Angled Depth sounder !

[capt_birdseye]

I installed the transducer on my Invicta at an angle of 30 degrees to the horizontal plane. This way 'hopefully' I was using Trig ratios of 1 : 2 : Root 3. With 1 being the 'Small' Vertical of the triangle ( And being the ACTUAL depth of water ) and the Hypotenuse being 2 ( Or twice the depth of water, and what would be the 'Indicated' depth ), and the 3rd side of the Triangle equating to the horizontal distance from any object picked up by the Fish finder.
I used it for 4 years, and became used to looking at the display, seeing X feet of water, dividing it by 2 to give me the 'Actual depth'.
It WAS handy for spotting rocks etc., that I was approaching, instead of being sat on top of.
Never came across any containers, or frig's and freezers, so cannot say if it works for that purpose.
Never used the 'Fish Finder for fishing in any case ! Good Luck !

 

[Kantara]

Does that work? I thought the transducer transmitted over quite a wide angle. Surey if it only did it in a straight line then the depth would appear to increase as the boat heeled. I've never noticed that happening.

 

[fisherman]

Should work. The beam angle means that as the boat rolls the reading does not change because it records the nearest echo, which will be the actual depth until the boat heels beyond half the bee mangle.
So if you angle the tranny forward by half the bee mangle, you should get accurate depth readings, but advanced warning of obstructions? Interesting.

Google 'transducer beam angle' if you want to be really confused.

 

[Kantara]

That's what I would have thought. However I read capt_birdseye to say that he used trig to calculate actual depths ahead.

 

[capt_birdseye]

If you look at at the 30 : 60 : 90 degree triangle you will see that the shortest side is for example ONE unit in length, the Hypotenuse is TWO units in length, and the other side is Root 3 ( Or 1.732 X the ONE unit ). Therefore if the reading from the Angled Transducer ( 30 degreees to the horizontal ), then the actual 'Depth' is half of what the transducer sees.
I tried it first with the 30 degree angle and the transducer taped on a pole. Easy to set up and try ! Hence my reference to TRIG. One : Two : Root Three. or, 30:60;90.

 

[Kantara]

I know what you mean. However, that assumes that the transducer is transmitting in a straight line, yet fisherman and I both think that it actually transmitts over an angle and then takes the first response. In that case even if the transducer is pointing ahead it will surely pick up the return from the bottom as the first response, until you come up against a breakwater that is a shorter distance ahead than the depth of water you are in.

 

[Graham_Wright]

Does the honey separate? /forums/images/graemlins/cool.gif

 

[aitchw]

Surely that would mean that if you were stationary in the water the display would reduce to a flat line i.e. constant depth but it doesn't, it still shows a bottom contour, at least I think it does.

 

[Bodach na mara]

I don't think Capt Birdseye is correct. The transponder transmits returning echoes from whatever angle. The speed of sound in water is about 1000 metres per second. If an echo is received from the bottom(30 degrees off line) 50 milliseconds after the outgoing pulse, the sound has travelled 50 metres. The depth is therefore 25 metres and that is what the meter will read. If the echo is received from an object on the axis at the same time it will still read 25 metres. Trig is irrelevant. I do wonder however what the efective conical angle of the transponder is.

 

[Kantara]

Oh for a drawing facility!
Boat



---A-----------------------B

A is the bottom directly under the boat
B is the bottom 30 degrees ahead
Boat - A is 10 metres
A - B is 20 metres
Boat - B is square root of (100 + 400) or 22.3 metres

I believe that the transponder will bounce off A first and therefore give a reply of 10 metres. However, even if it was highly focussed, I think capt_birdseye is wrong in saying that he would divide his answer by 2. OK, not wildly wrong, but his answer would be 11.15 metres when the depth is actually 10.
Now prove me wrong - it's a long time since I did Pythag.

 

[alienzdive]

Wouldnt different manufacturers have different cones etc making it specific to a certain transducer rather than broadly speaking for all transducers. Not sure about this but just adding my bit.

 

[Danny]

I think the 'beam angle' for most echo sounder transducers is between 10 and 20 degrees (-3db points). However don't imagine that the beam is exactly cone shaped. There are side lobes, etc.

 

[capt_birdseye]

As I said before I based my 30 degree angle, and assessments on the 30 : 60 : 90 Triangle. One of the 'Standards' in drawing and Trig. THEN, I tried it on my boat. Seems to work well enough to tell you that there is something ahead, and not directly below, as with all 'correctly' mounted depth sounders. Any advance warning is better than being sat on the rock ? I wonder what the various manufacturers would say ? Probably ''It will not work, but we do have an arm and a leg job that could buy ! '' ?

 

[capt_birdseye]

How to fit an Angled Depth sounder !

I didn't make a permanent installation until I had tried it. I shaped a piece of plastic drainpipe to fit against the hull ( In the bow ), where the angle looking FWD would be 30 Degrees, and used Silicone sealant to seal the pipe to the hull. The transducer was put in place, and the pipe filled with ordinary water. ( If it leaked, then there would only be a bit more water in the bilge ). After initial 'testing' I Glassed the pipe in place, and still used ordinary water to fill the pipe.
Good Luck !