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Relationship Counseling for
Spray Skirts
Why doesn't my squirt boat skirt fit my creek boat?
by John Mason, Mt Surf
As a sprayskirt designer and manufacturer I would love to
make a single indestructible skirt that would provide a
bomber dry fit on both your squirt boat and your creek boat.
Regrettably, it just ain't going to happen. I don't believe
that any single skirt can be all things to all kayaks or
paddlers. Life is never that simple. If you ever find such a
skirt, please let me know... because I'd like to buy one for
myself!
Realistically, my goal is to make a dry, secure, easily
removable, and indestructible skirt. Unfortunately, skirt
manufacturers face the thankless task of designing skirts to
fit boats after those boats are on the market. And some boat
makers just do not design their cockpits to enhance skirt
seal or to optimize skirt life span. To make matters even
more complex, there are no industry wide "standard" cockpit
shapes and sizes. Every time a new boat is released,
sprayskirt designers must scramble to find or produce a
skirt that provides an acceptable fit.
Imagine if each car manufacturer produced wheels of
different sizes and shapes for every model of car and truck
they make? Tires that fit correctly would be hard to find,
not to mention expensive! Well, sprayskirt designers and
manufacturers have been dealing with analogous circumstances
for years.
Meanwhile, boating skills have progressed exponentially and
boaters are venturing onto increasingly difficult and
turbulent whitewater. And New School Freestyle moves pose an
incredible challenge to spray skirt fit. We are tackling
rivers and performing stunts today that would have boggled
my mind just five years ago. When I started paddling kayaks
more than 30 years ago using a canvas skirt, I could never
in my wildest dreams have envisioned what whitewater boating
would be like today.
Kayaks and sprayskirts share an interdependent relationship.
The kayak needs a dry, secure, removable and durable seal,
while the sprayskirt needs a cockpit rim designed to enhance
these performance characteristics. A well designed rim will
help any skirt do its job better, but a badly designed skirt
on a good rim will still make a poor fit. It is also
possible to design a kayak rim so badly that even the best
designed skirt will not seal properly.
Sprayskirts have also come a long way, but the demands on
them have also increased tremendously. Keyhole cockpits are
now 40% to 50% larger than the old standard (Dancer) cockpit
size. And keyhole cockpits just keep getting larger. The old
bungee cord skirts that sucked up tight around your waist or
laid flat like a tray when you were out of your boat were
fine for the old fiberglass and plastic boats with small
cockpits. But bungee cord skirts just do not work
efficiently on modern keyhole cockpits. It takes a lot more
skirt seal tension, mechanical grip, and de-tensioning of
the deck than most bungee cord skirts can provide to create
an efficient mechanical and hydraulic seal on a large
cockpit.
The purpose of a keyhole cockpit is to make your boat easier
to exit in the event of entrapment. Keyhole cockpits are
longer and wider, so there is a much a greater surface that
must be covered by the skirt. This large surface area
increases the vulnerability of the skirt to damage.
Fortunately, many of the new boats have recessed cockpit
rims to help shield the sprayskirt from paddles, rocks and
other boats.
Cockpit Design and Performance
From a sprayskirt designer's point of view, the ideal
cockpit shape would be perfectly round. This would
distribute the tension around the skirt rim evenly. Of
course, keyhole cockpits are longer than they are wide for
ergonomic reasons. In an oblong or keyhole cockpit the
tension on the skirt is greatest where the curvature is most
acute (the front and then the back), and least where the
curvature is less acute (along the sides). That is why the
sprayskirt seal is always less effective along the sides,
and why it is more difficult to slip a skirt over the end of
a keyhole or oblong cockpit. The more oblong the cockpit,
the more noticeable this will be.
The shape of the rim itself is also critical. It is meant to
hold the sprayskirt in place during normal use, but it
should also facilitate the quick release of the skirt when
you pull the ripcord because you need to exit your boat.
Ideally rims should have a one-half to three-quarter inch
lip to hold the skirt in place. And the distance between the
lip and the deck of the kayak should also be one-half to
three-quarters of an inch. You should be able to reach under
the rim with your fingers and pick up the boat without
pinching them or feeling like the boat wants to slip off
your fingers. Also, the radius where the skirt seal seats on
the underside of the rim should be as large and level as
possible so that a good seal will be obtained, without
making the skirt too difficult to remove. The corner on the
underside edge of the rim should be fairly aggressive to
hold the skirt seal more effectively, but the edge can be
cut back around the front to equalize the aggressiveness of
the seal and make the skirt more removable without making it
less secure. Imagine that you are going to hang from the rim
of the upside down boat by your fingers. The more secure
your grip, the better it will hold a skirt.
Cockpit rim design also has a great effect on skirt
longevity. Recessing the cockpit rim not only makes the
hydraulic seal less vulnerable to high- pressure blasts of
water (skirt less likely to pop), it also makes the skirt
less vulnerable to abrasion and impacts. Some popular rims
are so deeply recessed that when you lay (or slam) your
paddle across your deck, it won't even touch the cockpit rim
or skirt. Others rims protrude so far above the deck that
they leave the sprayskirt vulnerable to impacts from above
(including your paddle) or the side. Try this test to see if
the rim on your boat will be hard on skirts. Gently kick
your cockpit rim while the boat is lying on the ground. If
your foot glances off the deck and over the rim, it's a good
bet that a skirt will be fairly well protected. But if your
foot squarely hits the rim (or you stub your toe), it's a
good bet that a rock, paddle or another boat will do some
damage, no matter how tough the skirt you choose.
