Humminbird Side Imaging Forums
Other Interest => DIY - Side Scan Sonar and towfish => Topic started by: Dale on December 17, 2010, 07:52:03 PM
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G'day all,
As a lurker on the forum, I thought that having built and deployed a fish that I should report some results.
I've put up an initial still and a short video clip of the fish on Flickr
http://www.flickr.com/photos/miniop/sets/72157625620469360/ (http://www.flickr.com/photos/miniop/sets/72157625620469360/)
I'll post more on this thread as time permits.
Dale
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Now I know how to embed video into a post...
Towfish & Video (http://www.flickr.com/photos/miniop/5267439049/#secret9abcda73e6)
This is the fish on shallow tow, with a splashcam video camera in front. The reason for the shallow deployment is obvious! I shot this clip using the rather brutal method of taping my offsiders camera to a boathook and shoving it over the side!
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Hey, that looks pretty nice!
Is the transducer already mounted to the fish ? I just didnt see a cable going down. Any further informations and ofc some more pics welcome !
greetings,
Del
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I could not see the transducer either. It also looks like that is a piece of PVC without a nose on it. Can you confirm this and maybe post some build pics and a picklist when you get it all working?
Beautiful looking beach area in the background!
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If you mounted a transducer show some pictures. Also some comments on how well the fish tows and how stable it is. Do you get any side to side sway.
Chuck
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Sorry all, been busy.
This is the first fish I have built, having some experience in using high end fish (Klein etc) It was whipped up out of available materials.
Stats:
PVC tube 50mm dia
Length 1200mm
Fins (4) 250mm x 130mm
aluminium channel
two 500g bar type lead diving weights
one squished 500ml plastic drink bottle
cable ties
Construction:
Fins and tow point welded to tube.
Transducer mount riveted to backing plate inside
Tow cable is waterski rope with the transducer cable threaded inside. I used three cable ties to connect the fish to the rope, after I carefully placed the shackle on the gunwhale minutes before... and I can thus confirm that the Humminbird will not resolve a shackle on the seabed.
The fish construction was finished enroute to our test grounds.
Experience:
We did just over four hours of towing with the fish, and 40 min with fish and video. Conditions where not perfect, with tide runs of 2-4Kn.
Fully weighted (1kg lead in the nose) and a nose cap, the fish tows well, in this case with almost no layback. We needed to be able to sight the fish as the area we where working had depth ranges of .5m to 14m. We removed 500g and retested. I rammed a 500ml drink bottle down the tube to get some more buoyancy and that achieved the desired result. The nose cap was removed to make sure the nose section flooded.
The video was shot with us towing cross tide on a transect. The fish can be seen walking around slightly. We think that this is current, wake and design induced.
More sea trials are to take place very soon. We will move the tow point forward, and test in a variety of waters. (without current and with a shackle)
[attachment=1]
Mount for transducer
[attachment=2]
Welded fins
[attachment=3]
The fish and a foot.
[attachment=4]
End view
I'll post up a clipped portion of the mosiac we produced next. With our next tests we will run the splashcam pointing aft and get some video of the fish running in a variety of configurations.
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And the results!
The data was processed using DrDepth. The image below has a 10m grid overlaid. The aim here is to collect data to habitat map large areas rather than find fish, or gold!
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I could not see the transducer either. It also looks like that is a piece of PVC without a nose on it. Can you confirm this and maybe post some build pics and a picklist when you get it all working?
Beautiful looking beach area in the background!
The beach area in the background is beautiful! Every couple of years or so the bomb disposal crews come out and blow up UXBs as they show up on the same beach. The place is littered with shipwrecks just to add more interest.
The link below is well worth exploring, it shows the area we are working in. As an aside we Aussies have something the rest of the world does not, NearMap. Have a good look at the point to the west and use the time buttons to reveal a shipwreck.
http://www.nearmap.com/?ll=-38.30653,144.662996&z=19&t=k&nmd=20101028 (http://www.nearmap.com/?ll=-38.30653,144.662996&z=19&t=k&nmd=20101028)
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Hey Dale,
you've got some verry nice results there and your towfish looks quite simple. Nice one, thanks for sharing.
Am I correct that your transducer cable is inside the rope ? Looks like this on the pics..
Thanks,
Del
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Del,
I rove the the transducer cable inside the waterski rope. Topside I have the plug just protruding from the rope, and use the tail to cleat. From what I can see so far, the transducer cable is not taking much of the tow load. I'll post up some images of both ends.
D.
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good job, congratulation
do you only want to use humminbird tranducer cable, or other for mutch longer and depht ?
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I'd use a longer cable for deeper depths, down to 120m. By that stage, we would be seriously considering using a more professional grade system and fish.
My main interest is developing systems that can be used by volunteers and staff to map change in waters less than 40m deep. We also have a bunch of wrecks, both recent and older, that we wish to obtain some data.
We will be testing deeper deployments using the ski rope in the new year. From what I've seen so far, the rope does not bind to the cable, so that the tow load is only on the ski rope.
Today would have been a good day to be out on the water, it hit 41 degrees C here!
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Today would have been a good day to be out on the water, it hit 41 degrees C here!
Hm, that makes 41 degrees more then here :-[
Happy New Year!!
Harry
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Happy New Year to you all as well. Snow and ice in the amounts we see on the news in Europe and Scandinavia are not things we consider when planning side scan missions!!
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As part of of a habitat mapping project we have just returned from three days of trialling our fish, and our mobile topside unit in three different places.
We used a 14ft rigid hull inflatable (RIB) powered by a small two stroke outboard. Two of the sites consisted of tidal mudflats, with deeper channels. The third was a combination of rocky reef shelving to sandy flats.
The fish was towed at depths of around 1m or less. We quickly learned that we could run with swath widths of 50m a side in water depths of 2m. As the mudflats are, well, flat, clear returns from objects 40 -50m off the vessel track could be seen. We planned our runs to cross the channels at 90deg, after initial tests showed trying to follow 2m wide channels using only sidescan was very difficult.
The vibration from the two stroke outboard was transmitted through the hull, and the buoyancy tubes to an extent that it could be clearly felt and seen! Holding the cable against any part of the hull transmitted that vibration to the fish. It thus became simple to use a leg and an arm to hold the cable and fish away from the boat.
As the fish was on a very short cable run (less than two metres) we could observe its tow characteristics. We noted that if held to short, the fish would roll, leaving the transponder with a fixed roll angle of around 10deg. By just letting out another metre, the fish would roll back to vertical.
Some detail images of the fish:
[attachment=1]
Cable join detail.
[attachment=2]
Nose (open as run) with nose weights
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End view of nose with first weight installed.
[attachment=1]
We ran the fish with no nose cap for about ten hours, at depths from 2m down to about 6m with no signs of pitch, roll or yaw (apart from that noted above)
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Dale,
The fish looks great. Harry and I were just talking about the open ended main tube on the fish. Looks like it flies great.
Look forward to some more images.
Robert
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Good to hear that Dale!
I think the longer the fish, the more stable it will be. Then there even might be no fins needed.
Regards and thanks for sharing Dale
Harry