for the poor performance offered by outriggers integrated
with the hull's rear end (stern) is that the buoyancy they add on the
sides of the stern is in fact taken away from the stern itself:
When the outriggers are deployed sideways the stern splits in two, and
its two halves are repositioned outwardly, so the kayak no longer
features a proper stern.
This means the user benefits from no additional support whatsoever when
they lean forward (hours 10 to 2), or sideways (hours 8 to 10 and 2 to
4), or if they lean backward (hours 5 to 7). The only gain in (initial)
stability is in case the user happens to lean in the angles in which the
outriggers are deployed (hours 4 to 5 and 7 to 8).
Bottom line: The gain in initial stability when the outriggers are
deployed is in a range of angles that add up to about 1/4 of the total
circle (just about 4 hours out of 12) around the kayak user.
This almost insignificant advantage is offset by the fact that it is
impractical to paddle that kayak when its outriggers are deployed, since
the amount of drag they add is considerable, and the main hull in this
position loses most of the hydrodynamic advantage offered by its initial
length (I.E. hull speed). The combination of these two negative factors
is critical to the kayak's speed, or lack thereof. It is probably the
slowest and most difficult fishing kayak to paddle, and this is no small
feat in a category of kayaks generally known as 'barges'...
Interestingly, since the little stability added to this kayak also makes
it so hard to paddle, anglers are effectively prevented from using it
for sight fishing and fly fishing in case they intend to cover any
significant distance. The vertical metal frame... -
Some SOT fishing kayaks, including the one discussed in the previous
paragraph feature a tall vertical metal frame, supposedly in order to
provide some support for the angler who's attempting to fish standing up
Practically, that vertical metal frame adds leverage to the angler's
weight if they lean on it or grab it, which makes the kayak tilt further
in case the angler loses balance and the kayak is tilting sideways.
Again, 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 the movies
on this page.