Do you calibrate you depth sensor to water level or keel?

[mjscottinnc]

Originally Posted by GreenWave

I am the other guy... I want it to read water under the keel. No math invoolved to know if we have a problem. Charts and water draft obviously come into play on route planning.

I’m with you, I want to know how much water is under the keel. Makes sailing in the shallow areas simple and easy.

[Mr B]

I set my depth sounder on the hard, It showed 14 feet with 4 feet under the boat from the transducer,
But in the water, I had 3 feet under the boat from the transducer,
Bottom of Hull to ground, Which is five feet from the waterline,

The reason I set it at a foot below the Hull, Is the transducer is 15 feet back from the Bow,
I could be aground at the bow before the transducer says Im aground 15 feet away back from the Bow,
Shallow water has bumps in it, Its not all flat and level,

Scope, You just add waterline to deck extra, Mine is one metre or 3 feet,
Being a Cat, I just lay my scope (chain) on the deck in one metre lengths, Before I let it out over the bow,
I already know the depth Im sitting in, So I just add the depth plus 20 feet or so,
20 feet is 6 x one metre loops on the deck, , 3 feet approx to one metre.
10 single loops is 30 feet,
Works for me,

Here, The chances of me parking any where near another boat,
Is Zero, Except in a Marina,
There are no other boats where I am sailing, Occasionally a Fishing boat might motor past on its way to some where,

[capt jgw]

The research boats I ran were set up by a retired USCG Boatswain Mate Chief. He set the sounders for actual depth from the waterline. Also placed a red placard next to the display reading "Depth from WL , Operational Depth 15 feet". Meaning we weren't allowed to go shallower than 15 feet. Draft of the boats was four to six feet. If the scientists needed to go shallower than that, we had jon boats they could use. I haven't labelled my own boat this way, but I try to stay deeper than 10 feet with my 5.5 foot draft.

[patprice]

I set my sounder to water depth.

And as an aside beware of crew that like to fiddle with things. My sounder got changed from metres to fathoms! So I dropped the pick in about 20, thinking metres, but had all kinds of strife after numerous attempts to hold!!!!

[Stu Jackson]

Originally Posted by Dockhead

Indeed. You're going to be doing a little first grade arithmetic in any case -- what difference does it really make?

I don't think it's a big deal which way you do it. I've had mine set both ways over the years and it doesn't make a big difference to me.

>>>>>>>>>>>>>>>>>>>>>>

In tidal waters you're not going to be seeing the depths on the charts anyway. As Lodesman said, its a doddle -- first grade arithmetic -- to get depth to waterline and depth to bow roller, and meanwhile, you can directly read clearance between keel and water, which is that datum which you most want on the fly in a tense situation. Works well for me; YMMV.


Don't ever set my chart plotter to course up, however, or you'll have a fight on your hands.

I agree, it simply doesn't matter. When I first got this boat in 1998, I ran into this question on the internet and thought a lot about it.

Then I ran my boat slowly and deliberately aground on a known soft sandbar and looked at the depthsounder! It read 4.4 feet, so I always now know that when it gets close to 4.4 I'm in shallow water.

It's that simple and NO MATH is involved. None.

WADR, "Chart sync" is an oxymoron.

Of course, the rest of the rode to depth requires some arithmetic. Always will, regardless of what method you choose. And regardless of whether you're in tidal waters or not.

I couldn't agree more with the course up comment! Although I'm known to travel often with my significant other who just loves to turn the map around when she's not driving!

Originally Posted by CarinaPDX

For those of us who learned to use depth as another source of piloting input the depth from surface, to compare against charts, is the way to go.

I agree, although I've found that the reality, especially in tidal waters, could be misleading, because the bottom as charted is not always "absolute" anyway. It is a guide.

[Martkimwat]

I think you'll find any professional sailor including sailing instructors, will tell you it's better to set you offset to waterline. You should know your keel depth of by heart and so easy to know when you are going to touch the mud! when you are contour sailing you only need to correct for tidal height.