There are several other aspects of rim design worth
considering. There should be adequate space in the well
around the rim to allow you to put your skirt on without
busting you knuckles. And the rim should have a soft rounded
lip on the upper edge to reduce the "knife edge" effect.
This will minimize the damage to the skirt when impacts
occur. The underside of the rim should also be fairly
square; this will provide a better purchase for the skirt
seal.
Sprayskirt Design and Performance... the Other Side of the
Equation
To understand how a skirt works you must understand the
functions of the different parts of the skirt and how they
work together as a whole.
There are four key components to any sprayskirt: the seal,
the deck, the barrel, and the ripcord or deck strap. The
design of each of these components and their interdependent
relationship with each other, the boat, and the paddler will
determine the performance of the skirt.
The seal creates the physical bond between the skirt and the
boat (cockpit rim). The shape, tension, and elasticity of
the seal synergistically contribute to the hydraulic and
mechanical seal. The seal must conform to the cockpit rim to
produce a seal without gaps that would allow leakage. The
shape of the seal also contributes to the mechanical seal;
some shapes inherently grip the rim better than others.
Tension is a double-edged sword; greater tension will result
in a better mechanical and hydraulic seal, but it will also
make the skirt harder to put on and remove. The elasticity
of the seal also has advantages and disadvantages. A very
elastic seal will allow the skirt to fit a wider range of
cockpit sizes, but it will inevitably compromise the
mechanical and hydraulic seal. Bungee seals are cost
effective but can not provide the mechanical and hydraulic
seal of a shaped rubber rand.
The sprayskirt deck size and shape also effects the
efficiency of the seal, durability, ease of getting the
skirt on and off and, of course, the cost. Neoprene is an
elastic and expensive material. The elasticity of neoprene
allows us to make the sprayskirt deck smaller than the
cockpit. This saves on materials and reduces costs and it
contributes to a tight deck, but there are tradeoffs. A
sprayskirt deck cut narrower than the cockpit will diminish
mechanical and hydrologic seal on the sides, where there is
not much curvature to the rim. This is where most leakage
occurs and where skirts are most likely to pop. A sprayskirt
deck that is cut too short for the cockpit is less likely to
result in a leak or a pop, since the curvature of the rim is
greatest in the front and back. But it could result in a
skirt that is difficult to put on and remove. A tight deck
has also lost the shock absorber that protects the skirt
seal from energy transfer from a shot to the deck that can
cause a momentary leak or a blown skirt. Tight decks also
compromise durability, since neoprene under tension is more
prone to wear and tear. A tight deck also restricts the
ability of a skirt to fit larger cockpit sizes, reducing
versatility. All things considered, the sprayskirt deck
should be as large as possible in relation to the cockpit
rim that you are using, without being baggy (which would
allow the annoying pooling of water).
Durability of the skirt is dependent on the strength and
abrasion resistance of the deck laminates and thickness and
density of the neoprene at the critical point where it wraps
around the cockpit rim. Generally, as laminates and coatings
become more abrasion resistant, they also become less
elastic and flexible. This diminished elasticity and
flexibility can make the skirt harder to put on and
compromise the mechanical and hydraulic seal.
The size, shape and placement of the barrel are also
critical to skirt performance. Barrel size (diameter)
affects the seal at your waist; the tighter and taller the
barrel, the better the seal. Just like dry suit gaskets,
neoprene skirt barrels can be trimmed down in height. But
the placement of the barrel in the skirt deck is critical;
it must mirror the placement of your seat with respect to
your cockpit rim. If the barrel is set too far back in the
sprayskirt deck in relation to your kayak's seat, then the
skirt will put disproportionate pressure on your abdomen and
try to pull you backwards off the seat. This can compromise
the hydraulic seal behind you, and, in a worst-case
scenario, cause the skirt to blow off at the back. A barrel
set too far forward in the skirt deck will result in the
reverse scenario.
What's Best For You
Each individual kayaker must decide what his or her
priorities are when purchasing a new sprayskirt. The
difficulty of the water you paddle, your ability level and
confidence, the likelihood that you will need to make an
emergency exit, your tolerance for leakage, your strength
and body habitus, and, of course, your ability to pay are
all important considerations. Compromises are inevitable. A
skirt that is easy to put on may tend to leak a bit or pop
in severe turbulence. A bombproof skirt that never leaks may
be a bit difficult to put off and on. If you plan to use the
same skirt on several different boat models, some compromise
in function must be expected. If you only paddle
occasionally, a cheaper skirt may be acceptable. But if you
are on the water a lot, a more expensive and durable skirt
might serve you better.
These days there are skirts on the market to fit virtually
every size, shape, and paddling style, of boat and paddler.
If you take the time to choose carefully, you should be able
to find that perfect sprayskirt to meet your particular
needs.
That's my story and I'm stickin' to it!
Editor's note: Mt Surf owner and designer John Mason has
spent thirty years paddling some of the world's wildest
rivers and creeks... field testing his spray skirt designs.
He has had his share of wet miserable days because of leaky
and blown skirts, but these days he almost always comes off
the river warm and dry! |
