【文章內(nèi)容簡介】 the other hand there may be no sheer at all on the deck, which will then be parallel to the base over the entire ：一方面，船舯兩側(cè)的某些長度方向可能是平的，沒有舷弧，但接著以向上的斜直線的形式向首尾兩端延伸；另一方面，甲板上面可能完全沒有舷弧，整個(gè)船長方向上甲板都平行于基底。 In older ships the deck at side line was parabolic in profile and the sheer was quoted as its value on the forward and alter perpendiculars as shown in Figure . So called ‘standard’ sheer was given by the formulae：老式船舶縱剖面上的甲板邊線呈拋物線狀，舷弧取自首尾兩柱方向上的值，如圖 所示。所謂的舷弧“標(biāo)準(zhǔn)值”用公式給出：首舷?。╥n）=+20 尾舷?。╥n）==+10 這些公式用英制單位表示為： 首舷弧（cm）==+ 尾舷?。╟m）==+It will be seen that the sheer forward is twice as much as the sheer aft in these standard formulae. 通過上面的標(biāo)準(zhǔn)公式可以看出，首舷弧值是尾舷弧值的兩倍。It was often the case,however, that considerable variation was made from these standard ，這些標(biāo)準(zhǔn)值也會發(fā)生相當(dāng)大的變化，這種情況時(shí)常發(fā)生。 Sometimes the sheer forward was increased while the sheer after was reduced. 有時(shí)首舷弧會變大而尾舷弧會減小。Occasionally the lowest point of the upper deck was some distance aft of amidships and sometimes departures were made from the parabolic sheer profile. 頂部甲板的最低點(diǎn)離船舯尾部偶爾有一段距離，有時(shí)拋物線狀的縱剖線會發(fā)生分離。舷弧值。The value of sheer and particularly the sheer forward was to increase the height of the deck above water(the ‘height of platform’ as it was called) 尤其是首舷弧增加了甲板離水面的高度（稱為“平臺高度”）and this helped to prevent water being shipped when the vessel was moving through rough sea. The reason for the abolition of sheer in some modem ships is that their depths are so great that additional height of the deck above water at the fore end is unnecessary from a sea keeping point of 。某些現(xiàn)代船舶廢除舷弧的原因是它們的型深如此之大，以至于首部額外的甲板高度就耐波性觀點(diǎn)而言是不必要的。Deletion of sheer also tends to make the ship easier to construct, but on the other hand it could be said that the appearance of the ship suffers in consequence.舷弧的取消也使得船舶的建造容易得多，但是就另一方面而言結(jié)果是船的外 表變得難看了。Draught and Trim（吃水和縱傾）The draught at which a ship floats is simply the distance from the bottom of the ship to the waterline. 船舶漂浮時(shí)的吃水指的就是船底離吃水線的距離。If the waterline is parallel to the keel the ship is said to be floating on an even keel, but if the waterline is not parallel then the ship is said to be trimmed. 如果水線平行于龍骨，那么就說船舶平?。坏侨舨黄叫?，那么就說船舶發(fā)生了縱傾。If the draught at the after end is greater than that at the fore end the ship is trimmed by the stem and if the converse is the case it is trimmed by the bow or by the head. 如果船尾吃水比船艏大，那么就發(fā)生了艉傾；若船艏吃水比船尾大，那么就發(fā)生了艏傾。The draught can be measured in two ways, either as a moulded draught which is the distance from the base line to the waterline, or as an extreme draught which is the distance from the bottom of the ship to the waterline. 吃水可以分為兩種：型吃水，即基線離水線的距離；計(jì)算吃水，即船底與水線間的距離。In the modem welded merchant ship these two draughts differ only by one thickness of plating，but in certain types of ships where, say, a bar keel is fitted the extreme draught would be measured to the underside of the keel and may exceed the moulded draught by 15~23cm (6~9in). 對于現(xiàn)代焊接形式的商船，這兩種吃水僅是相差一塊殼板厚度的區(qū)別，但是對于 有些裝有棒龍骨的船，計(jì)算吃水的測量至龍骨下表面，因此計(jì)算吃水可能比型吃水大1523cm(69in)。