Selecting Navigational Instruments

By Tom Burden, Last updated 11/30/2023

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Know What Functions You Need

The pillars of functional and practical onboard instrumentation are speed, depth, and on sailboats, wind data. Marine instruments are available as standalone units (basic depth sounders, for example) or as systems with identical displays. We'll walk you through the components of a typical system and help you choose the right ones for your boat.

Base Your Instruments on What Kind of Boat You Have

Racing sailboats should have a complete integrated instrument system, including boat speed, wind speed and direction, depth, and GPS data.

Cruising sailboats can get by with less complete instrumentation, but skippers interested in performance will probably want to have at least boat speed, depth and wind information.

Powerboats need to have boat speed and depth as well as the normal engine monitoring gauges, and may add wind information for voyaging or Race Committee duties. It’s nice to be able to monitor environmental conditions on a voyaging powerboat, since steering from a pilothouse or interior helm station makes it hard to determine the wind conditions.

Single-Purpose Dedicated Instruments

Knotmeter

Raymarine's i50 Speed Instrument is a great knotmeter for smaller powerboats, sailboats and rigid inflatables.

A knotmeter measures a boat’s speed, and knotlog records distance traveled through the water. Both are basic navigation tools and provide information of general interest. Virtually all boaters want to know how fast the boat is going.

Sailors want to trim sails to optimize boat speed, and the powerboaters want to optimize towing, cruising or trolling speed, or just know how quickly they are getting somewhere.

Depth Sounder

A depth sounder indicates how deep the water is so you can avoid running aground, can set your anchor with proper scope, and can navigate more accurately. Transducers, similar to those of a fishfinder, gather depth and speed information and pass it to connected displays.

Wind Instrument

The Garmin gWind Masthead wind instrument features twin-fin tech and a three-blade propellor for more accurate True Wind Speed (TWS).

Wind instruments display wind angle and speed in the cockpit or at the base of the mast. This information allows you to sail as fast and efficiently as possible, and helps you know when to reduce sail. Wind instruments are also helpful for night sailing, when watching the water for waves and gusts is impossible. They are occasionally found on powerboats, especially those that cruise or perform race committee duties.

Wind instruments, when connected to speed, depth, compass and GPS data, can calculate an array of useful data: true and apparent wind, velocity made good, closehauled wind angles and tacking angles. Instrument packages are a simplified way to buy three common sailboat instruments: a knotlog, depth sounder and wind instrument.

Repeater

As the name suggests, a repeater mimics information that is being transmitted on the data network, and can occasionally create new information by combining data. For example, true wind angle can be computed from boat speed, wind speed, and apparent wind angle. Repeaters do not have transducers; they merely process data measured by other instruments.

Compass

Digital and/or analog readout of a fluxgate compass.

Multifunction Instruments

Garmin's GMI™ 20 digital marine mulifunction instrument is designed for both power and sail vessels. GMI™ 20 clearly shows depth, speed, wind and 100+ marine and vessel parameters.

The instruments we described above display one sort of data only. A knotmeter, for example, outputs your speed and distance traveled. It won’t display wind or depth data. Multifunction instruments combine different information read outs, like depth, speed, wind and more, into a single display. Instruments that use the NMEA 2000 network are essentially small multifunction displays and can be customized to your preferences to show just about any information from anywhere on your boat’s network. Raymarine’s i70, Garmin’s GMI 20 and Simrad’s IS40 are examples of these NMEA 2000 instruments. The GMI 20, which is pretty typical, shows depth, speed, wind and more than 100 marine and vessel parameters.

Information Provided by Instruments

An instrument system allows you to view a variety of useful data when using your boat

Speed Data

Speed over the ground (SOG) allows you to see the effect of current, which may be substantial. Connected to a GPS, your instruments can tell both how fast you’re going through the water and your SOG.

Trip

Just like your car’s Trip Odometer. Good for determining your cruising speed and fuel consumption.

Water Temperature

Very useful for anglers, cruisers wondering if they have entered the Gulf Stream, or divers.

True Wind

The wind you feel when stationary is the true wind. Apparent wind is a vector that combines your boat’s speed with the true wind. True wind is useful for showing wind shifts, how high a sailboat is pointing and tacking angles.

Velocity Made Good (VMG)

Shows your true speed toward a waypoint. If you’re heading directly at the destination, your SOG and VMG will match, but when traveling off-course your VMG will be lower. Especially important for sailors going upwind. For example, if you point a little lower, but travel through the water faster, your VMG may go up or down.

Shallow Water and Deep Water

Alarms that show decreasing or increasing depth are very important safety features to keep from running aground, or show if your anchor is dragging.

Timer

Countdown or count-up timers provide a great way for racing sailors to keep track of their start time, with big letters visible anywhere in the cockpit.

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Instrument Display Type and Size

The Raymarine i50 Speed Instrument displays speed through water, speed over ground (GPS required), sea surface temperature, trip and log data.

The most affordable choice is a segmented monochrome display. Since you’re mainly looking at numbers on these single-purpose instruments, this inexpensive LCD display works fine.

Fully networked instruments take advantage of this pictorial format to show you a huge selection of gauges, diagrams, very large and bright numbers—with NMEA 2000 networking, the sky’s the limit.

