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BUYER BEWARE BY KEITH INGRAM I n New Zealand as a result of An accident the harder economic times we waiting to are seeing a growing number happen of new imported boats landing on our shores, along with an ever increasing number quietly entering our commercial industry and being approved by Maritime New Zealand as meeting our Safe Ship Managements standards for commercial craft. However, many of these imported components do not meet our previous known standards that we have been working to for the past 50 years under the old Marine Department surveys, M&I, SSM, Lloyds, ABS and so on. 'O' Ring or Circlip Groove For example, we have always been weakens the shaft required to have our marine shafts machined and supplied with shaft half couplings that are tapered and keyed with a retaining nut locked tight in the centre. This system is designed and recognised in marine applications as being acceptable for "axial" thrust loads, same as propeller end system, ahead and reverse also rotational. We are now seeing an increase of Grooved shafts on a surveyed "not fit for purpose" split couplings vessel is a no-no entering the market based solely on low cost and are concerned that well commercial or the leisure marine market. known and approved safety standards are being compromised, How can our marine industry and the regulator simply ignore which places vessels and people at risk. the changes that come with some offshore imported vessels that Unfortunately many imported parallel split couplings have are built outside both Maritime New Zealand and Australia's past zero allowance for axial thrust – ahead and reverse. This system minimum standards? is designed for industrial rotational loads. When the system fails MNZ have responded in answer to our question and say that in a boat, which we are increasingly seeing, the shaft will exit the current maritime rules are not prescriptive when it comes to hull allowing significant amounts of water into the vessel. Power propeller couplings. However, surveyors are expected to use to the drive train is also lost along with steerage. their professional judgement and use appropriate standards that In some cases general engineers try to improve the system by are within the rules. The old MOT Red Book is still used as a applying a grub screw, which apart from not being fool proof standard for shafts and couplings and this does not have mention also compromises the integrity of the shaft diameter. of split couplings. On another matter, as an example of shaft systems not Another standard allowed within the maritime rules is the being fit for purpose, there is a growing practice by overseas Australian USL code, soon to be replaced by the National manufacturers to groove rudder shafts. This allows them to be Standard for Commercial Vessels, both these allow split flange fitted with a cir-clip to hold the shaft in the vertical position in couplings but have arrangements for the fitting of a minimum of an attempt to prevent the spade type rudder sliding up or down, two cotter bolts per shaft let into the shaft between 0.25 times and or an "O" ring to seal water entry. These grooves not only and 0.5 times their diameter to take the astern thrust, reference lessen the diameter of the shaft, but also offer a focus point for NSCV Section 5 subsection 5A 3.12.5.1. weakness and fractures. The attached image of rudder failure was "From your photographs, the coupling shown would not be non-impact, the insurers declined the claim based on marginal acceptable as it does not meet any of the prescribed standards. design. When our professionals did their own calculations they Talking with a number of senior surveyors, the type of coupling agreed the rudder design/stock and material used was well shown has been found on a small number of yachts, but as yet in outside our New Zealand marine industry standards. their experience none have seen this on any other vessel," says As with the shaft coupling scenario this is becoming more Ken Wyatt, senior technical advisor (ship surveying) at MNZ. common on both imported yachts and power boats entering Presently MNZ are developing instructions and guidance for service and SSM in New Zealand. Which begs the question, surveyors, and it is intended to include this type of coupling why is Maritime New Zealand and our surveyors allowing such into the guidance notes. standards to creep into our safety standards, be they destined for May/June 2013 Professional Skipper 59