Page 246 - The ROV Manual - A User Guide for Remotely Operated Vehicles 2nd edition
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  9.2 TMS-based vehicle deployment techniques 235
 FIGURE 9.15
MacArtney’s active heave compensation winch.
tether, as described earlier in this section, is critical to the safety of the ROV and the tether itself. There are typically two types of TMSs: the top hat and caged systems. Both are designed to take the ROV to depth, using the umbilical’s strength, and then allowing the ROV to deploy the neu- trally buoyant tether as it maneuvers horizontally and vertically to the work site.
And here is where the terminology gets tricky—there are two types of actual subsea tether pay- out/take-up systems (also known as “TMS”): the slipring system and the baling arm system. With the slipring system, an electrical and/or fiber-optic rotary joint is embedded within the subsea tether drum, allowing for orderly tether payout/take-up which lessens tether wear (but adds a level of complexity due to the rotary joint). (The reader is referred to Moog Components Group, which acquired Focal Technologies, a leading manufacturer of fiber-optic rotary joints and electrical slip rings.) The baling arm system is similar to a spinning fishing reel. A baling arm grabs the line and physically reels the line around the spool (as opposed to simply rolling the drum). With a baling arm system, there is a solid length of wire and/or fiber from the winch to the vehicle with the bal- ing arm gathering the tether onto/off of a spool (thus eliminating the need for a rotary joint at the cage or top hat). The benefit of the baling arm system is the lack of a complex rotary joint with the cost of a typically uneven tether spooling along with added wear and tear on the tether.
Regardless of the design approach, the payout/take-up system can be mounted in either cage deployment (Figure 9.16(a)) or top hat deployment (Figure 9.16(b)).
Top hat TMS
Whether on top of the ROV or integrated within the launch cage, the primary objective is to get the ROV safely to depth, isolate the drag on the umbilical from the ROV, and keep the umbilical clear of obstructions during the operation. Once at depth, the TMS, via the operator, controls the tether deployment. A Schilling HD ROV is shown launched using a top hat TMS in Figure 9.17.
Deployment cage TMS
Unlike the top hat TMS, when a deployment cage, or “garage,” is used, the ROV is given addi- tional protection during launch and recovery since it is surrounded by the launch cage itself. Better to damage the cage than the ROV. In addition, the cage can be used as a transport mechanism for additional tooling and/or sensors. In Figure 9.18, SeaTrepid’s caged Mohican ROV is launched prior to a platform inspection.
 
























































































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