Depth gauge readout

[jbweston]

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By depth of water, I take it you mean depth under the transducer.

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I have mine set to depth of water by which I mean exactly that - that is depth below transducer plus depth from surface to transducer.

Depth below transducer seems to me the worst of both worlds - you have to do calculations to work out depth of water or depth below keel.

Also depth of water is easy to calibrate - just wait until you are in a berth with a level bottom, put the lead line over the side (or both sides and average if you want to be super accurate), and then adjust the sounder until it reads the same.

Honestly I don't think it matters whether you do depth below keel or depth of water provided everyone using the boat (including crew who helm or assist with pilotage) is absolutely clear which it is - and in a syndicate I'd seriously consider a label under the gauge or at least at the chart table saying which is the standard on the boat. And, of course, capital punishment for anyone who changes the setting!

 

[AntarcticPilot]

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Also depth of water is easy to calibrate - just wait until you are in a berth with a level bottom, put the lead line over the side (or both sides and average if you want to be super accurate), and then adjust the sounder until it reads the same.

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This may not be a safe way of calibrating an echo-sounder. The speed of sound in water is affected by both salinity and temperature. The salinity and temperature in a marina or in a river berth are not likely to be typical of those elsewhere (if there is fresh-water input the salinity may be low; if not evaporation and limited circulation may make it high). In a river berth, they will also change with the state of the tide.

Does anyone know a good way of calibrating a depth-sounder? I know how it is done for scientific purposes in deep water - the system is calibrated using a Conductivity-Temperature-depth probe, but few of us have the equipment to do that!

 

[l'escargot]

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...Depth below transducer seems to me the worst of both worlds - you have to do calculations to work out depth of water or depth below keel...

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No, you only have to do the calculation once - and remember it. You don't need to know how much water there is, only that there is enough. As I draw a metre and the transducer is about half a metre below the surface, I know if my depth sounder reads more than 1 metre I won't go aground. The advantage is that you never have to check what your settings are if you leave it on default - less room for error or setting it wrong, I also don't have to remember to recalibrate after the battery has been disconnected.

 

[LadyInBed]

I like mine to read 'Depth under keel' and inform anyone who is out with me.
I switch it to read in feet (and announce that I have switched) when going up the channel to the mooring, it quite often reads 0.1 ft!
Tacking along the coast into shallow water, I use the shallow alarm.
When I am out in deep water, (cross Channel) I turn it off.
It does not loose it's offset when the battery is disconnected.

 

[marklucas]

Depth of water every time!

Makes life so much easier with calculations. Also very easy to check the actual water depth e.g. heading out of Hamble, sail on the line of the piles marking the channel - they're on the 0m contour - instant height of tide!

 

[flaming]

The key thing is to know what it's calibrated to.

I do quite a lot of work for Sunsail, and all their depth sounders are set up to read depth under the keel. Along with a little notice to tell you.
However one "more senior" skipper hates this, and went through a stage of changing it every time he took a boat out. Of course he often forgot to change it back.... I remember leaving the dock on a low tide thinking "wow they must have dredged...." Oh bugger....

 

[john_morris_uk]

In answer to your original question - I don't think that there is a way you will persuade the other owners to change. There's no absolutely compelling argument either way.

I always set out echo sounder to depth of water - for all the reasons that others have already mentioned. It makes sense when you have done some tidal calculations not to have to remember to add 1.8 metres or whatever to your echo sounder to compare the depth where you are to what you think it ought to be.

Furthermore, and as I think I have said on these forums before, "If I can't remember that I need 1.8 metres of water to float in, I shouldn't be sailing."

Despite all this, I have a very good friend who sails with metric charts/chartplotter and then insists that his echo sounder reads out in feet under the keel. There's no accounting for taste - and if that is what he wants, than that's fine by me.

 

[snowleopard]

What sort of echo sounder do you have that loses its settings when you turn the battery off? Is it very old?

I would have thought depth below transducer would be the worst of all worlds, having to remember distance from surface to transducer and transducer to keel and do the mental arithmetic every time. Are you certain you can always remember which measurement to use and whether to add or subtract even when tired, rushed or stressed? I could certainly learn to live with it as I did in the old days with a neon Seafarer but do you ever have crew who aren't familiar with the setup?