Forward looking sounder.

[Graham_Wright]

Anybody ever tried or thought of trying a standard depth sounder pointed forward (below the water line) for detecting and warning of floating hazards (hard big variety like shipping containers of which we are told there are thousands lost)?

 

[BrendanS]

you mean like this?
http://www.echopilot.com/products/forward_looking_sonar/how_fls_technology_works.aspx

 

[bobgosling]

I think what graham is proposing is a normal standard echosounder but with the transducer pointing forwards instead of down ? the EchoPilot version scans with a narrow beam like a radar but is ludicrously expensive and has had a lot of bad comments in these fora.

I doubt that this would be as effective as you are hoping. A standard echo sounder throws a relatively wide beam ( like a torch ) which is why they still work when the boat heels.

I think you would find it difficult in practice to distinguish between an echo from an object ahead and one returned from the sea floor.

 

[hubert]

I have tried this without much success. The main problem are spurious echoes from surface waves. Each wave causes a discontinuity in the signal path and reflects some energy back to the transducer giving just lots of clutter. Perhaps going deeper would help but with the beamwidth of most transducers of about plus and minus 20 degrees it would have to be very deep to work reliably.

 

[Graham_Wright]

I thought that might be a problem. I wonder if mounting on the leading edge of the keel would help and whether it would be possible to screen off the upwards part of the beam with a flat plate.

The thought of hitting an almost submerged container in the dark is frightening.

 

[bbg]

Frightening perhaps, but (despite what we are told about thousands being out there) extremely unlikely. How many known or even suspected cases are there of yachts sinking due to this? And I would have thought that even if the worst happens, you would still have time to get off a distress message and launch a liferaft. True it would be better not to hit one, but if it were so easy to bodge up a reliable "container detector" don't you think there would be one on the market?

 

[DaveS]

I agree the FLS is dear (mine was a present /forums/images/graemlins/smile.gif ), there is certainly an issue with trying to fit the cheaper version of the transducer in anything other than a thin flat hull, and there can be problems with other sounders operating on the same frequency, but I don't recall any other adverse comments here or elsewhere. Do you have more details?

FWIW I have found mine extremely handy on the rare occasions that it really matters.

 

[2Tizwoz]

Although there is much concern expressed regarding semi-submerged containers, there must be greater numbers of trees and other semi-submerged pieces of timber which would not be nice to collide with but would forward sonar pick them up?

 

[DaveS]

I've never personally come across a container - as others have said they are thankfully rare - but it certainly does show things like pot buoys that could be a problem in the dark. The range ahead varies with depth: about 10X depth is claimed, but a small object needs to get a bit closer before emerging from the noise. You should still get a good few seconds warning, but of course whether you'ld want to spend a night watch staring at a wee screen... I personally rarely sail at night and use the FLS mainly for exploring "interesting" rocky places.

Your point about trees is well made. The next time I come across one I'll have a look at it with the FLS and see what it makes of it. I would expect it to show up, but it would be nice to get confirmation.

 

[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 !

 

[sjchilde]

Last time I grounded in the Tamar it was because I didn't know which way to turn. So I was thinking about putting one each side facing apart so I would be able to tell which side the deep water was. But I wonder whether they would interefere with each other - present one is thrown by a fluorescent light - and I'll probably never try it.

 

[DaveS]

I like that! Neat and cheap.