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Old 05-07-2020, 01:50   #1
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Bottom Imaging for Sailboats

I cruise in a lot of areas with rocky bottoms and I always feel like I'm rolling the dice when I throw the anchor down there. I have a couple of practices which I think reduce the risk, but I still think it's basically a crap shoot. Namely, I try to cruise the area where the anchor will go and watch the depth gauge (and my depth display shows a few minutes of history, so I can see what's going on), and I try to anchor in the deepest parts of coves where I hope there is an accumulation of silt.


But i wish I could just LOOK at the bottom. I know some fishing boats have all kinds of fantastic toys like side scan sonar. My B&G Zeus MFD's have some kind of sonar box built into them. Is there some device I could use to image the bottom, which would fit into a standard 51mm through hull?
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Old 05-07-2020, 02:25   #2
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Re: Bottom Imaging for Sailboats

My Furuno sounder/fishfinder has a display at the bottom of the screen that gives botton type ie sand mud rock; i think it is usually right, often scrolls and changes bottom type quite quickly. its a FCV-628.
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Old 05-07-2020, 04:51   #3
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Re: Bottom Imaging for Sailboats

Hi. I use an old sounding lead. Foolproof . There are fancy bronze ones available but a piece of copper pipe, some lead and epoxy will do just fine. Finds depth, makeup and density of the bottom and obstructions.
Gives details of bottom that no electronic instrument can match.
Please check for manatees before deployment.
Mark the manatee.
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Old 05-07-2020, 05:26   #4
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Re: Bottom Imaging for Sailboats

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Originally Posted by Manateeman View Post
Hi. I use an old sounding lead. Foolproof . There are fancy bronze ones available but a piece of copper pipe, some lead and epoxy will do just fine. Finds depth, makeup and density of the bottom and obstructions.
Gives details of bottom that no electronic instrument can match.
Please check for manatees before deployment.
Mark the manatee.

Pretty laborious to survey a whole cove for boulders, however.
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Old 05-07-2020, 06:27   #5
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Re: Bottom Imaging for Sailboats

Most depth sounders will give you some indication of the bottom type, if you can learn to interpret the display. That might mean see display, send down manatee bopping device to get coorelation, move to new spot, fight off pissed manatee, and so forth.
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Old 05-07-2020, 06:30   #6
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Re: Bottom Imaging for Sailboats

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Most depth sounders will give you some indication of the bottom type, if you can learn to interpret the display. That might mean see display, send down manatee bopping device to get coorelation, move to new spot, fight off pissed manatee, and so forth.

Well, that's what I do now. What greatly helps is a rolling bar scale like on one of the Triton displays which shows the 10 minutes history -- you can see the evenness of the bottom to some extent, and at least big boulders show up on the rolling scale.



But I would like to SEE the bottom -- it would really help and I think, reduce the risk of losing the anchor.
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Old 05-07-2020, 07:44   #7
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Re: Bottom Imaging for Sailboats

I too am searching for something that can tell me what is on the bottom. Diving to free the anchor in 5 degree C water has lost it's appeal. More than that, though, I worry about dropping in weed. We had a situation recently where we set the anchor in unknown substrate and it held well all night long in 35-40 knots. Come morning when the wind got up to 45-50, though, it was off to the races. When we pulled the anchor we found it covered in weed. Trying to find good bottom in those conditions (while several large, steel commercial boats were doing the same) was a challenge.

It looks like there are several options out there.

From what I have been able to gather it looks like Simrad and Lowrance displays support an "Active Imaging Transducer" that is basically a side scan and down scan sonar that give a pretty nice picture of what it below to 300'. For a little more money you can add CHIRP that will give depths to 1000'. As far as I can tell, B & G supports side scan and forward scan, but not down scan, which is unfortunate because I think the B & G displays offer more for sailors, while the downscan offers the best view for a cruiser.

Humminbird offers "MEGA 360 Imaging" that is a rotating beam, giving a 360 degree side scan, but no down scan. Ray and Garmin both have their vesions of side scan as well. I believe I read somewhere that Navico has some sort of patent on down scan?

Unfortunately, it seems that all of these require their latest and greatest MFD, which would add significantly to the cost. Also, I have no idea how well these things work in practice. I started a thread last year asking this question, but got no replies. I get the impression that most cruising boats are not fitted with these transducers as fisherman are their targeted market.
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Old 05-07-2020, 07:46   #8
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Re: Bottom Imaging for Sailboats

I had a down scan on last boat and have one one the dinghy now, current one is a Raymarine Dragonfly, they need a longish CHIRP transducer and about the only way you can make that work is to transom Mount.
Very good ones can be had for cheap, Dragonfly for instance if they are still made.

However you can learn to read the screen for bottom type if you have a sonar display, be sure you are in 200 hz and not the lower frequency, higher frequency gives better resolution but limited range of course.

A very real limitation of a down scan machine is waves, any boat vertical movement will display as a ragged looking bottom because the machine canít determine if the boat is moving up and down or if the bottom is irregular, it only knows the depth change.
Smooth water they are really cool though, you can see your anchor or a tree or a crab trap etc., but it has to be real smooth water for the photo realistic picture.

Last boat I used it to pinpoint dive spots, it was great for finding sunk boats etc. To dive on.
I put it on the dinghy for finding routes through unsurveyed areas.
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Old 05-07-2020, 09:00   #9
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Re: Bottom Imaging for Sailboats

The old-style LED rotary echosounders enable you to know if the bottom is smooth or weedy or rocky, once you get the hang of interpreting the display. The advantage is that the display is instant, in real time, not buffered.

https://www.nasamarine.com/product/stingray-echo-sounder/
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Old 05-07-2020, 09:29   #10
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Re: Bottom Imaging for Sailboats

Under water drones are getting cheaper! It might even be a help inspecting the mooring lines. Check youtube best of...some are around $500 that would be cheap for the risk right? My two cents...good luck!
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Old 05-07-2020, 09:30   #11
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Re: Bottom Imaging for Sailboats

Aahhhh, an anchoring thread! I used to dread them and now I'm delighted.

Thanks and carry on!

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Old 05-07-2020, 09:56   #12
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Question Re: Bottom Imaging for Sailboats

Quote:
Originally Posted by Manateeman View Post
Hi. I use an old sounding lead. Foolproof . There are fancy bronze ones available but a piece of copper pipe, some lead and epoxy will do just fine. Finds depth, makeup and density of the bottom and obstructions.
Gives details of bottom that no electronic instrument can match.
Please check for manatees before deployment.
Mark the manatee.
I fully understand the reasoning behind the sounding lead. How does it give you details of what's below???
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Old 05-07-2020, 10:02   #13
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Re: Bottom Imaging for Sailboats

I use a Garman fishfinder that shows bottom contour including rocks silt etc. The transponder is in the bow A few feet in front of keel mounted on the floor.
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Old 05-07-2020, 10:09   #14
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Re: Bottom Imaging for Sailboats

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I fully understand the reasoning behind the sounding lead. How does it give you details of what's below???
They are hollow and bring up a sample of whatever was at the bottom with them.
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Old 05-07-2020, 10:15   #15
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Re: Bottom Imaging for Sailboats

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Originally Posted by Uncle G View Post
The old-style LED rotary echosounders enable you to know if the bottom is smooth or weedy or rocky, once you get the hang of interpreting the display. The advantage is that the display is instant, in real time, not buffered.

https://www.nasamarine.com/product/s...-echo-sounder/
Man I last saw one of those LED rotary units about 1967..
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