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Electronics and Communications

Electronics and Communications

How to get your electrical system right first time.

In the last issue of Bow2Stern, we outlined how to plan the heavy electrical system, how to calculate the electrical loads and how to size the electrical system for your boat. 

In this issue, we will discuss the electronics and communications systems for your boat by address the following topics:

  • What components are there, what are their advantages and what should I look for?
  • Are different brands compatible?
  • What communications do I need and what is the difference?
  • The importance of quality antennas.

Marine electronics are in many ways, like household computers in that they are not the be all and end all of our navigation needs, we will not sail off the end of the earth without one, there are countless brands with everyone claiming to have the latest and the greatest and it always seems the minute you buy something there is a newer model or upgraded software!  However, marine electronics do make our boating life easier and in certain cases a lot safer.  Some of the most common and popular types of electronics are:

  • Direct sunlight view ability: many chartplotter displays can be very difficult to view when using it in a bright sunny environment or when the sun directly shines upon the display.   It is always best to try and view a chartplotter display in a bright environment to get an idea or talk to people with what experiences they have had;
  • Single or multifunction capability: most of the mid range to high end chartplotters on the market have multifunction capability meaning they have the functionality to operate as a chartplotter / GPS as well as a sonar / depth sounder, a radar (this multifunction is very useful for doing a radar overlay over the chart making navigation in unfamiliar areas at night far easier and safer), video inputs for running deck and engine room cameras and VGA outputs for sending the chartplotter information to a TV or PC just to name a few.   However, for those of you who like the security of having separate chartplotter, fishfinder and radar units in case of a display failure and all information being lost, you can purchase these systems individually;
  • Do you wish to run more than one screen?:  It is becoming increasingly common to see more than one screen being used on a boat, particularly on dual station boats, fishing boats and larger yachts with a separate helm and navigation areas.  In these cases, look for a chartplotter which has network capability.  Certain units such as the Raymarine E series and the Garmin 5008/5012 series can run up to five separate displays off the same network using only radar and sounder module/transducer.   It’s a good idea to take future expansion into consideration as a non networkable unit will have to be replaced if additional screens need to be added later.  Pay now, save later as they say!;
  • Screen size: this is an interesting one as most of the time we are limited to what will fit either flush mounted or gimble mounted on our dash board.  However when there is ample room, I always recommend to my clients that they go for as large a screen as possible.  The reason for this is simple.  When looking at electronic charts, it is far easier to read something when it is bigger, this is especially the case when navigating in rough water and we are being thrown around.  The same applies if operating a multifunction unit in a split screen mode with several different pieces of information being displayed.  A chart and a radar are near impossible to read when we are on a higher range and items of information can easily be overlooked.
  • NMEA 0183 and NMEA 2000 compatible: we will talk about these a little later in this article;
  • Easy to use menus and function keys:  whilst this is a very personal choice, my recommendation is to play with the unit before purchasing to find out what you like.  As technology is progressing, we are getting more and more functions all the time.  Some manufacturers such as Garmin have taken ease of use to new levels with the new touch screen displays and the unique Auto Guidance system which allows you select a destination and then the unit will plot a course through navigation markers whilst staying within your boats’ set safe depth and height limits. 
  • Software upgrades: this is something that is often taken for granted.  Some manufacturers actually post their software upgrades on their websites.   These upgrades can be downloaded onto an SD Card and then uploaded to the GPS chartplotter.  Many of these upgrades can include additional features, improved menus and improved system performance.  Whilst purchasing a unit which can not be easily upgraded may be cheaper, the downsides are the unit will date quickly and may end up being incompatible with component upgrades and future additions.

Depth Sounders / Sonar

It has to be said that digital technology has dramatically improved the performance of this technology.  Comparing an old fishfinder to a new digital one is like comparing the picture quality of an old VHS video player to the latest DVD player.

