Bottom Imaging for Sailboats

[clakiep]

Originally Posted by Dockhead

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?

Most amazing experience I had at the Island of Stromboli - Italy in 1975. I was reading 6 m on the depthsounder and told my mate 'drop anker'. I saw and heard the chain and then the line going out and out, the boat was not moving so I called 'stop, how much line is out' and she said '30 meters'. I told her 'get it up again' but after a few meters in stuck. I put on my diving mask and flippers to look at it and saw the line disappearing in a rift at the bottom. With much work and patience and with up and down we managed to make the anker appear again. But while in this area I never droped anker again without a diver examining the bottom carefully to find a propper place to put it down.

[mikereed100]

Originally Posted by a64pilot

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.
I

The transom mount seems to be a common feature of most of these units, which, for a cruising boat, is a big downside. I know that one would not last on my transom while underway. On the other hand, if you flipped it up while underway, then flipped down when puttering around looking for a place to drop the hook, it might work.

[a64pilot]

I don’t know why it won’t last on your transom, they do fine on 60+ MPH bass boats and they way they are designed if you hit something they pop up. But really hit something going real fast and they do pop out, works fine on my dingy at 25 kts, which is wide open.
On a planing boat they need to stick down 1/4” or so below the bottom of the hull so they are in the water flow no matter how fast you go, but on most sailboats I assume flush or even up a little is fine, but if you have a really fast sailboat that can plane or whatever, who cares if you lose your down vision when your hauling butt? I assume you really only want it when you going slow moving around looking at the bottom.

I’ve never seen one on a sailboat either. I bought my first Dragonfly with the GPS plotter and map built in when my Garmin 740S quit and we had no chance of finding dive sights without it, so I ran down to WM to see what they had and at that time it was new. Child’s play to install, only downside is the transom mount, never tried to see if it would shoot thru the hull.

[a64pilot]

Originally Posted by waterman46

Man I last saw one of those LED rotary units about 1967..

We called them “flashers” and a the time they were magic, but a real fishing boat had a chart recorder. Used paper about a foot tall and had a pen that drew a line across the paper as it went past like an old EKG did.
Big box about a foot tall and two feet wide and at least 6” deep, whole front was glass and opened up so you could put a new roll of paper in, the paper had lines on it that indicated depth.

[Manateeman]

Hi. Before electronic depth instruments and sonars, lead sounders provided mariners with great detail of the land under the keel. Most sounders have a hollow cavity which faces down, into which, various sticky substances are charged and can be examined topside. The findings were noted on charts to assist in determining vessel position and suitability for anchoring. The long-standing use of this simple device is testament to why all prudent mariners would be well advised to familiarize themselves with the wealth of information sounders can provide. I stand firmly behind my prior statement that no electronic instrument can provide as much information.
Many years ago while working for a Norwegian corporation, I had a sophisticated research vessel with state of the art large searchlight sonar and almost every subsurface instrument available. I had an unlimited budget and advice from friends at both Woods Hole Oceanographic and The Marine Biological Labratory in Woods Hole. Nothing beats examining an actual sample of the bottom. To this day, devices resembling a mini clam shell, bring up samples for science.
The more one uses a sounding lead, the more useful information one finds.
There are numerous examples in the earliest history of chart making by the great names in ocean expeditions. Dragging a lead in a few circles before anchoring takes only a few minutes but you will sleep a lot better.
And please...do check for manatees below as the can sleep on the bottom for 15 minutes. I did enjoy the manatee bopper post.
Regards, Mark the manatee

[a64pilot]

A sounding lead can’t tell you that there is smooth rock just a few inches under the sand bottom, knowing how to read your sounder can.
Plus obviously it tells you about the one inch surface that it lands on, nothing else.
Dropping an anchor getting a partial set and retrieving it can sometimes tell you a lot, like if there is grass or not, and then there is grass and and then there is grass, the kind with the deep intertwined light colored roots is what I want to avoid, and often it comes with very little actual above the sand grass. Then you can drop in quite a lot of grass that doesn’t have much for a root system and get pretty good holding.

[sailah]

My Garmin 942XS has sonar built in. (almost) Any transducer will match up with it. I considered doing this because why not. I already have a basic Airmar connected to Raymarine depth which is then fed to Garmin over Seatalk but I don't have sonar just depth.

I didn't want to mess with the Airmar nor drill another hole so my plan was to mount one of the in hull transducers that you silicone to inside of your hull and fill with oil. Sounds complicated but it's pretty simple. Then you have a real CHIRP transducer for doing sonar.

Like this

https://buy.garmin.com/en-US/US/p/530269

B&G has forward scan but not sure that's a replacement for real sonar

https://www.bandg.com/bg/type/forwardscan-and-sonar/

[Jammer]

Originally Posted by Dockhead

But I would like to SEE the bottom -- it would really help and I think, reduce the risk of losing the anchor.

??? Don't you dive?

[a64pilot]

Originally Posted by Jammer

??? Don't you dive?

I rarely will dive myself and I cruise in warm water, but he cruises I believe where there are solid bits of water about, which I think insane, but I guess people are different.

