How deep does your depth sounder go?

[AntarcticPilot]

My depth sounder goes down about an inch below the hull.



But you have to remember that metres are not as substantial as proper British fathoms, and so the signal probably passes through them that much easier.

Anyway, who'd care about the power requirements if the alternative was using the lead line in 1,000m/547 fathoms?

Well, wire line sounding was used by the Challenger expedition, and to this day deep sea dredges and other sampling gear is deployed on wire.

 

[Habebty]

Ours stops reading at about 120 metres.

At ocean depths (ie 1000 plus metres) it will sporadically read a few metres depth which I have always assumed was a fish or fishes.

Or a submarine! Had that sudden reduction in depth in Lyme Bay once.

 

[LittleSister]

One needs to know when has passed over the edge of the continental shelf when sailing up and down the East Coast!

 

[penfold]

We have a Lowrance combined fishfinder/chartplotter which tends to struggle beyond 100m and a NASA Clipper which is misbehaving as the oil filled tube it sits in has developed a leak; when working it also struggles beyond 80m or so.

 

[jamie N]

Depth displays are a very simple form of a proper sonar unit, such as are commonly used on ROV's.
I do know of 'bad boys' who'd change the 'speed of sound through water' parameter on the software from a nominal 1475m/sec to 15000m/sec, which could cause issues for the next user.
Irresponsible and not condoned by any professional of course.....

 

[Daydream believer]

Or a submarine! Had that sudden reduction in depth in Lyme Bay once.

How do you know that it was not an Orca sizing you up

 

[Porthandbuoy]

Interesting feedback everyone. Thanks. Looks like there’s something wrong with my setup. I think I’ll take the opportunity when she’s next out of the water to remove the two transducers fitted through the hull. Why two I don’t know. One has the cable neatly coiled and tied back, the other in use. Both work, but this arrangement can’t be for checking the depth after a tack as it’s major dismantling job to access both transducers and display unit (Stowe Navigator 1).

 

[johnalison]

If it'll reach 1000m, it must be a pretty beefy bit of kit. The power required goes up as the square of the maximum depth, so a sounder capable of reaching ten times the usual range of a yacht's echo sounder should use about 100 times the power!

I know nothing about acoustics, but would it be possible to focus the pulse to extend the range without demanding so much power?

 

[AntarcticPilot]

I know nothing about acoustics, but would it be possible to focus the pulse to extend the range without demanding so much power?

Not without increasing the size of the transducer significantly. The wavelength in water of a 200kHz transducer is 7.5 mm. This results in a beamwidth of around 30 degrees with our existing transducers (it varies). Reducing the beamwidth to 3 degrees might mean a transducer at least 10 times larger. Also, high frequencies such as we use are attenuated more rapidly by the water, and a lower frequency would require a correspondingly larger transducer.

 

[john_morris_uk]

Not without increasing the size of the transducer significantly. The wavelength in water of a 200kHz transducer is 7.5 mm. This results in a beamwidth of around 30 degrees with our existing transducers (it varies). Reducing the beamwidth to 3 degrees might mean a transducer at least 10 times larger. Also, high frequencies such as we use are attenuated more rapidly by the water, and a lower frequency would require a correspondingly larger transducer.

3 degrees beam width would be excessively intermittent due to boat rolling and pitching.

 

[Buck Turgidson]

Mine reads to about 300m then very annoyingly gives random shallow returns at greater depths. I’ve seen the raymarine displays just say deep which is a better solution as I had to turn my shallow depth alarm off