On Wednesday 25 May, a group of nearly 30 IIMS members met at the impressive Royal National Lifeboat Institution (RNLI) headquarters and training facility at Poole in Dorset, UK. Their mission? Firstly to have a close look first hand at the RNLI All-weather Lifeboat Centre and the various workshops to see and understand the activities going on. Then after lunch, the group combined with the surveyors at their conference for an invaluable afternoon of training and knowledge sharing.
At some time in his career the Diagnostic Engineer may well have to examine the running of a compression ignition engine. Many of the defects that occur on such units are down to wear in the main bearings causing the crankshaft to change its longitudinal straightness. Usually the first diagnostic test on such an engine is to take a series of measurements between the crank webs at various points round the circle of rotation called somewhat in correctly crankshaft deflections. If a driving engine is of the compression ignition type with a cylinder bore above about 250 mm (10 inches), it is also necessary to consider the alignment of its crankshaft. Below that size, the overall stiffness and small size of the unit and the fact that the crankshaft itself is an integral forging make the measurement of crankshaft deflections both extremely difficult and unnecessary.
We were lucky when we were struck by lightning on our small 35’ GRP cruising sailing boat in Turkey in 2013, but without an LPS. All the plastic and some of the metal gear at the top of the mast exploded (see photo below) and simultaneously the headlining in the saloon exploded downwards with a loud bang. So much smoke that we initially thought we were on fire; but my wife and I survived unscathed to tell the tale.
The most likely discharge exit was through the propeller shaft, but practically all electronics were violently destroyed and, as an electrical and electronic engineer, my assessment for our insurance claim afterwards showed that most devices had experienced severe arcing with small electronic components having exploded internally (see photo below).
Continue reading “An approach to a modern sailboat lightning protection system”
Feature article written by Eur. Ing. Jeffrey Casciani-Wood HonFIIMS
As the propeller turns it absorbs the torque developed by the engine at given revolutions i.e., the delivered horsepower – and converts that to the thrust which, in turn, pushes the vessel through the water. According to Bernoulli’s law the passage of a hydrofoil (propeller blade section) through the water causes a positive pressure on the face of the blade and a negative pressure on its back. It is the resolution of the pressures that results in the torque requirement and the thrust development of the propeller. The negative pressure causes any gas in solution in the water to evolve into bubbles similar to those found when opening a bottle of lemonade or champagne. These bubbles collapse and can cause hammer like impact loads on the blades often in excess of 7 kg/cm2. It is the collapse of these bubbles that results in the observed damage to the propeller blade surfaces.
The ratio of the absorbed power or the delivered thrust to the total blade area of the propeller is called, respectively, the power and the thrust loading. If either of these exceeds a certain value which depends upon a complex relationship between the propeller type, the flow in which it works and its mean depth below the water relative to its diameter then the flow pattern of the water over the propeller blades breaks down causing a severe loss of thrust and, eventually, physical damage to the surface of the propeller blades and, also, the rudder and local steelwork of the vessel’s hull. That flow breakdown is called cavitation and is strictly analogous to the water hammer often heard in old plumbing systems. Cavitation is a highly complex phenomenon and the pitting damage it causes usually – but not necessarily – appears on the back of the blade following a clear radial pattern. It can also appear as similar damage on the driving face of the propeller in which case, almost certainly, a further factor has entered the problem in the form of an incorrect pitch distribution along the length of the blade. Most small craft propellers are usually of constant pitch over the blade length and that regime is accurate enough for 99% of boats but on high speed boats with large propeller loading factors the pitch should vary over the length of the blade i.e., the boat should be fitted with a varying pitch propeller. The effects of cavitation including loss of speed and damage to the propeller blades can be minimised by ensuring that the propeller has sufficient blade area relative to the area of the circle described by the propeller blade tips.
Nick Wilcox, Senior Associate and Albert Levy, Partner, both of Ince & Co LLP, Partner, debate the vagaries and confusion surrounding one aspect of the MLC 2006.
The Maritime Labour Convention 2006 (MLC 2006) has been in force internationally since August 2013 and, in that time, it has become clear that it has received widespread ratification, that enforcement is a reality, and that ships run the risk of detention if they are not compliant. However, there has also been a good deal of confusion over the question of “who is the ‘shipowner’?” under the MLC. The answer to the question is important, since it is that person who has the principal burden of ensuring MLC 2006 compliance.
In the Maritime Labour Convention, the “shipowner” is defined to mean the owner of the ship or another organisation or person who has assumed responsibility for the operation of the ship from the owner and who in doing so has agreed to take over the duties and responsibilities imposed on shipowners under the MLC 2006. This is the case even if another organisation carries out some of the duties of “shipowner” on its behalf. Therefore, the owner and the “shipowner” may well be different persons or organisations. Note that “shipowner” does not necessarily mean the owner of the ship in the proprietary sense.
Readers could easily be forgiven for being confused by the terminology. Lewis Carroll put it well in Through the Looking Glass: “When I use a word,’ Humpty Dumpty said in rather a scornful tone, ‘it means just what I choose it to mean – neither more nor less.’ Are you a “shipowner” under your charter party? ‘The question is,’ said Alice, ‘whether you can make words mean so many things.’ ‘The question is,’ said Humpty Dumpty, ‘which is to be master – that’s all.” Continue reading “MLC 2006: Are you a “shipowner” under your charterparty?”
The IIMS UK Small Craft Working Group (SCWG) met for one of its regular meetings in early May at Grafham Water Sailing Club near Huntingdon.
The theme of the day was Metals in the Marine Environment. Although attendance was smaller than normal, those who did come to the meeting found the day both absorbing and highly informative too.
Three speakers spoke in detail and at length about their specialist subjects.
Carol Powell has been a consultant metallurgist to the Copper Development Association and Nickel Institute in the UK for over 20 years with particular specialisation in marine applications for copper-nickels, stainless steels and high nickel alloys. Furthermore, she has been a member of the Marine Corrosion Forum and Copper-Nickel Task Force since their inception and is currently deputy chair of the European Federation of Corrosion Marine Working Party.
Continue reading “Small Craft Working Group meets at Grafham Water”
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