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Validation_Box: third
From: Laughingcruiser
Date: 11 Feb 2008
Time: 22:00:33 -0500
Remote Name: 124.183.89.182
Tom, here are some additional views on twin keels from French designer Marc Lombard. Marc Lombard, architect of the RM boats, offers us his opinion : The twin-keeled RMs perform particularly well close-hauled, as they are a good solution for a broad or ‘planing’ bottom profile. When the boat heels, the submerged part of the hull moves downwind and the root of the keel tends to find itself close to the waterline, seriously impairing its effectiveness. So there are two solutions: - either you increase the draught substantially, so as to maintain an efficient plane acting against leeway. - or else you move the leeward fin, positioning it vertically at an average heel angle (around 15°), at the lowest point of the heeled bottom, to create a good plane against leeway while maintaining moderate draught. In addition, the leeward keel is positioned with a slight inward angle, which limits the leeway angle. This is the RM solution ! The second, ‘up-wind’ keel serves only to provide righting moment, and its inward angling (now in the reverse sense) increases the keel’s righting moment still further. This makes the boat very stiff. The additional advantage (over and above superior close-hauled performance compared to a single-keel solution of equivalent draught) is to allow beaching or long-term storage without using a cradle or legs. Many boat-owners – including myself – make use of this feature to leave the boat stored out of the water between trips, quite safely and of course more cheaply. In conclusion, as far as performance is concerned, the RMs’ broad, twin-keel bottom profile is an excellent solution to combat leeway when close-hauled and achieve good stiffness – two indispensable ingredients for a high-performance boat. What’s more, the use of a ‘broad’ bottom profile allows great off-wind performance (planing) and above all impressive course holding, a fundamental element for a boat that ‘really goes to sea’.