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Ship water drift5/18/2023 ![]() If the wind is on the port beam, there is every likelihood that the transverse thrust and effect of wind will combine and indeed take the stern smartly into the wind. The other complicating factor is transverse thrust. This, in turn, tends to reduce the magnitude of the turning lever WP. This situation is not helped by the center of effort (W) moving aft as the wind comes round onto the quarter. In such cases, the stern may only partially seek the wind, with the ship making sternway 'flopped' across the wind. Some caution is necessary, however, as the turning lever can be quite small and the effect disappointing, particularly on even keel. This will now cause the stern to swing into the wind. ![]() Assuming that the centre of effort (W) remains in the same position, with the wind still on the beam, the shift of pivot point (P) has now created a totally different turning lever (WP). In part this is due to the additional complication of transverse thrust when associated with single screw ships.įigure 3, we have already seen that with sternway the pivot point moves aft to a position approximately 1/4 L from the stern. The effect of the wind on a ship making sternway is generally more complex and less predictable. ![]() Even at very low speeds the ship is stable and will wish to stay with the wind ahead until stopped. When approaching a berth or a buoy with the wind dead ahead and the ship on an even keel such an approach should be easily controlled. When approaching a berth with the wind upon or abaft the beam that as speed is reduced the effect of the wind gets progressively greater and requires considerable corrective action. Although it will vary slightly from ship to ship, generally speaking, most will lay stopped with the wind just forward or just abaft the beam.Īt lower speeds the pivot point shifts even further forward, thereby improving the wind's turning lever and effect. The center of effort of the wind (W) and the pivot point (P) are thus quite close together and therefore do not create a turning influence upon the ship. With the ship initially stopped in the water this was seen to be close to amidships. This now needs to be compared with the underwater profile of the ship and the position of the pivot point (P). The center of effort of the wind (W) is thus acting upon the combination of these two areas and is much further forward than is sometimes expected. On a VLCC this could be an area as long as 280 x 10 meters. Whilst the large area of superstructure and funnel offer a considerable cross-section to the wind, it is also necessary to take into account the area of freeboard from forward of the bridge to the bow. It has the familiar all aft accommodation and we will assume, at this stage, that the wind is roughly on the beam. Looking at figure 1 we have a ship on even keel, stopped dead in the water. Needless to say, with no tug assistance, it is wise to get this area of ship handling right first time and also appreciate what the limits are. With or without tugs, if the problem has not been thought out in advance, or if it is not understood how the ship will behave in the wind, the operation can get out of control extremely quickly. All too often when slowing down after a river passage, whilst entering locks and during berthing, it can create a major difficulty. The ship handler faces many problems but there is none more frequently experienced and less understood than the effect of wind.
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