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[帆译作品] 基本导航—海图仪 Basic Navigation with a Chartplotte

发表于 2015-5-9 01:04 | 显示全部楼层 |阅读模式

Basic Navigationwith a Chartplotte

 基本导航—海图仪 Basic Navigation with a Chartplotte 3.jpg

Navigation involves knowing where your boatis, knowing how to reach a destination, and ensuring that the boat does reachthat destination. Historically, navigation-especially out of sight ofland-required many skills. Given a starting point from dead reckoning (calculationsbased on speed, time, and direction) or a sextant reading, you would track theboat's direction (with a compass) and speed (with a log) to continue to knowthe boat's position.


Now, however,most mariners use a marine GPS chartplotter to navigate.
The historicaldifficulties of being precise in every aspect of navigation resulted in manyshipwrecks. With the modern GPS system, in which a receiver on your boatinterprets signals from Global Positioning System (GPS)satellites, you can know your exact location to within a few feet. A marinechartplotter is a piece of electronic equipment that shows, or plots, theboat's position on a nautical chart, allowing youto see where you are in reference to hazards, points of land, and everythingelse on the chart. A plotter also runs software that allows you to easilyaccomplish other navigational tasks.


GPS plottersinclude both dedicated marine equipment, called chartplotters, and computersrunning plotting software. Some handheld GPS units also are plotters, if theyshow the position of the boat on a chart. A GPS unit that provides the positiononly in longitude and latitude is not considered a plotter.For all types of plotters,the general principles are the same
·        The screen shows a nautical chart. The chartmay be an exact representation of a NOAA paper chart (called a raster chart) or be agraphic representation in a format unique to the software (usually called avector chart). More sophisticated plotter screens may show additionalinformation such as photographic views, bottom contours, a radar overlay, andso on.

·        屏幕显示航海图。图表可以是NOAA纸质版图表的精确再现,也可以是矢量图的形象呈现。更加精确的海图仪器屏幕还会显示以下信息,例如高像素逼真显示、气象等高图、全覆盖雷达等等。

·           The boat's position is shown in real time against thechart. Theplotter may represent the boat with a simple dot, circle, or other symbol. Manyplotters also indicate the direction the boat is moving with an arrow or othergraphic indicator associated with the boat symbol. In some programs, the boat'sspeed may also be indicated graphically, such as by the length of the arrow. Inone software program, for example, the length and direction of the arrow showshow far the boat will move in the next 10 minutes if conditions remain thesame-giving an indication of how soon a turn may be necessary.

·        船体位置实时呈现。海图仪用简单的一个点、圆圈或者其他形式来表示船体。很多绘图仪还会用一个箭头或其他和船系统有联系的标识表明船行驶的方向。一些程序中,船的行使速度还会用箭头的长度大小表示。在软件运行系统中,箭头的长度和方向代表在外界环境保持不变的情况下,未来10分钟船将移动的距离,用这样的方法给出船员提示多久让船体转弯是合适的。

·        Specific user-designated locations can be shown on thechart. Sailorsenter these points in a variety of ways, such as entering the longitude andlatitude or moving the cursor to a specific place on the chart and clicking.Special symbols then show these points, called waypoints, on the chart. Forexample, you might enter a waypoint for your destination, if you can make astraight-line approach to it, or you might enter a string of waypoints tofollow if turns are required. Waypoints are now often printed on charts andcruising guides, and some software programs or built-in plotter programs alsoinclude useful standard waypoints. Waypoints are the basis of much of thefunctionality of a plotter.

·        表中能显示使用者专门指定的位置。船员可以用多种方法输入这些指定点,例如事先输入经度和纬度或是把光标移到指定点再点击确认。设定后的点叫做导航点,表中会用特殊的标识显示。例如,如果你能直达目的地,就可以预设导航点,又或者路线需要转弯时,还可以设定一连串的导航点与目的地连接起来。按现在的技术来说,图表上会印有导航点做巡航使用,一些软件或内置航海程序中还会自带标准导航点。导航点只是众多海图仪功能中基本功能。

Basic PlotterFunctions基本海图仪功能
Originally, most plotters were fairlysimple and straightforward in their functions for navigation. Like mostsoftware, however, these programs have become increasingly sophisticated andnow offer more advanced functions than most of us will need. Described here areonly the most basic functions found in almost all chartplotters and navigational software. For specificadvanced functions, consult the user manual for a particular device.


·        Go to. The go-to function is a simple way tonavigate from where you are now to a waypoint destination that you can reach ina straight line. The screen tells you everything you need to know: whatdirection to go (bearing), the distance to go, the estimated time before youreach the waypoint (based on current speed), etc. Also provided is yourheading, the direction you are actually moving in; if a current or the wind iscarrying you off course (called cross-track error), you may not be moving in a straightline to your destination.

·        出发。该出发功能是出发点至目的地的直线距离的简单方式。屏幕上显示一切你必需的信息:前进方向、前进距离、到达下一导航点所需时间(以当前速度为基准)等。同时还会提供当前的实际行进方向;如果气流或风导致你偏离航线(联络测线错误)这样你就无法笔直到达目的地。

·        Tracks. You usually have the option for the plotter torecord your path through the water, leaving a "breadcrumb trail" onthe chart. This can be useful, for example, if you are navigating through achannel or deep fog or in other circumstances when it is important to return bythe exact path you took.

