Depth Measurement


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Bill Balme
Bill Balme
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My depth sounder is set to display the depth of the water. Over here in the UK, it seems most are set to depth under the keel. Both seem to have some logic to them - but I can't see how depth under the keel is helpful except when in very shallow water... in which case, I just have to subtract 2M from whatever it displays.

When anchoring, I want to know depth - not depth under the keel. When following a contour line, I want to know what depth it is - and even then I have to work out tide heights, etc....

Why the prominence of depth under the keel over here??

Bill Balme
s/v Toodle-oo!

Dick
Dick
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Bill Balme - 6/1/2019
My depth sounder is set to display the depth of the water. Over here in the UK, it seems most are set to depth under the keel. Both seem to have some logic to them - but I can't see how depth under the keel is helpful except when in very shallow water... in which case, I just have to subtract 2M from whatever it displays.

When anchoring, I want to know depth - not depth under the keel. When following a contour line, I want to know what depth it is - and even then I have to work out tide heights, etc....

Why the prominence of depth under the keel over here??

Hi Bill,
I do as you do with this for similar reasons. I also like my depth sounder to read the depth indicated on the chart +- tidal conditions. Two calculations (tidal and adding draft) in my head are beyond me. That said, I suspect that this is more an issue of personal preference than one or the other being “best practice”.
I know that some sailing schools push for certain practices and I wonder what the RYA teaches their students: they are a pretty influential teaching institution in those parts.
My best, Dick Stevenson, s/v Alchemy

Bill Balme
Bill Balme
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One thing is important... IF you set the depth to overall depth and then have crew aboard that are used to seeing depth under the keel - make sure they know... Recently our crew was helping me out on a chain storing procedure and so we dropped in about 20M depth and started to drop back... when he got to 3M he was still happily motoring back - fortunately my wife saw the numbers and screamed! Not the crew's fault - definitely mine... fortunately, no damage done! That incident prompted this thread...

Bill Balme
s/v Toodle-oo!

Simon Currin
Simon Currin
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Bill
I hadn’t realised that there was a trans Atlantic divide on this and so it is good to be forewarned in case we ever ship North American crew. We are firmly in the ‘depth under the keel’ camp.
Simon
Dick
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Simon Currin - 6/2/2019
BillI hadn’t realised that there was a trans Atlantic divide on this and so it is good to be forewarned in case we ever ship North American crew. We are firmly in the ‘depth under the keel’ camp.Simon

Hi Simon,
Is this a preference: 6 of one 1/2 dozen of another; or does some argument sway you? And I am not sure there is that trans-Atlantic divide: I did under the keel for a while and I know others in the US who did/do so. Generally, though, I have little experience on OPBs, so I have little sense of what others do. However, it is an important piece of information for those that take on crew. Dick
Simon Currin
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Dick,
I’ve never really thought about it before but assumed that everyone measured depth below the keel. It is certainly the safer of the options if sailing with crew. In every other respect it is 6 of one as you say.
Simon
Dick
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Simon Currin - 6/2/2019
Dick,
I’ve never really thought about it before but assumed that everyone measured depth below the keel. It is certainly the safer of the options if sailing with crew. In every other respect it is 6 of one as you say.
Simon

Hi Simon,
This is almost a real time conversation: cool.
Yes, I can see why you say it is the safer option. Interesting. I would be interested in the % of boaters choosing one over the other (and also territorial proclivities). Hard to get that kind of data. Dick
Dick
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Hi all,
I suggested to George Day, ed of “Blue Water Sailing” an American publication, that the sounder question might be a good one for his weekly “Cruising Compass”, a nice little newsletter that he/BWS sends out twice weekly or so. He intends to do so shortly. CC has a regular survey question embedded in the letter. CC is free and comes via email: google for more info.
I believe he will be asking about what choice boaters make rather than the territorial question. We shall see.
I will report on the results.
My best,

Daria Blackwell
Daria Blackwell
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We are in the depth of water camp.  I never thought of resetting to water under the keel. It would be much less hairy traversing our inlet over the oyster beds at half tide with our 8.5-foot draft. :-{   I'll have to read up on that. 

On the other hand, I do use depth for navigation in some places, so less mental calculation is better, especially when sailing under bridges. :-} 

Vice Commodore, OCC 
bwallace
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On Darramy we use depth of water. We know we need 2.3 meters to float. So mental calculation works, And you know when looking at most charts where you may run aground.
Lead lines don’t have an offset. What did Captain Cook do?
Sail safe
Brian
S/V Darramy. Enjoying the Peloponnisos
GO

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