ROV umbilical Pay out limitation in shallow water

[kamyar]

I need some information about the maximum ROV umbilical Pay out limitation in 80 meters water depth. The ROV is work class with TMS. I need the maximum distance that ROV can fly from it’s TMS.

[Savante]

depends on your ops procedures and vessel set up – some people don’t like large distances when upstream of vessel.

Physical Distance limit = roughly Number of turns * 2 * pi * r ? (and leave a couple of turns on your tms drum??)

Also r will change as you get to outer layers, but never mind that too much.

Have you not got a tether length in the spread log book?

hth

[luckyjim37]

Also depends on the vehicle trim. If you trim it slightly heavy and lose power it sinks. In theory then you should have the same senario as working at any depth as you physically cannot surface into thrusters etc.

If you are light then you have to work out what the situation would be should the vehicle lose power and surface. Will you have time to get the vessel out of the way so you do not go into the thrusters. Are there any other vessels/rigs/structures which you could surface into.

Any shallow water working it is my personal feeling to keep excursions to a minimum in eighty metres of water I would not go much over about 50m from the TMS. However if you are vessel working you should not really have to if he can move with you.

[luckyjim37]

I assumed by umbilical you are actually refering to tether.

[Andy Shiers]

The problem with having a heavy sub is vert thruster wash ,
Why not just have the ship up current.
Also it depends on what exactly you are doing on the seabed.
Is this Touchdown monitoring by chance ?
Is the vessel DP1, does it have DP ?
Whats the viz like ? Seabed profile , Silt , heavy sand or……….. Coral ?
Where is the contract location ?
Do you have good hard wire comms to bridge ?
You say Umbilical which means from winch to TMS ?
Tether from TMS to ROV ,
Pipeline inspection – 10 m off the seabed is the norm meaning thirty metres Excursion ( Forty metres of tether out to play with on stop/starts and ship over-runs )
Is the vessel moving with you or stationary ?
Is the tether heavy ?
Is the TMS tophat then ?

I need the maximum distance that ROV can fly from it’s TMS.

The question you ask is very vague old chap 8)

[Savante]

see, interpretation interpretation interpretation….. i wisnae sure if he was looking for the physical maximum length of tether he could pull off the drum !! 😆

[Andy Shiers]

Also depends on what size the tether is or heavy or light 😀

[effinreps]

Why would someone ask that??? Supervisor who obviously is not experienced enough to be in that position or P/T /Sub eng who is questioning his supers decisions but not got the cohones to come out with it. Or as a long shot it could be a sneaky co rep or party chief trying to stiff the ROV crew. I’d go for the former.

[SGB]

A good rule of thumb when operating in say 80 mts with a positively bouyant sub is to to assume the worst, ie if the TMS depth is 50 mts it could be argued that if 50 mts or more is paid out and you get a dead sub, the sub could float up to the Vessel and get damaged by the thrusters – ok, the more astute would be paying in on the tether but the smaller amount paid out in the first place will lessen the chances of any damage. However, this concept is blown out of the water by Schilling who advertise their TMS with a capacity of 800 mts, which really pleases accountants as they can dispence with a tail end charlie boat while on pipelay operations.

[Savante]

carunt in me says google catenaries and hydrodynamic forces on cylinder….

[Author]

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