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Old 03-18-2018, 07:08 PM   #301
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It is almost impossible to take pictures of your boat while underway.
Really??
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Old 03-18-2018, 07:19 PM   #302
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Put the dink in the water, move a way from the boat and hope you can catch up to it when you are finished taking pictures.
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Old 03-18-2018, 07:55 PM   #303
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We will definitely verify as soon as we can. David had the low water alarms set to 5 ft. Just to be on the safe side.

I think ďmyĒ preference would be for it to show the amount of water from the lowest part of the boat to the bottom. I wanna know how much water I have under the boat.
True, but thete are othet ways of thinking that when push comes to shove, knowing the actual water depth is nice.

True the math can be worked either way....just some orefer true water depth as it is easier to compare with charts or other water depth input.
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Old 03-18-2018, 08:35 PM   #304
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It is almost impossible to take pictures of your boat while underway.
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Old 03-18-2018, 09:22 PM   #305
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One other thing not asked, "How often are your depth instruments inaccurate?" New boat to you, might be worth really checking out. Is 5' really 5' and if it is then how much is my draft and how much space does that leave.

Great point B. Very important for you folks that boat in skinny water on a routine basis. I have double checked my depth sounder on several occasions with a lead line. I have then set the offset on my depth sound to show depth under the keel and then have a label on the depth instrument saying as much.

So there are a lot of assumptions that can be made. I recommend that Stat take a lead line and measure the depth and compare it to the reading on the instrument. Then figure out how to set the offset to either show actual water depth, or to show depth under the keel, whichever system they like to use.
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Old 03-18-2018, 09:22 PM   #306
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We will definitely verify as soon as we can. I think ďmyĒ preference would be for it to show the amount of water from the lowest part of the boat to the bottom. I wanna know how much water I have under the boat.
Agree. Important to quickly know how much water is under the keel. Trying to match chart depth with actual water column requires a quick estimate of time to next tide, a consult of the tide table, the mental calc requires time. And then the transducer might be transom mounted so information is too late.

Nice to have an in hull transducer or a thru hull with the right deadrise angle and then calibrate them when on the hard. I have been known to tie a large nut to a string and use it as a leadline when in shallow areas.
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Old 03-18-2018, 09:49 PM   #307
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True, but thete are othet ways of thinking that when push comes to shove, knowing the actual water depth is nice.

True the math can be worked either way....just some orefer true water depth as it is easier to compare with charts or other water depth input.
Wifey B: I've always worked with water depth so that's what I'm use to and prefer.
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Old 03-19-2018, 07:18 AM   #308
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True, but thete are othet ways of thinking that when push comes to shove, knowing the actual water depth is nice.

True the math can be worked either way....just some orefer true water depth as it is easier to compare with charts or other water depth input.

Am i correct in assuming that each device has its own transducer?
David said he knows where one is. He found it in the engine room.

Would it make sense to have one device calibrated to show actual water depth and the other depth under hull?

I put above what I thought ďmyĒpreference would be....and I put it in parentheses because I donít know what David wants and ultimately thatís what matters and how it will be. I just get to throw my opinion out there once in a while. Lol
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Old 03-19-2018, 07:24 AM   #309
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Wifey B: I've always worked with water depth so that's what I'm use to and prefer.
So yours shows actual water depth and you just mentally subtract your draft to know how much clearance you have under you if itís a concern?

We donít really have this issue at home. Not many shallow waters we regularly boat in. But since we plan to actually go places in this boat, itís now something we need to be sure about.
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Old 03-19-2018, 07:57 AM   #310
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I want 'water under the keel'
IF I want to know where the transducer is, I will add 2 feet.

Water measured by weighted line = 10 ft, transducer 2 feet up from keel, depth of water under the keel = 8 ft.
That 8 ft is the part I worry about.
I might set the alarm at 3- 5 ft so I have a reasonable amount of time to stop the boat if I see a trend to shallowness.
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Old 03-19-2018, 07:57 AM   #311
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The other thing is what you have already learned: that just because the water is deep enough doesn't mean there is nothing to hit. Due to Irma, Florida is going to be a minefield for a while (I remember how long it took to find and remove all of the Katrina debris from the water).

We moved from a five foot draft sailboat to a four four foot draft twin inboard. But, where as the sailboat's almost indestructible lead keel hit first, and the prop was two feet higher, our props now hit first. One of the worst offenders around here is old abandoned crab traps. They sit, a foot to a foot and a half high and wait for inboard props to come along and grab them and get twisted up in them.

So as where I only started to get nervous in six feet of water with the 5' draft sailboat, I get antsy now in less than seven feet of water with a four foot draft
And, we carry spare props in the engine room, because I know, sooner or later, we're going to need them!
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Old 03-19-2018, 08:58 AM   #312
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Would it make sense to have one device calibrated to show actual water depth and the other depth under hull?
I would not want to do that. I want them both the same whether I have to mentally subtract or if I program the offset.
KISS.

