Side scan sonar recommendations for shipwrecks

[hobbit]

I know this is a topic that has been brought up in the past, but since the major manufacturers keep pumping out new and upgraded units, I thought I would bring it up again.

I am ready to take the plunge and buy a side scan and I hope some of the experts on this forum can lead me in the right direction.

Can you tell me the features I most need for shipwrecks/ debris trails?

At what point, depth and resolution wise, would I seriously start to see benefits from building and deploying a towfish?

Are there any unforeseen problems, performance wise, from lengthening the transducer cable to accommodate a towfish?

I am primarily interested in colonial era wrecks and so I am hoping to achieve bottom image resolution capable of picking up a single cannon or large anchor. What is the best frequency to achieve this type of resolution? How close will I need to get the towfish or hull mounted transducer over the target to achieve this resolution?

I know this query is somewhat vague, but there is so much information out there, it is somewhat difficult to sift through it all in order to select a capable unit. If an older model will suit my needs, I am not averse to buying used.

Thanks in advance.

 

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[Denniss]

I have a hummingbird 997 but I'm thinking of upgrading to a Mega when it is released. It's not a Klein but it does give a pretty good image. People have rigged up DIY towfish for the Hummingbird units

http://www.humminbird.com/MEGA/

More than you want to know about Hummingbird sidescan

DIY - Side Scan Sonar and towfish

 

[Darren in NC]

I'd be interested in the pros and cons you fellas have found between the Humminbird and the Lowrance models. These two are constantly upgrading, and it would be nice to hear the latest. My experience with the Humminbird 1198s has been outstanding, but I'm open to any advances made in the newer tech.

 

[Rüdiger]

Hi All
I use a HB 898 with a self-made Towfish and am very fortuitous.
For a new acquisition, I would decide however for the largest possible display.



Self-built towfish in combination with LAWRANCE I have not seen any, but there are HB owners who combine the LSS2 transducher from LOWRANCE with the original HB transducher. In Denniss 2. Link you can find all information about this.

mvh
Rüdiger

 

[diver9]

I run both a Humminbird 1197 on the helm (the biggest and best available from them when I bought it new in 2009) and a 2013 commercial EdgeTech 4125P towed system; I have used both systems extensively in a wide variety of water, both salt and fresh, shallow and deep, in lakes, rivers and the ocean off Massachusetts.

BUILDING A UNIT

- As to building one yes this can of course be done; now more than ever these Humminbird forums:

Unofficial Humminbird Side Image Forums www.sideimageforums.com - Index page and http://sideimagingsoft.com

offer all the info one could want when trying to determine if this is the way to go;

- Home-built units have many limitations; one big one is software; both the Humminbird and the EdgeTech have software that allows me to nail a target’s
Latitude and Longitude to pinpoint it for a dive or, to make close sonar passes with either unit for better images and analysis;

But adding a towfish (and of course now cable) changes everything for a unit generally not designed to use a towfish.

In 2006 when I got my first Humminbird I tried to find software to drive it as I considered building a towfish but found nothing; perhaps this has changed but I never considered it after that.

That said, any commercial system (EdgeTech, Klein, MarineSonic etc.) and any non-commercial system (Humminbird, Lowrance, Raymarine etc.) all have this targeting capability and it is vital to have;

a) I don’t know if home-built towfish units can do this and considering you are looking for things you want to locate, how will you actually find them/dive them easily without capturing the Lat/Lon?;

The EdgeTech software (and other commercial units) allows me to factor in how much cable is in the water (called layback and absolutely critical to have), to change the Range of the sonar wave, to change palette colors, to run one or both frequencies at the same time, to take into account salt water, fresh water, speed-of-sound issues, integrating the data automatically with the GPS, setting my lane spacing using their “Coverage Mapper” for mowing the lawn as well as lane over-laps for 100%-200% bottom coverage and on and on; unless there is off-the-shelf software available to buy that can at least provide a minimum number of basic search functions, a homebuilt won’t do it for the serious searcher;

Your post had asked for some of the features you need most for what you want to do-start with what I just wrote above.