A depth sounder / fishfinder / sonar works by a transducer converting electronic impulses from the fishfinder to sound waves, which then travel down through the water at about 4,800ft per second, regardless of frequency.  When the sound waves bounce off the bottom or a fish, the returning echo is picked up by the transducer, which converts it back to electrical impulses.  These impulses are then converted by the fishfinder into a picture of the bottom and, hopefully, fish.  The higher the frequency of the impulse, the more detailed the resolution.  For deep sea fishing, a lower frequency transducer may be a better choice, since it can be used at greater depths.

When selecting a depth sounder / fishfinder / sonar many of the features we need to look at are the same for the GPS chartplotter.   However in this instance, the most important factor is the transducer selection and there are several choices available:

  • Transducer composition – transducers are made of varying material types to suit different hull composition:
    • plastic transducers - suitable for fibreglass or metal hulls
    • bronze transducers - suitable for fibreglass or wood hulls
    • stainless steel transducers - suitable for steel or aluminium hulls
  • Transducer type – there are three basic types of transducers:
    • Thru-Hull Transducers - These are mounted through a hole drilled in the bottom of the boat and protrude directly into the water.  This type of transducer generally provides the best performance.  Thru-hulls are recommended for displacement hulls and boats with straight-shaft inboard engines.  You will also need a fairing block to enable the transducer to be mounted properly.  Thru-hull transducers must be installed with a fairing block to ensure proper alignment and a secure fit. 
    • In-Hull (also commonly known as Wet Box or Puck transducers) Transducers - These are mounted directly on the inside of the hull.  These are only used in fibreglass hulls.  In-hulls will not work with wooden aluminium, wood, or steel hulls, or in foam sandwich or hulls that have air pockets.  Any wood, metal, or foam reinforcement must be removed from the inside of the hull for an in-hull to operate effectively.  With an in-hull transducer, the signal is transmitted and received through the hull of the boat.  As a result, there is considerable loss of sonar performance.   In other words, you won’t be able to read as deep or detect fish as well with an in-hull transducer as with one that’s transom mounted or thru-hull mounted.  These are popular transducers with sport cruisers and yachts where high performance is not critical and the fact that drag in the water is also reduced.
    • Transom Mount Transducers - These are installed on the boat’s transom, directly in the water and typically sticking a little below the hull.  Transom mounts are composed of plastic and tend to be less expensive than other transducers.  Transom mount transducers are recommended for planning hulls under eight metres and trailer boats, such as powerboats with outboard, inboard-outboard and jet drives.  They are not recommended for large or twin screw inboard boats because aerated water from the propeller reduces performance.  They are also not suitable for boats which are permanently in the water as transducer life and performance is compromised over time.

The main features of transducers that you should consider are:

  • Transducer Power – power refers to the strength with which the transducer sends the sonar ‘ping’, expressed as watts RMS.  Higher power increases your chances of getting a return echo in deep water or poor water conditions.  It also lets you see what’s under the boat in better detail, such as bait fish and structure.  Generally, the more power you have, the deeper you can reach and the easier it is to separate echoes returning from fish and bottom structure from all the other noises the transducer detects.  Most sport cruisers, yachts and cruisers will generally find 600W more than enough power, while sport fishers and game fishing boats will generally have a minimum of 1kW with many game boats using 2kW or even 3kW transducers for the best possible performance when looking for canyons off the shelf. 
  • Transducer Frequency – today most transducers over 600W are dual frequency meaning that the transducer has the ability to look at high and low frequencies at the same time.  50/200 kHz is by far the most common in transducers however in upper end 1kW plus transducers 28/200 and 38/200 kHz is also common.

Basically the differences in frequencies can be explained as follows:

  • 200 kHz is the best option in water under 200ft/60m if you need to get an accurate reading while moving at faster speeds.  High frequencies give you greater ability to detect very small objects but over a smaller portion of water.  High frequencies typically show less noise and fewer undesirable echoes while showing better target definition.
  • 50 kHz is the best option for deep water.   This is because water absorbs sound waves at a slower rate for low frequencies and the signal can travel further before becoming too weak to use.  The beam angle is wider at low frequencies, meaning the outgoing pulse is spread out more and is better suited for viewing a larger area under the boat.  However, this also means less target definition, separation and increased susceptibility to noise.  Although low frequencies can see deeper, they may not give you a clear picture of the bottom.

