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| | Relationship Counselling 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 deckstrap. 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 drysuit 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!
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