b) The deeper the water the more of a problem this will be with a home-built that doesn’t have the ability to capture coordinates; it could be such a big problem in the end you are wasting time and money going with a home-built because at some point you won’t find what you are looking for even though you have a SSS image that is really interesting; I’m a diver too so I know exactly how hard it can be to locate something on the bottom; even with a great set of coordinates if you have “black water” or deep, dark water, or the target is small, the challenge can be huge, depending on other variables also;

c) Powering a homebuilt may present problems as well because now you are sending lots of data over a cable-can the unit-presumably not designed for a towfish-handle it without crashing? You might need a generator, something else to factor in; there can be other electricity-related challenges I cannot get into here in detail because I am not qualified however I see the potential for a heck of a lot of questions to overcome with a home-built related to electronics; I really hope the Forums for home-builts can give you answers;

d) Unless you have a lot of knowledge about electricity etc. at some point the unit will likely fail-then what? To whom do you go for repair or diagnosis?;

e) If you go this route, Rudiger has it right-go for the largest display you can get;

f) As to problems lengthening the cable I do see issues; that’s why what you get from the factory for cable for a helm-mounted side scan sonar/SSS unit should never be cut but instead, curled up un-cut and stored safely; use the entire cable as it came from the factory;

However people who like this technology and have built their own towfish may have much better answers to this question and that’s where the Humminbird Forums could be of great help because if anyone has messed with cable lengths while building their own towfish, they have;

My advice, assuming you have the money, is to buy a commercial unit (new or used) so none of the points I made above (and that’s the SHORT LIST) will be something you have to deal with if you go commercial vs. home=built. Just too much trouble and time in my opinion to build one.

TOWFISH ADVANTAGES

If you visualize the sonar wave not as a sound wave but as a beam of light, you will understand the geometry involved in ensonifying things on the bottom with a towfish. One huge advantage a towed system vs. a transducer mounted on the hull has, is the ability to get the towfish closer to the bottom, thus generating very very important shadows. The things shadows can tell you is spectacular (technically it’s a loss of sonar data but we call them shadows because that’s what they look like).

The higher in the water column the transducer is, relative to depth, the worse the shadows get. The angle-of-attack sucks. At some point you will not be able to recognize a great target because the angle-of-attack of the sound wave has degraded so badly.

Test: Put a beer can on a table and shine a flashlight on it from say, a 45 degree angle and two feet away and see the shadow it produces. Then lower the flashlight to say, 12 inches off the table from two feet away. The shadow of the can is radically different-and better. This is the benefit you get from towing the transducer lower to the bottom. Getting close to the bottom is really really important.

My Humminbird 1197 works great in “shallow” water but as I get into deeper water it degrades badly for the reasons I just detailed. Of course this has nothing to do with the Humminbird itself, it just the way it is using any hull-mounted transducer regardless of the Brand of the unit.

To answer your question about at what point you would you would start to see benefits from using (any towfish), the answer is the benefits would be immediate and dramatic.

I love the EdgeTech I bought (great people and great products/www.edgetech.com) and I love the Humminbird (www.humminbird.com).

But buying the EdgeTech towed system-a commercial system-opened a huge new world of exploration for me that has been a great experience that isn’t over yet.

I love the things I can do with a towed system as both a sonar owner/operator and a diver. But I am not a pro, just a hardcore amateur with this sonar technology.

If you have other questions, post them here. If you care to contact me directly, email me through this Forum privately and we can go from there off of the Forum. I’ll help you any way I can.

 

[Rüdiger]

Diver9 is right

If you have the money for it, a commercial sonar is definitely the best solution.

Software for analysis of HB data are several, partly written for comercial systems.

Mvh
Rüdiger

 

[hobbit]

Hi All
I use a HB 898 with a self-made Towfish and am very fortuitous.
For a new acquisition, I would decide however for the largest possible display.

View attachment 1389781

Self-built towfish in combination with LAWRANCE I have not seen any, but there are HB owners who combine the LSS2 transducher from LOWRANCE with the original HB transducher. In Denniss 2. Link you can find all information about this.

mvh
Rüdiger

Thanks for the response, Rudiger. That's an interesting looking towfish that also looks like it might be relatively easy to construct. Is it your own design? Does it work well for your purposes? It looks like it is constructed primarily from PVC, perhaps??

 

[hobbit]

I have a hummingbird 997 but I'm thinking of upgrading to a Mega when it is released. It's not a Klein but it does give a pretty good image. People have rigged up DIY towfish for the Hummingbird units

http://www.humminbird.com/MEGA/

More than you want to know about Hummingbird sidescan

DIY - Side Scan Sonar and towfish

Thanks for the response and the links...you're sure right about the information overload !!! It's an embarrassment of riches, which I guess is better than the opposite !!

 

[hobbit]

I run both a Humminbird 1197 on the helm (the biggest and best available from them when I bought it new in 2009) and a 2013 commercial EdgeTech 4125P towed system; I have used both systems extensively in a wide variety of water, both salt and fresh, shallow and deep, in lakes, rivers and the ocean off Massachusetts.

