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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.

The sonar system ready to use. The buoy is used to mark interesting spots. The electronics is housed in the blue box and the display is a modified Si-Tex fish finder.

The sonar fish. The sound plate is visible.

Deploying the sonar off the back of the "Bottom Dollar", my research vessel.

The fish tows nicely.

The prototype units have been well tested.

Sonar installation aboard the "Bottom Dollar".

Wreck researcher Jonathan Hanks and technical diver Joe Razo.

I am ready to do some searching on a beautiful day.

Jonathan concentrates on a search.

You must watch the GPS, fishfinder, compass, and sonar all at the same time.

A fishing boat, the “Connie Marie” was easy to locate with the sonar.

Wreck diver, Joe Razo, looks for treasure.

Another murky scene aboard the “Connie Marie”.

Priceless artifacts were left behind and are waiting to be discovered! A Charlie Daniels music CD was found in the debris.

This wreck was discovered thanks to research by Jonathan Hanks. We used the sonar to help finalize the position. Nobody knew that the wreck was there and we were the first group to dive on it.

OK, it’s not the “Andria Doria”, but Jonathan made his china haul anyway. The dishes turned out to be sold by K-Mart.

Taylor smiles because his first ever wreck dive was a virgin wreck!

Jonathan scored a radar unit from the wheelhouse.

Another wreck found using the sonar.

A fishing boat in much deeper and clearer water.

More views of the fishing boat.

A different fishing boat wreck that we named the “Poppy Trail”.

These interesting plates were found in the debris. The design is known as “Poppy Trail” and they are collectable antiques now. The fishing boat crew probably bought them at Sears back in the 1950s.

The cleaned up “Poppy Trail” plates.

The paper display is easy to see in the sunlight. The plastic cover can be removed to allow writing notes on the paper while searching. Very handy.

This recording shows a very pronounced wreck at about 600 foot range. The horizontal lines on the paper are generated by the sonar circuitry. These lines are 100 feet apart. Zero range is at the top of the paper and the bottom line represents 600 feet.

A newly discovered wreck detected at 400 foot range. The other images are the same wreck. After seeing the first image on the paper, I turned the boat causing the sonar beam to sweep across the wreck twice more.

A wreck at 450 foot range. This is an isolated object on an otherwise flat sandy bottom.

A boat wake (left) and a wreck (right). The wreck is well defined and what appears to be a school of fish is near the wreck. Often the fish living near a wreck will show up stronger than the wreck itself.

Objects on the bottom. Could be wrecks waiting to be explored.

The distance between objects and their orientation can be estimated.

The fish is constructed from laminated wood.

The wood is carved to shape and the transducer fitted.

The transducer contains six piezoelectric drivers.

The piezoelectric drivers are industrial parts used in ultrasonic cleaners.

The fins are made of steel.

The transducer is entirely homemade.

The transducer fits in the fish.

Newly designed electronics is installed in the Si-Tex case. The original electronics is removed and only the paper transport is retained.

The stylus writing circuit (left) and the motor control circuit (right) installed in the Si-Tex unit.

The transmitter board (top) and the receiver board (bottom) separated by a metal shield.

The electronics is an original design. The transformers are also homemade.

Home Built Sonar © Copyright 2010, by Mark Thompson

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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!

Mark Thompson

FREE PDF Download: Home Built Sonar

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