Kerl offset confusion - SailNet Community
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post #1 of 8 Old 07-26-2019 Thread Starter
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Kerl offset confusion

Trying to set keel offset. Hunter 37 with 4.75' draft. Im in 8.5 feet of water. Don't know where the transducer is , but with keel offset set to 0. I read 4.0 feet.

So i think the transducer must be 4.5 feet below the waterline. But im having trouble figuring the 4.75 feet of draft, it seems the transducer is darn near the bottom of the keel which i know is not the case. What am i doing wrong. Instruments are B&G Triton.
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post #2 of 8 Old 07-27-2019
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Re: Kerl offset confusion

Your instincts are right, there is no way itís mounted 4.5 ft below the waterline.

Canít help with your programming, but what you describe doesnít make sense. As you know.

How certain are you of the actual depth? Did you lead line it or just reading a chart? Tides? Say itís really 6ft deep and your transducer is 2ft below the waterline (which still seems like too much). That would read 4ft, with zero offset. Another possibility is grass that is distorting the transducers feedback.

On a related point, I prefer to read actual water depth, not depth beneath the keel. That requires offsetting the installed draft of the transducer, not the additional draft of the keel. Water depth aligns better with charted depths, as Iím poking around the shallows and trying to confirm where I am.
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Jeanneau 54DS

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post #3 of 8 Old 07-27-2019
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Re: Kerl offset confusion

+1 for actual depth, same rationale.
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Re: Kerl offset confusion

When asked 'How deep is it?' My reply 'Goes all the way to the bottom.!'
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post #5 of 8 Old 07-27-2019
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Re: Kerl offset confusion

If this is an Airmar smart transducer outputting NMEA2000 directly, these can be internally programmed for offset by other instruments. If it has been in the past, then the Triton will be applying an offset to an offset.

Either way, I'd just keep applying offset until it reads correctly.

And not knowing where your transducer is on a 37' monohull is strange - they aren't that hard to find.

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post #6 of 8 Old 08-15-2019 Thread Starter
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Re: Kerl offset confusion

M y fellow dockmates tell me the bottom of the well is notoriously uneven , and will read different depths in different places, I plan to measure it with a depth line in 6 - 8 places around the boat , by the keel, and see what depth is the most consistent. I'm sure that will work.
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post #7 of 8 Old 08-16-2019
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Re: Kerl offset confusion

Good plan. Confirm the depth, then troubleshoot. Let us know how you make out.


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Re: Kerl offset confusion

I keep a lead line aboard, but admittedly rarely use it. I made it many years ago, after having awoken once too often in a transient mooring field to read depth more shallow than my keel. To date, it's always proven to be grass or some other interference.

I have a length of nylon line attached to a large lead fishing sinker. I tied a basic knot every foot. The lead has to be heavy enough to sink in a current, then I just read how many knots are submerged. Very Tom Sawyer. I stumble upon it's hiding place every once in a while, as I forget I have it.


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