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Old 16-10-2009, 20:01   #1
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Device to Survey an Anchorage?

I like to go places other boats don't (or can't). Sometimes this has a negative effect on the condition of my bottom paint. And seeing a rock on the chart is not much consolation. I want to know exactly where that rock is.

I find myself wanting a portable device with a gps and depthsounder that I can use to reconnoiter an anchorage (or a channel) in the dink before bringing the big boat in. Ideally this device would create a bathymetric chart that could be used for navigation. And maybe have some buttons to indicate obstructions or bottom type at a particular location (sand, weed, coral, etc). It might as well beam the data back to the big boat wirelessly in real-time so it can follow behind instead of having to wait for the dinghy to return. Of course the charts should be saved for re-use and should also account for tide.

So, does such a thing exist? I've seen the Brookhouse data logger, but I'm hoping to find a more complete solution.

Since I'm likely to get it anyway, I might as well welcome any appropriately salty advice for how to do the same thing without electricity and geosynchronous satellites.
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Old 16-10-2009, 20:20   #2
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It's not portable, but I love my Garmin 5208 chartplotter with 3-D Fisheye display.
Check it out.

Steve B.
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Old 16-10-2009, 22:06   #3
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Yes there is a solution!

Some superyachts have a wireless connection between the depth sounder in the tender and the plotter on the bridge. As the dinks races around in front of the big boat the bottom is instantly relayed. Neat!

I don't know what they cost.

I use a long piece of string with a blob of lead on the end I am patenting it called: String with Blob
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Old 16-10-2009, 22:34   #4
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Yes there is a solution!

Some superyachts have a wireless connection between the depth sounder in the tender and the plotter on the bridge. As the dinks races around in front of the big boat the bottom is instantly relayed. Neat!

I don't know what they cost.

I use a long piece of string with a blob of lead on the end I am patenting it called: String with Blob
MarkJ ...I'm thinking Mark Twain. You could call out the soundings from your dink to your "daughter" on the boat.
Common Soundings

Sounding line - Wikipedia, the free encyclopedia
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Old 17-10-2009, 00:16   #5
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Surveying with laptop & GPS in the dinghy is easily done with MaxSea software (bathymetric module).

Another option is a forward looking sonar on the big boat and going slow.

We go with the dinghy, a portable sounder and markers (empty bottles with strings and weights) and mark a route.

cheers,
Nick.
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Old 17-10-2009, 01:44   #6
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Used to be done by setting up 3 points ashore in accordance with the grid datum of that country (or to establish a grid datum if a new land) These three positions would be established by use of astronavigationand would be the baseline for establishin the coast (Trig points). The depth around the coast would be established by hand heaving line and two horizontal sextant angles on the trig points.

A lot of the charts around the world are based on this method. Remembering of course that this only providesa clue to the trend of the bottom, and does not provide any information on isolated pinnacles, unless discovered by accident.

Some of these isolated pinnacles are still uncharted even in relatively well used areas and can lead to groundings.
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Old 17-10-2009, 09:46   #7
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Surveying with laptop & GPS in the dinghy is easily done with MaxSea software (bathymetric module).

Another option is a forward looking sonar on the big boat and going slow.

We go with the dinghy, a portable sounder and markers (empty bottles with strings and weights) and mark a route.

cheers,
Nick.
Thanks for the tips.

The big boat has forward looking sonar, but it is horizontal only and I don't find it very useful. It can only see forward about 3 x depth. I'll probably change the transducer eventually to one that can do vertical scans.
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Old 17-10-2009, 10:57   #8
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Jay sounds like a great open source project if you can get someone to take it up.
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Old 18-10-2009, 07:28   #9
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Portable Yeoman chart plotter interfaced with portable GPS, 12V battery, paper on plotter with calibrated coordinates marked, pencil, leadline and away you go.
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Old 24-10-2009, 12:28   #10
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I have the Echo Pilot FLS and it can see about 50 feet in 10 feet of water, however, in shallow water, say 5 feet, it only sees 25 feet ahead but it is set in the middle of the boat which is 30 feet back from the bow, so when you see something it is too late.

It does have its uses, but unfortunately, not where you need it most which is shallow water.

I have used it when entering a small bay to check out the area by turning the boat around I can see where or which direction it drops off.

FLS is probably a whole other discussion on its own.
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Old 24-10-2009, 13:02   #11
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I just bought a 7 amp hour 12v battery so I can bring chartplotter along on dinghy. Already had a back up cable. Also have hand held depth sounder. I figure I can enter anchorage and hit waypoints at the limits of my accessability. Tide tables on chartplotter make sure I won't run out of water at low tide with a simple calculation.
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Old 25-10-2009, 08:46   #12
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... I use a long piece of string with a blob of lead on the end I am patenting it called: String with Blob
Sorry Mark... but the Navy has called these "lead lines" for a few hundred years already... "By the mark - SIX!"

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Old 25-10-2009, 08:55   #13
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Sorry Mark... but the Navy has called these "lead lines" for a few hundred years already... "By the mark - SIX!"
Your lead line should have a hollow underneath which would have been filled with tallow. Then when recovered, the tallow would reveal what sort of sea bottom it was. This was very important to the navigators of that era, as the nature of the bottom could provide as much information as the actual depth. This is why the charts have symbology showing the nature of the bottom.
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