[IMACSS]

Originally Posted by Tillsbury

Absolutely water depth. Otherwise you're making all sorts of calculations when approaching an anchorage and considering the tidal change expected later in the night. And you can check it easily with a lead too.

If you set it to anything other than water depth, make sure you put a big sticker next to it saying so, as anyone else on your boat won't be expecting that.

I like your logic here Tilsbury (and others) as there is also the benefit of others on board keeping watch on depth.

[Reefmagnet]

I'd suspect a lot of the "keel depth = 0" crowd either don't sail in significant tidal areas or are otherwise unaware of the "rule of twelfths". Besides, you still need to calculate the height of your bow roller to the sea floor in order to figure out how much rode you need to lay out.

[mjscottinnc]

It’s all math one way or the other. So as captain you can setup your vessel anyway you want... ain’t technology wonderful!

[Mike OReilly]

Originally Posted by skipgundlach

Not every depth sounder has that option; I wish mine did!

Worse, the offset on ours is in full feet, which leads to some inaccuracy of depth under the keel on both (we have one through-the-hull and another inside-the-hull; circumstantially the one inside is more accurate, but not exact)...

True. I think mine is limited to whole numbers as well. I don't think this is a problem though. I just round up to just make sure my reverse offset is conservative. This builds in another safety factor.

I really don't get why some of you are so bothered by what others do. Either way works. Just be consistent and clear with anyone sailing with you.

[Dsanduril]

Originally Posted by Reefmagnet

I'd suspect a lot of the "keel depth = 0" crowd either don't sail in significant tidal areas or are otherwise unaware of the "rule of twelfths". Besides, you still need to calculate the height of your bow roller to the sea floor in order to figure out how much rode you need to lay out.

Why? I really don’t see how tides make a difference in how someone likes to read their depthsounder. I’m in the keel crowd and tides here are 4m neaps and 7m springs, pretty similar to Mackay.

There are a number of passages here that are dry at low or mid tide. I use the chart and the rule of twelfths to estimate when I can use them. But when I’m in them I use my depthsounder to tell me if there is enough water and it doesn’t matter what the chart or the tide tables say.

[garychurch]

I have my depth meter set to clearance under the keel. No math needed to figure out actual depth under keel. If I used waterline what is my draft, what are the tides, what are charted depths. In areas like the ICW and rivers shoaling is constant in many cases causing charted depths to be inaccurate. Many times buoys are set to new channels that don’t reconcile with charted channels adding uncertainty to actual water depths.

[ArmySailor]

Water depth for me.

-i use water depth checks to assist in piloting and use as another source of position check. ("Terrain association" except under water"

If I set keel depth, tides and charted depths would still absolutely dictate where I go. So I just know anything below 5ft, is close to her butt. There's no math involved, just a cutoff depth for both charts and real time reading. 5. Period.

I think math would be involved for me if I was using both charts and trying to compare my keel depth to. In real time.

The only way I think keel depth would be helpful for me is when I'm going 1/3 knot, nosing around gingerly to find that snug spot in a gunkhole. But then, I just use math. And bumps as feedback.

No charts involved.

[zboss]

Under the keel. Our Cabo Rico depth sounder was exactly 3 feet below the waterline - our new cat is exactly 1.5 feet below the waterline so the calculations aren't that difficult if I want to know the actual depth.

It helps that my wife is a math whiz. She is one of those people that can do very complex math very quickly in her head, including using large and complex numbers so things like scope and tides is no problem for her. It takes her about 1/2 second to do the math. She is also really good with dates... she can tell exactly what we were doing on a certain date like 8 years ago.

[fxykty]

Originally Posted by garychurch

I have my depth meter set to clearance under the keel. No math needed to figure out actual depth under keel. If I used waterline what is my draft, what are the tides, what are charted depths. In areas like the ICW and rivers shoaling is constant in many cases causing charted depths to be inaccurate. Many times buoys are set to new channels that don’t reconcile with charted channels adding uncertainty to actual water depths.

Huh?

Why do you need tide and charted depth to figure out the depth of water under your keel only when the offset is to the waterline? Isn’t all you need is your draft?