The only specialised marine publication in Oceania that focuses on the maritime industry, from super yachts to small craft to large commercial ships, including coastal shipping, tugs, tow boats, barges, ferries, tourist, sport-fishing craft
Issue link: https://viewer.e-digitaleditions.com/i/119485
The davit and winch Launching and retrieving is a simple affair REMUS, and all the associated gear has to be carried, launched, and recoverable by davit. Then there is a raft of onboard electronic equipment to support both the REMUS and military hydrographic work. The project design was inspired by the Mac Attack operation out of Paihia and its Cougar Cat design with a proven record of daily trips out to the Hole in the Rock in most weather conditions. But the project was not just about the vessel: ���We also had to provide road trailers, ramps to load the vessel and trailer onto the aircraft, a cradle to secure the vessel to a ship, and a method of lifting the vessel on and off the ship,��� Alan said. The aircraft cargo space had plenty of length at 12m, so it was the overall towing length of vessel and trailer that dictated the length. However, the overall width was restricted to 2.7m and height on the trailer to 2.6m. It was apparent from that start that they would have to have a removable cabin top, so the original plan was to be able to lift it off and forward, so that it would sit on the forward deck while the vessel was in transit. However it was found that with the cabin top stowed forward, aircrew access through the vessel was restricted, so the removable cabin top is now stowed in front of the vessel on its own transport frame, secured to the cargo ramp of the aircraft while in transit. Another quirk created by the aircraft transport needs, was to create a bow door access to be used when in the aircraft, to enable the aircrew to do their rounds and safety checks in the cargo hold while in transit. At present there is only 20mm clearance either side and 30mm above the cargo access door at the stern ramp. In talking with Alan, he said the first iteration of the vessel was a monohull, however, it was difficult to get the stability required when using the small crane with a one metre reach, lifting 250kg over the side of the vessel. He also ran into issues with freeboard and overall height so they then decided to look at catamaran hull. The vessel is expected to be used at under six knots around 60 percent of the time, but it also needed to have a service speed of 24 knots and given the waterline length, the only option was a planning hull. ���Conventional symmetrical cat hulls proved to be too deep to keep within the height envelope so we opted to use the ���sea sled��� type hull. We had used this before in a water taxi, with the tunnel width dictated by the required hull volume,��� says Alan. At the first Preliminary Design Review both he and Terry presented their concept prompting many questions and suggestions, mainly 22 Professional Skipper March/April 2013 from the personnel who were to be the vessel���s operators, as they have particular ways they conduct their various operations. Overnight, Alan updated the design and they received the go-ahead to proceed to the Critical Design Review stage with their catamaran concept. With such a narrow beam-to-length ratio, weight, and more importantly balance, had to be calculated very accurately and every component, expected load and so forth had to be accounted for. To add to the debate Terry was not going to build an ugly boat! This was not a barge and It had to handle a reasonable sea state when in service. The problem was, the Navy kept adding weight, so to ensure that the hulls would be able carry the loads, the traditional tunnel between the hulls has ended up more like a slot. It took almost 12 months to get to final design approval, and there was still plan approval, and additional stress and fatigue analysis on the lifting lugs in the vessel and the lifting arrangement, to be conducted. The vessel also had to have tiedown lugs to secure it to the trailer fore and aft, and from a central point in the tunnel, through the trailer to the cargo load point on the aircraft. All tie down points had to withstand 3G in any direction so further analysis was required in order to be certain that they had achieved the required specifications. ���Due to the length of the design and acceptance process we were now beginning to find that a number of items that had been specified were no longer available, or the models had been superseded,��� said Terry. Equipment space was also limited and due to additional items having been requested after the design was complete, minor changes were required to relocate equipment. However, with lateral thinking by the build team they managed to achieve a vessel package that exceeded the required specifications and, the Navy���s expectations. After such an interesting start, we took the opportunity to seatrial the first vessel, under civilian protocol flying the red duster. SEA TRIALS The second vessel was still in mid-construction in the workshop giving us a chance to check out the internal workmanship. Having the build split in a follow-on situation was good given the unknown nature of these vessels. By sea-trialling the first, a number of key modifications became apparent that could be corrected in the second vessel during the build, meaning that only minor retro-changes were required on the first vessel.