Manufacturers today have product ranges that incorporate most electronic instruments and not just radar. Typically, multi-function electronic displays include the following.
Regardless of type and cost, echosounders are susceptible to two main operating conditions which affect the clarity of their read-out and their accuracy. External factors, such as the type of seabed, as well as variations in the salinity and temperature of the water, affect performance.
Signal frequency is gauged to give the best possible echo response from the seabed. Higher frequency signals might be less affected by changes in salinity etc. but the echo from a sandy, silted or weedy seabed would be weaker and less reliable. All that can be done is to become familiar with the way in which the reading changes owing to the variables mentioned above.
Installation-induced faults however can be overcome. These are essentially of two types:
1. Poor positioning of transducers The transducer must be positioned below the water-line, in clear water, parallel to the sea level. If the transducer is placed too near the water-line, propeller keel or bilge keels, turbulence will result, and the echo response will be lost. If the transducer is placed too close to the keel, it may also be masked from the echos and give a maximum depth reading irrespective of the true depth. To avoid these problems, the transducer is usually situated slightly forward of amidships, just below the turn of the bilge. Prominent fixtures should be streamlined with fairing-in plates.
2 Wiring and interference faults The coaxial cable from the transducer to the echo sounder unit should be kept well clear of other wiring which might generate interference. Sheathe the cable if necessary. Ignition systems and strobe lights are often the cause of inconsistencies in the read-out.
Marine electronics service of multi-function electronic displays.
Individual units like echo sounders are virtually maintenance-free. Weed or barnacles growing on the transducer will impair its performance. Scrub away weed, and remove barnacles by squashing them with a pair or pliers or a ‘mole’ type wrench. Make sure that the coaxial lead in the bilges is protected against damp.
It is when the units are combined in multi-function electronic systems that marine electronics service by professionals is advisable.
In contrast to the normal reception when listening to a radio at home, the performance of a marine ship-to-shore radio is often disappointing. There are many reasons. Some are related to the transmission frequencies and the quality of the received signals, but a significant cause of poor performance is often found to be in the installation itself.
The fitting of the radio and erection and tuning of the aerials should be left to professional marine electrical engineers. However, the following points may help to improve the radio’s performance.
1. Power leads should be short and of ample capacity. 50 per cent excess capacity will ensure that voltage drop is minimal. Bunch the leads together, and shield where necessary. If there is excessive noise, remove the aerial lead at the radio. Noise conducted through the power cables may remain, and should be suppressed.
2. Make sure the radio is thoroughly earthed. Over half the power of the radio can be lost if the ground connection is poor. All ground terminal connections should be clean, soldered or clamped, and protected against corrosion. Fit several earthing leads, including one to the earth plate of the bonding system. A separate copper mesh, soldered around its edge and fitted outside the hull, in addition to the earth plate, should improve radio reception.
3. Fit a suitable aerial. In small sailing boats the most satisfactory aerials are of the ‘L type, utilizing the rigging with strain insulators wherever necessary. Shipboard-radiated sound will be picked up both by unsheathed power lines and by the aerial. The distinctive sounds made by the boat’s equipment might help to identify and suppress the interference sources.
Popping regular, synchronized with engine speed – ignition system
Popping but not synchronized with engine revs – fuel depth gauge
Howling pitch varying with engine – generator
Whistling varied with engine revs – alternator
Sizzling crackling – voltage regulator
Pulsed tone regular and monotonous – digital read-out from adjacent equipment
Prop shaft similar to alternator
These units should be professionally installed and adjusted. Poor performance is usually the result of shipboard-generated interference or aerial location. The ground wiring should be heavy and well connected.
Loran C and radio ground leads should be kept separate. Improved performance can often be obtained by moving the aerial away from metal structures, horizontal wires and other aerials. Position the aerial temporarily. and check the signal, both with other equipment turned off and with each item of equipment turned on before making a permanent installation.
The microwave energy emitted by a radar scanner at close range can be dangerous. Avoid looking directly at the scanner while the radar is switched on, and do not come within 39 inches (1m) of a small yacht scanner, or 8 feet (2 1/2m) of a larger commercial unit, while they are working.
If the scanner is enclosed in a radome, make sure it is switched off before venturing close.
The installation and care of an AIS radar system should be left to the manufacturer or his agents. Do not tamper with the installation and seek advice from professional marine electronic service professionals before siting any other electronic equipment near the AIS radar.
Faults can be inherent in multi-function electronic systems through poor installation or subsequent alteration to power lines aboard. They can also develop because of poor maintenance.
These occur when the scanner is situated close to an obstruction. Often this will be only a small, perhaps I° loss, and the motion of the boat will eliminate the blind spot. If the blind spot persists move the scanner or the obstruction.
These reveal themselves by a double echo on the display. Usually the ranges of the two echoes are similar, the false echo generally the more transient of the two. The false echo occurs when a transmission is deflected by rigging or part of the superstructure, and returns from the target by the same route. Fitting deflector plates which will absorb or scatter the signal will remedy this problem.
Loss of performance
Loss of power, brilliance or range is often caused by a faulty or overheating power unit. Power units should be situated in a cool place where heat can readily be dissipated. Cable runs should be kept to a minimum to prevent voltage loss.
When the scanner becomes dirty and encrusted with salt, loss of definition results. Switch off and clean it.
This might be an obvious fault, or show itself in continual variance between compass bearings and bearings taken from the radar. The radar display is sensitive to external magnetic influences. Compass, electrical equipment or power cables which distort radar alignment, may have to be moved. Occasionally the scanner bearings fail. This causes a slop as it rotates, which is noticeable on the scanner as a variable heading line. Seek expert help.