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Sailing the SEDNA IV
Sailing the SEDNA IV
SEDNA IV is a motor/sailor, which means that it can be powered by its diesel engine, or its sails, or both at the same time (when winds are light). The sails are more effective, however, and let SEDNA reach higher speeds than its 500-horsepower diesel engine. This engine, manufactured by Deutz in Germany, drives the ship’s 4-blade, variable-pitch propeller. This propeller has a diameter of 1.60 metres and can take the 394-tonne SEDNA up to speeds of 8.5 knots while turning at 1400 rpm (revolutions per minute). In light winds, the sails let us run the engine at lower rpm and thereby reduce the vessel’s diesel consumption and operating costs without reducing its speed. In our voyage from the Magdalen Islands to Vancouver via the Northwest Passage, we travelled nearly 10 000 nautical miles and used our sails for half the trip. Two factors that limited the time that we could run under sail were the sailing conditions in the Arctic ice and the lack of wind in certain areas.
SEDNA is a schooner-rigged, three-masted vessel, with five Indo sails. From bow to stern, these are the genoa, the fore staysail, the foresail, the mainsail, and the spanker. All of these sails are made of a fabric that is highly resistant to wear and to ultraviolet radiation. This fabric has been chosen for strength rather than performance. Since SEDNA is not a racing vessel, there is no point in using high-end materials with lower endurance ratings. SEDNA deploys 700 square metres of sail, all operated by electrical winches and rollers. A crew member can raise or lower a sail with the touch of a finger on one of the five electronic controls. SEDNA has 15 winches in all: 5 for the rollers, 4 for the sheets, 4 for the travellers, and 2 for the genoa sheets. These winches are very powerful, and their force is multiplied by a gear box that lets us use them for other purposes, such as operating the loading arm to bring goods and equipment on board or to place Musculus (our 1.3-tonne, 225 HP rigid inflatable tender vessel) in the water.
Sailing a sailing vessel of this size is much like operating a smaller sailboat, and the same basic principles apply. You use all your sails, in all weather. As the wind freshens, you reduce your sail area to maintain a balance among all the sails. Remember, a sailboat operates on the same principle as an airplane, and a sail, or a set of sails, is like an airplane’s wing. If you reduce your sail area by lowering one sail completely, instead of each of them slightly, it’s as if you were cutting a hole in the wing of an aircraft instead of using its flaps. That said, SEDNA’s very high tonnage lets us keep 100% of our sail deployed even when the winds exceed 25 knots (60 km/h). Under such conditions, most other sailboats would already have reefed down their sail area by 30%. We adjust our sails as the wind speed or direction changes, as well as when we alter the vessel’s course.
Given SEDNA’s weight and long reaction time, any manoeuvres, such as tacking, must be made much more slowly. For example, we have to bring in the genoa sail every time we tack, because it is too large to pass easily in front of the lower stay and the fore staysail. Things can thus become complicated when, for example, we are sailing up a narrow body of water and have to tack tightly several times in succession. Worth noting: SEDNA can sail at an angle of 50 degrees into the wind (where 0 degrees is a direct headwind). In comparison, an America’s Cup racing vessel (the Formula 1 of sailing) can sail at 28 degrees into the wind, and a typical cruising sailboat at 40 degrees. With SEDNA, jibing is very tricky, especially in heavy weather. Jibing consists in tacking in such a way that the stern of the vessel passes through the eye of the wind. When we jibe in SEDNA, we have to reduce our sail area, or even completely furl certain sails, such as the foresail and mainsail. Because these last two sails are square, they catch more wind. Under the best conditions, SEDNA can reach speeds of up to 10 knots under sail alone.