The proportions of the human body are the basis of all design. Cockpit seating, as with any seat or chair design, is one of the most complicated problems facing the designer. Niels Diffrient, an industrial designer and one of the world’s leading authorities on aircraft seating, says that, “Chair design is the acid test for designers”. If you’re a typical sailor, it has been estimated that you spend most of your valuable and limited time on the water in the cockpit.
Cockpit seating and layouts on sailboats need not only accommodate a wide range of body types, but also conflicting task requirements including steering, sail trimming, navigating, sitting while eating, lounging while socializing or reading and perhaps sleeping both at anchor and heeled 20° to 30°.
The amount of clothing worn also can have a considerable impact on seat function and comfort. Non-skid can be quite uncomfortable while wearing bathing suits or other thin clothing. Likewise, in cold conditions multiple bulky layers of clothing can substantially change your body’s proportions, requiring different seat dimensions. Seats may also have to function with and without cockpit cushions, which will additionally alter their dimensions and comfort.
Aesthetic considerations must be considered, too. Unfortunately, this often means that coaming/seatback heights are lower than ideal. Given the many variables, tasks and body types to take into consideration, one begins to understand the true complexity of this design problem.
Assessing a comfortable seat is a more complex problem than it may seem. Rarely is a seat that seems comfortable initially, ideal in its support for long-term comfort. It’s no accident that the best of today’s firm and contoured office chairs, including those from Herman Miller and the late Sunar Hauserman that are designed for eight hours of continuous use, have very little in common with the often poorly designed soft couches and chairs commonly found in the home.
Because sailboats are constantly in motion, round corners are the first step toward a well-designed cockpit. Round corners are easier on the body, inherently stronger and are more durable over time.
All vessels “work” or flex in a seaway to a certain extent. These stresses become concentrated in sharp corners into what is known as the “hinge effect.” Although it is rare, if a vessel sees enough stress cycles, sharp corners can weaken and potentially fail. Round corners are also easier than sharp corners to build in fiberglass. So why are sharp corners seen so often? Usually it’s a matter of the designer wanting a crisp look or style; it’s also somewhat easier to produce tooling with sharp corners although the gain is more than offset by the difficulty later of laying-up the fiberglass cloth into these corners on the mold without creating voids.
Cockpit seats should be 6′ 2″ to 6′ 6″ long to allow three people to sit side by side, or one person to sleep in relative comfort.
The cockpit seat faces (or footwell area) should not be much more than about 28″ to 30″ apart or you may not be able to brace your feet when heeled. The minimum footwell width is 24″. Footwells less than 27″ wide, however, do not allow people to comfortably sit directly opposing each other. Cockpits with permanently mounted cockpit tables can be wider as the table structure provides foot bracing. The seating area forward of the table, adjacent to the companionway, is often a problem as neither the table nor the opposite seat provides a foot brace.
According to Niels Diffrient, seat lengths less than 13″ do not give adequate seat support under the thighs, the load on other tissues is consequently increased and the resulting discomfort is reflected in shorter sitting times. Seat lengths greater than 16″, however, do not accommodate the small person as the front edge of the seat comes in contact with the back of the leg, forcing him or her to sit toward the front or to slide forward away from the backrest support, resulting in poor posture. Diffrient’s research points out that if the seat comes too far forward it will put pressure on the bottom of your thigh at the point where there is a nerve that crosses under the thigh over a bundle of muscles. Pressure on this nerve over a period of time can cause your foot and leg to go to sleep. For long-term comfort there should be a gap of about 2″ between the seat edge and the back of your lower leg.
The front of a seat should be rounded with a minimum radii of 1″ to 2″ to further reduce tissue pressure. In a well-designed seat the sitter should not be aware of the front edge of the seat. The rounded seat edge is also easier on the feet when the leeward seat is used as a foot brace while going upwind.
A fixed seat height of 17″ accommodates the largest number of adults, while seats lower than 15″ are hard to get up from. Seat flat angles from about 1-1/2° to perhaps 8° would be appropriate for cockpit seating.
An angle of about 3° is desirable from the front edge of the seat down to foot level, as an assist in rising. This feature, unfortunately, is not seen very often in fiberglass boats as it requires a more complex and therefore costly two-part mold.
Correctly contoured seats and seatbacks (on which much study has been done, and an abundance of information is available) are the ideal in terms of long-term sitting comfort. Seat flats with as little as 1/2″ curve toward the rear of the seat can substantially increase long-term sitting comfort and security while still allowing the seat to be walked on and slept on.
A backrest that does not maintain the natural curvature of the hollow of the back (the lumbar region) may induce backaches. Backrests under 15″ high are too short for relaxation comfort. Backrest-to-seat angles of 95° to 120° are recommended.
Because cockpit seating is not as task specific as chair design, the above dimensions derived from Diffrient’s research are, we believe, somewhat on the small size.
Diffrient’s own research backs up our intuitions.
Anthropometry is the measure of humans. Anthropometric data is largely gathered by governments for military purposes and clothing sizing. This data has, we think, some rather surprising findings. We all are aware that the average person’s height in the US is increasing, but you may not realize that people on the West Coast average an inch taller than people in the east! or that offspring of wealthy families are taller than average by more than an inch. This leaves designers in something of a quandry, trying to figure just who they are designing for. Certainly, tall people have a poorer selection when it comes to choosing a boat with adequate headroom, leg room and berth lengths.
We believe seats should be about 17″ or 18″ from the sole and about 17″ to 20″ wide. The wider seat dimension would accommodate backrest cushions and sleeping. If this data seems politically incorrect somehow, it must be kept in mind that by accommodating the average size adult as opposed to the average size “sailor” you are still comfortably fitting only 50% to 60% of today’s overall adult population.
Seat cushions are largely a matter of preference, the potential for added comfort must be weighed against their effect on seat geometry and difficulty in stowage when not in use. They may also require fiddles to keep them in place, making sitting uncomfortable when the cushions are not in use.
Perhaps the best argument for the use of cushions is shock and vibration. When you initially sit down, or as the boat falls off a wave, the shock compresses the discs in your back, leading to strain in your lower back.
Long periods of time are also often spent motoring or with a generator operating; vibration-sensitive people can become ill as a result of vibration.
For maximum long-term comfort, seat cushions need not be more than about 2″ thick. Construction should be comprised of 1-1/2″ medium foam padding glued on top of 1/2″ firm, closed-cell foam. Seat covering material should not be coarse or slippery, but should breathe, resist mildew and have UV protection. Marine acrylics do a good job.
As for color, a non-reflective light gray is the best choice for cushion coverings, for the same reasons light gray non-skid is popular (i.e., it has low reflectance, stays relatively cool and is psychologically neutral). If you find gray too boring, a neutral green or blue green is also a good choice. Green, not only low in reflectance, has been found to have a calming psychological effect and isn’t that why many of us go sailing in the first place?