[Manateeman]

Sand over rock. Paper, rock , scissors ?? I’m confused.
I guess someone might think the serious shortcoming of the physical sounder is that it cannot tell you anything about the bottom with the exception of the first inch whereas a sonar can...thus advantage sonar.
Well this is not entirely true. First, a pointed sounder or a heavy sounder will easily find out a shallow sand over rock bottom. Let’s say there is a foot of sand over solid rock. You are going to need a lot of sound energy to see deep into the sand. It’s a transducer not an oil field boom boat.
Let’s begin with another statement. Sand is simply ground up rock. Well again not entirely true. If you bring up sand ... well that can tell you nothing because you might be trying to anchor on solid rock. Or the sand might tell you ...this sand is actually ground coral. That fact would alert you to the possibility there is solid coral rock below. Sand will always tell you a lot more than sonar.
The more you learn about sand, the more confidence you will have not just in anchoring but in navigating close to shore. Why for hundreds of years, were charts marked with notations as to bottom composition.
Hold the sand in your hand. Feel it. Look at it with a lense. Smell. Taste. Read how whalers and the great explorers used physical information gathered from the bottom to aid then in safe navigation. There is no electronic substitute for
the simple and reliable sounding lead.
Well unless you can carry a vast quantity of Romain lettuce.
Then you can train a manatee to bring you a bottom sample.
Which will require a Federal permit.
And the skill to win at : rock, lettuce, scissors .
Happy trails to you.
Mark the manatee.

[Dockhead]

Originally Posted by Jammer

??? Don't you dive?

I'm at 60N latitude.

[Dockhead]

Originally Posted by Manateeman

Sand over rock. Paper, rock , scissors ?? I’m confused.
I guess someone might think the serious shortcoming of the physical sounder is that it cannot tell you anything about the bottom with the exception of the first inch whereas a sonar can...thus advantage sonar.
Well this is not entirely true. First, a pointed sounder or a heavy sounder will easily find out a shallow sand over rock bottom. Let’s say there is a foot of sand over solid rock. You are going to need a lot of sound energy to see deep into the sand. It’s a transducer not an oil field boom boat.
Let’s begin with another statement. Sand is simply ground up rock. Well again not entirely true. If you bring up sand ... well that can tell you nothing because you might be trying to anchor on solid rock. Or the sand might tell you ...this sand is actually ground coral. That fact would alert you to the possibility there is solid coral rock below. Sand will always tell you a lot more than sonar.
The more you learn about sand, the more confidence you will have not just in anchoring but in navigating close to shore. Why for hundreds of years, were charts marked with notations as to bottom composition.
Hold the sand in your hand. Feel it. Look at it with a lense. Smell. Taste. Read how whalers and the great explorers used physical information gathered from the bottom to aid then in safe navigation. There is no electronic substitute for
the simple and reliable sounding lead.
Well unless you can carry a vast quantity of Romain lettuce.
Then you can train a manatee to bring you a bottom sample.
Which will require a Federal permit.
And the skill to win at : rock, lettuce, scissors .
Happy trails to you.
Mark the manatee.

I'm sure this is all very well for the purpose of determining the bottom composition -- at least the first inch, as A64 said.


But that's not my purpose. For bottom composition, I'm OK with feeling how the anchor goes in, and looking at the anchor when I bring it back up after it fails to set.


What I'm interested is not so much bottom composition, as the layout of the bottom in the place where I'm about to anchor, whether there are rocks or boulders down there or other hazards. A lead line won't help with this unless you completely survey the bottom with it, which is obviously impractical.


Imaging sonar would really be the thing for this, but other than transom-mounting a CHIRP unit, which I don't think I want to do, I haven't figured out a solution.


I have a forward looking sonar with the sensor mounted in a large through hull (an old Echopilot Gold). I might be willing to sacrifice that to put in a large CHIRP or tilted element transducer.


Better would be a normal 51mm transducer as I will have a free through hull after I install my DX900+ DST transducer, but I can't figure out whether there is anything which would work.

[sailah]

You could buy a cheap Garmin Echomap and then match it up to any of the ClearVu, Chirp transducers. They make glue down, ice fishing(hand held) and thru hull transducers. Also serves as backup nav.

[Dockhead]

So here at last is a CHIRP transducer which looks like it would fit in one of my existing through-hulls:

AIRMAR

So could I use this with the built-in sonar in my B&G Zeus plotters?


The manual doesn't say much about compatibility. It says "The Zeus Touch has an Internal Broadband Echosounder. Navico transducers fitted with the 7 pin blue connector can be plugged directly tinot the corresponding blue socket." Then it's also possible to fit the "optional external sounder", i.e. BSM-1, LSS-1, BSM-2, via Ethernet.


The Zeus has StructureScan.


But no clue as to what kind of transducer is required to use StructureScan

[Ivanvet]

Hi,
I'm in the middle of testing this very same thing. I currently have a B&G suit with the Zeus3 MFD, a sonar hub and fwd looking sonar but no 'fish finder type' transducer. Last time I talked to one of the B&G representatives about fish finder transducers they weren't very helpful, and the guy at West Marine, who was surprisingly knowledgable about fish finders was worried about the ability of the MFD (Software) to recognize the transducers.

I currently have a Garmin Fish finder on the dinghy and I explore the anchorage to 'see' what type of bottom I have around the sailboat. Since Lowrance and Simrad are part of the Navico family with B&G, I just bought (as in 3 days ago) a Lowrance fish finder with a 3-in-1 transducer (it has Chip sonar, down scan and side scan). I do a lot of fishing, hopefully this helps me do a lot of catching too...

My idea is to use it in the dinghy, but bring the transducer to the sailboat when cruising. Once I get it, I'll connect it to the MFD, and if it works I'll let you know.

Keep in mind, the transducers that give you side scan (or structure scan, or side view, all the same things but with names varying among manufacturers) are elongated (no through hull shape). If you want to 'fill' an existing through, you will most likely have to get Chirp sonar only.

I'll report back once I connect the Lowrance transducer to the B&G Zeus3.

I.