【正文】 river or a canal then this decrease can be up to 60 6 The ship may start to vibrate suddenly This is because of the entrained water effects causing the natural hull frequency to bee resonant with another frequency associated with the vessel 7 Any rolling pitching and heaving motions will all be reduced as ship moves from deep water to shallow water conditions This is because of the cushioning effects produced by the narrow layer of water under the bottom shell of the vessel 8Turning circle diameter TCD increases TCD in shallow water could increase 100 9 Stopping distances and stopping times increase pared to when a vessel is in deep waters 10 Rudder is less effective when a ship is in shallow waters What are the factors governing ship squat The main factor is ship speed V Detailed analysis has shown that squat varies as speed to the power of 208 However squat can be said to vary approximately with the speed squared In other words we can take as an example that if we have the speed we quarter the squat Put another way if we double the speed we quadruple the squat In this context speed V is the ships speed relative to the water Effect of currenttide speed with or against the ship must therefore be taken into account Another important factor is the block coefficient CB Squat varies directly with CB Oil Tankers will therefore have paratively more squat than Passenger Liners Procedures for reducing ship squat 1 Reduce the mean draft of the vessel if possible by the discharge of water ballast This causes two reductions in one a At the lower draft the block coefficient CB will be slightly lower in value although with Passenger Liners it will not make for a significant reduction b At the lower draft for a similar water depth the HT will be higher in value It has been shown that higher HT values lead to smaller squat values 2 Move the vessel into deeper water depths For a similar mean ship draft HT will increase leading again to a decrease in ship squat 3 When in a river if possible avoid interaction effects from nearby moving ships or with adjacent riverbanks A greater width of water will lead to less ship squat unless the vessel is outside her width of influence 4 The quickest and most effective way to reduce squat is to reduce the speed of the ship False drafts If a moored ships drafts are read at a quayside when there is an ebb tide of say 4 kt then the draft readings will be false They will be incorrect because the ebb tide will have caused a mean bodily sinkage and trimming effects In many respects this is similar to the ship moving forward at a speed of 4 kt It is actually a case of the squatting of a static ship It will appear that the ship has more tonnes displacement than she actually has If a Marine Draft Survey is carried out at the next Port of Call with zero tide speed there will be a deficiency in the displacement constant Obviously larger ships such as Supertankers and Passenger Liners will have greater errors in displacement predictions Summary In conclusion it can be stated that if we can predict the imum ship squat for a given situation then the following advantages can be gained 1 The ship operator will know which speed to reduce to in order to ensure the safety of hisher vessel This could save the cost of a very large repair bill It has been reported in technical press that the repair bill for the QEII was 13 million plus an estimate for lost Passenger bookings of 50 million 2 The ship officers could load the ship up an extra few centimetres except of course where loadline limits would be exceeded If a 100 000 tonnes dwt Tanker is loaded by an extra 30 cm or an SD14 General Cargo ship is loaded by an extra 20 cm the effect is an extra 3 onto their dwt This gives these ships extra earning capacity 3 If the ship grounds due to excessive squatting in shallow water then apart from the large repair bill there is the time the ship is out of service Being out of service is indeed very costly because loss of earnings can be as high as ￡ 100 000 per day 4 When a vessel goes aground there is always a possibility of leakage of oil resulting in pensation claims for oil pollution and fees for cleanup operations following the incident These costs eventually may have to be paid for by the shipowner 備注Drass． ShipDesignandPerformanceforMastersandMates[M]． ButterworthHeinemann2020． 148179 大于 0700 那么最大下沉將出現(xiàn)在船首 如果小于 0700 那么最大下沉將出現(xiàn)在船尾 如果非常接近 0700 那么最大下沉將出現(xiàn)在船尾船中和船首這里的船舶坐底只考慮了船體下沉而沒有考慮船舶縱傾的影響 這必須是普遍的因為在過去的二十年幾個船型往往趨向于垂線間長變短和船寬 變大這導(dǎo)致了當(dāng)船舶存在橫搖時因坐底使得船中處擱淺 為什么船舶坐底現(xiàn)象近 40 年來變得這么嚴重 船舶坐底總是存在于較小和較慢的在航船舶這些下沉僅數(shù)厘米因此也就無關(guān)緊要了 然而從 60 年代中期到這個新千年船舶的規(guī)模穩(wěn)步增長直到我們擁有了350000 噸及以上載重噸的超級油輪這些超級油輪在其訪問的港口即使是在小靜態(tài)時平吃水 水深 除了船型的不斷發(fā)展船舶的速度也在不斷增長例如集裝箱船其速度已經(jīng)逐漸從注冊時的 16 節(jié)增至現(xiàn)在的 25 節(jié) 船舶設(shè)計在 20世紀 80年達和 90年代發(fā)生了巨大的變化油輪的設(shè)計我們擁有了 564739 載重噸的 Jahre Viking 號其垂線間長達到 440 米這相當(dāng)于五個足球場的長度 在 2020 年迄今為止最大的集裝箱船即香港快運投入使用載重噸 82800航速 253 節(jié)垂線間長 304 米船寬 428 米吃水 13 米 由于靜態(tài)時船底龍骨下富余水深的減少和船速的增加船舶坐底現(xiàn)象逐漸增多他們現(xiàn)在 間這當(dāng)然絕不是無關(guān)緊要的 運輸部 M 的通知 在英國過去 20年英國運輸部已發(fā)出的 M通知有關(guān)船舶坐底和船舶淺水航行時所有的影響問題這些警告所有和船員相關(guān)的危險 船舶進入淺水域?qū)⒂幸粋€或者多個以下現(xiàn)象 波浪的作用增加特別 是船首波 船舶操縱變得更加遲緩一個引航員的說法就像在粥里 在橋上的吃水指示或回聲測深儀的回波將最終確定吃水的變化 螺旋槳轉(zhuǎn)速指示器將明顯減少如果該船在開敞水域例如沒有寬度的限制這種減少將高達額定轉(zhuǎn)速的 15 而如果在受限航道這中轉(zhuǎn)速減少量將高達額定轉(zhuǎn)速的 20 同時也將有船速的下降如果在開敞水域船速下降高達 30 如果在受限航道船速下降則高達 60 船體開始突然震動這是因為夾帶的水造成的自然頻率和船舶相關(guān)的另一種頻率的共振效應(yīng) 任何的橫搖縱搖和首搖運動將會減輕從深水駛?cè)霚\水時這是因為船底的狹小空間起到了緩沖作用 回旋半 徑增