Determining the location of the transducer

A single answer to the question “where to install the transducer” cannot be given. The physical location of the transducer depends on the vessel's design and construction, the shape of the hull, and the way the water runs along the hull. However, several important guidelines exist, and some of these are even conflicting.

The information here must be considered as general advice. Depending on the transducer's characteristics and the hull's design, you must handle each transducer installation separately.

Avoid protruding objects

Objects protruding from the hull, such as zinc anodes, sonar transducers or even the vessel's keel, generate turbulence and flow noise. Holes and pipe outlets are also important noise sources. They may act as resonant cavities, amplifying the flow noise at specific frequencies.

Do not place a transducer near such objects, especially not close behind them. For the same reason, it is very important that the hull area around the transducer face is as smooth and level as possible. Even traces of sealing compound, sharp edges, protruding bolts, or bolt holes without any filling compound will create noise.

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Choose a position far away from the bow thruster(s)

Bow thruster propellers are extremely noisy. When in operation, the noise and cavitation bubbles created by the thruster make the echo sounder or sonar useless, almost no matter where you have placed the transducer. And when not in operation, the tunnel creates turbulence. If your vessel is pitching, the tunnel can be filled with air or aerated water in the upper position. It will then release this water or air in the lower position.

Generally, all transducers must be placed well away from the bow thruster. However, a location forward of the bow thruster is usually advantageous.

However, this is not an invariable rule. Certain thruster designs combined with its physical location on the hull may still offer suitable locations near the thruster. If you are in doubt, consult a naval architect.


(Photo: Brosen, Wikipedia)

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Go deep to escape the boundary water layer

The upper water layers of the sea contain many small air bubbles created by breaking waves. The uppermost 5-10 metres in heavy seas may be air-filled, with the highest concentrations near the surface. Air bubbles absorb and reflect sound waves and may, in the worst conditions, totally block sound transmission.

When your vessel moves through the sea, the friction between the hull and the water creates a boundary layer. The thickness of the boundary layer depends upon the vessel's speed and the roughness of its hull. Any objects protruding from the hull and any dents in the hull will disturb the flow and increase the thickness of the boundary layer.

The flow in this boundary layer may be laminar or turbulent. A laminar flow is a nicely ordered, parallel movement of the water. A turbulent flow has a disorderly pattern, full of eddies. The boundary layer increases in thickness when the flow goes from laminar to turbulent.


(A) Turbulent flow
(B) Laminar flow
(C) Air bubbles in the water

Furthermore, the air bubbles in the seawater are pushed below the hull and mixed into the boundary layer. The boundary layer is thin underneath the forward part of the vessel and increases in thickness as it moves aft. If the sides of the hull are steep, some of the air bubbles in the boundary layer may escape to the sea surface along the vessel sides. It is our experience that a wide and flat bottom, with a rising angle less than about 13 degrees athwartship, is prone to cause air problems for a transducer.

The conclusion is that the transducers should be mounted as deep as possible in the hull's forward part.

However, this is not an invariable rule. Certain thruster designs combined with its physical location on the hull may still offer suitable locations near the thruster. If you are in doubt, consult a naval architect.

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Stay away from the propellers

The propulsion propellers are most vessels' dominant noise source. The noise is transmitted through the seawater and may often reduce the performance of your system.

For this reason, the transducer must be placed far away from the propellers, which means on the fore part of the hull. Positions outside the direct line of sight from the propellers are favourable.

On small vessels with short distances, it is advised to mount the transducer on that side of the keel where the propeller blades move upwards because the propeller cavitation is strongest on the other side. The cavitation starts most easily when the water flows in the same direction as the propeller blade, and that is, to some degree, the case at that side of the keel where the propeller blades move downwards.


Cavitaion example (Photo: US Navy / Wikipedia)

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Summary and general recommendations

Some of the installation guidelines provided may be conflicting. You must treat each vessel individually to find the best compromise.

Generally, the most important factor is avoiding air bubbles in front of the transducer face. For this reason, the recommended transducer location is normally in the fore part of the hull, well ahead of the noise created by the bow wave. The maximum distance from the bow is normally equal to one-third of the total waterline length of the hull.

Typical recommended location:


(A) Transducer
(B) Inclination angle
(C) Hull length at the waterline 
(D) Maximum 1/3 of the hull length at the waterline (C)

If the vessel hull has a bulbous bow, this may be a good location for the transducer. However, you must consider the aerated water's flow pattern. Often, the foremost part of the bulb is preferable.

Typical location on a bulbous bow:


(A) Thruster
(B) Transducer location

This location applies to the normal trim and speed of the vessel. Under no circumstances should the transducer be tilted backwards when the vessel is moving at an appreciable speed. Mounting screws must never be extruding from the transducer, and you must fill the space around the screws with a compound or a locking ring.

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