Plantation, FL, USA More User infoCrew Level II Status: Sailor Qualified days: 45
not clear on offset
Posted 2015, Sep 07 20:37
Just looking at the picture. If my depth is 8ft. for example, I would like to see either depth below the keel or 2ft or depth of the water or 8ft. I'm trying to do the math by using the offset in the example to get either reading.
Austin, TX, USA More User infoCaptain Level V Status: Really Big Time Sailor Qualified days: 502
Reply 2015, Sep 12 16:02
So if the real depth say via a lead line was 8 feet. And your transducer was 1 foot below the water line. The depth meter with no offset would read 7 feet. If your keel is 5 feet long below the hull (where the transducer also sits) and you put -5 feet as your offset then the depth meter would read 7-5=2 feet. In reality you should give yourself a little extra offset for safety this depends on your operating waters. In the Bahamas say you couldn't do an extra 5 feet because it would aways say you're aground. You'd do like maybe 1 foot extra i.e. a -6ft offset. Essentially you want to set your offset to the keel depth plus a bit. Yacht charter companies typically give it an extra 5 feet but you really don't know. Plus you don't know the last person who was on the boat maybe mucked with the offset and set a positive number. That's really bad. If they set positive 5 you'd run aground when the depth meter was saying you still had 9 feet of depth left. When I charter a boat, at the very first anchoring I go for a swim and check the depth below the keel vs what the meter says. Especially if you will be operating in shallow waters like Belize or Bahamas.