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.
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.
The moving paper display is visible even in bright sunlight.
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.
The newly designed electronics installed in the Si-Tex case. All original electronics is removed.
The motor stylus driver board and motor control board.
The transmitter and receiver unit prototype.
The electronics is an original design including custom wound magnetics.
Typical paper recording from a sonar search. Zero feet is at the top and the range lines are 100 foot intervals. In this recording, a very pronounced wreck is visible at about 600 foot range.
A paper recording of a newly discovered wreck detected at 400 foot range. The second and third more blurry images are the same wreck, printed again, as I turned the boat slightly to cause the sonar beam to sweep by the wreck a second time.
Diving on the Connie Marie, a fishing boat located using the sonar. The vis is poor but it’s a cool wreck nevertheless.
Wreck diver, Joe Razo, looks into the wheelhouse of the Connie Marie.
The fishing boat crew left in a hurry, leaving their Charlie Daniels CD behind.
Diving on the newly discovered wreck depicted in the scan above. The water is murky but lots of cool junk is lying around.
Shipwreck researcher and diver Jonathan Hanks shows his china haul taken from the new wreck. Ok, it’s not the Andrea Doria, but still not bad for Southern California.
Diver Taylor also scored a fork.