Building an ROV for operation in extreme environments introduces some interesting design challenges.  Here are some hints to help you prepare for the conditions that you’ll encounter at the international competition.

First, consider your human factors.
Your launch and recovery team may be getting wet and can pretty quickly become useless as they start to focus more on keeping warm than completing the mission.  Dress appropriately!

Your tether handling team could be miserable.  Cold wet hands don’t handle a tether well.  Bring insulated water proof gloves for all your team members.  You may want to think about changing out the tether handlers during your mission run.

Your pilot is going to be sitting relatively still in a cold air environment, attempting to operate your control box.  If you are using switches to control your vehicle, space them wider to accommodate the wearing of gloves.  Metal surfaces should be covered to reduce heat loss.

Next, consider your operating conditions.
The Ice Tank will be at -1˚ C (30.2˚ F) while the Flume Tank can be as warm as 18˚ C (64.4˚ F).  At -1˚ C you can expect ice to be forming on the surface of the water around the vehicle.  Think about how this will affect your tether and vehicle buoyancy.  Where previously a buoyant tether may have been a good idea, with an ice sheet it could hamper mobility or even cause a vehicle failure.  Additionally, there is no diver rescue during the mission in the Ice Tank.  Redundant features and “graceful degradation” of systems can be a good design point.

The Flume Tank will have a current (0.5 m/s or 0.1 m/s, Explorer or Ranger, respectively) that again makes for interesting challenges.  Your vehicle may need to be able to move sideways at speeds sufficient to maintain position in this current.  Don’t forget to include the drag of your tether from this current in determining how much power you will need for station keeping.

The Offshore Engineering Basin will add the challenge of surface waves.  With a height of 10 to 16 cm and a period of 1.2 to 1.3 seconds, expect these waves to bounce your vehicle around on the surface making it difficult for it to hold onto something.  You might also plan for your tether to be tugged on by these waves causing some degree of vehicle motion.  Finally, consider that breaking waves near the surface can deposit a lot of air bubbles on the lens of your ROV camera.

Third, consider material properties.
Your ROV will not be operating at room temperature.  Material properties can be very dependent on temperature.  Plastics get stiff and brittle at cold temperatures.  Oil, grease, and wax all become less fluid, potentially causing problems.  Insulation on wires gets stiff.  Water vapor in room temperature air can condense out and short wires when a junction box is subjected to -1 C.  A strength member that works fine at room temperature may shatter under the same load when frozen.   A prudent engineer will conduct ice box tests of materials and possibly do vehicle tests in buckets of icy water.

Don’t get caught in the fog.
Also, be aware that your camera lenses may become clouded as your ROV moves from warm to colder temperatures.  To prevent this, you might consider applying a clear defogging compound to the inside of your camera viewport (SCUBA divers use a defogger to keep their masks from fogging); purging your camera housing with nitrogen gas or compressed air from a SCUBA tank or “cleaning duster” that photographers use to dust off their camera lenses; or placing desiccant packs inside your camera housing (think of rice in salt shakers!).

If you are waterproofing your camera using an encapsulation technique, make sure that you carry this out in an area of low humidity so that the air trapped between the lens and viewport is “dry.”  For example, you could turn a large plastic container (e.g. Rubbermaid tote box) and a transparent lid (e.g. clear polyethylene painter’s “drop sheet” or Saran wrap) into a “potting room.”  Cut arm holes into the sides of the plastic container, secure the lid, and slowly blow air from a SCUBA tank into the container while you make the pour.  The steady flow of dry air will lower the humidity inside of the container and help to ensure that you have a fog-free view.

Whatever defogging technique you decide to use, you can test whether it works by placing your camera in a freezer or in a bucket of ice water after it’s been in a warm room.  Make sure that you leave enough time for the entire camera to cool down to ambient temperature.  If your lens fogs up after 10 minutes, try another tactic. 

Follow the Boys Scouts motto – be prepared.
Aside from engineering an ROV capable of operating in extreme environments, one of the best ways to overcome environmental challenges is to prepare for contingencies.

Bring spares of parts and pieces that might need replacement, such as thrusters and cameras.  Think modular – you’ll want to be able to change out defective parts easily and quickly so that you can continue on with the mission.

Finally, consider that practice can make perfect.
Finally, practice, practice, practice!  You might not be able to recreate the mission environment (current, ice, and waves), but you can prepare for these challenges.  Practice piloting your ROV and handling your tether.  Learn to use checklists and procedures for set-up and break down.  Develop a way to effectively communicate among team members.  And come prepared with the know-how and confidence to deal with u
unforeseen situations.