Opinions of Side Scan Sonar

[GaryF]

Gary, I was interested in how you used the SS sonar to locate a lost anchor. What's involved in determining lat-lon numbers for an object observed on the sonar? Does it require a fair amount of math/geometry between the measured GPS position of the boat, boat-towfish distance, towfish depth, estimated range to object based on position in frame, etc?

Hello,

Yes, it does require some trigonometry just as you described. The Lat/Lon indicated when you roll your cursor over a visible target (within the Sonar Viewer application) is the position of the GPS antenna only, not the position of the target. So you need to first calculate the position of the towfish (you need to know the approx. cable length for this), then from there you can use the towfish altitude and slant range to the target to calculate the actual position.

It's a little tricky at first, but I used all the standard side scan formulas to make the calculations. They work. My calculated positions are quite accurate. I should also note that all of the data needed for the calculations is imbedded (towfish altitude, slant range) or can be derived from the imbedded data (Course Over Ground) in the sonar file. The only thing you can't derive from the data is the towfish layback, so you need to keep good notes as to how much cable you use. I've marked my cable every 25' with colored electrical tape exactly for this purpose. Simple and fool-proof.

Gary

[Unregistered]

Thanks, that's very interesting. Do you try to keep to a north-south or east-west heading when you're taking side-scan data? I'd think that traveling at some other random angle would greatly increase the complexity of pinpointing the location of observed objects.

Also, re "all the standard side scan formulas," is there any reading you can recommend that introduces them?

[GaryF]

Thanks, that's very interesting. Do you try to keep to a north-south or east-west heading when you're taking side-scan data? I'd think that traveling at some other random angle would greatly increase the complexity of pinpointing the location of observed objects.

Also, re "all the standard side scan formulas," is there any reading you can recommend that introduces them?

North-South or East-West is not that critical. I find that it's important to hold a STEADY course. Although that's not always an easy thing to do. Regardless, an accurate course over ground (COG) can be derived later from the recorded data. In SonarViewer simply pick two lat-lon positions along the course line (or on either side of a desired target) and calculate the bearing between them. This works quite well.

As for reading I would recommend "Sound Underwater Images: A Guide to the Generation and Interpretation of Side Scan Sonar Data, by John Perry Fish and H. Arnold Carr". It's a very good text but somewhat expensive. I would recommend their advanced book as well. You can order them direct from the authors here.

http://www.instituteformarineacousti.../IMABooks.html

Gary

[Frank O]

Hi all, I've been lurking here for a bit but thought I should introduce myself. I'm wondering what those of you who have systems like the one discussed in this thread are using to keep the towfish cord away from propellers on the back of your boat? I recently ordered one of Burton's systems to use on my 21' Boston Whaler with a single outboard engine, and am trying to sort out how all to rig it.

[Glennk]

Hi all, I've been lurking here for a bit but thought I should introduce myself. I'm wondering what those of you who have systems like the one discussed in this thread are using to keep the towfish cord away from propellers on the back of your boat? I recently ordered one of Burton's systems to use on my 21' Boston Whaler with a single outboard engine, and am trying to sort out how all to rig it.

We have just let it run over a floating pillow that we have laying on the stern of the boat. But we are building a small A-frame to run the cable through.

Just remember that the Twinax cable has a bending radius of at least 3", just so that you don't accidentally break it.

Regards,
Glenn

[Frank O]

But we are building a small A-frame to run the cable through.

Thanks. Are you aware of any pictures out on the web of an A-frame along those lines? I was hoping to get some ideas that might inspire me. Preferably I'd like to fabricate something out of PVC that can be knocked down when not in use, if that'd be sturdy enough.

[Glennk]

Something like this?



Perhaps it won't fit on your boat, so that you need to down-scale it a bit....

Just google for "a-frame" +cable and you'll find some pictures of A-frames that you can use as an idea for your own design.

PVC should be good enough, if you buid it out of thick profiles and not 1mm pipe. But I would preffere to use a aluminum frame, as it would be more stable and be less "wiggly" when the cable runs trough the water.

regards,
Glenn

[Glennk]

More pics!

A smaller version of this is something like the one we are planning to build.




I hope this can help you.

Please share your pictures with us if you build you a A-frame for the cable.

regards,
Glenn

[GaryF]

I use a simple crab pot puller mounted on a removable aluminum davit. This works well for keeping the cable away from the props as well as for hauling in the towfish. The electric Safe-T-Puller has a large diameter rubber-lined sheave that holds the cable securely while underway.



