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Old 26-10-2020, 14:40   #1
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Do you calibrate you depth sensor to water level or keel?

Got a new plotter, and had to replace the depth transducer since it had become a random number generator.

All working but my plotter has a calibration setting for "offset" which the manual says I could set for water level (sensor is 2 ft down) or depth of keel (4 ft below sensor).

What did you all choose to use?
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Old 26-10-2020, 14:44   #2
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Re: Do you calibrate you depth sensor to water level or keel?

I personally set for water depth (from the waterline). It's easy to know what depth is "minimum" before I'm at risk for bottom contact. And depth from surface is easier to correlate to depth markings on a chart.
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Old 26-10-2020, 14:47   #3
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Re: Do you calibrate you depth sensor to water level or keel?

We set for water depth, not depth under keel. Makes it more straightforward to navigate against charted depths when comparing charts to sounder readings.
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Old 26-10-2020, 14:51   #4
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Re: Do you calibrate you depth sensor to water level or keel?

I am the other guy... I want it to read water under the keel. No math invoolved to know if we have a problem. Charts and water draft obviously come into play on route planning.
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Old 26-10-2020, 14:54   #5
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Re: Do you calibrate you depth sensor to water level or keel?

I calibrated for depth under keel as I used the sounder for nosing around shallow areas (usually with scant chartered depths).
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Old 26-10-2020, 14:59   #6
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Re: Do you calibrate you depth sensor to water level or keel?

Quote:
Originally Posted by Off Trail View Post
We set for water depth, not depth under keel. Makes it more straightforward to navigate against charted depths when comparing charts to sounder readings.
Charted depth doesn't necessarily take tide into account.

I use keel depth - when it reads 0 I expect a bump.
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Old 26-10-2020, 15:05   #7
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Re: Do you calibrate you depth sensor to water level or keel?

Water depth. As someone said, correlates directly to the charts. Easier to gunkhole when you're looking for depth contours. And since I know how deep my keel is, it's pretty simple to know how much water is below it (depth-6').

But I suspect it's more about what you're used to. Either way would work. Just don't be switching it without telling others on board .
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Old 26-10-2020, 15:09   #8
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Re: Do you calibrate you depth sensor to water level or keel?

Absolutely water depth. Otherwise you're making all sorts of calculations when approaching an anchorage and considering the tidal change expected later in the night. And you can check it easily with a lead too.

If you set it to anything other than water depth, make sure you put a big sticker next to it saying so, as anyone else on your boat won't be expecting that.
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Old 26-10-2020, 15:27   #9
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Re: Do you calibrate you depth sensor to water level or keel?

Considering the actual depth is constantly changing and is often difficult (even impossible) to calculate from published information, it is moot point (IMO) where to set the calibration point.

If your primary need is to know how much water is below your keel, adjust the offset for keel depth however if your primary need is to know the water depth at your waterline, adjust the offset accordingly.

IME, many don't even know it is possible to adjust an offset or just don't bother.
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Old 26-10-2020, 15:32   #10
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Re: Do you calibrate you depth sensor to water level or keel?

Quote:
Originally Posted by Lodesman View Post
...I use keel depth - when it reads 0 I expect a bump.
+1

I've gone both ways but in the end it's just a personal preference thing. If anyone else will be operating the boat then a note needs to be posted somewhere as there is no "standard" - if I had to guess I would assume that most people expect water depth, but this thread seems pretty close to 50/50.
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Old 26-10-2020, 15:58   #11
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Re: Do you calibrate you depth sensor to water level or keel?

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If you set it to anything other than water depth, make sure you put a big sticker next to it saying so, as anyone else on your boat won't be expecting that.
I'd suggest the sticker is more critical if you set it to water depth, along with noting the draft.

I'm used to keel depth, meaning if I took the helm and didn't know both your draft and the calibration setting, I could easily run it aground while thinking I still had 6' under the keel.
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Old 26-10-2020, 16:01   #12
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Re: Do you calibrate you depth sensor to water level or keel?

I just leave mine set at 0 offset. Gives me a bit of a buffer is I assume it's a waterline reading when in skinny waters.
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Old 26-10-2020, 16:08   #13
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Re: Do you calibrate you depth sensor to water level or keel?

So happy to see there is a strong community consensus on this.

Now that I think about it, I have never inquired as to how it was set up on any boat I've ever rented and now I feel like I've been dodging bullets in the dark with the bliss of the totally ignorant.

Whichever I do, I definitely see a new placard in my future.
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Old 26-10-2020, 16:10   #14
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Re: Do you calibrate you depth sensor to water level or keel?

We set ours to keel depth. IE, 10 is 10 beneath the keel
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Old 26-10-2020, 16:14   #15
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Re: Do you calibrate you depth sensor to water level or keel?

I just thought of another reason for surface depth. Easier to give depth info to other people.
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