NEW PROPULSION SYSTEM WAS A EUREKA MOMENT
F
ollowing on from the success of Abel Tasman Sea Shuttles' Crusader, the family behind the business has added another boat to its existing fleet.
The company originally ran monohulled jet boats powered
by diesel engines. While the concept was fine, it became obvious the diesels were working too hard and the coarse sand of Abel Tasman National Park's beaches was destroying the impellors at an alarming rate.
After some hard thinking it was decided catamarans were the way forward for a number of reasons, including their stability. The ability to have front-loading ramps allowed the propellers to be kept away from the beach.
Each time the Sea Shuttle team has built a boat for the company they find new and better ways of doing things. Their latest vessel, Ataz, is no exception.
The wave frequency in the park made a boat of at least 15m long the optimum length to operate. Adding the extra length provided a much easier ride for the passengers and made room for two Iveco NEF 450hp common rail diesels. This has made the Ataz extremely agile and fuel efficient.
Another reason for the extended length was to provide space for co-owner Paul "Smithy" Smith's beloved coffee machine! Well, it wasn't just installed for Smithy. Abel Tasman Sea Shuttle's customers like to enjoy the ride. With ramps, room to move, toilets, snacks and now the coffee machine, travellers can relax and take in the passing scenery.
The extended length clearly indicated a new propulsion system was required. In the past, the other co-owner, Keith Knapp, has put his thinking cap on and come up with some ingenious ways to get their vessels through the water, and more importantly, onto the shallow beaches of the park.
Anyone can drive a catamaran onto a beach, but the company wanted to protect the marine environment and the seabed. The damage done by larger vessels with fixed screws ran against their philosophy of being as environmentally friendly as possible. Tim Barnett of Barnett Offshore Design has designed all their boats with a shallow draft (The 23.9m Crusader draws just 700mm) and the propulsion system needed to be complimentary. It needed to pull Ataz economically and, arguably more importantly, land her with minimal damage to the seabed. The design draws just 450mm with a laden weight of nine tonnes. Keith's eureka moment came one night in his comfortable chair while he was staring at the television but not watching it! In his head he designed a system whereby the propellers
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January/February 2012 Professional Skipper 63
face forward and have unimpeded access to clear water. The propellers are driven from the motors via an enclosed Kevlar belt.
As the vessel nears the beach the skipper rotates the legs outward from the stern. This still gives the screws access to clear water and he can drive the boats forward or back with a minimum of effort.
Keith says his KNS propulsion system is revolutionary because unlike other sternlegs, this one doesn't have gears, it has the Kevlar belt, and legs that swivel to the outside, so the propellers are always in clear water.
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