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 Catalina 25 Specific Forum
 Depth Sounder		  New Topic  Topic Locked
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swilliams
Deckhand

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11 Posts
Initially Posted - 04/08/2004 :  09:55:59  Show Profile
I have a question regarding depth sounders. The draft on my boat is 4 foot, but my standard horizon (probably original, 1982 model) depth sounder is reading around 3 foot at the dock. Is it taking into account the draft of my boat? I just assumed that if the depth was 7 foot, it would read 7 foot on the instrument....
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Derek Crawford
Master Marine Consultant

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USA
3323 Posts
Response Posted - 04/08/2004 :  10:24:32  Show Profile
I believe that a depth sounder should be calibrated to read the depth BELOW the keel - saves having to do mental arithmetic when getting into thin water!
Derek
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Bill Holcomb
Admiral

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USA
769 Posts
Response Posted - 04/08/2004 :  10:33:56  Show Profile
First - The depth sounder is reading the distance from the transducer to the bottom. The chances are that your transducer is a foot or so below your boat's waterline.

Second - The depth sounder may be old enough that it is no longer adjusted properly; so reads incorrectly.

Third - C25 draft should be: Fixed Keel = 4', Swing Keel = 2' 8" up and 5' down, Wing Keel = 2' 10"

Bill Holcomb - C25 Snickerdoodle #4839
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dlucier
Master Marine Consultant

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Virgin Islands (United Kingdom)
7583 Posts
Response Posted - 04/08/2004 :  13:24:28  Show Profile
Another thing to consider when measuring depth, especially at the slip, is vegetation because seaweed can throw off your depth reading.

I like to know actual depth so my meter is set to read from the waterline down because, unlike Derek, I find it takes less calculations than with an offset for the keel. To verify my depth sounder is reading accurately, I use my telescoping boathook at the slip to measure the distance to the bottom in the vicinity of my depth transducer then compare this measurement to my depth sounder.
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Champipple
Master Marine Consultant

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USA
6855 Posts
Response Posted - 04/08/2004 :  13:42:05  Show Profile  Visit Champipple's Homepage
Your standard Horizon should have a dampener knob (real small) on the back. You should calibrate it at the dock where the depth is known. If your reading three feet, its probably set for beneath your keel....or as Don mentioned you have seaweed.

I agree with Don - no need to do any math. Plus you only have to do it once to know that 6 feet on the depth sounder is getting close. All you need to do is set the alarm for your level of comfort.

Keeping it at actual water depth and not adjusted depth makes it much easier to correlate to the charts when cruising in unknown waters.
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Derek Crawford
Master Marine Consultant

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USA
3323 Posts
Response Posted - 04/08/2004 :  18:22:22  Show Profile
"Keeping it at actual water depth and not adjusted depth makes it much easier to correlate to the charts when cruising in unknown waters."
Good point Duane - I hadn't considered that aspect
I keep mine at "below keel" depth 'cos we have a lot of sand/gravel bars on the lake and we often have to skirt them when racing - I have enough to worry about without having to subtract 4' each time I glance at the depth meter.
Derek
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ClamBeach
Master Marine Consultant

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3072 Posts
Response Posted - 04/08/2004 :  20:54:52  Show Profile
The unit may have a 'keel offset' programmed into it. Reads water depth under keel rather than from transducer.

Some folks like to use an offset, some don't...
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Notice: The advice given on this site is based upon individual or quoted experience, yours may differ.
The Officers, Staff and members of this site only provide information based upon the concept that anyone utilizing this information does so at their own risk and holds harmless all contributors to this site.