Tips for Operating an ROV in Strong Currents
Depending on the assignment, you may encounter confined spaces or cluttered areas when operating your ROV. Under such circumstances, you need to consider several things before proceeding:
Do you truly need to enter the confined space or area? The best way to mitigate risks is to avoid them all together.
Do you have permission to enter the confined space or area? For instance, some wrecks may be preserved sites and off limits to ROVs.
Like driving somewhere new, it is best to have a map. Are there plans of the space that you can use as a reference?
What is your goal – general observation, mapping the space or area, detailed inspection, retrieval of an object? This may affect how you configure the ROV and how you operate within the space.
One way to practice for such encounters is to operate the ROV in a swimming pool. Here are some tips to consider:
- Direct the ROV back and forth though a submerged hoop (use a hula hoop with a weight and a float, or a more elaborately shaped object like the opening you expect to penetrate. Practice going in forward and turning around to exit, as well as coming back out in reverse too. You should be able to judge the size of the opening relative to the ROV and be able to penetrate it without bumping it. Use an increasingly smaller size opening to hone your skills.
- Submerge something that has protruding spars. Wrap your tether around one or more of the spars. Use your manipulator to remove your tether from the spar.
- Practice following your tether – fly out, turn around, find your tether and follow it back as closely as possible.
Here are some other suggestions before embarking on a real-life situation:
- You should install and use a manipulator to be able to move objects or manage your tether.
- Tether management is critical – make sure to use an experienced tether handler. For example, when returning from the confined space, you want to minimize any loop of tether behind you to avoid it getting snagged on something, but at the same time, you don’t want the tether handler to pull too hard on the ROV. The handler and pilot should practice in the pool.
- Plan ahead for the worst-case scenario – will you attempt a recovery, or just cut the tether? If you plan a recovery, you may need a second ROV equipped with a cutter and manipulator jaws. If you are not comfortable with your skills or your situation, be ready to abort and regroup for another attempt rather than risk entrapment and loss of expensive equipment.
- As a pilot, you need to be able to estimate the size and shape of the area – do you have enough room to fit? Do you have enough room to turn around, or do you need to back out?
- Plan your penetration carefully. If the opening is smooth on one side but ripped open or jagged on the other, it will be better to approach from the smooth side to prevent damage to the tether.
- Always be on the lookout for tether snag locations (spars) or pinch points (v-shaped notches). Avoid these!
- Here’s a video of tether management to remove tether from a snag. This was a combination of the tether handler and the pilot working together to overcome the obstacle. Neither could do the job on their own.