Chartplotter

A Chartplotter is a specialized computer used in marine navigation that integrates GPS data with a chart. They automate several navigational tasks, principally plotting position. Advancement in electronic chart plotting technology has now made traditional paper charts obsolete. This is evident in regulation allowing commercial vessels with chartplotters to not carry paper charts. They have become commonplace among both commercial and recreational users.

Limitations

The prudent mariner does not rely on any single source of information for navigation. Chartplotters are only as accurate as the position data and cartography. Like any piece of electronics, chartplotters are at risk for freezing or low power or power surge damage. A secondary form of navigation should always be maintained.

System Components

Typical chartplotters are composed of a GPS receiver, a computer with graphic (image) display, and an electronic navigational chart. Chartplotters can be dedicated or non-dedicated units. Dedicated units only do chart plotting functions, which is the case for most handhelds. Large scale dedicated chartplotters are also referred to as Electronic Charting Systems (ECS). Any home computer running a chartplotting software is inherently non-dedicated. Most fix mounted chartplotters are referred to as multi-function displays (MFD) because they can display information from a radar, fish finder, or weather receiver.

Physical Components

GPS receiver

Hand-held and small fix mounted units have the GPS receiver within the body of the chartplotter. Almost all fix mounted units have a receptacle for an external receiver so that the unit may be mounted in an overhead environment. Most receivers utilize a form of accuracy improving technology, namely DGPS or WAAS, sometimes both.

Size

Screen size is the principle dimension used for comparing chartplotters, although weight is considered for hand-held units as well. Hand-held units have screens 2.3" to 3" and from 5 to 7 oz. Fix mounted units designed for recreational vessels start at 5" and go up to 19", although most products fall between 5" and 12". Chartplotters on commercial vessels, especially those using them as a replacement to paper charts, can be over 28". This allows them to show large areas at high detail, much like a traditional paper chart. For larger units the central processing unit (CPU) is separate from the display, increasing flexibility in installation. The CPU’s are referred to as “black boxes” because of the usual color and such systems are referred to as “black box systems.”

User Interface

Hand-held and self-contained fix mounted units have keys on the front of the unit. Higher end products have touch screens. Black box systems may have either buttons on the display unit, touch screens, or a separate user interface. The simplest chartplotters simply disply the vessels position, as determined by a GPS or Loran reciever, on an electronic chart.

Electronic Charts

An individual electronic navigational chart, or, more commonly, a database of charts, is at the heart of a chartplotter. The chartplotter system can be no more accurate than its charts and position data. Many different formats exist within to classifications: raster and vector. The type of chart used affects the functionality of the chartplotter. As raster navigational charts (RNC) are basically image files, there can be no automation of route planning or alarms for running aground. Vector navigation charts (ENC) provide these functions because the computer looks at a set of coordinates.

Usage

Basic Navigation

Chartplotters serve to digitize several navigational operations: plotting position, determining speed over ground, waypoint navigation, and monitoring anchor drag. Chartplotters automatically plot the vessels position on the chart. The simplest way to use a chartplotter is to select a location on the screen and select "Go To," creating a waypoint. The chartplotter then calculates the range, bearing, and course to steer.

Route Planning and Waypoint Navigation

Waypoint navigation is done by selecting a series of points and sailing between them. This method is used to sail a vessel around obstructions or to simplify a great circle route. Route planning is when a navigator can identify a series as a route from one location to another. When underway, the route can be selected and the chartplotter will graphically display the bearing, course to steer. The user can view the area chart or a “highway” display that graphically shows cross track error. Sophisticated have automated route planning functions. This allows the navigator to set a destination and the chartplotter calculates a route around obstructions. Vector charts are required for this as they contain the data needed for obstruction avoidance. If connected to an autopilot, the chartplotter will order the course changes necessary to follow the selected route.

