A few weeks ago I fell out of a power chair descending a gangway to a fast ferry. Fortunately no harm was done, but such falls can have devastating consequences. Previously I’ve had problems around marinas and commercial ports where link-span or gangway gradients have been prohibitively steep for both manual and power wheelchairs, and observation suggests were difficult for people using other mobility aids like crutches too.
Ensuring equity of access for disabled people to on water activity or transport depends on good design on the architecture between the land and vessel, or floating structures like pontoons.
Link-spans connect land infrastructure at a fixed height to a floating structure which is in continual motion because of sea state, and variation in tide or river level. This motion of the floating structure results in variation in the link-span gradient. The steepness of the gradient between land and floating infrastructure depends on the pitch point, and the vertical distance between the floating pontoon and the land, which in many tidal regions is large. This results in link-span gradients which often exceed the recommended gradient in accessibility codes.
Better link-span design is possible
Two obvious changes to link-span design can reduce the gradient facing users of mobility equipment. The simplest is simply to increase the length of the span. This is unattractive because the link-span becomes unfeasibly long and expensive complicating integration into marina or port designs.
One simple solution does exist. That is to fit the pontoon with a fixed ramp, such that when the pontoon is at Mean Sea Level, the top of the fixed ramp is level with the quay. This reduces the maximum slope of the link-span by half, albeit at the cost of introducing an uphill gradient to the top of the fixed ramp at High Water. This design doesn’t of itself reduce the estate required for a longer ramp, but one further intervention can do so…
Reducing the space needed for more accessible link-spans
By orientating the link span parallel to the quayside, rather than perpendicular to it, and fitting the a rest area on the pontoon at the top of the fixed ramp, the total length of the link-span arrangement can be reduced by half, while retaining the advantage of reducing the maximum gradient users of mobility devices face. This arrangement has the added benefit of introducing a rest area at the top of the fixed ramp that permits mobility equipment users to rest.
Reducing link-span gradient improves experience for all water users…
Reducing the maximum gradient faced on a link-span benefits all water users. Whether they are pulling a shopping trolley, wheeled luggage, wheeling a buggy (stroller in US), or a heavy marina trolley filled with gas bottles or fragile electronics, this reduction in gradient positively increases safety and usability.
I’m indebted to a paper by Matthew East (2018) for some of the ideas in this post. His paper on improving the land – water interface for commuter ferry structures in in Australia is a helpful contribution. I have reservations about whether the design decisions described were genuinely influenced by the user groups consulted, or were a matter of engineering convenience.