Arriving for the cut and add
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be added without making the vessel look like a flying pencil. Stability would always remain a significant factor in the working capability of the vessel. "First we had to estimate how much needed to be added to make the job economically feasible," said Richard. This turned out to be the equivalent of a full truck unit plus all the other equipment and gear a working marine farm vessel has to carry … something between 30 to 36 tonnes all up. The contract was let to AIMEX Service Group of Nelson, where both Ross Harvey and Steve Sullivan had previous experience in constructing large alloy aquaculture vessels and major projects. This was effectively going to be a "cut and grow" and could have been fraught with dangers for the unwary. After visiting the Morning Star in the water and talking
through the project with the owner, a comprehensive plan evolved to work with the designer and get plan approval to build the centre section on site while the vessel remained in work. The goal was to keep downtime to a minimum. Any
margin for error had to be allowed for because there would be no turning back, as the bits had to fit. The confidence for this was built into the sponsons and the project was given the go-ahead. In lengthening any vessel under survey it is necessary to go back to the original design and look at the scantlings to see if there is any reserve longitudinal strength in the existing vessel to ensure the bit being added in the centre can carry the bits at each end. This is because longitudinal strength is based on the L or scantling measurement and if this is increased, the strength of the entire vessel has to be increased, not just the extra bit in the middle. It quickly became obvious the Morning Star was originally designed to be a robust little workboat. Her
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PASSENGER & WORKBOATS
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www.mcbridedesign.co.nz VIP.WB12 NZ WORKBOAT REVIEW 2012 19
VIP.WB12
