Beni,

To search for bottom features in 200 or 300 feet of water, you will definitely need to use a towed side scan sonar which will provide a much better view and range for detecting the bottom topography protruding from the sea floor that you are not directly passing over with your boat. Thru hull or hull mounted side scan units have several limitations as follows:

1 To obtain good imagery you need to operate in fairly calm seas because every turn of the boat by the waves will distort the image because the sonar transducer is constantly being shifted back and forth with the boat. This is not the case when you are towing the sonar transducer as it will stay true to the course that you are on regards of the slight movements of the boat by the waves.

2) In deeper depths the image definition of of the bottom features will not be very good because you are looking mostly down on the seafloor and not much off to the side

2) If there are thermal layers in the body of water where you are operating, then the range will be severely limited when using a sonar transducer at the surface. When the sonar signal hits a thermal layer at some critical angle and range, that interface acts like a mirror bouncing the signal away from the bottom and not providing any return signal.

Typically, the hull mounted side scan sonar units are of good benefit to fisherman and to some amateur shipwreck hunters in depths of 50 ft or less. Serious shipwreck hunters are using towed side scan units.

Searching for a Drowning Victim: This is very hard to do even with the best side scan equipment. The best success is when the bottom of the sea floor is very soft and has no other objects in the area such as rocks, coral, or vegetation that give a much stronger signal return. If the bottom is not clear of other stuff, then finding a body is going to be next to impossible. You must also get the sonar transducer close to the bottom as a body will not be a strong target and will not have much of a profile above the sea floor.

For your particular requirements you should be looking at manufactureres of towed side scan sonar units. If you want to search both in depths of 50 ft or less and don't want to deploy a side scan towfish but also want to search in deep water, then you might take a look at the DeepVision DeepEye HM340 Hull Mounted side Scan Sonar system. This system will allow you to use the same Surface Unit and software of the HM340 with a DeepVision Towfish when you want to search deep. This might be the best of both situations for you.

Best of luck with your shipwreck searching and I hope this information helps.
Jim