Towfish advice and reviews please

[Fletch_Scott]

Hi, I'm new to the towfish world and am looking at buying one for some academic research. We will be surveying in depths up to 50m, nearshore on lakes and sea and have tried boat-mounted sidescans before but suffer a lot with roll and pitch instability.

I've been looking at the Imagenex YellowFin, EdgeTech 4125, Tritech DST.

Has anybody any advice on which is the best performer? What aspects of the towfish really contribute to it's stability (i.e. should I be looking for large fins and long, thin bodies? What else?)

One thing I'm concerned about is the towfish getting snagged on something. Are there any fail-safes on some models?

I'm really interested in the towfish itself as we have experience of the sonar equipment.

Thanks,

Scott

[Mikediver]

In my opinion 4125-P is the best solution for low range and very high resolution sidescan. Don't bother with snagging. Always you can look for fishing nets using lower depth and later make scans with near bottom depth. As you told transom mount transducer is very vulnerable for boat tilt, so the resolution is poor for greater depth or you must hunt for extremly calm weather.
4125-P is lightweight and mobile. Supply is possible using ordinary car accu. Resolution is excellent ( you can estimate single cod length!). Swath width for higher freq is good.
Towfish stability is mainly influenced by the position of tow rope gimball. Fins are not so important. Removing fins in well made towfish has nearly no influence on stability. You can improve the stability and the angle of attack using simple depressor unit, also homemade. In this way it is possible to reach 40% increase in the depth.
I am not aware about any fail-safe device, but for the depth up to 50 m the snagged towfish can be rescued by scubba diver.
Now you have no other sidescans with such parameters. So go and buy!
I scanned more than 200 miles using this unit and was satisfied.
Mike

[chris]

I would start with your budget and what kind of detail you would like to be able to see. Another thing to consider is what your final goal will be.

Most towfish will have some sort of safety release mechanism that causes them to be towed by the tail instead of the mid point of the towfish in order to prevent them from getting stuck in something.

Some of your stability or decoupling of the vessel comes from how you rig the towfish. You can use a block supported by a bungee cord. This will decouple some of the boats motion from the cable.

I agree with Mikediver's opinion as the 4125 is the best of the 3 that you had mentioned. Since you are in that price range have you considered any other side scans such as Klein's 3900, any of Marine Sonic's sonars, Sonar Beam, Falmouth Scientific, or J.W. Fisher? Most notably the first two being in the same class as the 4125 for image quality.

[kag00]

You may find the following evaluation of sonar systems of value in your selection. It is a zip file.

Garry Kozak

[chris]

Thanks for the information Gary. It is good to see a review of more than one side scan sonar system in one nice neat document. Looks like a consumer reports article , though it is from the government.

[DELPH]

Hi,

For your information, Hydro magazine just released the yearly side-scan sonar product survey which presents major references on the market with specifications:

http://www.hydro-international.com/p...rDecember.html

Regarding the choice of a side-scan sonar with regard to its stability, I suggest that you look at not-so-light models. Heavier (but not too) sonars will require less cable to dive as well. Recent lightweight sonars (Edgetech 4125, our ELICS 400-1250 and others) prove to require either heavier or longer cables to dive (a depressor might be used as well). Those sonars in their highest frequency (900-1250kHz) have a very short range (<50m), which means that for having a suitable coverage they need to be used in very shallow water or towed close to the seabed. A typical use for such sonars is for harbour, river, breakwater inspection with a pole mounting. Another use in search and recovery is to use the 400kHz for coverage and detection, then make a run on spotted objects with the higher frequency for identification. Due to the short range it is strongly advised to use real-time mosaicking functions to pick objects at the optimal range.

I would recommend that you look for a sonar in a standard form factor like Edgetech 4200, Klein 3900, GeoAcoustics, IXSEA Elics and others with a sufficient weight do properly dive and navigate. A pole mounting bracket can still be designed for those sonar in specific applications.

Then, regarding the safety feature, most (all) sonars come with a safety cable linked from the tow point to the tail of the sonar. The fixing at the towpoint is made using a weak safety pin. In case the tow-fish hits an object/the seabed, the safety pin breaks and the fish flips and gets towed by its tail using the safety cable.

Can you please be a litle more precise regarding the academic applications that you mention ? One important aspect in choosing a sonar is the acoustic frequencies which results in data resolution and range. Lower frequencies (~100kHz) are suitable for sediment mapping on large areas while medium frequencies (~400kHz) are good for habitat mapping and object detection. Higher frequencies (above 700kHz) are more suitable for very specific applications due to the very high resolution but very short range. Another aspect is in the sonar topside quality, meaning the acquisition harware and software including the necessary real-time capabilities and mapping functions. The file format used for data storage, processing and mapping/mosaicking is also important for being able to interprete and use the produced data.

Philippe
http://delph.ixsea.com

[geosonar]

Edgetech 4125 side scan system

Hi,


Edgetech has recently made some major changes to the 4125 SS system.(see attached press release) the 4125 now employs the same Full Spectrum CHIRP technology that is used in all Edgetech side scan systems.
This CHIRP pulse technology allows for longer ranges and better resolution than conventional pulse side scan systems at similar frequencies.

For instance, the 4125 max range for the 1600 KHz frequency is 30+ meters per side, while conventional pulse system would get half that range. The 900 KHz CHIRP frequency range is 75 meters per side compared 50 meters per side for 900 KHz conventional pulse SS systems. This range and resolution advantage means that you can use higher frequencies and still obtain long ranges for optimum target resolution.

The 4125 side scan sonar is equipped with a safety breakaway pin at the tow arm that will shear off and flip the fish 180 degrees and tow from a stainless steel recovery cable if you hit an obstruction.

The 4125 also has an option 15 lb keel weight that can easily be attached to the bottom of the tow fish to add weight to the tow fish if you need to survey in deeper water.

Feel free to contact me if you have any questions,

Regards,

Rob Morris
Edgetech Marine Customer Service Manager
4 Little Brook Road
West Wareham, MA 02576
e-mail: [email protected]
Tel: 508-356-9712
Mobile: 508-524-8894