Side Scan Sonar Wanted

Dave Sutton

Gary Burton is from Rhode Island, and I've hosted him aboard my boat for trials. His system is a towfish which he makes, connected to a commercial Lowrance fish finder/GPS system. As such, it only scans to one side, not both sides of the towfish. What I found is that the system works fine, but the on-site resolution on the screen of the fishfinder is really pretty poor. The recorded image on the removable media, when played back on a PC or laptop using the inclouded software is actually pretty good. What discouraged me is that you end up squinting at the fishfinder hoping to see something, but only get the best resolution after the fact when you remove the media chip, plug it into your laptop, and begin working with the files. There is no way to parallel a computer to the system in real time, and there's no plan to do so.

My impression of the system is mixed: The towfishes are hand made and are not what you would call "factory", really glorified homebuilt stuff. Not that this is bad. The transducers are top quality. Cabling quality is, again, "homebuilt". I did not really find that the single-sided scan was an issue, and the images are actually very good. But, you end up not seeing the real images until after the fact, and you end up using the system almost blind in real time. That was a total show stopper for me. The bottom line is that when I brought Gary out for the trials, I intended to write a check at the end of the day. I did not do so.... which says it all.

The attached file photo is an image that Gary and I got here off of my boat. The image is a crane barge laying on its side, with the crane laying out in the sand. The crane boom is only about 30 inched across, and the system was able to resolve the lattice structure of the boom. That's the good news. The bad news is that we could not see that detail on the boat, only on my laptop after we got back home. I'm not sure that this represents a usable system for any real searching. We were only able to image the barge because I knew it was there, but I don't think we would have found it "in the blind" if we were searching.

I'm still looking for a side scan for EXPLORER, and have not found what I want yet at any sort of reasonable price. The modified Sportscan, as described, seems like it would do, but I am not the one to make the mods to allow a longer cable, and as-sold the Sportcan does not work to the depths I need if to work at. So far I'm still shopping.


Dave

Attached Images

Crane[1].jpg (23.7 KB, 302 views)

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jasonvds

Check this out - a very sweet high quality unit from the UK.

StarFish Seabed Imaging Side Scan Sonar Towfish

lamont

Will the burton towfish go to 100m and can you use a long towcord with the stock unit to get it down there, without requiring the kinds of mods posted earlier for the SportScan?

EDIT: It looks like the burton only comes with a maximum cable length of 200 ft which would indicate that it would not be suitable down to 100m? ( and how much scope do you typically get on a tow cord at different speeds? )

EDIT2: At 1-2 knots and 45 degree angle (per the previous post) that means you need about 110m or 370 ft of towcord to fly about 20m above the bottom...

Dave Sutton

I'd call Gary and ask, he knows what he makes. I seem to remember from talking to him (3 years ago, so details are fuzzy) that the cable can be extended. The strong point of his units are his transducers, which he designed and manufactures personally. Apparently they are very good. Google his system, as there are various treasure hunting forums with large side scan sonar forums, with lots of discussion if his (and other) units. Gary is a good guy, drop a dime and call him. He's not all that responsive to email (replies average a week).

I'm holding out for a Klein or Wesmar.... But then again I've got the cabin and generated electrical power aboard EXPLORER to run a "ships sized" industrial unit.


Dave

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PPA

How deep was the crane barge?
Pedro

Benthic

Dave,

Thanks very much for the detailed feedback!

Brian

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DanFountain

The first thing a potential sidescan buyer needs to do is define the mission for the machine. If the mission is to find a known wreck within an area of a very few square miles or to survey a known target and get pretty pictures of it, then a Sportscan or even a Burton sonar might be a suitable tool. These high-frequency sonars have high definition but limited range. The scan that Dave posted is a good example of what a high frequency sonar can produce, but it was obviously shot a short range - I'm guessing 150-200 feet - with the towfish very close to the bottom (about 10 feet?) indicating a dead-slow tow. Do the math - how long would it take to "mow the lawn" over a single square mile at 200 feet per side at 1-2 knots? Don't forget to overlap the scans by at least 1/3 to allow for track line errors and possible poorly ensonified areas directly below the boat.

