T&T: Depthsounder offset

[Jim Ague]

People have good arguments on each side of whether to set the Depthsounder 
to "Depth from Keel" and "Depth of water". Some choose the first so that 
when the sounder reads zero, they know they have run out of water, as far as 
the boat is concerned.

I chose the latter, waterdepth, I think for two reasons: (1) my keel is 4 
feet underwater, the arithmetic is simple. If it were 4' 7" I might have 
gone the other way. (2) I like to use the depthsounder as another Aid to 
Navigation. If the charts say I should be in 12' of water and shaIlowing, I 
like immediate confirmation when I look at the depthsounder.

That being said, I found that after years of living on and with the boat, 
when the water got thin, the depthsounder was used qualitatively, rather 
than quantitatively. That is, when the number said 8 it was time to be 
concerned, when it said 6, it was time to slow down and be worried and when 
it said 5, it was time to really, really pay attention.

(The above numbers based on flat water bottoms, hilly ones are another 
matter.)

-- Jim Ague