Hi folks!
I solved an interesting problem recently and wanted to share the result, since it seemed useful!
Square Peg, Round Hole
Our guide to choosing the right WetLink size for your cable never explicitly states that a round cable is required, but flat Ethernet cable like this would obviously fail to seal, at least without some modification…
This type of cable comes standard, potted 
into a 360bubble camera housing: a unique, incredibly expensive, handmade solution for enclosing many types of 360 cameras underwater.
The fish farm near me wanted to evaluate this housing as part of their testing campaign to improve visibility for operators and machine vision models. It’s been a great partnership for field-testing the new 4K Cam and upcoming WetLink connectors (as mentioned in our Building Subsea Cameras guide) in one of the toughest ocean environments out there.
Making Flat Round
So… what to do? The full 1000 m depth rating likely isn’t achievable, but if I could make the cable round, the seal should still squish with enough pressure to prevent leaks.
Stripping the cable was a bit of a hassle, but I found that by making three cuts in the end and using pliers, I could tear the four twisted pairs out of the black jacket, creating the length that would extend from the bulkhead into the enclosure.
I set about 3D printing some half-cylinder pieces to wrap in heat-shrink, but realized this might just create a corridor for water pressure if the heat-shrink didn’t seal to the cable.
Putty to the Rescue
In a moment of inspiration, I grabbed some two-part plumber’s putty and formed the same half-cylinder shape along a short (~1.5") length of the cable. It has about a 3-minute work time before it starts to harden, so after about 2 minutes I pulled some clear heat-shrink down over it and hit it with the heat gun. With a gloved hand, I pressed the hot heat-shrink tightly into the putty, rolling it between my fingers to get it feeling as round as possible.
The cable’s rectangular width was about 7.5 mm, and since this was a generally sketchy solution, I opted for the taller HC plug to compress the seal. I waited about 10 minutes for the putty to harden, then tightened the plug into the seal on the modified cable end.
I did this on both ends of a ~1 m length of cable (cut from the excess we wouldn’t be using) to make a test article for sanity-checking the approach.
Taking It for a Dip
I plugged both ends into a WetLink splice kit and took it for a scuba dive (with the T500 DPV, of course). After a quick stop at 150’, I stayed just inside the no-deco limit to maximize time at depth on the return. No bubbles ever came out, so I wasn’t surprised to find no water in the enclosure once I was back at the car!
clear heat-shrink used to visualize potential leak path
The test article is now hanging at ~25 m at the farm. If it stays dry inside after a few days, we’ll go ahead and install the new camera system!
The Rig: 360° of Fish
This latest live-view camera rig uses 140 m of Fathom tether, terminated with prototype WetLink connectors. A 40 m length of that runs from a 3" enclosure housing a DC-DC boost 52 V PoE supply, which powers a Kandao QooCam Enterprise 360 camera through a PoE splitter. It’s quite a power-hungry little beast, pulling 20–30 W, but it has some nice features, like automatically starting an RTSP stream as soon as it’s powered. The image quality falls short of the Insta360 X5, but when you’re limited by a medium-bandwidth WiFi link to shore, the 15 Mbit stream is plenty.
The camera will be strapped to the central spar in the pen, and an inline WetLink connector will join it to the rest of the tether at the top of the (submersible) pen. I brought the flat ethernet cable from the actual device into another WetLink splice kit, with a WetLink connector on the other end, so should the gland or bubble seal fail the electronics in the 3" enclosure will stay dry.
Interestingly, because this camera draws so much power, I had to move the Pi running BlueOS to the surface enclosure. That isn’t an option for our other systems built around 4x exploreHD cameras, since those need to connect to the Pi directly. Luckily, the QooCam’s network connection made the rearrangement trivial.
A Year in the Pens
Two other similar systems have been in pens like this for about 6 months now, and we’ve been quite happy with how the WetLink connectors have performed! When the inevitable cable damage happens, trimming off that length and re-terminating what remains takes ~15 minutes. Gotta love the lack of potting!
Operators pull up to a pen and grab the “feed package,” the air hose and fish feed delivery hose used to service the residents. The Fathom tether is routed along this bundle and plugs into a topside box containing a Fathom-X and a travel WiFi router. That router links to the farm’s local network, which has a long-range WiFi backhaul to shore about a mile away. They, along with anyone with access to the system, can then watch the fish in near real-time!
Stay Tuned
I’ll follow up in this thread with pictures from the install! If you find this kind of blog-style report on prototype field testing and problem solving in the marine robotics space helpful, sound off!