 Mud, soft sand, and plant life on the bottom absorb and scatter sound waves, resulting in a thicker bottom image.  Rock, coral and hard sand reflect the signal easily and produce a thinner bottom display.  This is easier to see using the 50 kHz setting, where the bottom returns are wider.


Radar is an acronym meaning Radio Detection and Ranging.  It is a device which not only measures the time it takes for a pulsed signal to be reflected back from an appropriate object, but also determines its bearing relative to your position.  Once the time and bearing are measured, these targets or echoes are calculated and displayed on your radar display.  This will give you a bird’s eye view of where other targets are relative to you, even when you cannot see them with your eyes due to low visibility.

What can radar do for me?  With radar acting as your eyes, you have the ability to see objects (targets) such as landmasses, weather systems and other vessels to assist you in the navigation of your vessel.

There are many things to consider when buying radar.  Here are a few:

  • Boat Size – radars are available in various sizes and configurations.   The most popular are Radomes and open array scanners.   Radomes are the most popular configuration due to their compact size, lower power consumption and lower purchase price.  Open array scanners are popular with larger vessels because of their increased performance due to the narrower beam angles, higher transmitting power and better target definitions.
  • Transmitter Power Output – a higher power output level increases the radar’s ability to receive signals reflecting off objects and show them as targets on your display.  Higher-powered radar also has greater capacity to ‘punch through’ fog and precipitation, allowing you to see objects around your vessel.
  • Beam Angle – this specification is related to the length of your antenna.  The longer the antenna is, the narrower the beam angle.  This narrow beam angle increases the radars bearing resolution allowing you to discriminate easily between two objects that are close together.  It also shows land mass contours and inlets with much greater resolution.

Can I navigate with radar?  Fishing vessels and pleasure boats commonly use radar to help them navigate to their favourite fishing spots.  When heading to a particular spot, the forces of wind and current combine to shift the vessel off its intended course.  To determine your position and to counter vessel drift, use the VRM (Variable Range Marker) and the EBL (Electronic Bearing Line) to mark range and bearing to fixed targets.


For any passage making boat or yacht, an autopilot is a necessity.  The thrill of steering a boat on the open ocean is quickly diminished when one realises how tiring it is especially if there are many more hours ahead.   An autopilot gives you the ability to accurately navigate to a point without having to touch the helm.  In many ways an autopilot especially if fitted with a rate gyro and interfaced with a chartplotter can out steer and navigate a straighter course than even the most seasoned skipper (and it doesn’t get hungry or thirsty!).

Autopilots comprise of several main components:

  • The Head Unit – this is the controller for the autopilot.  Every manufacturer has different styles to suit various applications and tastes.  Many can have multiple stations and be wireless giving the skipper the ability to tend to lines and rigging while underway or just sit on the deck and enjoy the surroundings.
  • The Course Computer – this is the brains of the autopilot.  It basically takes the information from its sensors/GPS chartplotter and tells the drive unit which way to steer the boat.
  • The Drive Unit – this creature steers the Rudder, sterndrive or outboard.  There are several types or drive units with the most popular being hydraulic drive (for hydraulic steering), rotary drive (for chain steered yachts), linear drive (for mechanical steering), wheel drive (attached to the helm wheel) and tiller drive (attached direct to the tiller).
  • The Rudder Angle Indicator – This device tells the course computer what position the rudder is, thus allowing the course computer to calculate how much rudder or counter rudder needs to be applied.

When selecting an autopilot you first need to select your drive unit to suit the steering mechanism of the boat.  Secondly, select a course computer/corepack.  This is sized to the boats size and weight.  The key point here is not to undersize a system for when the seas are rough, you do not want the system struggling and or worse, failing.  The final step is to select a head unit to drive the system.