ALSO, if you do not know where the transducers are in relation to the waterline/lowest part of your boat you should measure this while the boat is on the hard.
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Old 03-19-2018, 09:38 AM   #313
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Am i correct in assuming that each device has its own transducer?
David said he knows where one is. He found it in the engine room.

Would it make sense to have one device calibrated to show actual water depth and the other depth under hull?

I put above what I thought “my”preference would be....and I put it in parentheses because I don’t know what David wants and ultimately that’s what matters and how it will be. I just get to throw my opinion out there once in a while. Lol
I was trained to " navigational depth"

Meaning if running a shallow mud river and my draft is 4 feet, I want a nav depth of say 5 or 6.

If running coral or rocks, I might want 8 feet.

As I change locations, I just think, for now, what is my navigational depth and when I see it aoproaching on the sounder, I take action.
Its not the right or wtong way, just one way.

When I anchor, the sounder is giving me water depth, so rode calcs are easy without the added step of "under the keel".

So both ways have some calculating involed, thats why neither is necessarily better, just prefetence.

Usually government and commercial boats are set up for water depth, and I have to stay tuned to that freq.
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Old 03-19-2018, 09:49 AM   #314
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I would not want to do that. I want them both the same whether I have to mentally subtract or if I program the offset.
KISS.

ALSO, if you do not know where the transducers are in relation to the waterline/lowest part of your boat you should measure this while the boat is on the hard.

+1

If you have two depth sounders, set them up the same. If you donít, then you will have to be consciously thinking about that each time you look at a display. Let David pick a system he likes and you both will rapidly get so accustomed to it that no real math is involved. It will become almost instinctual.

Frankly, I donít recall why I switched on this boat. Maybe because my brain was so used to subtracting 7í of depth on my sailboat that it was hard to make the mental switch to subtracting 4 1/2í on my current boat?
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Old 03-19-2018, 10:44 AM   #315
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I was trained to " navigational depth"

Meaning if running a shallow mud river and my draft is 4 feet, I want a nav depth of say 5 or 6.

If running coral or rocks, I might want 8 feet.

As I change locations, I just think, for now, what is my navigational depth and when I see it aoproaching on the sounder, I take action.
Its not the right or wtong way, just one way.

When I anchor, the sounder is giving me water depth, so rode calcs are easy without the added step of "under the keel".

So both ways have some calculating involed, thats why neither is necessarily better, just prefetence.

Usually government and commercial boats are set up for water depth, and I have to stay tuned to that freq.
Your thinking is similar to ours. Also we switch boats and while draft may vary, the water depth isn't dependent on the boat so it's more a constant, relatable to charts. When we get ready to plan a trip, if we have a 5' draft, we may set our "depth" for planning purposes at 8', which is what you call navigational depth. Only if that is a problem, will we reduce it and then we'll know to take extra care. If we have the choice between 6' of water and 8' of water and 8' lengthens our trip by 30 minutes or even an hour, we'll always take 8'. Most of the time it just lengthens distance but we don't have to slow down as much and the time is nearly the same, while the stress is far less.

We set alarms at anything less than the expected channel. If the channel is 11', we may have an alarm at 10'. It's to give us a quick warning that we may be straying from the center or that the channel may be compromised in some way. By the time we can react to 10', we're usually either back in 11' or down to 7 or 8'.

I find it easiest to visualize water depth and draft vs draft and depth below keel or below lowest point or any other combination. If you're asking someone about depth, you don't ask about how far below your keel it is because they don't relate to your keel, you ask how deep it is. They'll tell you the least they encountered was 5' or they'll say their draft was 4' and they touched so the shoal was less than 4'. So all charts and most conversation is around water depth.
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Old 03-19-2018, 02:10 PM   #316
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Interesting to see the different thought processes on depth readouts.

I personally want to know how deep the water is as I already know how much my boat drafts.
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Old 03-19-2018, 02:38 PM   #317
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Old 03-19-2018, 02:46 PM   #318
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I personally want to know how deep the water is as I already know how much my boat drafts.
That brings up an interesting question. Do you really know your draft? Do you know it under all conditions? Most boats vary anything from 3 to 6" between various loads.

We've had discussions here of how to verify air draft but never water draft. We actually do it much the same way which all starts with some initial measurements. We start with measurements from the lowest level, whether prop or keel or rudder to the bottom of the hull at the stern to the top of the transom to the top of the flybridge to the top of the electronics, etc. Let's say you've identified that the bottom of the hull at the stern is 5' above the lowest point, if you see that that point is 4" below the water surface then your draft at that moment is 5'4". Similarly if your transom top was 4' above the bottom of the hull and you measured the distance from the water to it and it was 3'6" then you'd know that your draft was 5'6". Our builders provided these measurements but we checked them. They don't change but water draft and air draft sure do.
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Old 03-19-2018, 04:03 PM   #319
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I always want to work from UKC (under keel clearance), this relieves the different vessel factor. UKC means actual draft as opposed to keel only.
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Old 03-19-2018, 04:14 PM   #320
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Considering the work you do, certainly a concern.

I am sure Submariners have a totally different thought process when it comes to water depth and nav....
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