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1、译文:航海学704. 重新设置航位推算重新设置航位推算图，使之反复逐个修复或者运行修复。此外，如果安装了一个惯性系统，就需要考虑重新设置航位推算到一个惯性估计的位置。如果一个导航器在长时间内没有被修复，航位推算图没有复位固定，将会累积时间误差。随着时间的推移，错误可能变得越来越严重，以致于航位推算将再也无法显示该船舶的精确位置。如果该船舶配备了一个惯性导航器，那么导航器可以考虑到重新设置航位推算到惯性估计的位置。作出这项决定时，需要考虑到以下这些：1、自上次修复和修复信息的可用性的时间。如果自上次修复到现在的时间距离很短，并且修复信息将很快成为可用的，那么等待下一次重新设置航位推算是明智的选择

2、。2、动态导航情况。举个例子，假如一艘水下潜艇在墨西哥湾流行驶，修复信息可用但是运行方面的考虑也许会阻碍潜艇潜望镜深度得到修复。同样，一艘配有一个惯性导航器的水上舰艇也许会被卷入动态电流，并且电子修复设备的临时损失。无论如何，修复信息的可用性是短期的，但是动态的情况需要更准确地评估船舶的位置。绘制一个惯性估计位置和复位航位推算，估计位置可以让导航器更加准确地评估导航情况。3、修复源的可靠性和准确性。如果一艘潜艇在冰下运行，例如，只有惯性估计位置修复在几周之内可用。鉴于惯性估计位置和高度准确修复系统之间的高度相关性，比如 GPS，以及惯性导航器持续的正常运转，导航器可以决定重置航位推算到惯性 E

3、P。航位推算与船舶安全正确地一个航位推算图对船舶安全。航位推算可以让导航器在计划的，并且采取适当的计划和行动来避免它们。轨道中检查一个点。它让他预见到记住一点，航位推算的位置只是近似的。使用一个称为修复扩展的概念对航位推算的误差进行修复，并允许导航器使用航位推算进行更有效地，避免。705.修复扩建在通常情况下，一艘船在开放的海洋上行驶，长时间得不到修复。这可能会导致从大量的错误到无法获得修复故障的电子导航系统。在潜水艇上进行修复更是罕见。无论什么原因，在某些情况下，导航员也许会发现他不得不在航位推算的单独处理好几个小时。导航员必须采取预防措施，以确保所有危害通过一个近似航位推算的位置。可以使用

4、的方法之一就是修复扩建。修复扩展应该考虑到在倾向于影响船的实际路线和速度在地面造成的航位推算可能导致的错误。导航员考虑所有这一类并且在航位推算图附近开发一个不断扩大的“错误圈”。修复扩展的基本假设之一是个别影响当前的回旋余地和转向错误相结合，导致错误不断累积。因此，随着时间推移，扩大的概念会不断增加。事实上，虽然错误可能互相抵消了，但是导航器必须到的情况，这是不断累积的。在修复扩展演算考虑的错误中，包含可能导致航位推算不精确的所有错误。一些最重要的是电流和风、 指南针或陀螺仪误差以及转向错误。尝试确定错误圈子中的任何方法都必须考虑到这些。导航员可以使用一整套的漂移计算来判断航位推算图的严重程度

5、。请参阅第 707 篇文章。他可以从试点图表或天气预报中获取当前的估计程度。他可以确定从天气仪器中风速。他可以通过罗盘误差与一个准确标准相比来获得方位的罗盘错误。导航员要确定这些错误在他的路线和速度结束地面的作用，并且申请错误，用于修复扩展的演算。如上文所述，时间是一个错误的函数，它随着船沿轨道而逐渐得到修复。因此，导航器必须纳入到半径随着时间而增长的错误圈子里。例如，假设导航员计算错误的所有各种各样的误差源可能创造一个累积位置误差不超过 2 毫微米，然后他的修复扩展错误圈子将以该速度不断增长，在第一个小时以后，它会变成 2 毫微米，两个小时后，它会变成 4 毫微米，以此类推。导航员使用这个错