It is important to know the draught of a ship, or how much water the ship is ‘drawing’, and so that the draught may be readily obtained,draught marks are cut in the stem and the “吃”水量，這很重要，因此一艘船的吃水能夠直接獲取，船艏和船艉都刻有吃水標(biāo)志。These are figures giving the distance from the bottom of the ship. 吃水標(biāo)志也就是一些離船底有一定距離的一些數(shù)字。In imperial units the figures are 6in high with a space of 6in between the top of one figure and the bottom of the next one.這是數(shù)字用英制單位表示，6in 高，而且上下相鄰的兩個(gè)數(shù)字的間距也是 6in。 When the water level is up to the bottom of a particular figure the draught in feet has the value of that ，吃水就是那個(gè)數(shù)字的英尺值了。If metric units are used then the figures would probably be 10cm high with a 10cm ，那么這些數(shù)字就可能是10cm 高，間隔10cm。In many large vessels the structure bends in the longitudinal vertical plane even in still water t with the result that the base line or the keel does not remain a straight line. 就許多大型船舶而言，即使是在平靜的海況下，它們的縱向垂直面都發(fā)生了彎曲，結(jié)果是基線或龍骨都不能保持為一條直線。The mean draught at which the vessel is floating is not then simply obtained by taking half the sum of the forward and after draughts. 這就意味著船舶漂浮時(shí)吃水不能僅僅用艏艉吃水和的一半來表示。To ascertain how much the vessel is hogging or sagging a set of draught marks is placed amidships so that if da，dx and df are the draughts at the after end,amidships and the forward end respectively then為了確定船舶中拱或中垂程度，在船舯做了一套吃水標(biāo)志，因此如果船尾、船舯和船艏吃水分別為da、dx和df那么中拱或中垂=dx+（da+df）/2When use is made of amidship draughts, it is necessary to measure the draught on both sides of the ship and take the mean of the two readings in case the ship should be heeled to one side or the ，測量船舶兩側(cè)吃水，使用兩個(gè)數(shù)據(jù)是必要的，以防船舶向一側(cè)或另一側(cè)傾斜。The difference between the forward and after draughts of a ship is called the ‘trim’, so that trim T = da df, and as previously stated the ship will be said to be trimming by the stern or the bow according as the draught aft or the draught forward is in excess. 船舶首尾吃水的不同稱為“縱傾”因而縱傾T= dadf，正如前面所說的那樣，船舶艉吃水或艏吃水過多時(shí)，將發(fā)生艏傾或艉傾。For a given total load on the ship the draught will have its least value when the ship is on an even keel. 對于穩(wěn)定航行的船，在已知的總載荷作用下，船舶吃水將有一個(gè)最小值。This is an important point when a ship is navigating in restricted depth of water or when entering a dry dock. 這一點(diǎn)對于在限制水深的區(qū)域航 行的船或船舶進(jìn)入干船塢時(shí)很重要Usually a ship should be designed to float on an even keel in the fully loaded condition, and if this is not attainable a small trim by the stem is aimed at. 船舶的設(shè)計(jì)通常應(yīng)滿足在滿載荷作用下船能夠平浮的要求，如果船達(dá)不到這種狀況，那么就設(shè)計(jì)成小角度艉傾。Trim by the bow is not considered desirable and should be avoided as it reduces the ’height of platform’ forward and increases the liability to take water on board in rough ，應(yīng)該避免,這是因?yàn)轸純A會降低艏部“平臺高度”，增加在惡劣海況中甲板上浪的可能性。Freeboard（干舷）Freeboard may be defined as the distance which the ship projects above the surface of the water or the distance measured downwards from the deck to the waterline. 干舷被定義為船舶離水面的距離，或甲板與下部水線的間距。The freeboard to the weather deck, for example, will vary along the length of the ship because of the shee