Forward Scanning Sonar (Depth)

[Victor Robert]

I am considering adding forward scanning depth electronics to my helm instruments. If you have experience with any of the products on the market, I would appreciate sharing it. My objective is to navigate in the Bahamas and Florida (5' to 10' with a 5' draft) using less of the Braille method. My main question is how far ahead can you practically 'see' in shallow water (i.e. how slowly do you have to be moving to detect an object or change in depth in time to avoid it) ? Also, I am trying to clarify the advantage of the dual transducers versus the single.Thanks for your help.

 

[Alex]

It varies..

..In general ,in shallow water it 'looks' forward about the same , or up to 1.5 times the actual depth..in deeper waters it looks much more , around 10 to one , and up to around 150 m max in optimal conditions. One have to take in consideration thatwhatever other depth transducer is mounted 'upstream' this unit transducer ,it has mostly to be turn off , due to severe interferances between the transducers.There are several brand in the market , some more thecnically advanced than others , although they look the same.

 

[Mickey McHugh]

Interphase

I added the Interphase TwinScope Sonar last Aug to a 40.5 for $1700. It is mounted right next to the Raytheon fishfinder dual speed and depth transducer forward of the keel. The sonar 'dome' is rather large; 4" deep, 5" wide and 9" long so I guess I added some drag but haven't noticed it. In the past 6 months I have used it around Galveston Bay and on a cruise from Texas to Baltimore. The Raytheon can transmit at either 200 KHz or 50 KHz and the Interphase transmits at 200 KHz. There has never been any interference between the units. I was sure there was going to be but glad there isn't. It is very comforting to have 2 sources of depth readings at all times. In the 'Probe' mode the unit can look forward at 6 times the depth so at 10' you only see 60'. But in the Gulf we were spotting fish and dolphins out as far as 600'. In the 'Scan' mode it looks 45 degress on each side of the bow at a 20 degree down angle. The beam width of the transmission is 10 degrees in both modes. The Scan mode was helpful in the ICW at night since it showed the 'edge' of the channel. But in really shallow flat bottoms it does not help that much. We are divers so finding wrecks and structure on the bottom of the Gulf of Mexico is where it is invaluable since it 'paints' a very clear picture of the bottom.