True Depth or Depth Under the Hull ?

[Blue Stocking]

Originally Posted by Juniper

I set mine for 1 foot below the keel, that way if it says 0 I haven't bumped yet, then it's by brail. But I only draw 3'8"

+1. I draw 5' 9"

[hummingway]

Mine is set to the hull but with semidiurnal tides that reach 17ft and probably average 12 the depth never stays the same for any length of time and can change very quickly so the tide tables and charts have to be constantly consulted to see what the reading is going to mean.

[Astrid]

I suppose my preference may be based on being a pilot--one wants to know what the distance is between the plane and the ground, not the distance between plane and sea level (unless one is flying over the ocean, and at take off so one can set fuel mixture to optimum); one may not have time to do simple math, or one might forget to do it, when things get busy in the cockpit.

[conachair]

mine is set to under the keel, 0 is touching. If it's that shallow then my mind is in panic mode and incapable of the easiest arithmatic
Each to their own.

[Alecadi]

Originally Posted by Astrid

I suppose my preference may be based on being a pilot--one wants to know what the distance is between the plane and the ground, not the distance between plane and sea level (unless one is flying over the ocean, and at take off so one can set fuel mixture to optimum); one may not have time to do simple math, or one might forget to do it, when things get busy in the cockpit.

I was also a pilot, and had tod o basic math in teh cockpit!!

[LifeJacket]

When in a soaring program in Colorado, we always set the altimeter to field elevation (5820' if my memory is right) and you just knew that if it read lower than that you were in heaven ... or the weather had changed. ;-)

I appreciate everyone's thoughts ...

[Talbot]

It really doesnt matter which it is set to. What really matters is that you either know what it is, or treat it as depth to the waterline.

[Pelagic]

Personally I set mine on SG to Surface (true depth) mostly for navigational reasons and to confirm/calibrate actual depth by using a hand line at anchor once in a while.

From a commercial standpoint, the calibration decision is often made base on the type of ship and the waters you are cruising in as well the quality and frequency of the transducer.

If you are a bulk carrier with large differences in light/loaded conditions you would probably set it to read at surface(True depth) as a default and apply your draft (and Tide) based on varying conditions

If you are a tug towing various deep laden barges you would again set it at surface and be aware of your tows draft limitations

If you were a Passenger Ferry or landing craft often docking with minimum clearance then setting to your keel helps to confirm when you are dragging thru the mud

[cal40john]

You're all wrong. You buy three different depth sounders with 3 different frequencies, set each one to the different clearances, and maybe label them.

So there!

John

[sailorboy1]

Don't know on current boat as I haven't even been on it in the water yet. Guess I better find out!

But my last boat it was depth under the hull. But I always in my mind called it total depth so it really met I had more water under the boat than shown. But I also found out what it read when aground (a good use of going aground I guess) so knew if it was more I was good.

[kiper204]

Mine is set to depth under the keel .... it keeps the count down accurate, and much more fun when running aground

[witzgall]

Depth of the water for us. No math, easy to compare against the charts. Also, I think the average person would assume it is depth of the water, so if you have a guest onboard, they are less likely to make a mistake.

Chris

[Blue Stocking]

One thing for certain. When the boat stops going ahead, and you want it to, if the depth sounder in not showing "0", you need to rethink your math.

[Auspicious]

Depth of water.

[pteron]

Under the keel on monomarans - when you are worried is not the time to be doing maths.

On the tri it is set to true because the daggerboard varies between 1 inch and 2 meters. (who needs consistent units? Not us outlaws )