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 Your Boat Type
- Single-Purpose Instruments
- Multifunction Instruments
- Information Provided by Instrument Systems
- Display Type and Size
- Wired vs. Wireless Instruments
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.
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.