keel offset used for depth sounder?

[AusCan]

Also Depth of water, IMO, gives you better situational awareness when referencing against your chartplotter or other references....

Easier to track along a shoal line, verify chart data etc..

Exactly!,

My depth sounder tells me the depth of water. That number should match my charts. It should also match my vision.

I know what my draft is. There is no calculation required. When depth of water equals draft, I will be touching bottom. Simple.

(Disclosure ....... I still ran aground last month.)

 

[Ski in NC]

I did not bother messing with offsets. I learned a while back that if there is blue between surface line and bottom line, I'm good to go. No blue, in trouble.

 

[eagle419]

My sounder reads actual water depth, and radar and chart displays are always set to North Up.

This suits me fine but it's sometimes interesting defending these choices to watch keepers not so used to my boat - especially at night.

Magnetic vs True settings on chart readouts and electronic compass is another One. I have all mine reading magnetic - again a purely personal choice/habit.

 

[DHeckrotte]

Depth of water. The numbers correspond to the chart...mostly. Not enough tide here to worry about it. No need to do math; I simply begin to panic at keel depth plus 1'.

 

[twistedtree]

I guess I don't see the great mental processing required to interpret depth of water. It's either greater than your draft, or you are aground. It doesn't take much to know if a number is greater than 7' (my draft), and whether there is a comfortable margin or a butt pucker margin. But whatever works for you is just fine.

 

[Nightsky]

Exactly!,

My depth sounder tells me the depth of water. That number should match my charts. It should also match my vision.

I know what my draft is. There is no calculation required. When depth of water equals draft, I will be touching bottom. Simple.

(Disclosure ....... I still ran aground last month.)

Chart readings in tidal waters display lowest low water numbers. Depending where you are you could see 20 ft tidal swings. Now you have another calculation to make (stage of tide) if you want the number on the sounder to match the chart.

 

[psneeld]

Either way...all the ways take a mental calculation for diffetent info....so it boils down to personal choice...no right way or better way.

 

[Bill Ranson]

I have two depth sounders. One with no offset and one with offset for bottom to bottom. The one with no offset shows in a data box on my chart plotter that lets me compare against chart depth. Best of both worlds. If I only had one it would show amount of water under the keel.

 

[AusCan]

Chart readings in tidal waters display lowest low water numbers. Depending where you are you could see 20 ft tidal swings. Now you have another calculation to make (stage of tide) if you want the number on the sounder to match the chart.

I wish our charts matched up with actual depth at low tide. I know that is what the theory is but in reality the depth is + or - up to 20 feet in our local coastal waters outside the main shipping channels. Our tidal variation is 6 feet. That makes doing any precise calculations somewhat irrelevant.

 

[Wxx3]

Third option, set the offset so the depth sounder shows depth from the bottom of the keel. This is what I do currently.

There are plenty of arguments for different ways of doing it and for a long time I had sounder adjusted to show actual water depth. I finally decided to just have it read water under the keel since that is what I really am interested in. In my area, with large daily tide variations and very infrequent depth updates, there is no way that the 4.5 foot difference is going to help with navigation.

ditto
I've also done it all three ways and find depth under keel most useful and needing no interpretation in skinny water situations.

 

[denverd0n]

There are plenty of arguments for different ways of doing it...

This ^^^^^^^^

Whatever works for you, and makes sense to you.

 

[sdowney717]

The most sensical idea especially to the inexperienced boater is have it offset so that if it's close to zero, your close to touching the bottom. And that is how I set mine.
I tested my offset by measuring from water surface to the sandy seafloor with a stick. I found it very accurate.
I think mine also has an audible alarm, reading this thread, reminds me to recheck how I have it setup.

 

[dhays]

The most sensical idea especially to the inexperienced boater is have it offset so that if it's close to zero, your close to touching the bottom. And that is how I set mine.
I tested my offset by measuring from water surface to the sandy seafloor with a stick. I found it very accurate.
I think mine also has an audible alarm, reading this thread, reminds me to recheck how I have it setup.

I used a lead line while anchored in Desolation Sound last summer when I reset the offset. I took the depth from lead line, subtracted out the draft, and adjusted the offset so the depth sounder gave me about a 6" margin. So if the depth shows "0", I should be hitting the bottom in the next wave trough.

I did use my depth alarm at first, but found it too annoying when I was going in and out of my own harbor at low tide. A depth alarm is not that useful where I am. Normally the water is very deep, except where it isn't. I am always on my toes for when the water isn't deep. It could be different in some parts of the East where skinny water is the norm.

 

[psneeld]

The most sensical idea especially to the inexperienced boater is have it offset so that if it's close to zero, your close to touching the bottom. And that is how I set mine.
I tested my offset by measuring from water surface to the sandy seafloor with a stick. I found it very accurate.
I think mine also has an audible alarm, reading this thread, reminds me to recheck how I have it setup.

Don't be so sure, after teaching many new to boating and new boats to them owners.....most asked if the depth sounder read depth of water first....then it became a dance to see what they wanted. That seemed logical in their minds.....not everyone see things the same way as we see with the spread of posts between experienced boaters.

But it really doesn't matter, as long as the helmsman knows what it is on the boat they are driving.

 

[Peter B]

I never bothered adjusting the keel offset, because the boat draws 1 metre, where the transducers are (I have three sonars, 2 down, one up), I know when the depth shows 0.6m we are kissing the bottom. I set the alarm at 1m, so if it goes off I know I have 0.4m under the keel. If I set it to 2m, it is going off too often, as we boat where there is a lot of narrow channels and shoals with skinny depths. As others have mentioned, setting it to water depth is not so intuitively quick, because you are always needing to do a subtraction, in my case depth minus 1m, whereas all I have to do is ask myself is it more than 0.6m. Works for me.

 

[sdowney717]

I used a lead line while anchored in Desolation Sound last summer when I reset the offset. I took the depth from lead line, subtracted out the draft, and adjusted the offset so the depth sounder gave me about a 6" margin. So if the depth shows "0", I should be hitting the bottom in the next wave trough.

I did use my depth alarm at first, but found it too annoying when I was going in and out of my own harbor at low tide. A depth alarm is not that useful where I am. Normally the water is very deep, except where it isn't. I am always on my toes for when the water isn't deep. It could be different in some parts of the East where skinny water is the norm.

I have also seen coming in and out of shallow slips, the props can stir up so much mud and muck, the depth reader errors out. And seen that happen in and around the creeks here. A look behind the boat and you can see a cloud of mud stirred up. And mostly exist large flat muddy areas close to shore around the bay. In the lower Chesapeake Bay here, much of the bottom is muddy mucky and soft close to shore. I have hard grounded into the muck, slid to a stop and it was a weird feeling with the boat not moving. Happened on a rising tide, so we waited and then lifted off in an hour. If your not paying attention to the chart gps, you will be far enough from land you'd think you have plenty of water, but the depth might quickly be only 2 feet. Our tide runs about 3 to 4 feet