For more info on the Safe-T-Puller puller look here.
http://www.reddenmarine.com/site/safe-t-puller.cfm

Gary

[Frank O]

Thanks to both Gary and Glenn for the ideas. The crab pot puller and davit sounds like a simple approach. I'll have to take a look at my whaler this weekend to see about attachment points near the transom. Gary, was that an existing rod holder that your davit fits into on your boat?

Edit: I just took a look at the Safe-T-Puller page. Prices for their three models of electric pullers run from about $750 to $1,200. That's a significant percentage of the cost of the sonar system. Not to sound cheap, but do any (much less) expensive alternatives come to mind for a similar wheel-type device that would keep the cable from kinking, but perhaps without as much user convenience?

[GaryF]

The davit mount was built into my boat during construction. You can see the mounting tube inside the gunnel in the photo. I was able to do this because I knew I would be needing the davit in advance, but I believe these davits come with alternate mounting options to accommodate existing boats.

I'm sure the bulk of the cost of the system is for the electric puller. The puller is very high quality and quite robust. I'm sure you can fashion a davit with just a simple large diameter pulley or sheave to get the same result without the automatic assistance of pulling in the towfish. I sure like the electric puller, but it's certainly not required.

Deploying the cable from the tall davit keeps the cable well above my outboard motors when using longer cable lengths. I'm able to make sharp turns without worry. However, when running short cable lengths you do have to be mindful not to make sharp turns as the fish tends to run directly under the boat.

Also, my davit is the two-piece model joined with a stainless steel pin. It breaks down to a nice small package for easy stowing. I'm very happy with it.

Gary

[Unregistered]

Hi

Hi, new to ths site.
I am currently looking to purchase a side scan sonar to mount an expedition to look for a lost aeroplane here in sunny England.
I have never heard of the Garry Burton side scan before? Is it any good-The photos look amazing and better than any i have seen taken with the imagnex sportscan. Has anyone got the website for the Garry Burton one?
The area i have to cover is quite large so i think the extra coverage given by the sportscan would be better, but is it as good?
Does anyone have any photos of the sportscan in action, apart from the ones given by the makers.Could you put them on please as i would love to see them to compare them with the garry burton photos.

Also instead of towing the fish behind the boat would it be possible to put it one a solid pole straight over the side of the boat. The area i am searching is not that deep 30Mts very max with most depths around the 5-10 m mark, but can go shallow very quickly. Would having it on a solid pole be better for control and safety of the towfish in these conditions.

What is the best speed to tow a fish with?

Will using the fish when the tide is running make a difference to the picture quality?

Hope someone can answer these few questions- have loads more, so look forward to talking to you guys
Cheers
Jeff lewis

[Unregistered]

objective

Hi, new to ths site.
I am currently looking to purchase a side scan sonar to mount an expedition to look for a lost aeroplane here in sunny England.
I have never heard of the Garry Burton side scan before? Is it any good-The photos look amazing and better than any i have seen taken with the imagnex sportscan. Has anyone got the website for the Garry Burton one?
The area i have to cover is quite large so i think the extra coverage given by the sportscan would be better, but is it as good?
Does anyone have any photos of the sportscan in action, apart from the ones given by the makers.Could you put them on please as i would love to see them to compare them with the garry burton photos.

Also instead of towing the fish behind the boat would it be possible to put it one a solid pole straight over the side of the boat. The area i am searching is not that deep 30Mts very max with most depths around the 5-10 m mark, but can go shallow very quickly. Would having it on a solid pole be better for control and safety of the towfish in these conditions.

What is the best speed to tow a fish with?

Will using the fish when the tide is running make a difference to the picture quality?

Hope someone can answer these few questions- have loads more, so look forward to talking to you guys
Cheers
Jeff lewis

You must define your mission. What is your objective? Do you want to cover as much area as quickly and cost effectively as possible? Do you want to simply locate the missing plane or do you want pretty pictures?

[diverelvis]

sidescan photos

Hi
Looking to find the plane - we have access to very cheap fuel so cost is not a problem.
Pretty pictures are not the concern, but being as the object is quite small, being able to define it is.
I still have not seen any photos of the sportscan in action apart from the makers ones, so am looking to check to make sure this machine does what in says on the can?

Cheers
jeff

[Diver]

I believe you can find a link to some pictures at the bottom/right of this page.
On the page, you can see how the team deploy a Sportscan.
http://www.doe.mtu.edu/Agassiz_sonar/Agassiz_sonar.html

Not much , but a start