Forward Sonar

[Lynx]

With the threats of hitting objects I was wanting to have put in a Forward Sonar. Are they worth the money?

At what speed are they not effective?

[Alan Wheeler]

What objects?? Are you talking about surface objects like logs etc, or below surface objects like a large Rock or the Bottom rising?
They are no good for detecting floating objects, unless it is very large and has a significant amount below water. Like a container, but even then it depends on the installation and how much forward "view" the transducer is allowed.
Speed? they will work faster than you can go, but effective advance warning is subject to many things. The object you are detecting, the forward distance your unit is set to scan to and the speed thus reaction time of your self and the vessel.

[knottybuoyz]

I've read somewhere that a lot of users end up taking the units back because they can't interpret what they're seeing on the screen. The two dimensional representation of a 3D array image can be difficult for the unitiated to understand. I think canibul works with advanced underwater systems maybe he can chime in.

http://www.echopilot.com/products/fo...een_shots.aspx

[rsn48]

Knotty, my understanding is that we are in the early stages of forward looking sonar. I thought I read somewhere that most modern units can be used at 10 knots or lower.

I know the BC Ferries could have used one with the loss of its ship the Queen of the North.

I suspect as the units are developed over time, they will become easier to read and the prices will have dropped, just look at the development of radar and fish finders. Eventually most of the larger boats will have one, and some of us smaller boaters will have one as well; in colour of course.

[Lynx]

I really do not know what the units can sonar (see?). I was hopping that it would detect logs and such floating stuff that would damage my boat. I have read that they are good for finding your way in the shallow water of the Bahamas.

I was hopeing that it would save me from hitting something in any weather. Before I buy one I wanted to know.

[GordMay]

You might be interested in reading:

“Looking Ahead” ~ by By Ben Ellison (Power & Mororyacht, July 2002)
Magic it’s not, but cruisers who understand forward-looking sonar’s limits are pleased with what it can do for them.
http://powerandmotoryacht.com/electronics/0702sonar/

and

”SONAR for Navigation” (Part Two) ~ by Steve & Linda Dashew
http://www.setsail.com/s_logs/dashew/dashew299.html

Manufacturers:

EchoPilot Marine Electronics Ltd
http://www.echopilot.com/contact_us.aspx

FarSounder
www.farsounder.com

Interphase Technologies Inc.
http://www.interphase-tech.com/

Pilot Marine International Inc.
http://www.pilotmarine.com/

[Canibul]

Sonars do take some thinking on the part of the operator. It has to do with having to wait for one pulse to go out and reflect back before putting another pulse in the water. The speed at which this happens (sampling rate) is controlled by the range setting. If you are trying to look long range, you might entirely miss a small reflector that is between 'pings'. If you can limit your range requirement you get a faster sampling rate and increase the chance of returns from obstructions. This is also tied to vessel speed. If, for example, you are stopped dead in the water or at anchor, the constant returns from a stationary target can look like a wall.

Boat speed can also affect signal-to-noise at the transducer. Bubbles will of course screw it up everytime, no matter what the manufacturer says. mechanical noise in the right freq. band can also do it, unless your system is sophisticated enough to use chirp technology, Kalman-based filtering, and platform motion correction.

The filtering has to be good enough to grab the correct return ( the first one back) and ignore all the reflections that come rattling in right behind it. This is called multi-path distortion.

Organic growth on the transducer will reduce snr, as will a layer of paint or especially silicon. If your transducer goes through an oily patch, you need to use some good old dish soap to wash it off. Need a good acoustic coupling to the water. the soap will 'wet' the transducer.

You gotta think like a sound wave when operating a sonar.