·        轨迹。通常可以选择让海图仪记录整个过程中的行进路线,并在图表上保存浏览路径记录。该功能在遭遇以下情况时就显得尤为重要,比如,航行穿越隧道、浓雾或者其他需精确记录往返路径的环境条件。

·        Routes. A route is an organized set of waypoints. Typicallyyou set up a route before leaving for your destination, planning the best wayto transit a channel or get around islands or other features that prevent adirect go-to sail as the crow flies. Waypoints are collected into a route, andthe plotter makes it easy to simply follow along from one point to the next. Aswith waypoints, the plotter keeps you informed of the distance to go and theestimated time remaining. Lengths of each leg and the entire route are alsoprovided, along with bearings to steer during each leg. Depending on thehardware used, one might plan a complicated route while in port or at home,print out chart pages showing each leg and the vital navigation information, tobe fully prepared. This is like having a computer do for you what pre-GPSnavigators had to do on paper charts: draw in lines for course legs, usingparallel rules to
determine bearings from the compass rose and dividers tomeasure distances. Learn more about how to use chartplotterroutes.

·        路径。路径是由一系列的导航点组成的。在出发前往目的地前先设定好路线,规划出最佳的方式穿过隧道、绕过海岛或者其他阻止你直达目的地的地方。航行过程中会收集导航点的信息,海图仪能轻松实现从一个点到另一个点的切换。参照行进中的导航点,海图仪能及时提供与目的地的距离和仍需航行的时间,同时还提供每段和整段的航行距离以及航行的掌舵方向。借助于硬件设备,人们可以在港口或在家就能规划复杂的路线,打印出带有重要航海信息的海图表,为航海做充分的出发前准备。这就类似于用电脑替代替GPS导航仪替你完成了图表的绘制:先画出航海路线,用平行尺示意出指南针所指的航行方向,在用两角规测量距离。想了解更多关于海图仪的使用方法,请点击此处。
Again, these are only the most basicfunctions of chartplotters. With some advanced systems, the plotter can beintegrated with a boat's autopilot so that steering is done automatically tofollow the route. Other systems integrate information from other instruments,such as the boat's knotmeter and wind instruments, to make sophisticatednavigational decisions about how to reach the destination most expeditiously.


Hardware and Software硬件和软件
A wide varietyof plotters and navigational systems are now available for all needs and allbudgets. Almost all of these fall into one of two general categories: dedicatedmarine plotters or computers running navigational software. Since each offerscertain benefits and has certain drawbacks, one should choose a system onlyafter carefully thinking through how it may be used for some time to come.
Marineplotters arededicated systems. Although some are handhelds that run on batteries and havesmall screens, most are installed on the boat and wired into the boat'selectrical system. Mounted systems generally have larger screens. All plottersare weatherproof and built to stand up to the harsh marine environment. Thenavigational software is built in, and often some or many charts as well,although specific additional charts usually must be purchased. Complete systemsrange from $400 for a handheld unit all the way up to $6000 for a full-featuredplotter with a 15-inch screen.


Advantages ofmarine plotters include their resistance to weather and ease of use withoutrequiring software installation or complicated chart downloads. Disadvantagesinclude higher costs (compared to an inexpensive laptop) and having to useproprietary charts purchased from the same company.
Computernavigational systems are essentially regular personal computers, usuallya laptop or PDA, to which a GPS receiver is connected.The computerruns navigational software and can have essentially all the same functions as adedicated plotter. Charts must be loaded into the computer. Except forexpensive "ruggedized" laptops, most computers must be shielded fromwater and moisture when on the boat. GPS receivers for laptops area availableas USB units or built into PC cards (under $100).

Advantages of computers include their lowercosts, their ability to serve other uses when cruising, the choice of variousnavigational software packages, and the ability to use them also at home toplan routes. Budget-minded sailors can use a free program called SeaClear, which has all basic functions butfewer frills than commercial packages. SeaClear and some other software useelectronic versions of NOAA charts that are now free for download on theweb. Disadvantages include having to protect the computer from the elements,having to install the software and set up the hardware connection between theGPS receiver and the computer, and having to install all charts.


Morerecently, smart phones with anintegrated GPS receiver and running a navigational app can also function as achartplotter. Many inexpensive marine navigation apps offerfunctionality that used to cost hundreds of dollars.


·        Because a plotter can fail, always have paper charts onboard. Even the most rugged electronics are still somewhat delicate in themarine environment, and you don't want to end up drifting onto the rocksbecause of a sudden power failure. To be prepared for all eventualities,learn how to navigate with only yourdepthfinder and a chart.

·        海图仪可能会死机,所以在船上要常备纸质图表。即便是性能最优的电子设备,有时候在海上这种恶劣的环境下也会很脆弱。如果不想因为设备的突然死机,而导致整艘船撞上岩石,那就针对不同事故提前做好准备,谨记如何仅依靠个人经验和图标进行航行。

·        Beware the temptation to stare too long at the plotter'sscreen, especially when mounted on the binnacle just above the wheel. Boatershave been known to suffer collisions with other craft (which of course don'tshow up on the plotter!) when they failed to keep an adequate lookout ahead.

·        尽量避免长期盯着海图仪显示器,尤其是当它就安装在罗盘箱上面时。众所周知,如果没有充分关注前方航行情况,很有可能会与其他物体相撞。

·        Watch out for cross-currents when headed for a waypoint -the boat can drift sideways and suddenly get into trouble if it leaves achannel or is swept off-course into a problem area.

·        在向导航点行进时,小心逆流——在驶出隧道或偏离航线驶进问题海域时,船体可能偏离正常航线,陷入困境。

·        A plotter doesn't replace the need for good seamanship.If a waypoint is directly upwind, for example, you may have to use traditionalnavigation methods to choose which tack to take off the route-line to reachthat destination most effectively.


 基本导航—海图仪 Basic Navigation with a Chartplotte 4.jpg

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