防泥沙型船開發迫在眉睫

大連遠洋運輸有限公司 李玉平

防泥沙型船開發迫在眉睫

大連遠洋運輸有限公司 李玉平

我國港口水域有一個顯著特點，那就是多泥沙，這給船舶安全帶來了巨大隱患。以油運主角VLCC為例，它們在卸下原油的同時，大量含泥沙的海水也被注入了船艙。這些泥沙天長日久就會將船舶縱骨掩埋。由此，船舶風險將不可控制。那么，如何破解這一困擾中國船東的難題呢？

結構強度遭遇泥沙“劫”

長江、珠江都是多泥沙河，船舶在泊靠上海、寧波-舟山等長江沿岸港口及珠江水域港口時，我們常常會發現這樣一種現象：船舶在卸下貨物的同時，成千上萬噸混濁的壓載水也被灌注到船舶底層壓載艙內。由于含沙量大，這些壓載水在船舶每個航次都要積淀下幾十甚至上百噸的淤泥。這些淤泥有的伴隨到船舶拆解才得以見到光亮。據史料記載，曾有一艘早期的8.7萬載重噸散裝船，拆解時從雙層底艙中挖出4700噸淤泥。而導致該船拆解的最直接原因，是船中拱起異常，船底中部縱骨60%斷裂，特別是已斷裂的縱骨基本被淤泥掩埋。因為船舶強度構件已被淤泥掩埋，令船級社無法做出評估。船底堆滿淤泥，配載數據顯示的剪力和彎矩就會失真。所以，眾多的船舶損毀事故，有依據證明是由泥沙所致。

泥沙之禍，讓船東苦不堪言。特別是作為石油進口大國，油運主角VLCC的命運特別值得關注。不久的將來，我國原油進口將達4億噸，而其中2億噸要用100艘VLCC送到寧波—舟山港口，卸下后經由輸油管道送往上海、南京、武漢等地煉制。這些VLCC在卸下原油的同時，每船至少要把當地含有約1.5%泥沙的7到10萬噸海水注入船艙。如果不及時將泥沙處理掉，一條新船在經歷大約30個月的運營后，泥沙就會全面封住船底縱骨和橫肋板的流水孔，日久必然將縱骨掩埋。之后，在雙層底艙內形成寬60米、長約250米、高0.8米的厚厚堆積層。約12000噸的淤泥被大艙拖來拖去，無法檢查到船舶的腐蝕、皺折、屈曲、斷裂等情況。由此引發的油耗、航速、載貨、吃水、操船等風險都會不可控制。造成上述問題的最根本原因，就是現有船型不適合我國港口和水域情況。

對此，船東也想出了一些應對之策，如盡可能尋找時機將中國港口的壓載水在合適海域海況早些置換掉；在船舶滿載而且有涌浪時，用壓、排少量海水進艙晃蕩；修船時盡量掏挖。最常用的辦法是在滿載時可以進人下到壓載艙并用高壓海水沖洗，但這項額外維修保養工程做起來艱苦異常，而且都非長久之計。

如 果 說30年前買歐洲和日本的二手船，中國船東無法改變既定船型，20年前我們也無造船和設計能力，那么近10年來，中國造船業已飛速發展，在船型設計上我們理應有所作為，針對中國港口和水域泥沙多的實際情況，設計出適合中國港口和水域的“防泥沙型船”。

壓載水處理再添難題

中國船東面臨的問題不止是防泥沙，還有一個大的難題是壓載水處理。

我國現有的VLCC，設計上基本是沿襲日本VLCC船型：平底、邊底雙層連通，底部隔柵分艙結構。這些船的經典航線是中國至中東，中東至歐洲，中東、西非至美灣。由于每航次這些船舶都要在裝貨時向港內傾倒十萬噸左右外來壓載水，因而歐洲、美灣乃至中東各港口國紛紛要求這些船舶在距海岸200海里、水深200米以上的水域把艙內壓載水置換掉；更進一步的要求是，船上必須裝備經IMO認可的壓載水處理裝置并確認排放在當港的壓載水已經處理達標。還有一個不容忽視的問題：國際壓載水公約即將生效。

如此，每年超過億噸的舟山海水被攜帶到中東港口，中東港口國又要求這些壓載水必須處理掉，龐大的VLCC船隊如何解決這一問題？

目前的辦法是早換水，離開舟山就盡快換水，主要目的是防止泥沙沉淀；接近阿拉伯海時還要換水，為滿足中東各港口國的要求。但航行中頻繁把壓載艙內的水排空、壓進，船舶受力就無法控制。所以，換水只是權宜之計，最終還是要處理壓載水。