You quickly realise how useful an autopilot is when correctly sized and installed.


Most modern marine electronics now support either NMEA 0183 or NMEA 2000 which are combined electrical and data specifications for communication between marine electronic devices such as fish finders, autopilots, GPS receivers, engine data and many other types of instruments.  NMEA communicates via data sentences between devices which support either 0183 or 2000 so that different brands can be used in a system.  In most cases this is perfectly fine, however if any of the data (check sums) is different then certain functions may not work between the two devices. 

If you want the best reliability in a system between devices, it is often best to stick with the one brand throughout, from both an aesthetic and resale perspective.


Marine radios are essential safety equipment for communicating with other boats, marine rescue groups and to receive navigational warnings and weather updates. There are three types of marine radios:

  • 27MHz are relatively cheap transceivers available for general use, however they do not provide the coverage of a VHF radio and are limited to a range of around 10-15km. 27MHz also suffer from increased interference and the audio quality is less than when compared to a VHF Marine radio. Also, it is not compulsory for the monitoring of emergency channels on a 27MHz by coastal and limited coastal stations. However many limited coast stations such as Coast Guard and VMR do monitor 88 and 86 (27Mhz Emergency Channels). Check with you local authority for coverage.
  • VHF - the VHF radio remains the most versatile communication device for a boat and is often the only communication device most pleasure boats carry. Due in part to its versatility , the VHF is arguably the most valuable piece of safety gear aboard, delivering any call for assistance to dozens or hundreds of nearby listening ears. The States and Northern Territory marine authorities have also set up very high frequency (VHF) stations in certain areas of Australia.  These stations provide VHF radio distress and safety services including 24 hour monitoring of VHF Channel 16 for distress, urgency and safety traffic and the regular broadcast of weather information on VHF Channel 67.  

     Fixed-mount or hand-held? - modern hand-held VHF radios are full featured, extremely convenient, and they have the significant advantage in an emergency of being independent of the boat's electrical system. Where maximum range and/or continuous use are more important, you will want a fixed-mount unit. If your budget allows, having both offers additional advantages, such as two-way communications with an excursion party (but note, transmissions from ashore are prohibited without a coast-station permit).

The VHF radio is NOT a telephone
Boaties often use the VHF much like a telephone to call other boats and shore stations to relay information, to make appointments, or sometimes just to chat. Before you join in, however, you should recognize the differences between VHF radio and telephone communication: Radio conversations are not private. When you talk on the VHF, everyone within range tuned to that channel is listening. A radio conversation ties up the channel you are using. No one else up to a 25 mile radius can use it until you release the transmit button on the microphone.

Use of low power
All fixed-mount VHF radios can transmit at either 25 watts or 1 watt. The maximum power from a handheld is typically 5 watts. With either type, if your radio contact is nearby, set the power setting to low (1 watt) to reduce the distance the signal carries beyond your target. Also watch your language; not only is profanity over the air against the law, it will be particularly offensive to other boaties with children aboard.

HF Radio

HF radios have a greater communication range if travelling long distances from shore. Queensland HF services cover coastal waters to a minimum of 200 nautical miles seaward from sites located at Cairns and Gladstone. These Stations maintain 24 hour listening watches on 4125 kHz, 6215 kHz and 8291 kHz for distress and safety situations. It is important to restrict radio traffic on these frequencies to distress, safety and urgency calls. The 'Coast Radio' Stations will also broadcast navigation warnings on 8176 kHz.

HF radios are expensive to purchase, they require far more experience to operate than a VHF as you have to tune them in and they also require careful consideration with installation as earth plates, grounding straps, antenna tuners, deck insulators and special antennas will be required. If not installed correctly radio performance can be severely hampered as HF radios are very prone to electrical interference. Cost is install is also far greater than that of VHF.

