Part 2 in our series about the jobs that are done with Dynamic Positioning Vessels. You can view the first part of the series HERE.
Another important task offshore is ROV support.
An ROV, or Remote Operated Vehicle, is a tethered robot designed to perform tasks underwater. They are controlled via the tether by a Pilot onboard the vessel. ROV’s are highly maneuverable & are equipped with Manipulator arms so they can perform subsea jobs such as hooking up cranes & operating valves.
Many times you will see supply boats converted for ROV work, so they will have a Class 1 DP system. The level of risk to human life or the environment is much lower on an ROV vessel, so redundancy is not necessarily required. A portable ROV spread is installed on the working deck that consists of the ROV & its TMS (Tether Management System), a launching davit, hose reel, power pack & control station.
DP systems have an ROV Follow function, in which the vessel will “tag along” with the ROV as it flies along its route. It does this by referencing off of the ROV’s beacon, then ensuring that it stays within a defined radius. As an Operator using this function it is important to keep in mind that the ROV pilots cannot see the surrounding area so could fly you right into harms way!
ROV follow mode would generally be used during an operation such as Pipelay touchdown monitoring. In this case, the ROV boat follows the pipelay vessel & the ROV surveys the exact point where the pipeline touches the bottom. The ROV needs to be in constant forward motion so it makes sense to have the vessel tag along.
Other jobs, such as working off a platform, will be more restricted in movement & the DPO’s will move the vessel as required in AUTO-DP mode.
As with all jobs utilizing DP, communication between all parties is of the utmost importance.
Dive support vessels come equipped with the gear needed to support deep sea divers in performing underwater installations & associated tasks. If the job is too deep or dangerous then an ROV can be sent instead, but a human diver can obviously perform with greater spacial awareness & dexterity.
It is important to note that most DSV’s will additionally be equipped with one if not 2 ROV’s. They also have cranes capable of lifting the heavy loads to the subsea worksite.
With a person being tethered to the vessel it is required that the DP be a Class 2 or greater system due to the risk to life.
DPO’s onboard a DSV will work closely with the dive department who will relay requests for vessel movements from the diver. Much of the time the crane will also be in the water offering support to the diver, so communication between all working parties is very important.
Maintaining redundancy must always be at the front of the DPO’s mind when working with divers & any status changes must be relayed promptly.
These vessels can have multiple operations going on at one time & it is the DPO’s duty to retain situational awareness of all aspects of the operation. Helping you in this is the fact that the ships work permit system will also be run through the bridge, so there should be no jobs going on that the bridge team is not aware of.
Additionally it falls to the bridge team to be aware of any other vessels in the fleet & be in communication with them when required.
Multi Service Vessels
It should be noted that Dive & ROV operations are often combined on purpose built MSV’s. As with Dive vessels these will also be equipped with one or more large cranes, with the largest being on multi service construction vessels, such as the newly launched OSA Goliath.
While the Goliath doesn’t have a dedicated Dive Spread installed, it has a moon pool in place to give a third party client the ability to install one.