Topic: 797 Towfish

[PT]

I've been reading with interest the discussion regarding DIY towfish; which I find most interesting. It's almost impossible to buy CAT6 PIMF cable here in Australia (without buying 200 metres of it). After reading Rickard's hints from some time ago, I ordered 3- 10 metre cables and a transducer from the USA. I had the techie at work cut off the connectors and join the cable, then shrink wrapped the joints making a 36 metre cable. I then taped a 2mm stainless steel wire to it. I emailed Greg; who sent me a number of designs, built the unit and installed a 6 kilo weight in the nose. I found the balancing point and attached my tow point there. The fish works really well, and I'm most happy with it.

The usefulness of these units has been well and truly proved, as I've managed to find wreck sites that would have been almost impossible to find with a magnetometer, or normal depth sounder. I originally had the transducer mounted on the stern of my boat, but found that much better results can be achieved by running with the 6 metre cable on the fish, then if something is found, attach the 36 metre extension for a closer look.

Please keep up the excellent discussion forum regarding various designs, and people's results. Abra and Rickard's results are quite amazing.

PT

[abraquelebout]

nice PT
welcome to the forum, you have got good result with your towfish and i see you find  wreek that's impossible to find with mag. would you publy picture to see what it look like ?
in sonar picture experience may be the thirst thing to make indentification of object

[Jolly Roger]

Wow PT,

the fish looks good, congratulations! What dimensions does it have and how have you stowed your cable?

Keep the pictures comming.

Regards / Harry

[PT]

To stow the cable I use an old computer cable reel. Out in my boat I reel out enough cable for the job, plug the connector in and tie the cable off with 4 half hitch knots. Most times I am by myself, so I have the boat go in a straight line, and slowly let the fish (Rex) out.

The ballast barge is 17 x 6 metres, and is fairly flat on the seabed. The port authorities had no idea that they had a wreck in their fairway. Considering the wreck is made of wood, the reflection off the wreck is surprisingly good, frames and stringers can be easily seen.

I've been mapping an area of the port, looking for wrecking and stranding sites, and have so far found at least one, plus a number of other targets.

I usually start out by plotting a grid on my marine chart, then work out an area to search- say 500 x 500 metres, work out my lane widths and turning points. I put all this info into my independent GPS and run a series of lines until the whole grid has been covered. Then it's back home to spend a few hours on the computer reviewing the search. Anything of interest is then taken note of, and dived at some point.

It is also a good idea to keep a note book on board, making an observations, and recording what you did that day. I also keep a log (hard copy) of the searches so that I know what I have done, and anything of interest.

Attached is a picture I took of a stranding site, in 1866 a clipper ship caught fire and sank off the Port of Melbourne, it was re-floated two years later. However, there was a contemporary lithograph which showed the vessel's location. I plotted this up and eventually found the stranding site. Although the image seems unremarkable, there is still a great deal of material on site. This has been reported to the Heritage Office here. Good fun!

PT

[Jolly Roger]

Excellent work PT, my respect.

the cable reel was something I was thinking of as well. I searched the web and found this one:

http://musikerkabelladen.de/shop/category_168/Netzwerkkabel-Twisted-Pair-CAT.6-PUR-und-CAT.5e.html?shop_param=cid%3D%26

But 850.- Euros??? Hm..... No!

Rickard told me to have the cable stowed away in a figure eight to avoid interference, therefore I bought a square plastic bucket and that worked good so far.



The other problem I have is that I have attached stainless steel eyes to my tow cable every five meters and they would be hard to reel in.

I found an interesting report about PIMF cables in Wikipedia:

http://en.wikipedia.org/wiki/Category_6_cable

It's very informative and worth to read  .


Keep us updated on your work PT. Not much going on here with sonar in the northern hemisphere at the moment  .


Best regards / Harry

[Dale]

Gday there PT.

Nice fish.

I'm in Melbourne as well.  Send me a pm and if you are keen to share notes, and a couple of possible tasks we can meet up.

I have a roll of UG phone cable (Gell filled 6 pair) that we could use to make a longer cable.

We will have our fish and camera gear out working out at Ricketts Point on Sunday, then Westernport the following week. You would be most welcome.

Dale

[PT]

Righteeo Dale,

I've sent you a message.

