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Fiber Optic Tether works!

Our first commercial job with a fiber optic tether was a success. This may be half build/half dive log. We performed a 1km tunnel penetration and our new F/O tether durability was more than satisfactory. Specs: 4.2mm OD, 300kg breaking strength, 4x 9/125um core/cladding, plastic tube, PU jacket. The 1GB bandwidth and 4 port Ethernet hub enabled us to run full speed on the Gemini sonar + profiling sonar + 1080P. We find we reach the limit of a VDSL modem around 1km with only 480P video and the mechanical scanning 831 profiling sonar (no chance of running an imaging sonar). Now with the fiber and a proven tether, up to 3km (no water flow) won’t be an issue for this specially modified Lanai ROV system. The only issue was running a full 3 batteries and the added weight required some float blocks.


Amazing work! Congratulations

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Looks great!

How do you tether manage that huge length of cable!


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Thank you for the compliments.

We have 1,500m of the tether (4.2mm OD) on an old hand reel (not a Blue Robotics Fathom). One of the reasons for the old surplus reel is because we wanted to run a copper slipring (gigabit Ethernet rated) so that the media converter (F/O LC to RJ45 Ethernet) is housed inside the rotating Junction Box. This eliminates the need for an optical slipring.

In this case, we are still evaluating optical sliprings. There are many on the market, but the more robust ones can be very expensive. I have personally signed a PO for a $15,000 USD set of 4-pass optical sliprings, but these are very industrial and for high reliability applications. When we find one that works well, we may well begin selling optical upgrade kits or making the documentation available so that other users can convert it themselves.

I know of one BROV that has been on 9km of fiber. Worked flawlessly.