6、误圈子到底意义呢？从每个修复中撤销航位推算。所有的修复来源有有限的绝对准确性，并且初始的错误圈子应该反映出这种高准确性。例如，假设导航系统有 0.5 毫微米的准确性，那么应该设置的最初的错误圈子的附近修复在 0.5 毫微米。首先，将一个圆的半径用于获取此修复系统准确性的修复位置。其次，计划有序的路线和速度来修复位置。然后应用修复扩展圈子于每小时的航位推算，每次增加错误圈子的半径错误。在上述例子中，一个小时后，航位推算的圈子半径将会变成 2.5 毫微米，两个小时后，将会变成 4.5 毫微米，以此类推。围绕了四个小时的航位推算与错误圈子，导航员将绘制原产与原始错误圆相切，并且与其他错误圈子同时相切

7、的两条线。然后导航员严密检查导航到的两条切线之间的区域。修复扩展包括船的总面积（只要所有误差源都被考虑）。如果有任何在锥体之内被表明，那么导航员应该对那些警报尤其。举个例子，例如修复扩展表明船也许驶入浅滩水，不断监测回声测深仪。同样，如果修复扩展表明船也许会阻碍图的绘制，那么岗位要被额外监视。修复扩展可能的增长速度也许会变得难以控制。显然，如果修复扩大增长，覆盖面积太大，作为导航员的一个工具，它失去了它的有用性，并且他应该通过所有可利用的获得新的修复。确定一个估计位置估计位置 (EP)是为余地、的错误和电流的作用修改的航位推算位置。该部分将简要地造成航位推算位置从船的实际位置分流的。然后，将计

8、算集合和漂移，以及运用这些价值于航位推算，最终获得一个估计的位置。706. 影响航位推算位置准确性的潮流是月亮和表面的潮汐引力引起的水的表面的周期性水平运动。潮流是气象，海洋学或者地形学作用造成的海表面的水平的运动。无论它的来源是哪里，海的表面的水平运动是船行驶的一股重要的动态力量。设置指的是当前的方向和漂移提到潮流的速度。回旋余地是指船舶由于这部分垂直于船舶航迹的风产生的矢量背风运动。回旋余地和当前相结合产生的最显著的影响是让船行驶得更加顺利。回旋余地对于航行的船只和双面高的船只影响尤其之大。除了这些自然力量之外，相对较小的舵手和转向指南针相结合也许会产生错误，并且导致航位推算其他的错误。外

9、文原文：The American Practical704. Resetting the DRReset the DR plot to each fix or running fixurn. In addition, consider resetting the DR toan inertial estimatedition, if an inertial system is installed.If a navigator has not taken a fix for an extended period of time, the DR plot, noving beenreset to

10、a fix, will accumulate time-dependent errors. Over timet error maye sosignificantt the DR will no longer show the shipsition wicceptable accuracy. Ifthe veis equipped win inertial navigator, the navigator should consider resetting theDR to the inertial estimated determination are:ition. Some factors

11、 to consider when making thisTime since the last fix and availability of fix information. If is been a short timesince the last fix and fix information may soon wait for the next fix to reset the DR.e available, it may be advisable toDynamics of the navigation situation. If, forexle, a submerged sub

12、marine isoperatinghe Gulf Stream, fix information is availabut operational considerationsmay preclude the submarine from going to periscope depth to obtain a fix. Similarly, asurfa loss of shortlyhip win inertial navigator may be in a dynamic current and suffer a temporaryelectronic fix equipment. I

13、n either case, the fix information will be available but the dynamics of the situation call for a more accurate assessment of thevesition. Plotting an inertial EP and resetting the DR tot EP may provide thenavigator wimore accurate assessment of the navigation situation.Reliability and accuracy of t

14、he fix source. If a submarine is operating under the ice,for exle, only the inertial EP fixes may be available forks aime. Given a high ch as GPS, andprior correlation betn the inertial EP and highly accurate fix systemthe continued proper operation of the inertial navigator, the navigator may decid

15、e to reset the DR to the inertial EP.DEAD RECKONING AND SHIP SAFETYProperly maaining a DR plot is important for ship safety. The DR allows the navigator toexamine a futureition in relation to a planned track. It allows him toipate charted ition is onlyhazards and plan appropriate action to avoid the