Anchor Alarm

It is often integral to the safety of a vessel that its anchor does not drag. An anchor alarm is function that alerts the crew should the vessel drag. This is done by entering the position of the vessel when the anchor is lowered and a threshold range. For example, a vessel puts down 100 feet of anchor rode and sets the threshold for 100 feet. In order for the vessel to be more than 100 feet from the anchor location, the anchor must drag or the rode part.

Grounding/Obstruction Alarm

When using vector charts, the chartplotter can monitor the depth ahead of the vessel. If the user-set threshold is crossed, an alarm is sounded. Similarly, if an obstruction, such as a lighthouse or island, is in the projected path of the vessel an alarm is sounded.

Replacement to Paper Charts

In an effort to increase efficiency commercial vessels are allowed to use chartplotting systems instead of carrying traditional paper charts. When the chartplotter and charts meet the technical requirements of the International Maritime Organization (IMO) and national hydrographic bodies, the chartplotter can qualify as an Electronic Chart Display and Information System(ECDIS). It must be inspected and certified by a regulatory or law enforcement body to gain this qualification. The ECDIS is then a legal substitute for paper charts while navigating in active waterways.

Variations

Increase in price generally brings: faster processing, more channels for signal reception, DGPS and or WAAS accuracy improving techologies, larger screens, touch screen technology, color screens, daylight viewable screens, increased functionality, and more or expandable memory.

Many chartplotting softwares exist, allowing a navigator to use a home computer instead of a fix mounted unit. This does not increase functionality compared to a fix mounted unit by the same manufacturer with comparable processing power. However, it provides flexibility in screen sizing and location, portability, and computing power. The principle limitation is that home computers are not "marinized", or adapted for marine environments. Some manufacturers, namely Panasonic, produce computers specifically for extreme environments.

One manufacturer offers a wireless touchscreen repeater display as a complement to their chartplotting software. It runs the same program as the master computer. Data from other units, such as GPS, is relayed from the master computer to the wireless display using a 802.11b ad-hoc network. Route and planning information is dynamically shared.

Another brand of chartplotter utilizes traditional paper charts rather than electronic ones. Before navigating, the user must geo-reference the chart by selecting two locations and entering the coordinates. This allows the computer to compute scaling and range. When navigating, indicator lights on the cursor direct the user to the position of the vessel. Position is plotted by inserting a pencil through the cursor onto the chart. Range and bearing are indicated when the cursor is moved over any point other than the vessel position. A waypoints is then created by pressing a key. The advantage of this system is the elimination of downtime in moving from electronic to paper navigation, should the electronics fail.

Some chartplotters can use position information from a Loran receiver, saving the expense of a GPS receiver for existing installations.

A video plotter is similar to a chartplotter in that it electronically plots position but has limited or no charting.

Integration with Related Applications

Most chartplotters are capable of overlaying radar images and or weather maps over the chart. Automatic identification systems (AIS) can display position, heading, and speed data of other vessels on the chartplotter. Information broadcasted by the AIS, such as position, heading, and speed, are obtained from the chartplotter. AIS depend on cooperative data communications among ships. Advanced chartplotters can reconcile AIS targets with radar targets tracked by an Automated Radar Plotting Aid (ARPA). This creates an integrated solution to collision prevention. ARPA is generally not able to reconcile targets with fixed objects on a chart.

Chartplotters may be networked to other equipment such as: radar, sonar, fish finder or fathometer, satellite weather service receivers, and AIS transceivers. Networking is generally done using either Ethernet cables or one of the industry standards, NMEA 0183 or NMEA 2000, although other proprietary solutions exist.

Additional Information

Curiosity

The first chartpotter has been made in Italy from an italian firm "NAVIONICS" with the brand "GEONAV".

References

External Links

NOAA, Office of Coastal Survey, Chart Products: http://www.nauticalcharts.noaa.gov/staff/charts.htm

IMO: http://www.imo.org

[[Category:Navigational equipment]] [[de:Kartenplotter]] [[fr:Chartplotter]]