Skip to main content

System diagram

The Simrad SN90 comprises  a computer with an operating panel, a transceiver and a transducer. As an option, a hull unit can be used for forward looking installations.


(A) Display  (the second display is optional)
(B) Processor Unit (computer)
(C) Operating Panel
(D) Transceiver Unit
(E) Hull Unit (optional, commonly used on trawlers)
(F) Transducer

The cable between the wheelhouse units and the SN90 Transceiver Unit in the sonar room must be a high-quality Ethernet cable. It 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 Processsor 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 modes and the images that are created, it holds the menu system, it communicates with the Transceiver Unit, and reads information from the peripheral units. The Processor Unit is a marine computer using the Microsoft Windows® operating system. It is designed for rugged use, and placed on shock absorbers. The computer is based on a commercial design, but the software and hardware has 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 cabinet is by default fitted with a heat exchanger. This means that a stable internal temperature and humidity is ensured independant of the sonar room environment. It will also prevent dust particles from contaminating the electronic circuitry.

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. It is fitted with powerful shock absorbers to withstand the violent motions of a vessel at sea.


The rectangular SN90 transducer allows the sonar beam to provide the swath coverage of the water volume using electronic tilt. The transducer is rather small. Its face measures 184 x 184 mm, and the total weight (with cables) is approximately 60 kg.

For installation, the transducer is mounted in a metal mounting house, which is placed inside a blister. From this blister, a watertight metal pipe must be designed to reach well above the water line. The transducer cables penetrate through the rear side of the mounting house, and must be pulled through this pipe.

As an option for trawling use, you can install it using a hull unit. That allows you to retract the transducer for protection when the SN90 is not in use.


Note: The red protective coating is an 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, sand blasting, metal tools or strong solvents to clean the transducer face.
  • Do not damage the outer protective skin on the transducer.