When it comes to designing adjustments for shock-mitigating marine seats, there are plenty of factors to consider. Adjustments are popular because they help customize the ride experience, and this can be done in more than one way. Spring-rate, progressivity, and damping characteristics may all be tunable, but each requires a different adjustment mechanism, and not all mechanisms are suitable for use at sea.
This may best be illustrated with the example of a hand-powered air pump to adjust pressure in an airspring. While adjustable pressure is desirable, operating a pump in the dark or freezing cold while wearing gloves can be a tall order. It is time-consuming, and in critical deployments the pump may be abandoned, much to the risk of the seat’s occupant. An electric pump may be a viable alternative, though it introduces new complexity and expense.
Adjusting spring progressivity is a more subtle approach to improving the ride quality on a suspension seat. A spring’s progressivity determines how its force response changes with displacement. For a simple spring, the response is linear with restoring force proportional to displacement. For airsprings, a form of nonlinear spring, the force response is approximately hyperbolic, growing rapidly as the air chamber approaches full compression. By controlling this progressivity, the isolator stroke used during an impact can be altered, leading to better shock mitigation.
SHOXSPRO is an example of a spring-progressivity adjustment. With the flip of a lever, the system alters the exposed air volume of the suspension, reducing the rate of increase of force under compression. This is especially beneficial to light seat riders, as it enables them to travel further into the suspension for a given impact. In fact, a goal of the SHOXSPRO system is to unify performance across rider weights. The simple binary nature of the adjustment makes it quick and feasible irrespective of weather and lighting conditions. This ensures the adjustment will be employed, and it reduces the chances of operator error.