Depth below Keel or depth of water ?

Mine is a repeater display from an Actisense box and has no adjustment for offset.
I know that she'll touch at 1 metre displayed, and I have to add 0.4 metre to get 'depth of water'.
 
Depth of water below keel, since we sail the east coast, often in very shallow water I want to know what's under the keel at a glance.

I have noticed that when we are about to touch the turbulence under the hull gives false readings from about 0.3 metres or less, therefore if it jumps from 0.3 to 2.3 I know we're about to touch!
 
I was getting readings from the weed on Windermere. I could be moving through the water with -1 foot showing (the weed grows about 4 feet tall)
Very confusing. Better without it.
 
depth below keel - you know immediately how much water you have left. for depth of water add your draught

the old boat had a keel offset so that's what i did. the new boat is still fitted with a seafarer with no offset so i've got a bit of a compromise - deoth below transducer whoich means i go aground at 1.2!
 
Metres of water depth.

Metres because I can't be doing with these feet, fathoms, furlongs and things. The depth sounder can be calibrated in feet or metres, so can the chart plotter, but the paper chart is fixed in metres.

Total water depth because it just seem more logical. If the number gets close to 2.0, I'm in danger of grounding. No different to setting it to the keel and grounding at 0.0.
 
Pagetslady said:
Where do you have your echo sounder depth set from I have always set the offset so that I get a reading that tells me how deep it is in mtrs what do you prefer?
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My last boat was commissioned with the depthsounder being offset to water below the keel. This seemed an excellant idea, until I found out that the it was consistently underestimating the depth. My theory is that someting was lost in translation when applying the offset causing it to under read.

Having made this 'discovery' I have never applied an offset and then learnt from experiance when the boat stops moving :)
 
Why bother? Choose feet or meters, your choice. Fathoms if you like.

But then, simply quietly run your boat aground on a soft bottom and see what the depthsounder says when you hit.

Then you'll know. On my boat if it reads 4.4 I'll hit.

I could care less what the offsets or depths are. Once you do that, you can "calibrate" what real depths are by noting what the tide level is when you do your test.

Simple.
 
Shamal said:
Depth of water below keel, since we sail the east coast, often in very shallow water I want to know what's under the keel at a glance./QUOTE]

My Seafarer whirly shows the keel bulb on the Jouster (lying Kirkcudbright, no reasonable offer refused) as well as the bottom, so it's dead easy to see how much there is below.
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This is one of those questions that comes up from time to time and one in which I really struggle to understand some peoples logic. I can just about understand why people "see" feet rather than meters in their minds eye, although I still find it strange to think of having all the charting and tidal data in meters and still have your echo sounder in feet! However I have a good friend who is a Naval Architect who works entirely metrically at work yet keeps his echo sounder set to feet so it must make sense to some people somehow.

What I utterly can't understand is the logic that some apply to "I must have depth below keel so that I know when it's getting towards zero I'm going to run aground". I know that we are all different, but if I can't remember I need 1.8m to float in I am not sure I should be sailing.


Everything useful in navigation calculations that you use an echo sounder for requires depth of water. You have probably worked out by now that our ech sounder reads in metres and it reads depth of water.

One of the first things I do whenever I get on a strange boat is dangle a spanner over the side and check what the echo sounder is reading. It's a common courtesy to put the calibration back to how you found it when you leave, of course.
 
Quite. Why bother with the maths at a point when you need instant information.
Relating info to a chart you have more time.
I can't remember how deep my keel is. But I know I should still be sailing.
 
john_morris_uk said:
What I utterly can't understand is the logic that some apply to "I must have depth below keel so that I know when it's getting towards zero I'm going to run aground". I know that we are all different, but if I can't remember I need 1.8m to float in I am not sure I should be sailing.
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I absolutely agree. I suspect that chart plotters are something to to with the depth below keel thinking. Plotters have taken away the need to relate true depth to a chart in order to help confirm position. When approaching a harbour or jetty I can absolutely assure anyone on here that the tide gauge on the wall won't show the depth from your transducer or under your keel.
 
A dangerous business ... .

SolentBoy said:
Depth below the keel in metres.

I really don't care about anything else and it makes death calculations for anchoring very easy. Plotter tells you how much the drop is to low water, as long as you have that below the keel then anchor away!
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"death calculations when anchoring" ...I like it.
Re. the thread: one person almost made the point that amateur button pressing on the echo sounder may unwittingly change the offset and lead to problems later. Nevertheless we always have the display reading water under the keel- maybe because we're both maths. types and like to see the origin of any graph as zero i.e. the boat starts or ceases to float at zero reading. Many or most graphs in newspapers disobey this rule in order to dramatise trends.
 
.
Why do people get so exercised over this? Surely it is a matter of personal preference. It is no more difficult to add the draught of the boat when using depth for navigation than it is to subtract it when working out when you are going to ground.

As usual some people on here are taking this rather too seriously. Do what you want. if you 'really can't understand' why people do it a different way to you then you need to loosen up a bit.

If you are sailing someone else's boat then I would consider it very bad form to change the echo sounder offset - if you are unsure then use a leadline to work out what it is then live with it.

- W
 
Absolutely Webby. Didn't want to sound preachy, but what business is it of anyone else?

As I sail on a lake I don't make tidal calculations. I just want to know where it's too shallow for me.

(Of course as I sail on a lake, I don't count)
 
Perhaps I should have made it clearer that I don't really mind what other people do - after all it's their choice. I was merely pointing out that I don't understand their way of thinking.

It might say more about the way that I navigate - with always one eye on the echo sounded when I plot on the chart to make sure that where I think I am makes sense on the charted depth? However just because I do it that way doesn't make it the only right way of doing it...
 
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