In last month’s blog we touched on how our dive support vessel, CRC Sentinel, is unique in the industry in being able to provide a bespoke four-point anchoring system. Designed and supplied by Hercules Hydraulics, Sentinel’s mooring system is a key selling point, enabling the safest possible dives to take place in depths of over 50 meters on a range of seabeds.
In offshore diving it is essential that the dive platform you are operating from is stationary and secured. This gives the best possible working conditions for the divers under the surface and ensures there is no risk of injury or entanglement. Sentinel utilises the design characteristics of a catamaran and has one winch on each ‘corner’ of the vessel, providing excellent station-keeping ability in wind speeds of up to 20 knots and tidal streams of 4 knots.
Specification
- Hercules Hydraulics AMW350 winches – 6 tonne snatch load, 50 meters/min (x4)
- 450 meters of 12mm Dyneema – minimum 13 tonne breaking load (x4)
- 27 meters of 14mm stud link chain (x4)
- 200kg super high holding power (SHPP) galvanised Pool anchor (x4)
Two key advantages of Sentinel’s mooring equipment is the independence and redundancy. Unlike many other small workboats such as tugs and multicats, Sentinel can deploy and retrieve its anchors independently without the need for a second vessel to carry the anchors. To achieve this Sentinel is fitted with three power take-offs (PTOs) which are fitted directly to both MAN D2862 main engines and the starboard Cummins Onan generator. These directly power the hydraulic pumps needed to operate the deck winches but only one is ever required to power the entire system, providing excellent redundancy if an engine is lost. In normal operation, our crew will utilise the generator PTO to keep noise levels low and to reduce engine hours on the main engines.
So how do you lay the anchors correctly? This is a key skill which all of Sentinel’s masters hold but put simply it’s come from practice, skill, and good communication with your crew! Firstly you need the vessel pointing into wind or tide first while one of the bow anchors is deployed. Depending on the water depth and seabed conditions, perhaps 100 meters of Dyneema line will be payed out whilst the vessel is then crabbed sideways to where the second bow anchor will lie. Once let go and the position plotted, the vessel now needs to edge backwards to one of the stern anchors whilst simultaneously paying out on both bow anchors. Once a stern anchor is laid, the vessel can then be crabbed sideways again to the final anchor, ensuring adequate tension remains on all the deployed lines and the vessel’s heading remains pointing into the elements.
When the final anchor is laid the master will cut off all propulsion to the jets, take the remote control for the winches and walk around deck with their deckhands, visually inspecting each anchor line carefully and taking up or releasing tension where needed. The objective here is to be precisely in the middle of the box you have just created to ensure the vessel is held from all angles. It’s easier said than done but our most experienced masters and crew can safely secure the vessel ready for diving in under an hour!
To watch Sentinel’s mooring system in action check out this video here and why not take a tour around the vessel yourself through our online 360 video tours. Read more about all our dive support services here!
