System diagram

The Simrad SC90 sonar system comprises a processor unit (computer), a transceiver unit, a power supply and the hull unit with the Motor Control Unit and the transducer.

A colour display is also required. This display is normally not a part of the sonar delivery.

The cable between the wheelhouse units and the transceiver in sonar room must be a high quality Ethernet cable. It can be purchased locally, or ordered from Simrad.


(A) DIsplay
(B) Processor Unit
(C) Operating Panel
(D) Transceiver Unit
(E) Power Supply Unit
(F) Motor COntrol Unit
(G) Hull Unit
(H) Transducer

The cable between the wheelhouse units and the CS90 Transceiver Unit in the sonar room must be a high quality Ethernet cable. This cable can be purchased locally, or ordered from us.

Installation drawings

Outline dimension and production drawings are provided in PDF and DWG formats. Use the link to open the drawings page in a new window.

Processor Unit

The Processor Unit comprises a single powerful maritime computer. It is provided as a standard part of the delivery. It serves several functions.

The Processor Unit handles the advanced signal processing required to present the information on the display, and it allows you to control the sonar. It provides the graphic presentation of the sonar views and the images that are created, it holds the menu system, communicates with the transceiver circuitry, and reads information from the peripheral units. The computer is based on a commercial design, but the software and hardware have been specified and assembled specifically to meet the sonar requirements.

Operating Panel

The Operating Panel allows you to access to the most frequently used functions in a fast and efficient manner. It also provides a trackball and the necessary control buttons to operate the menu system.

Transceiver Unit

The Transceiver Unit contains the transmission and reception circuitry for the sonar.

The transceiver transmits acoustic energy through the water. This transmission is commonly referred to as a "ping". After each transmission, the transceiver receives the echoes from the targets in the water and/or the seabed. These echoes are filtered and amplified and then converted into digital format.

The connections for power and communication are made under the cabinet. The transducer cable is connected using a large proprietary plug on the side wall.

The Transceiver Unit has been designed to be mounted on the bulkhead in the sonar room. It is fitted with powerful shock absorbers to withstand the violent motions of a vessel at sea.

Power Supply Unit

The Power Supply Unit provides the necessary operating voltages to the Transceiver Unit. The unit is designed for bulkhead mounting.

How it works

The transducer converts the electric energy generated by the Transceiver Unit to physical vibrations. These vibrations alter the water pressure and create an acoustic pulse that is sent into the water. The acoustic signal is transmitted as a beam. The duration of the acoustic pulse, as well as its frequency and shape, are controlled by the Transceiver Unit. The direction and opening angle of the beam is controlled by the Transceiver Unit and the physical properties of the transducer. After the transmission, the transducer works as a "microphone". It converts the water pressure created by the acoustic echoes to electric energy. These weak echo signals are sent to the amplifiers in the Transceiver Unit.

Transducer location

The transducer is mounted at the bottom end of the hull unit’s transducer shaft. This allows the transducer to be lowered into the water for operational use and retracted for protection when the sonar is turned off. By lowering the transducer into the water, you may also be able to reduce the noise created by the laminar flow of water along the hull.

Transducer handling

Note: The red (or black) protective coating is a vital part of the transducer. It is very important that neither this coating nor the internal parts of the transducer are damaged during the handling, installation or cleaning. Any holes and/or scratches in the transducer surface will allow water to penetrate the transducer. If a leak occurs, the transducer must be replaced.

The transducer must always be handled as a delicate item. Wrongful actions may damage the transducer beyond repair. Observe these transducer handling rules:

  • Do not activate the transducer when it is out of the water.
  • Do not lift the transducer by the cables.
  • Do not step on the transducer cables.
  • Do not damage the transducer cables, avoid sharp objects.
  • Do not handle the transducer roughly, avoid impacts.
  • Do not expose the transducer to direct sunlight or excessive heat.
  • Do not use high-pressure water, sandblasting, metal tools or strong solvents to clean the transducer face.
  • Do not damage the outer protective skin on the transducer.

Hull unit

The hull unit is designed to lower the transducer down below the ship’s hull when the sonar system shall be used. When the sonar is turned off, the transducer is hoisted for protection.

The hull unit is a mechanical construction. It is mounted on the top of the installation trunk. The installation trunk penetrates the ship's hull and allows the transducer to be lowered into the sea. The hull unit is normally located in the forward part of the vessel. This location is recommended to avoid the noise from the propellers and the engine.

Hull units for the Simrad SC90 Fish finding sonar

Hull unit Lowering depth Transducer cable Maximum speed
SC90 1 m 4.6 or 10 m 20 knots
SC94 2.1 m 4.6 m 19 knots

The hull unit is a large mechanical construction. It is mounted on the top of the installation trunk. The installation trunk penetrates the ship’s hull and allows the transducer to be lowered into the sea.

The purpose of the Motor Control Unit is to control the hoisting motor on the hull unit. When you make the appropriate commands on the sonar, the Motor Control Unit will start and stop the motor. It will also make sure that the motor rotates the correct way. The motion sensor for the built-in electronic stabilization of the sonar beams is provided.

  • To lower the transducer, press Down on the Operating Panel. To indicate transducer movement, the Down indicator lamp flashes, and an audible signal is sounded. When the bottom position has been reached, the indicator lamp is lit, and the audible signal stops.
  • To retract the transducer, press Up on the Operating Panel.

The transducer can also be lowered to any selected middle position. On the Operating Panel, press Middle.

In case of power failure, the transducer can be raised or lowered manually by means of a hand crank.

If you forget to hoist the transducer before the sonar is turned off, the transducer is hoisted automatically before the power is disconnected. The transducer is also hoisted automatically if a serious malfunction occurs in the communication between the bridge and the hull unit.

Caution: If the transducer hits larger objects or the bottom, the transducer shaft may be bent, or - in the worst case - it can be broken off. A broken transducer shaft will cause water leakage through the top of the shaft. If you suspect that the transducer shaft is seriously damaged with holes, do not retract the transducer to its upper position. To prevent serious damage to the vessel or the vessel's stability, you must have a water pump and a warning system in the sonar room.