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Old 06-08-2012, 19:31   #1
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Caliber 40 LRC Depth Display

Can anyone tell me what the offset should be set for on a Caliber 40 LRC depth meter? We always seem to run aground before the display shows zero feet. Some people tell me that the offset should be set from the water level but I believe it should be set from the bottom of the hull where the sensor is located. The present offset is set to negative 2 feet 6 inches. Doesn't make sense if I have a 5 ft 1 inch keel.

Any thoughts on this?
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Old 06-08-2012, 19:47   #2
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Re: Caliber 40 LRC Depth Display

Depth is measured from the sensor and it has no conceptions of where the keel or the water level is. You need to add the distance from the water line to the sensor. Some people add a fudge factor so the depth will read more shallow than it really is to hopefully save yourself. If you measure the depth in the slip you'll know what it should read. My own thoughts is make it read what it really is and you'll soon remember the keel depth.

Your keel depth will increase when fully loaded for cruising and be higher when you don't have much crap aboard. It also changes the delta from the sensor to the water line. So the bottom line is no answer is always correct so make it close to something so you'll know so you can account for a extra heavy load or a super light load.
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Old 06-08-2012, 20:00   #3
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As you know, you can program the offset between the sensor and the keel. This offset does not change regardless of boat displacement. Typically the offset is positive but that depends on the make of the display unit. You can tell whether the sign should be positive or negative. Set the offset to zero. Record depth displayed. Change offset and read depth again. If it reads less depth then you have the right sign. I would guess the LRC 40 will have an offset of about 4 feet between sensor and keel. If in doubt set the offset equal to your draft. Then you will have an insurance of whatever depth the sensor is below the waterline.

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Old 06-08-2012, 20:40   #4
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Re: Caliber 40 LRC Depth Display

Thank you for your in depth response. No pun intended. Our boat is fully loaded so this would be a good time to measure at the dock what my offset should be. I like the idea of using the fudge factor. Maybe this will help keep us out of the mud.
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Old 06-08-2012, 20:42   #5
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Quote:
Originally Posted by revere
Thank you for your in depth response. No pun intended. Our boat is fully loaded so this would be a good time to measure at the dock what my offset should be. I like the idea of using the fudge factor. Maybe this will help keep us out of the mud.
The offset between sensor and keel has nothing to do with loading. That distance never changes.

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Old 07-08-2012, 07:06   #6
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Re: Caliber 40 LRC Depth Display

Quote:
The offset between sensor and keel has nothing to do with loading.
Actually nothing to do with anything would be more accurate

Quote:
Maybe this will help keep us out of the mud.
A little mid is OK A little rock would not. Personally, I prefer it to be accurate. When it gets dicey like several inches I find doing the math to know the real value may keep your shorts cleaner. There just are times with any draft boat where you get pretty close. We draw 4-9 so I plan my routes for 6-0. You still have tide variations and other issues as well as the local terrain. Bottoms are not uniform and the depth sounder may be reading in a hole or the top of the rock. Waves just makes it all the harder to guess. These variables will play into how you think about any situation. Just the reading on the depth meter isn't the whole thing. You need to understand how you got there and again where you need to be

I also disable the alram. When it goes off and you are sorting through what you need to do I find the constant beeping makes me more anxious than I need to be. Everytime the depth goes below it sounds then shuts off when you come up. The on and off repetition is more than I need. If you need the alarm it means you didn't plan the route well enough or were failing to keep watch. Poor planning is more dangerous than shallow water. When there is a chance of shallow water you need a tight watch.
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Old 07-08-2012, 11:17   #7
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Re: Caliber 40 LRC Depth Display

I have a Caliber 40LRC and just did this a few weeks ago. The offset may not be the same depending on where your transducer is. I recall something around 2 ft. I determined this by measuring the depth of the water below the transducer and then adjusting the offset so the display matches the measured depth.

BTW, I like to know exactly how deep it is with no fudge factor. I would rather do the math when navigating rather than on the fly when I might need to make a quick decision. And in Maine, some of the nicer gunkholes are very shallow so I want to be able to easily calculate the relative tidal depth.
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