THE FLOATING DOCK

Conceptually, the Floating Dock’s fairly simple. Twin, 13.7m long longitudinal cylinders support a grated raft floor 9m wide. Six, 3.4m high vertical cylinders are mounted on the longitudinal cylinders to give three compartments each side.

Similar to a submarine’s pressure hull, each compartment has large holes in its bottom, and there are intake and outlet air pipes in the top of each vertical cylinder. To sink the dock, the air is bled from the top of each cylinder, which then allows water to enter into the lower compartment to flood the raft floor.

To use the dock, it’s flooded deep enough in the water to suit the boat’s draft. The boat enters the dock and is held centrally by hydraulic arms either side. Compressed air is fed into the top of each cylinder forcing water out of the bottom of the six compartments until the buoyancy counters the boat’s weight and the grated floor reaches the surface. It has a maximum 20-ton payload.

Each cylinder is individually controlled, so the raft floor can be levelled sideways, as well as fore and aft. Fore and aft tilt is set to suit each boat. For example, launches are generally raised slightly bow high to ensure their exhaust pipe(s) drain aft. As boats sit on their keels, there’s no stress from travel lift strops, ideal for classic keelers, nor is there the risk of damaging speed and depth transducers. The lifting process takes three to five minutes. When water-blasting the bottom, a tank down the middle of the raft floor collects the water, which is then fed through a sand filter to strain the contaminants. The clean water is then pumped into the Auckland City Stormwater system. Periodically, the sand filter is raked over and the heavy paint particles bagged and disposed of.

As well as water-blasting boat bottoms, The Floating Dock is regularly used for surveys, anode replacements, propeller servicing and overnight/weekend antifouling applications.