One of the challenges which the Crewtender looked to overcome was the apparent fragility of the tubes traditionally built for this sort of vessel. Gerrit van de Burg of the KRVE points out that each tender makes something in the region of 100 controlled collisions per day as it delivers or collects pilots and other crew members.

The tube therefore has to act as a shock absorber/fender, and resist collisions with sharp objects such as broken ladders, or steel bolts or pieces of reinforced concrete, as well as acting as a buoyancy aid to ensure that the vessel remains afloat even if completely full of water.

Poly-Marine in Maassluis, a company specialising in solving these sorts of problems, developed a special tube for the boat. Drawing upon their offshore experience, Poly-Marine has produced a tube with a hard exterior but filled with foam. This formula appears to work, as tests have included driving a fork lift truck hard into the tube without affecting its functionality in any way. Any boat using these tubes can thus be pushed bow first or alongside against another surface without serious damage.

More info:

Poly-Marine Service B.V.