If the machine is to be used primarily as a search tool, a lower frequency, high power model such as a Klein is needed. Lower frequency sound travels better through water. Depending on the size of the target and the bottom topography, a quarter mile or more per side may be be practical. An intact steel wreck on a flat sand bottom will stick out like a sore thumb. A broken-up wooden schooner on a rocky bottom might be nearly invisible - the rock is actually more reflective than the water-logged wood. A shipwreck probably won't look like much on the display, especially at longer ranges - maybe just a smudge or a slight shadow. Here's where experience with the unit can count for a lot.

Just a comment on fishfinder-based sidescans - most consumer grade fishfinders do not have time varying gain (TVG). Remember that the intensity of both the transmitted beam and the reflected echo vary as the inverse square of the distance. A target at 100 feet will return an echo 4 times stronger than the identical target at 200 feet, 9 times stronger than one at 300 feet, etc. "Real" sidescans have TVG - an automatic gain control that ramps up the gain as the time for the echo return increases. This allows the sonar to display distant targets as well as nearer targets. On a fishfinder-based sonar, detecting distant targets often means turning the gain up so high that the first 1/4 or 1/3 of the range is saturated, hiding any possible near targets.

I'm using a Lowrance LMS-480, which I believe is what Mr. Burton supplies with his sonar. What Dave said about the screen resolution is very true - with only 480 pixels of resolution, the real-time displays are not very good. For a comparison, go to the Lowrance web site and download both the LMS-480 simulator and the Sonar Viewer programs. There's a nice sidescan of a barge on the sidescan sonar forum at Opinions of Side Scan Sonar - Geotech Forums. It looks beautiful on the Sonar Viewer, but on the simulator - which seems to accurately represent the actual unit - it is nearly indistinguishable.

Bottom line - there's no affordable "one size fits all" sidescan sonar If there was, I'd own one!

-Dan

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Dave Sutton

40 feet. And as Dan says, the fish was positioned about 100 feet away from the known target, was about 10 feet off the bottom, and was towed at about 1 knot. Not useful for looking for unknown targets.

Read what Dan F. writes. He knows his stuff, and is "not an unknown" on the Sidescan forums elsewhere. I've followed his sonar writing for a while. He knows his stuff.

The good news is that the Starfish seems to be a useful unit, and I was quoted about US$4000 for one today, with a 6 week delivery. I might bite on one just to give it a test. Price seems fair, and specs look OK. Just wish I could afford a Klein...


Dave

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lamont

well, there can't be no way all, just no way which is supported with the existing hardware. instead of dumping to the media card it should be possible to dump to a PC-compatible interface and then its a matter of writing the drivers and display software to get it up on the laptop's screen.

if gary created the hardware for an output interface and openly published the specs, he'd almost certainly get some software/driver contributions to support displaying in real-time on a laptop...

Johnny Christensen

Just a heads up.
Within the next 6 months it's being desided if we are going to upgrade our sidescan system. That means the fully modified SportsScan unit may be for sale. I just talked to the owner of Havgus, he just completed a 3 weeks scanning and diving operation in the northern Jutland area. During that time they found 89 new targets and managed to survey about 50 of them. That turned out to be some 40 locations of coldwater coral growth that always suspected must be out there, but now its confirmed.
These corals are made much like the area Hirseholmene, but from a different kind.
The Bubbling Reefs . com - a World unique phenomenon under water - the film
Also one previously unknown shipwreck was located, but only dived briefly IMO they need to adjust their priorities.

The modified SportsScan has done really well, but due to option of different scanning frequencies offered by the Yellowfin we are now considering that. The singlefrequency SportsScan can give a picture of whats down there, as long as the target stands clear of the seabed by more than 20cm (guess thats about 8 inches)
The Yellowfin is thought to be better in making really fine detailed images when there is some doubt if its worth to send down a survey diver. Every time a diver is to enter the water, it takes away time that could be used for scanning.
That's the reason why we are considering a upgrade. For hunting shipwrecks, as that usually is a larger target, it's still a very good unit.

If we deside to upgrade, I'll post a message.

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Wreckphotography from the cold north