If you are venturing far off the coast then a HF Radio is a good investment as it offers a far superior range than a VHF radio and it also offers more security than a Satellite phone. You can only call one person on a Satellite phone where as you can reach many people in one call with a HF radio.

Both VHF and HF radios require the operator to obtain a Marine Radio Operators Certificate of Proficiency (MROCP), which covers the operation of both VHF and MF/HF equipment. The Marine Radio Operators VHF Certificate of Proficiency (MROVCP) has a somewhat simpler syllabus, but only covers the operation of VHF equipment. Most coast guard, VMR and certain yacht clubs will run these courses though out the year.


Knowledgeable boaties realise that even the most expensive radio will perform poorly with a second rate antenna that may well save you money up front, but may jeopardises the welfare of those aboard in time of need.  That’s why we prefer the quality, performance and reliability of Shakespeare marine antennas. 

Reliability begins with quality construction

Shakespeare fibreglass antennas are built with precision, beginning with hand-soldered connections, brass and copper elements, strong mechanical joints and superior electronics.  The radiator and electrical elements are then encased in an exclusive Shakespeare fibreglass radome.

Tips on choosing the proper antenna

Since there are many factors that influence the selection of a proper antenna for a specific application, we encourage consultation with a local dealer, whenever possible.

When this is not possible, the following tips should be considered before making a final decision.

  • Antenna Length – height is paramount in getting the greatest range, and encourages the selection of an antenna that can be placed as high as possible on the boat.
  • Sailboats – as a general rule, sailboats have a 3’-5’ antenna mounted on the masthead.  Some racing enthusiasts opt for an 8’ antenna mounted on the stern in the event demasting should occur.  Either is acceptable.  A decision should be made on personal preference.
  • Powerboats – most power boats from 16’ to 25’ in length use a standard 8’ antenna, while bigger vessels have the option of larger antennas with more gain.  Caution: be sure to allow enough lay down room for clearing low bridges or other limitations.  Whichever choice is made, a sturdy mounting arrangement must be used to avoid damage to both boat and antenna.
  • Gain ­– this is a rating stated in decibels (dB).  Generally, the higher the gain, the greater the communicating range.  However, keep in mind that the higher the gain, the more compressed the beam width becomes.  A narrow beam can cause fading in rolling seas.  Small, lightweight boats, which roll excessively in heavy seas, normally do not use a gain rating above 6dB.  The more stable the platform of a vessel, the higher the gain that can effectively be used.
  • Mounts – be sure to pick the mount style that will best support the antenna on a particular boat.  When using a two-piece antenna system greater than 10’ in length, an upper support clamp is necessary.   For antennas of 14’ to 18’, the upper clamp should be 3’ to 5’ from the bottom.  For antennas of 18’ to 23’, the upper clamp should be 4’ to 8’ from the bottom.  Positioning the upper clamp too high or too low can significantly increase the potential for structural failure. 
  • Cable  – RG-58 cable is sufficient for cable runs up to 20’.  For runs over 20’, larger and better, low loss RG-8/X, RG-8A/U or RG-213 are preferable.  Shakespeare uses Low loss, UV stable RG-8/X throughout its Galaxy antenna line.  Today’s enhanced cellular services, which operate in the 1800-1900 MHz range place even more importance on using a high quality coax.  That’s why Shakespeare developed its exclusive Lo-Max® cable for dual band cellular antennas.  Its low loss characteristics are near those of larger RG-8A/U and RG-213 cables, without the extra bulk and rigidity.  For optimum performance from your VHF, HF/SSB and cellular communications systems, the cable should be kept as short as possible.  Caution: cable supplied with some antennas may not be cut or altered.  Be sure to check the instruction sheet before attempting to shorten the cable.
  • Low Angle Radiation – Shakespeare pioneered low angle techniques in marine antennas in the 1960s and built them into many models.  Low angle minimises fading while maximising range even during excessive boat roll in turbulent seas.  A normal angle shortens the range and wastes power. 

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