ROV / TMS long excursion Tethers

[DANFROV]

Does anyone have any experience in using long excursion Tethers 600 metres +

DanF

Workocean Limited

[Scott Beveridge]

Does anyone have any experience in using long excursion Tethers 600 metres +

DanF

Workocean Limited

Sorry Dan… 500 was the most.

[nosub]

Dan your old company
Sonsub would be your boys,
Bluestream was 1100m back at 2200m deep.

Takes a lot to beat an Innovator.

[Andy Shiers]

Absolutely Yonks ago , I pulled 1400 feet of 225 tether along a storm pipe with a Mini Rover 😯

[xxx]

Used 850m for touchdown monitoring and 2000m on 4000m Prestige job. Best bit of advice would be to fit a downward looking camera on TMS so you can monitor the state of the tether entering the TMS and catch any loops before they enter the TMS. Apart from that it will just depend on keeping the ROV in position against the tether pull. A bit like having a constant current in the direction of the teher.

Have fun!

[rovnumpty]

xxx

The tethers on prestige were the 1200m ones from bluestream, running on the extended Tekmar TMSs. The TMSs were lowered to 3000m, then the rest on the tether.

I beleive sonsub currently has a plan to squeeze 2000m onto one their extended TMSs, but it’s by going down to a very small diameter tether. With an Innovator on the end, can see lots of reterms coming on that one. Plan is to do touch down monitoring from the deck of a a standard S-lay pipe barge.

30m water depth with a 1500m excursion anyone?

Dan

As Nosub says, sonsub’s the boys for the long excursions.
Anything in particular your looking to know?

[rovnumpty]

Forgot to say standard 150hp Innovator comes with 800m of tether on the drum.

[Moon]

😯

[DANFROV]

I am trying to collect some good arguments for why we should have long excursion TMS’s for touch down monitoring.

Ideas flying around are AUV’s? , Sonar’s?, barge on tow for TMS?

Open to all ideas

DanF

[Andy Shiers]

Well ,touch monitoring is a moot point but distance should invariably be shortened by main lift and TMS transfer.
How about 500 m Zone / H2S
FSO Inspection or Interior Dam inspection through the tunnels ?
Just a thought 🙂

[rovnumpty]

Dan

Saipem do touch down montoring from both the S7000 and the FDS when they’re J-laying using the long excussion TMS. Works OK on both of them. But that is in deep water.

I be a bit concerned trying it in shallow water from a standard lay barge though. IF everything works OK, then , theoretically, yes it should work.

The risks involved if something (such as hydraulic failure) should go wrong gets a bit silly. Could end up with and ROV and/or 800 m of tether wrapped around and under your product. If the barge is DP, you’ve got issues with entaglement with the vessel’s thrusters. if you’re running anchors, a failure at touch down 800m away would put a light ROV bobbing up right in the middle of the anchor pattern, or a heavy ROV acting as another anchor as the barge continues to lay.

The shallower you get, the harder it is to use accoustic positioning of any kind either.

At sonsub, we found the long tethers great for simops work with other vessels, and for multiple ROV spreads, as you can reach whatever is required while keeping the vessel in position so the other ROV(s) can work with the crane etc. It also meant 4 or 5 reterms wasn’t you starting to run out of tether on the drum.

In short, the longer tethers gave the company the ability to carry out a greater variety of jobs without large capital outlays for new tethers, and/or huge modifications to the LARS position.

The ‘Prestige’ project was a case in point. Sonsub was able to carry out the salvage work on the tanker at 3700m of water depth with a minimal of modifications to the ROVs and launch systems. They used the extended TMS’s that had already been built for the Bluestream project to allow the subs access to that water depth. Thales, on the other hand, had to build a complete new ROV to do the work, which then proved unreliable on the job.

[Andy Shiers]

I did many T.D’s in the middle East to as shallow as 18 m . The beacon did not work very well but they still layed the pipe in the right place.
I transfered the TMS to the end of the Stinger by use of a monkey plate.
Considering it was a "Suck it and see" It worked very well.
I believe a Scorpio or Triton was used in Wales with a long excursion tether inspecting the internal tunnels.
Can be very finiky 😕
You obviously end up with an extremely large Drum on the TMS making the TMS very very large !
Or else an extremely large winch on the topside with a free flying Umbilical.
My preferance is the latter with Armoured Umbilical .

[Bill]

Dan, anyone,

What about crosshauling the TMS and attaching it to the product being laid by means of a running sheave. Obviously engineered to take into account emergency situations and anodes etc ?

[James McLauchlan]

If it’s a long term (high value) ‘project, why not use another, smaller, boat trailing the lay vessel and run the ROV off of that? Seen that done a few times.

[Scott Beveridge]

If it’s a long term (high value) ‘project, why not use another, smaller, boat trailing the lay vessel and run the ROV off of that? Seen that done a few times.

And to add to James’ post:

The vessel could have a full survey team on board for side scan surveys and / or be running around the field (close by to the lay barge / ship) for other ancillary work such as pre-site surveys for lay path /crossing areas and general obstructions and / or debris clearance. Post lay work such as grout bag installation, plem installation, spool piece installation, and the likes of could also be achieved using the same vessel.

However, it may not be a small vessel to do all the above….

[Author]

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