Homebuilt Side Scan Sonar
This section is for those persons who are interested in electronics as it relates to scuba diving and searching for shipwrecks. My current project is a homemade side scan sonar. By avoiding specialty parts and using common industrial and hardware store materials, I have kept the cost low. My electronics design follows the same philosophy by using well proven analog circuitry and discrete components. No software is involved because the display is a vintage Si-Tex fathometer. Although the cost is low and the design is simple, the results have been well worth the effort.
The purpose of the sonar is to search for shipwrecks and other interesting dive spots in my local area. The ocean bottom offshore from Ventura, Ca. is a vast area of mostly sand that extends out several miles before becoming too deep to dive. At 4 miles out the depth is barely 100 feet. Isolated reefs and shipwrecks exist here and there and they are not all known or charted. For years, I have heard of shipwrecks that somebody dove “back in the 70s” but are lost now. The old loran-C numbers don’t work or in some cases the old visual landmarks have been altered so much that you cannot use them. As a diver, I want to locate these interesting spots and visit them.
If you have ever searched using a typical boat fathometer, you know how hopeless it is. The area that the fathometer beam covers on the bottom is only a few feet wide. You can be close to a large wreck and never detect it. A side scan sonar is needed to increase the area covered in a search.
My side scan sonar is designed to tackle this situation. I designed a long range system that will cover the maximum possible area. With lots of effective power and an efficient transducer, the system can search an area hundreds of feet wide. Since I am looking for large items, the resolution is not as important as the range. Although you cannot identify the objects seen with the low resolution display, you know something is there! Objects really stand out on a flat sand bottom.
Technically this is a low frequency sonar. The operating frequency is about 25 KHz and the pulse width is long. The physics of sonar relates the feasible resolution of the display to the frequency of operation and the pulse width. Most commercial units utilize frequencies of hundreds of KHz to maximize the resolution. These units have expensive high performance transducers and electronics that are not easy to duplicate at home. I chose to forgo the resolution in favor of search area.
When you operate at low frequencies, everything is easier. The transducer is big and can be fabricated at home with simple techniques and the electronics is non critical. The physics of sound in water also favors low frequency operation because the attenuation is lower and the sound signal has more effective range. The Navy uses low frequency sonar because they are looking for the same thing divers are: big ships under the water.
This web page contains pictures of the sonar system and the effort to find shipwrecks and other dive spots. I have written a manual with the specific plans and instructions to duplicate the sonar system. The manual is described and offered for sale on the bottom of this web page.
Side Scan Sonar Picture Gallery
This is a collection of pictures relating to the homemade side scan sonar and the effort to find shipwrecks in the local area around Ventura County, California.
Home Built Sonar © Copyright 2010, by Mark Thompson
This do-it-yourself manual describes the construction of the complete side scan sonar system. I took numerous pictures during the construction of the prototype system. Later when I saw how well the system worked, I decided to produce this manual for people with similar interests.
This manual contains 96 pages of information with 75 illustrations. The actual prototype unit is pictured during the building process. All the details of construction are visible in the pictures and explained in the text.
The electronics is an original design using common off-the-shelf parts as much as possible. The few unusual or critical components are noted and sources are suggested in the parts list. Also included is an explanation of the operation of the circuits along with setup and adjustment details.
Although the circuit schematics and parts lists are explained in detail, the method of construction of the circuitry is left to the builder. Pictures in the manual and on my website show how I constructed the circuitry, but other methods will work. Since the circuits are mostly non-critical, any type of electronic prototype construction can be used. The builder should use his preferred method of construction.
An important section contains information about testing the transducer and electronic circuitry. Since the sonar is home made, some testing and adjustment will be necessary before optimum results are obtained. This section suggests what test equipment is necessary and how it is used. Included is an explanation of the testing, tuning and impedance matching of the transducer and how this relates to the electronics. This section is aimed at the person who has moderate knowledge of electronic testing and the use of common test equipment.
During the building and testing process, you will become very skillful at side scan sonar operation. Other books go into great detail about interpreting sonar information and I haven’t tried to duplicate that information. This manual contains suggested procedures for adjusting the system for best results and how to use it to search the bottom from a small boat.
The purpose of the manual is to detail how my side scan sonar system project was built and how to duplicate it. I hope you will enjoy building and using it!