BUILDING A UNIT

- As to building one yes this can of course be done; now more than ever these Humminbird forums:

Unofficial Humminbird Side Image Forums www.sideimageforums.com - Index page and http://sideimagingsoft.com

offer all the info one could want when trying to determine if this is the way to go;

- Home-built units have many limitations; one big one is software; both the Humminbird and the EdgeTech have software that allows me to nail a target’s
Latitude and Longitude to pinpoint it for a dive or, to make close sonar passes with either unit for better images and analysis;

But adding a towfish (and of course now cable) changes everything for a unit generally not designed to use a towfish.

In 2006 when I got my first Humminbird I tried to find software to drive it as I considered building a towfish but found nothing; perhaps this has changed but I never considered it after that.

That said, any commercial system (EdgeTech, Klein, MarineSonic etc.) and any non-commercial system (Humminbird, Lowrance, Raymarine etc.) all have this targeting capability and it is vital to have;

a) I don’t know if home-built towfish units can do this and considering you are looking for things you want to locate, how will you actually find them/dive them easily without capturing the Lat/Lon?;

The EdgeTech software (and other commercial units) allows me to factor in how much cable is in the water (called layback and absolutely critical to have), to change the Range of the sonar wave, to change palette colors, to run one or both frequencies at the same time, to take into account salt water, fresh water, speed-of-sound issues, integrating the data automatically with the GPS, setting my lane spacing using their “Coverage Mapper” for mowing the lawn as well as lane over-laps for 100%-200% bottom coverage and on and on; unless there is off-the-shelf software available to buy that can at least provide a minimum number of basic search functions, a homebuilt won’t do it for the serious searcher;

Your post had asked for some of the features you need most for what you want to do-start with what I just wrote above.

b) The deeper the water the more of a problem this will be with a home-built that doesn’t have the ability to capture coordinates; it could be such a big problem in the end you are wasting time and money going with a home-built because at some point you won’t find what you are looking for even though you have a SSS image that is really interesting; I’m a diver too so I know exactly how hard it can be to locate something on the bottom; even with a great set of coordinates if you have “black water” or deep, dark water, or the target is small, the challenge can be huge, depending on other variables also;

c) Powering a homebuilt may present problems as well because now you are sending lots of data over a cable-can the unit-presumably not designed for a towfish-handle it without crashing? You might need a generator, something else to factor in; there can be other electricity-related challenges I cannot get into here in detail because I am not qualified however I see the potential for a heck of a lot of questions to overcome with a home-built related to electronics; I really hope the Forums for home-builts can give you answers;

d) Unless you have a lot of knowledge about electricity etc. at some point the unit will likely fail-then what? To whom do you go for repair or diagnosis?;

e) If you go this route, Rudiger has it right-go for the largest display you can get;

f) As to problems lengthening the cable I do see issues; that’s why what you get from the factory for cable for a helm-mounted side scan sonar/SSS unit should never be cut but instead, curled up un-cut and stored safely; use the entire cable as it came from the factory;

However people who like this technology and have built their own towfish may have much better answers to this question and that’s where the Humminbird Forums could be of great help because if anyone has messed with cable lengths while building their own towfish, they have;

My advice, assuming you have the money, is to buy a commercial unit (new or used) so none of the points I made above (and that’s the SHORT LIST) will be something you have to deal with if you go commercial vs. home=built. Just too much trouble and time in my opinion to build one.

TOWFISH ADVANTAGES

If you visualize the sonar wave not as a sound wave but as a beam of light, you will understand the geometry involved in ensonifying things on the bottom with a towfish. One huge advantage a towed system vs. a transducer mounted on the hull has, is the ability to get the towfish closer to the bottom, thus generating very very important shadows. The things shadows can tell you is spectacular (technically it’s a loss of sonar data but we call them shadows because that’s what they look like).

The higher in the water column the transducer is, relative to depth, the worse the shadows get. The angle-of-attack sucks. At some point you will not be able to recognize a great target because the angle-of-attack of the sound wave has degraded so badly.

Test: Put a beer can on a table and shine a flashlight on it from say, a 45 degree angle and two feet away and see the shadow it produces. Then lower the flashlight to say, 12 inches off the table from two feet away. The shadow of the can is radically different-and better. This is the benefit you get from towing the transducer lower to the bottom. Getting close to the bottom is really really important.

My Humminbird 1197 works great in “shallow” water but as I get into deeper water it degrades badly for the reasons I just detailed. Of course this has nothing to do with the Humminbird itself, it just the way it is using any hull-mounted transducer regardless of the Brand of the unit.

To answer your question about at what point you would you would start to see benefits from using (any towfish), the answer is the benefits would be immediate and dramatic.

I love the EdgeTech I bought (great people and great products/www.edgetech.com) and I love the Humminbird (www.humminbird.com).

