Hello Mark,
I saw your message on the forum en maybe I can help you in the right direction.
Last december I had almost the same question, since I also want to use the AS 360 TM as a sector scan. We use it in turbid water with a visibility of 10 to 40 cm, we are a group of amateur underwater archeologists and we recover mostly wooden vessels.
When a diver is in the water he is very easily disoriented by the poor visibility. I needed a steady AS 360 TM. My idea was to built a triangle bracket from stainless steel en put it on de bottom of the lake or sea. In doing that you eliminate the influence of wells or instable ship.
The question what I send to the importer of Humminbird in the Netherlands was “Can Humminbird deliver a AS 360 TM with al longer cable for the 12v and sonar data, perhaps 25 or 30 meters”.
I received the follow answer by e-mail:
We would not be able to build anything differently than what is built today.
You would need to use Ethernet extension cables.
The longest we could recommend is a total of 75 meters with no signal lose.
Please make sure you are aware, this product has not been tested to be lowered into the water more than 15 meters.
Lowered deeper than 15 meters could incur pressure issues that have not been tested. You could see water ingress into the pod and other areas of the assembly.
Ethernet connections are not waterproof and if you have to extend the power cable to accommodate these types of depths, there will be voltage and current drops that we have not designed for.
The e-mail contained good en bad news. The good news was that I have a official answer from Humminbird that the AS 360 TM is test till 15 meter (45ft) water depth, the bad news was that I must built a waterresist cable connector.
What I did was the following;
I bought few Humminbird Ethernet Extension cable AS ECX 760025-1 and connected them together to the length that you want (the maximum length is 75 meter (225ft) without signal lost). The connectors have I taped with an overlay of 3 times with self amalgamating tape (RS-online partnr: 494-455).
The 12v cable is also original, on the end that you normal connect to the fuse box have I welded a 25 meters (75ft) cable. On both wires I used scrim protection and also self amalgamating tape.
When my test gives good results in a few months, than I consider changing the connectors for a 10- or 12-pins waterresistant connector from
http://www.axsub.com/axsub/leurs_fichiers/sc-standard_circular_connectors_(6-8-10_pins)_en.pdfAnother suggestion is to connect the GPS-antenna to the top of the triangle bracket (when it is in shallow water), so the antenna is located 50 cm above the water. The only problem is the maximum length of the signal cable from the GPS antenna. This cable can have a maximum length of 16 meter (48ft), otherwise you’ll lose the GPS-signal. You can use the Humminbird AS EC 10 - 10' Accessory System cable 720050-1 for the length you need.
Good luck with your experiments en let me know how it’s going.
Kind regards
Bert