Let me know if you receive it.

PT

[Rickard]

I ordered 3- 10 metre cables and a transducer from the USA. I had the techie at work cut off the connectors and join the cable, then shrink wrapped the joints making a 36 metre cable.

PT,

This was interesting and also what I have suspected, the HB cables are excellent, but the way they are wired when used as extensions is not optimal. Now when we know long extensions are possible I think HB could offer their cable without connectors and accept orders for any desired length. This would be an easier thing to do than coming up with a complete sidescan/towfish transducer.

Very nice to see towfish images from a 797 model. I think these are the first presented ever!

Kind regards
Rickard

[sonar2000]

Are these cables made by HB or do they purchase them. If bought on the market can we also buy these cables in lengths.  Maybe one could buy a spool and then each person wanting a cable length could get it from that person.

Just a thought..
Chuck

[PT]

Thanks Rickard.

I agree, it would be much easier to buy a single long length to build a towfish.

I do have lots of projects to do in my part of the world, with a number of them being small targets (wreck mounds and stranding sites). Without the Humminbird, this job would be almost impossible.

An example attached is that of a small iron box 600 x 600 x 800mm, on diving the site I located associated ballast and other material, quite remarkable.

Best regards

Peter

[abraquelebout]

nice and interresting, i use my towfish for submarine archéology
why don't you use deepview to get a beter image than humviewer
i wonder what's smaller target whe can find, i hope that 100 x100 mm it's possible
i find logboats who are 90 mm over ground.
i use humminbird only for scaning, and opencpn for navigation.
it's possible to make charts with dr depht and see them whit opencpn
imagine what you can do with this system, i join a sample

[PT]

Thanks Abra,

I haven't tried any other software.

[Jolly Roger]

I usually start out by plotting a grid on my marine chart, then work out an area to search- say 500 x 500 metres, work out my lane widths and turning points. I put all this info into my independent GPS and run a series of lines until the whole grid has been covered.

I don't know if the 797 has the ability to show a chart, but have you tried using the unit to set the search grid?

I did that a couple of times last year and it worked very well:
I create a waypoint in the center of the area I want to scan. Next I go to the Navigation menu choose the way point and have it overlaid with a grid. By changing the zoom factor I can vary the distance between the search lines.
I have the screen split during the runs. One side for Si, the other showing the chart with the grid. Usually I take one recording from two parallel lines, so I can verify targets from two different directions.

Then it's back home to spend a few hours on the computer reviewing the search. Anything of interest is then taken note of, and dived at some point.

Same here. I do a review in the evening on my laptop. Quite amazing what one can see if the recordings are reviewed on a bigger screen.

Regards / Harry

[Kimi]

Same here. I do a review in the evening on my laptop. Quite amazing what one can see if the recordings are reviewed on a bigger screen.

That's true! If you own Adobe photoshop, Corel Photopaint, or similar programs you can make magic in some cases. By change the contrast, sharpness, brightness, etc. you may find  something you wont see on the original version.

You can also make mosaic photos over bigger areas.

[MLauterbach]

Hi,

i used CAT7 patch cable from Draka for my fish ( http://communications.draka.com/sites/eu/Datasheets/uc09ss27s-ftp_e.pdf ). It works very well with 50 meters.
Now i would recommend this cable:  http://communications.draka.com/sites/eu/Datasheets/uc09ss27pur_s-ftp_e.pdf
For example here for € 120 / 100m
article #1001136-00100RW from http://www.steckenborn.com/

Martin

[abraquelebout]

hi kimi
You can also make mosaic photos over bigger areas.
for making mosaic photos i use SIVIEW
this log cut  scan in lot of parts, you can export them in JPEG and after i go in corel draw or photoshop to make a big photo
this picture is made in 4 parts
the original has 2 m lengh, i join it in pdf
 montage eyriaud.pdf (1351.68 kB - downloaded 248 times.)
for real mosaic i use dr depht
i create ozi explorer chart and translate this in opencpn
then i can sail with my scan chart when i arrive near waypoint
i join sample

in my search i separe scanning and navigation
i use humminbird only for scan and portable pc with opencpn or maxsea to take track and navigation
and gird into charts created by lot of paralelle roads  in function of scle scanning