ROYAL AUSTRALIAN AIR FORCE/PPL
ORC Worth some effort
2021 will hopefully see the return of the marquee offshore races, Fastnet, Transpac, Sydney Hobart, Chicago and Bayview Mackinac and so on. All these races have stringent safety requirements that are based on the World Sailing Offshore Special Regulations (OSR), with local adjustments such as the Safety Equipment Rules (SER) in the US. The regulations cover storm sails, crew safety and training, struc-
tural integrity and stability. Since the 1979 Fastnet race the regu- lations to ensure adequate capsize recovery have developed in scope and complexity; ISO has produced a worldwide standard for ‘Small craft – stability and buoyancy assessment and categorization’.* Although this runs to 90 pages the assessment of capsize vulner -
ability can be captured in a single data plot (Fig A). Plot the yacht’s overall length on the X-axis and its range of positive stability on the Y-axis and see where it falls relative to the known capsize casualties. The reality is that this simple plot is really all the data available to assess the offshore fleet’s vulnerability to capsize incidents. The grey triangles show individual boats for which there is reliable
data of LOA and range of positive stability, ie the heel angle at which the boat continues to capsize rather than come upright. For a self- righting boat the range of positive stability is 180°. The purple triangles are boats that suffered a knockdown incident but recovered to remain floating upright. The red circles show casualties where boats have capsized and in some cases lives lost. There is obviously a size effect in terms of a boat’s vulnerability
to a capsize. The casualties lie towards the left of the graph, and catastrophic incidents are more prevalent in boats with a low range of stability. This is to be expected – whether you’re sailing a 10m yacht or a 50m yacht the waves remain the same size. In a 10m yacht the chances of encountering a breaking wave whose height is similar to the boat’s beam are relatively high when sailing offshore, while for a 50m yacht you would be in ‘Perfect Storm’ territory to find a wave 10m high. This is at the heart of the matter: if you are caught beam on to a breaking wave that is as high as the yacht is wide you could
be rolled; after that happens the higher your range of stability the better your chances of coming back upright. Safety regulators have sought to strike boundaries through this
thankfully sparse data-set of incidents to establish ‘safe zones’ depending on the sailing area. The solid lines on the plot show the limits defined by the UK Government’s Maritime and Coastguard Agency (MCA) and the Offshore Special Regulations. The MCA ‘Code of Practice for the construction, machinery,
equipment, stability, operation and examination of sailing vessels up to 24 metres load line length, in commercial use and which do not carry cargo or more than 12 passengers’ sets stability require- ments for unrestricted and Category 1 operation that avoid the known casualties (in red). The OSR limits defer to the ISO standard which defines category
limits based on vessel weight. The limits plotted in the figure are based on an LOA calculated from the boat mass using a typical displacement/length ratio for the ORC fleet. This formulation implies that increasing mass reduces your vulnerability to capsize. But the experimental work carried out by the Wolfson Unit
(University of Southampton) after the 1979 Fastnet race did not find increasing mass much improved resistance to capsize in break- ing waves. This work is summarised in Adlard Coles’ Heavy Weather Sailing which is about to be published in its eighth edition. The ISO standard gives a less stringent limit than the MCA. This
might be expected because the MCA are looking after paying passengers, and ISO Category A is by no means the equivalent of the MCA unrestricted category. The ISO standard is a product safety standard for production yachts, in the same way that standards exist for road vehicles, washing machines and so on. The standard is set to balance safety against cost and complexity of manufacture. So compliance with ISO Category A does not guarantee your safety on a trans-ocean crossing. Product standards ensure you are tolerably safe on the motorway in a Honda Jazz but you’d be unwise to set off on the Paris-Dakar Rally without some safety upgrades. Any owner with an ORCi certificate can put his boat on this
The luckiest Imoca skipper in history? There were several candidates in the stormy 1996 Vendée Globe – when ‘angle of vanishing stability’ moved onto the front page. During the 1979 Fastnet race all of the many capsized yachts self-righted, though some later sank. In the 1990s there were too many cases of Open 60s that simply stayed upside down – even after the first canting keels had appeared in the class. This is Thierry Dubois, who after losing his liferaft tied himself to the rudder and clung onto his Nivelt design just long enough to be rescued. During the same huge storm Tony Bullimore would become trapped inside his inverted yacht and Groupe LG skipper Gerry Roufs would lose his life when his Finot-designed ‘aircraft carrier’ capsized and also stayed upside down; Roufs’ yacht was still inverted when spotted months later drifting towards Chile. It was also in this race that Raphael Dinelli had his miraculous escape when he was rescued by British skipper Pete Goss as his own rapidly sinking yacht slipped beneath the waves
40 SEAHORSE
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