When choosing an instrument system, consider how close you’ll be when reading the numbers. If you’re looking at mast-mounted instruments from the cockpit of a 40’ racing sailboat, you’re going to want bigger displays than if you’re reading a dash-mounted display on your 19’ Sea Ray. Look at B &G and Nexus for sail racing instruments for all sizes of boats.

Wired vs. Wireless Instruments

The availability of wireless connections for boat instruments eliminates the headaches associated with drilling holes in the deck or hull and routing cables up the mast. Micronet instruments talk to each other through a secure wireless network that does not interfere with other onboard systems and that does not transmit one boat’s data to another with the same system.

Visual ATON Signals - IALA Maritime Buoyage System

This online article is an advisory summary of different ATON marks. For detailed recommendations refer to IALA Maritime Buoyage System.

Regions

Buoyage system has been geographically divided into two regions; A and B. Lateral marks differ between Buoyage Regions A and B, and other five types of marks are common.

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ATON Marks

Lateral marks indicate the edge of a channel.  In a river, the direction of buoyage is towards the river's source and in a harbour, the direction of buoyage is into the harbour from the sea. Red and green colors mark the port (left-hand) and starboard (right-hand) sides of channel in Region A, and reversed colors red to starboard and green to port in Region B. Therefore the area between red and green buoy is a safe route for a vessel to navigate. In some regions also bifurcation buoys are used to mark out the preferred channel.

Cardinal marks are different shaped yellow-black sea marks with top-mark. They indicate the direction of safe waterway, cardinal (compass) direction (north, east, south or west) relative to the mark. Cardinal mark can also indicate of a hazard.

Isolated danger mark is black-red colored and placed on or near to a danger. Safe water mark, also called a Fairway buoy is red-white colored and indicates navigable water around it. Special marks are yellow and they indicate a special area for example cables, pipelines, spoil ground, aquaculture or recreation zone. New danger marks are newly discovered hazards and wrecks that may not be shown in nautical documents. They are blue-yellow.

For marking different ATON applications around the world we offer a wide selection of buoy lanterns including both standalone (externally powered) and solar self-contained lanterns.

Self-contained solar lantern M650H on a red buoy.

Other marks are visual ATON signals assisting mariners in the navigation and not necessarily mark channel limits or obstructions.

1. Leading lines/ranges Leading lights, also referred to as range lights, are beacons that are used both day and night to mark safe passage for vessels along a fairway, through a shallow or dangerous channel, or when entering ports. They provide precise analog visual feedback to determine the vessel’s location relative to the center of the channel. Leading lines can be any color or shape that provides a distinctive mark from the background, determined by competent authority.
   
   LO200M range lights marking the leading line.
2. Sector lights display different colors and/or rhythms and the color of the light provides directional information to the mariner. Omnidirectional sector lights can cover multiple fairways with a single installation. They can also be used to mark out very wide sectors. When AtoN lighting needs to provide extremely precise guidance only projector sector lights can deliver the required accuracy. Some models of projector sector light can include an oscillating boundary. It gives more information of position near the sector boundary to the mariner by creating a light character with alternately flashing colours to further help the mariner to obtain his lateral position related to the mid of the safe channel.
   
   For more detailed guidance on choosing right marine lantern for specific applications see our QUICK GUIDE ATON SIGNALS focusing on sector, leading and PEL lights.
   
   
   

   Sector light ODSL 200  with different colored sectors cover multiple fairways at a same time.

3. Lighthouses are towers or substantial structures which show a signal light by night and operate as a significant daymark during daytime. Lighthouse structures can be of any color, shape or material.

   
   

   Rotating lighthouse beacon VRB-25

   combines LED technology with traditional rotating beam.
   

   
   
   

   Sabik Lighthouse Unit SLU modernizes the technology of the traditional lighthouses while preserving the historic heritage and look.

4. Beacons and other short range ATON are fixed navigation marks that can be of for example different shapes, colors and patterns. They can carry a signal light or operate unlit only as a daymark.
   
   LED 160

   on a fixed beacon in a large commercial port.

   
   
   
5. Major floating aids include for example light vessels or large navigational buoys. They are deployed at critical locations with a heavy shipping traffic to mark approach from offshore areas. They can also be a plaform for other ATON such as AIS.
   
   

   Lightvessels act as lighthouses in waters that are unsuitable for fixed constructions.

6. Auxiliary Marks are other minor ATON marks that are not previously described. They do not mark routes or obstructions and they are usually outside defined channels. They are used to assist navigation and convey information for general navigational safety.
   
   

   Auxililiary mark indicating cable lines in Finland.

7. Port or harbor marks are local marking measures like bridge lights and port traffic signals. Before transiting an area for the first time, mariners should be aware of local ATON marking.
   
   

   Sabik all-round LED 160 lanterns as bridge lights.

This online article is an advisory summary of different ATON marks. For detailed regulations refer to IALA Maritime Buoyage System; definitions and descriptions regarding each of the above marks, their color, shape, top mark, numbering, synchronization and light rhythm on full document R1001 IALA Recommendation IALA Maritime Buoyage System downloadable.   

For more information, please visit Marine Aids to Navigation Solutions.