boats racing for the America’s Cup. This trend continues to this day and very often, we become involved in surveying and overseeing repairs and rebuilds of some famous racing yachts built during the twentieth century. Many of the composite boats we visit now have welded steel or aluminium frames and backbones which are planked in various ways. Perhaps the most common method of planking these hulls is by using several layers of planking with typically two layers fitted diagonally at 45 degrees to the vertical in opposite directions known as ‘double- diagonal’ and a third layer fitted horizontally to simulate traditional planking. All layers of planking are normally fitted close-seamed and bolted to the metal framework with the bolt heads then plugged.
The ocean racing yacht shown below was designed by Sparkman & Stephens and was one of several composite boats built by Lallows of Cowes to the same design known as the S&S 41s. The first and most well- known boat of this class was the yacht built for the late Edward Heath in 1970 named ‘Morning Cloud 2’ and now renamed ‘Opposition’. We surveyed her sister ship, which was built in 1972 and, in 2016, went on to oversee her two-year rebuild which included a new deck structure of mahogany beam-shelves, over forty laminated mahogany deck beams, new carlins, epoxied marine plywood sub-deck, new teak laid decks, hatches, cockpit coamings and a complete upgrading of all the yacht’s systems. The hull was constructed with a laminated
mahogany stem, keel and horn timber with welded aluminium ring-frames and an aluminium grid of frames and floors below the waterline welded to a deep aluminium ‘I’-beam girder thru- bolted to the timber keel structure. The ‘I’-beam also incorporates a mast-step to spread the loads from the 60-foot mast as well as being part of the main structure for attaching the external lead ballast- keel with ten one-inch stainless keel-bolts.
Secondary Ring-Frame Main Ring-Frame c/w Mast-Partners & Chain plates
Double-Diagonal This construction method has been around for many decades and can trace its origins back to the late nineteenth and early twentieth centuries with many well documented early examples still in existence today. Perhaps the very first vessels to be built this way were high performance motor boats that were being used during the period as chase-boats for the testing and development of seaplanes and flying-boats. Many high-speed tenders were also built for the many large Victorian racing yachts of the day including steam- yacht tenders for European Royalty. Before the First World War stopped the production of private vessels, water-speed records were also being set and the majority of these lightweight hulls were built using double-diagonal planking mounted on light timber frames.
The new deck beams being fitted into the new beam-shelf and showing the two
aluminium ring-frames.
< A view of the ‘I’-beam keel- girder with mast-step and recessed thru-fastened keel-bolts.
During the war years, production in most boatyards around the country was switched to producing fast patrol boats and air-sea rescue launches for the Royal Navy and Airforce. The construction method is relatively quick and produces a light and strong hull structure which is ideal for fast vessels. Often the high-speed planing hull is of hard-chine design with double- diagonal planking on the topsides and bottom of the vessel. In between the two layers of diagonal planking, a calico membrane soaked in linseed oil would have been attached to the first layer to ensure that the finished hull remained watertight.
The Report • December 2018 • Issue 86 | 59
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