Subsea robotics continue to evolve at a fast pace. However, the operating and deployment models largely remain the same…
The most common way of deploying subsea robots into the water is to use some form of lifting system to splash them into the water from the back deck of a boat. Making this happen safely requires a deployment system that quickly gets incredibly complex.
The forces are not with you
A work-class ROV as used in the offshore energy industry can weigh up to 4 tonnes in air. The vehicle itself is not engineered to sink – they are generally close to neutrally buoyant in the water and their square, flat bottomed shape, wants to stop when it first hits the water – like a belly-first swimming pool entrance – this hurts!
Add to that the effect of waves and vessel motion, the challenge can be quickly amplified. It’s not uncommon for components in the deployment system to be designed to accommodate 3 or 4 times the weight of the ROV to account for the dynamic effects.
How it’s solved today
Over the past 40 years engineers have developed launch systems that are often as impressive and complex as the robots themselves. The deployment tool-box includes cranes, A-Frames, sheave wheels, constant tension winches, heave compensation systems, armoured umbilicals, tether management systems and deployment garages – sounds expensive, right?
All of this complex equipment needs deck space on a stable vessel so that the system can be operated in the harsh offshore environment. Going even bigger, so-called “Heavy Weather” deployment systems are actually built into bespoke, dedicated vessels, with cursor frames lowered through vessel moonpools or on special rails down the hull.
The umbilical cables which link the subea robot to the boat and deliver electrical power and communications, also act as the crane wire. This cable is heavy and can be over 3000m long; to reduce drag from subsea currents they are therefore highly optimised making them expensive and prone to damage.
The vehicle itself has to withstand the loads of the splash-zone, so the robots’ frames get stronger and heavier. Often we need to add some more tools (weight) to the robot for a specific job. Adding more buoyancy material to keep everything neutral in water further increases the in-air weight. Remember those forces we talked about? This is getting complicated…
How can we simplify all of this and make subsea operations more sustainable?
Great companies with incredible engineers have made it possible to deploy subsea robots at the scale we see today. Trade-offs can be made on robot capability (weight) and operating sea states, but the fundamental model remains – get a boat, splash it in the water.
Honuworx believes there is now a more elegant way. Connect with us to learn more about our submersible deployment philosophy for subsea robots.