But buying the EdgeTech towed system-a commercial system-opened a huge new world of exploration for me that has been a great experience that isn’t over yet.

I love the things I can do with a towed system as both a sonar owner/operator and a diver. But I am not a pro, just a hardcore amateur with this sonar technology.

If you have other questions, post them here. If you care to contact me directly, email me through this Forum privately and we can go from there off of the Forum. I’ll help you any way I can.

Thanks for taking the time to post a great, informative response.

While I knew constructing a homemade unit was possible, I actually never considered doing it myself.

It just seems there has been a bewildering array of changes and upgrades to the readily available commercial units over the last few years, especially the Humminbird line. Is the difference in display size between the 1100 series and the 900 series really that significant in practice? Anything else I should be looking for other than dual card slots?

On the target coordinate issue with a towfish---is the inaccuracy simply a function of transducer distance from the base unit, or does lengthening the cable cause electronic issues that affect accuracy? I am assuming the sonar simply meshes the GPS position of the base unit with the readout regardless of the actual position of the transducer.

 

[Rüdiger]

Hi Hobbit

No, it is not my desing, I have the idea from the HB forum DIY - Side Scan Sonar and towfish .
The towfish consists of PVC pipe and is glued with special glue.
As a cable I currently use 3 HB extension cable a.10m, sheathed with hollowbraid for strain relief.
With the running properties of the fish I am very satisfied.

mvh
Rüdiger

 

[Rüdiger]

On the target coordinate issue with a towfish---is the inaccuracy simply a function of transducer distance from the base unit, or does lengthening the cable cause electronic issues that affect accuracy? I am assuming the sonar simply meshes the GPS position of the base unit with the readout regardless of the actual position of the transducer.

When evaluating the sonar recordings, some softwars allow a shift of the GPS coordinates. One has to take into account, however, that the fish is not exat around the staked cable length behind the boat.
You can use the XY diagram (X = maximum cable length, Y = maximum depth) to find out more precisely. First, a quarter of a circle is taken from the common zero point with the radius of the plugged cable. Then draw a horizontal line, at the Y axis, with the value of the actual run depth (card depth - depth over ground) until the arc is cut. On the X axis, the "real" distance to the boat is located vertically above this section.
However, since the cable underwater does not run in a straight line to the fish, but due to the water resistance in an arc, this "real" value is still to be cemented. How much? There are only experiences.


Mvh
Rüdiger

 

[enrada]

If you want an education in side scan sonar you need to buy the following book.
ECHOES and IMAGES by Mark Atherton
This book has awesome images that make it easy to learn without knowing algorithms or anything else. A little expensive but well worth the knowledge that you learn from reading it.
Also another company that no one has mentioned is J.W. Fishers side scan which is more affordable than the high end units and also comes with navigation software.
Don't look for the cheapest unit, you will be disappointed. One serious find pays for it.
J. D.

 

[seekerGH]

These are very good as an entry level machine...I seem to remember about $5000. (it is badged under a few names, so check around)



http://sharkmarine.com/Products/SurveyEquip/SideScan.html

Rudiger. If you use a downrigger setup, with a weight and the fish attached to the weight (or wing)it is far easier to determine the location. Since the weight can be made to drop almost straight down, you just have the length for the weigh to the towfish to add. This is also a good way to insure that the fish is flying level.
In this config, you dont have the turbulence around the fish that messes up the readings...

I dont like these around the fish..



With a downrigger, you can also add a camera without affecting the fish.

 

[diver9]

Enrada is right-if you really want to understand SSS buy Mark's book.

I was at a training workshop for SSS in Michigan in 2013 for 3 days (on Lake Michigan at a university that taught Marine-related science) and two of the best in the business were instructors for it-Mark Atherton and Garry Kozak. Mark's book weighs approx. 5 lbs. and was required for the course. Costs about $180 but we got a deep discount. It's huge and has the best diagrams and explanations I have ever seen anywhere. I liked it so much I re-read it cover to cover every Spring before heading out once ice is out here in New England.

As to changes in non-commercial systems you commented on, in the last 5 years or so you are right-a lot of new stuff including touch screens, multiple transducers, bigger screens, Down Imaging coming standard, and higher frequencies passing the 1,000 kHz (1 MegaHerz) mark and more can get frustrating. I look now and then to see what's up but have no need right now to buy a unit to replace my Humminbird 1197. Good looking gear though-wow.