于是，花大價錢購置壓載水處理裝備就不可避免。即使如此，在正常裝貨期間處理完8至10萬噸壓載水，以目前的壓載水處理設備研發成果，則要再建一個類似現有機艙的設備間。無疑，代價太高昂了。

出路在哪里？即使是現有船型以犧牲船期為代價來換取壓載水處理達標，那么將來呢？辦法只能是減少在港口必須處理的壓載水量。那么，需要換一種思維方式：減少在港口必須處理的壓載水量，也就是進行設計開發新船型，并以當港壓載水處理量4至5萬噸為目標。

“國情船型”開發刻不容緩

大船管理的關鍵是結構強度。強度取決于結構構件完好，構件狀態取決于涂層完好率。為此，相關國際組織出臺了CSR（共同規范）和PSPC（涂層技術標準）。但是，CSR和PSPC生效前，航運市場的火爆導致船東搶訂了大批散貨船和油輪訂單。這些國內各大船廠的在建船舶均屬于不滿足上述規范的船舶。可以預見，這些船5年內水艙內表面會布滿銹釘，10年內銹層基本連片，構件開始腐蝕。15年后，腐蝕裕量消耗殆盡。到那個時候，船東為了維護強度，修船時就會割換1000噸甚至3000噸鋼板。即使換上3000噸板也未必能完全保證結構強度，腐蝕還會加速。到20歲或25歲船齡時，船員和公司管船人員要不停地監視每一塊強度構件，謹防某一局部皺折或斷裂。如果碰到惡劣海況等，將釀成難以預料的災難。

幾十厘米的淤泥布滿艙底，令船舶管理人員無法斷定船底縱骨和舷側縱骨是否有失穩及腐蝕程度。由此，不難看出，設計適合我們自己水域和港口的防泥沙型船舶已迫在眉睫。

The Yangtze and Zhujiang River are Sediment-laden rivers. Vessels reaching the ports along the rivers such as shanghai,Ningbo-Zhoushan, Ballast water with sediment is pumped into the ballast tank at the vessel bottom while unloading cargo, which leads to dozens or even hundreds of tons sediment left on board. The shear force and bending moment of load data would distortion. Lots of ship wrecks are proved to be caused by sediment.

China’s crude oil imports will reach 400 million tons, of which 2 billions will be send to Zhou Shan-Ningbo by 100 VLCCs. About 70, 000 to 100,000 tons local water with about 1.5% sediment will be pumped onboard the ship every time. If the Sediment can not be clean up timely, the drain hole of bottom longitudinal and transverse ribs of a new ship will be fully sealed up by sediment after operating about 30 months. Then the bottom longitudinal will be covered totally after years. As a result, a thick accumulation of sediment will be formed at the double-bottomed tank, which are 60 meters in width, 250 meters in length and 0.8 meters in height. About 12 thousand tons sediment will be carried back and forth about in the large cabin.The corrosion, corrugation, bending and fracturing of the vessel can not be detected timely. Risks related to fuel consumption, ships speed, haul loading, draft and operation will be out of control. The main reason for this problem is that the type of the existing vessels is not conformed with China’s waters and ports. The“sediment-proof vessel type” for China’s port and water needs developing.

The existing VLCC basically follows Japanese VLCC designs: flat bottom, double-bottomed and edge connectivity, grille-subdivision structure. Those vessels will dump to ports hundreds of thousands tons ballast water while are loading delivery every voyage. They are required to replace the ballast water in the waters deep more than 200 meters and 200 miles off the coast by European countries, U.S. and middle east port states. Those vessels are requested to equipped with the ballast water treatment plant recognized by IMO and confirm that the ballast water is conformed with the standards before discharging. Additionally,“IMO BWM Convention” be come into force in the near future.

After replacement of ballast water in advance, the vessels are required to do it again before reaching Arabian Sea by the Middle East port state authorities.Frequent replacement of ballast waters will make vessel stressed beyond control. It will cost a fortune to purchase ballast water treatment plant to treat the ballast water. But how about in the future? The only way is to design and develop new vessel forms, and aim at treating 40 to 50 thousands ballast water at ports.

Before the CSR and PSPC coming into force, a lager number of bulk carrier and tank ordered all do meet with this criteria. All those vessel will covered with rusty nail in the eternal surface of water tank in five years;the rusty scale will link up into a single stretch, the component parts start to rust in 10 years, corrosion allowance will deplete in 15 years. When repairing ship,steel plant of 1000 tons to 3000 tons will be renewed.The structural strength could not completely guaranteed yet. Corrosion will continue accelerating. After 20 to 25 years, every part of structural strength has to be noticed to avoid one of them winkling or snap real. Therefore,we are in urgent need to design sediment-proof vessel types suitable for our own water and ports.

To Develop Anti-sediment Vessel Form is Critical

By Li Yuping