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Old 05-05-2013, 21:55   #1
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Can you make a forward reading sonar?

I need to upgrade my transducers to work with a newly installed Raymarine e7D. I got the "D" version, built-in sonar/fishfinder, to avoid the problems that several other boats in our PNW marina have had, hitting something hard and messing up their keel to hull joint.

My 1981 sailboat has a 17 degree rise from the front of the keel to the bow. In talking to Airmar they suggest a sonar/depth/fishfinder that has a tilting element which can compensate for up to a 22 degree rise and image directly under the boat. But to avoid hitting stuff I really want to know what is in front of the boat.

What would happen if you used a 0 degree tilt sonar/fishfinder? Would that turn it into forward reading sonar so you could keep an eye on what you were about to hit rather than what was under the keel? Would the image be too distorted to be useful?
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Old 05-05-2013, 21:58   #2
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Typical transducers have a 60 degree angle? No? You should make a sketch to scale. The transducer measures a Radius so draw a semicircle centered at the transducer to see what would be reported.

You idea has some merit.
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Old 06-05-2013, 09:25   #3
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Re: Can you make a forward reading sonar?

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Typical transducers have a 60 degree angle? No? You should make a sketch to scale. The transducer measures a Radius so draw a semicircle centered at the transducer to see what would be reported.
If the slope/rise of the hull from the keel is 17 degrees wouldn't that suggest that you would just see 17 degrees more in front of the boat with a non-tilted transducer than with a tilted element transducer?
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Old 06-05-2013, 09:38   #4
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Re: Can you make a forward reading sonar?

I have wondered about the same thing about angling a transducer. First, maybe you already know that there are a couple of companies that make a forward looking depth/sonar unit. I have read user reports of how well these work and it seems that the general consensus is that their utility is somewhat limited.

The forward looking is not straight ahead but at a downward angle and if you look at the geometry the range is very limited, especially in shallow water. Unless you are going very, very slowly you won'tl see the rock on the display until a nanosecond before you hit. The results are worse in waves and swells so they are almost useless in spotting a floating hazard like a semi-submerged shipping container.

Seems like the best use is in deeper water to give you a little earlier warning of water shoaling ahead.
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