PassaCrane - A Creative Design Solution to a Complex Problem

This story began almost nine years ago when I first met our client through the architectural firm Barefoot Design, located in St. John, United States Virgin Islands.? As Nautical Structures’ Vice President of sales and Director of special projects at the time I was presented with a unique request; could we develop a gangway that could be land-based and deploy as a residential dock??The client built a beautiful estate on the north shore of the island of St. John, part of a picturesque bay with visuals of Tortola BVI just to the north.?The client is also an avid boater and wanted the benefit of bringing his boat to the dock behind his estate.?Only one little problem to be overcome; the property ends at the waterline and everything beyond is part of the US Virgin Islands National Park.?Building a typical dock was not an option as driving the pilings needed to construct a dock in the State Park waters is strictly prohibited. For the following seven years various ideas were exchanged while the client and the architectural firm worked through the red tape processes of obtaining the required building permits needed to construct the foundations for the specialized equipment we proposed to manufacture.

I was notified in August 2010 that the permit applications had been approved and we were going forward with the project.?This required a deep-dive into the needs and expectations of our client.?The machine we would build him was to be a uniquely custom boarding/docking system.?Eventually the addition of a hoisting crane element was brought into the specification.?The client desired to hoist one of his boats from the water to set ashore on custom cradles for storage.?We decided to describe this equipment as a hybrid passerelle – a PassaCrane.?

Multiple design challenges needed to be overcome prior to the start of construction.?First and foremost was the long-term storge location of the equipment; built into exterior landscaping, exposed to the sea.?The PassaCrane needed a significant foundation to safely mount the equipment, requiring excavation of the jobsite, a deep formed concrete pour with a custom stainless steel bolt-cage.??Infrastructure for hydraulic, electrical and freshwater supply needed to be created and integrated into the foundation and storage structure.?To combat the elements and ensure decades of useful service the structure was fabricated from a combination of aluminum and stainless steel alloys.?A specialized freshwater washdown system is built into the storage locker and automatically rinses the equipment every time it is stowed or deployed.?All the dissimilar metals are isolated with composite bushings and bearings.?All metal surfaces were treated, primed, fared and painted with a marine urethane paint system, identical to the paint materials used in finishing large luxury yachts.?

With the basic marinization design elements in place, the technical elements of the PassaCrane system itself needed detailed engineering analysis and design.?FEA (Finite Element Analysis) was utilized to identify the high load stress points in the design, as well as to engineer out unnecessary structural weight.?An over-all deployed length of 11.6m/38.0-ft was ultimately agreed to with the client, with the crane element positioned in the structure to provide a working radius of 10.75m/35.3-ft.?The crane’s SWL capacity at full-reach is 2,268-kg/5,000-lbs. ??Specialized brakes help control the rotational slew of the equipment and “lock” the dock into position when deployed as the property’s boat dock. ?The PassaCrane has a long-tapered design to reduce weight and enhance both its visual aesthetic and its load capacity.?The client wanted the PassaCrane to function as part of a lower patio that is integrated into the estate’s stone landscaping, so an additional structure of 3.6m/12.0-ft diameter was designed and integrated into the design and will rotate with the PassaCrane while in operation.?

Final finishing details we decided after many sketches and concept drawings.?The walking surface was agreed to be decking milled from a Brazilian natural hardwood and installed on the jobsite.?At the time of this article the decking material was still in-transit from Brazil and not yet installed.? Integrated LED lighting features illuminate the walking surfaces and areas directly below the walkway for both the visual aesthetic as well as safety.? Specialized handrails fabricated from 316L stainless steel, designed to fold-flat for storage are built into the dock-sections of the PassaCrane.?At one point in the design discussion the installation of a Tiki Hut on the patio section was considered, and later discarded due to wind-load concerns.?The PassaCrane as-built can elevate and depress +20°/- 15° to accommodate varied tidal heights and gunwale heights of the various boats that may decide to dock at the property.?If a boat were to come in to the dock too fast and strike the structure, relief valves in the hydraulic locking system will open and allow the dock structure to move with the boat and not cause structural damage to the foundation, equipment or boat.?

The installation and commissioning of the PassaCrane was conducted in early January, requiring just two weeks on-site to install and commission.?Our client and his staff were on-site for the commissioning and initial start-up of the equipment.?The established design parameters were all met, with the PassaCrane essentially hiding in plain sight built into the stonework.?When stowed the neighbors can’t see the structure, and when deployed the National Park Service is happy that there is no environmental impact to the site where the boats will dock.?This project certainly was A Creative Design Solution to a Complex Problem.

Rick Thomas is the founder of Nautical Structures and co-developer of this specialized PassaCrane project.?Rick is currently the President of JMS Yachting USA, an independent yacht management company, and operates “Rick Thomas Yachting Development” a business that brings multiple industry professionals together in collaboration for mutual benefit.