Regarding Hobitt’s question about target coordinates I will try to answer as best I can:

- Re: Inaccuracy: I wouldn’t use that word exactly because it’s not really an inaccuracy issue, it’s one of not having that data (how much cable you have out, called Layback) entered into the software at all because if I understand your question-you don’t have any software to enter the Layback number into in the first place;

One variable that commercial SSS software will handle for you automatically is how far from the GPS on the boat the towfish is; the Topside Processing Unit/TPU will factor this distance in to its calculations when you go to mark a target because I manually enter the Layback distance into the software before I drop the towfish over the side so the system now knows what I have out for cable; this is one of quite a few numbers and configuration changes I make before starting a scan, all in the software;

The SSS software will take into account:
a) where the GPS is (think for the time being, where your boat is) because the GPS is wired directly into the laptop which is wired directly into
the TPU;

b) how far back from the GPS the towfish is because I entered that Layback figure beforehand and

c) from these variables, will calculate the position of a target you mark; I hope this answers your question;

So it is not simply a function of how far the transducer is from the base-there is other “positional” information that needs to figured in to the calculations…….where’s the boat-where’s the towfish-and finally where’s the target based on this;

- As to lengthening a cable and thus creating “electronic issues”, in general terms and not getting into a Manufacturer-specific answer because I am not able to do that because I don’t know-I have never had to enter the length of my cable (50 meters/165 feet) into the software;

Obviously the system either already knows or, it doesn’t need to know, because I gave it the Layback figure; I believe now that you have me thinking about it, that the system only needs to know how much cable is in the water (Layback), which I tell it; and longer cables which I can get, don’t cause any inaccuracy problems at all;

- My system, as would any commercial system I believe, does indeed “mesh” as you say the GPS position of the base with the readout (I assume when you say “readout” you mean the Lat/Lon of a marked target); and in that process of making those calculations it must also know where the towfish is.

I am sorry answers can’t be shorter. I explain it as best as I can as an amateur.

 

[seekerGH]

It is a bit more convoluted that it appears. Towspeed, cable weight, and currents all affect the catenary arc in the cable, hence the location, with the extra drag/weight. You know towspeed is too high when you have a long yellow waterskiier following the boat!



Cable length will come into play with the additional weight of the cable. Harmonics has to be considered, especially when towing at higher speeds or in strong currents. The harmonics in the cable will translate the vibration to the fish. (another reason to use a downrigger type setup.) I dont really know of any rule on the length/harmonics/speed relationship, just trial and error.

In the diagram above, it is very easy to see the numerous advantages of using a downrigger setup, with a near vertical depth. You also dont have to play with the connector location on the fish to try to keep it level.

As a check, since you know the angle of your transducer splays, you know when the distance from the bottom when they meet in your scan image. You get the depth to bottom from your boat, and can cross ref that against the calcs you have for the towfish.

 

[Rüdiger]

Hi seekerGH

Thanks for the good schematic representation.
Yes, a downrigger is a good help to stabilize the fish and bring it to depth.

Mvh
Rüdiger

 

[hobbit]

Thanks for lots of great information, guys. Sounds like I have some serious reading to do. That's OK, just hoping to have a system up and running by spring.

 

[diver9]

I wanted to attach another diagram of catenary issues but don't see a way to do that. The link in the menu says only jpg, jpeg, png, gif-mine is a pdf.

My towfish weighs about 50 lbs. and sinks like a stone. I have not had any need for a (depressor) wing or other weighting system yet but they are common depending on what one is trying to do. I am glad I don't need one. However with a home-built system I can readily see why one could be needed because the towfish is just too light, as they are to my knowledge, not heavy enough.

I would really like to see images from home-builts. If anyone is inclined to post some that would be great.

 

[seekerGH]

I really would not be too confidant with that Edgtech, the large fins on the back will cause it to raise up under tow when the cable brings the nose up. The limited connection points at the top make it even more difficult to set up and fly level with confidence, let alone determine the depth. Edgetech has an option for a wing just because of that.



The diagram provided was an example, but in reality, it is a very simplistic example, as the combination of lift from towspeed, angle of the attachment varies with depth, simply due to cable weight and cable drag. This usually causes the lift, which is why the wings are so popular.
In reality, with the factors considered, it is usually a double catenary arc in the cable. That is why the cameras on the downrigger are great, you dont have to guess which way the nose is pointing and have a much better chance of flying the fish level.

 

[ropesfish]

While I hesitate to resurrect an old thread. sometimes it is neccessary for proper context...therefore:
Does anyone have a copy of this book for sale or know where one might be found at a reasonable cost? If so, let me know.
Thanks!
Echoes and Images: The Encyclopedia of Side-scan and Scanning Sonar Operations

Mark W. Atherton
OysterInk Oublications, 2011 - Acoustic imaging - 1018 page