16、m. Recallt the DRapproximate. Using a concept called fix expancompensates for the DRs inaccuracy andallows the navigator to use the DR more effectively toipate and avoid danger.705. Fix ExpanOften a ship any number oshe open ocean for extended periods without a fix. This can result fromctors ranging

17、 from the inability to obtain celestial fixes to malfunctioningelectronic navigation systems. Infrequent fixes are particularly common on submarines.Whatever the reason, in some instana navigator may find himselfheition of havingtomany hours on DR alone.The navigator must take precautions to ensuret

18、 all hazards to navigation along his pareaccounted for by the approximate nature of a DRition. One method which can be used isfix expan.Fix expan which tendtakeso accountsible errors in the DR calculation caused by factorsto affect the ves actual course and speed over the ground. The navigatorconsid

19、ers all such factors and develops an expanding “error circle” around the DR plot. Oneof the basic amptions of fix expanist the various individual effects of current, cumulative error which increases over time,leeway, and steering error combine to cause ahence, the concept of expan. While the errors

20、may in fact cancel each other out, the worstcase ist they will all be additive, and this is what the navigator mustipate.Errors consideredhe calculation of fix expanpass all errorst can lead to DRinaccuracy. Some of the most important factors are current and wind, compassyro error, and steering erro

21、r. Any method which attempts to determine an error circle must take thesefactorso account. The navigator can use the magnitude of set and drift calculated from hisDR plot. See Article 707. He can obtahe currents estimated magnitude from pilot charts or weather reports. He can determine wind speed fr

22、om weather instruments. He candetermine compass error by comparison win accurate standard or by obtaining an azimuthof the Sun. The navigator determines the effect each of these errors has on his course andspeed over ground, and appst error to the fix expancalculation.As noted previously, error is a

23、 function of time; it grows as the ship proceeds along the trackwithout obtaining a fix. Therefore, the navigator must incorporate his calculated errorso anterror circle whose radius grows with time. For exle, ame the navigator calculatesall the various sour Then his fix expanof error can create a c

24、umulativeition error of no moren 2 nm.error circle would grow att rate; it would be 2 nm after thehour, 4 nm after the second, and so on.At what value should the navigator start this error circle? Recallt a DR is laid out fromevery fix. All fix sourhave a finite absolute accuracy, and the initial er

25、ror circle shouldreflectt accuracy. Ame, for exle,t a salite navigation system has an accuracyof 0.5 nm. Then the initial error circle aroundt fix should be se0.5 nm., enclose the fixition in a circle, the radius of which is equal to the accuracy of thesystem used to obtahe fix. Next, lay out the or

26、dered course and speed from the fixition.Then apply the fix expancircle to the hourly DRs, increasing the radius of the circythe error factor each time. In the exle given above, the DR after one hour would beenclosed by a circle of radius 2.5 nm, after two hours 4.5 nm, and so on. Having encircled t

27、hefour hour DRitions with the error circles, the navigator then draws two lines originatingtangent to the original error circle and simultaneously tangent to the other error circles. Thenavigator then closely examines the area betn the two tangent lines for hazards tonavigation. This technique is il

28、lustrated in Figure 705.The fix expanpasses the total area in which the vecould be located (as long asall sourof error are considered). If any hazards are indicated withhe cone, the navigatorshould be espelly alert for those dangers. If, for exle, the fix expanindicatestthe vemay be standingo shoal

29、water, continuously monitor the fathometer. Similarly,if the fix expan extra lookouts.indicatest the vemight be approaching a charted obstruction,tThe fix expanmay grow at such a ratet ites unwieldy. Obviously, if the fixexpangrows to cover too large an area, is lost its usefulness as a tool for the

30、 navigator,and he should obtain a new fix by any available means.DETERMINING AN ESTIMATEDITIONAn estimatedition (EP) is a DRition corrected for the effects of leeway, steering error,and current. This section will briefly discuss the factorst cause the DRition to divergefrom the veualition. It will then discuss calculating set and dri