Looking to get the most out of your remotely operated vehicle (ROV)? We're here to help you with a new series called "Insights." These posts will provide guidance on how to operate your ROV during challenging missions and in a variety of situations, such as maneuvering in strong currents or deploying the sub in remote locations. We are sure you will find this information invaluable.
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Now on to our first "Insight":
Did you miss our recent webinar with Sonardyne? No worries! We have some great information to share with you from that program. Rob Cornick, Dedicated Technical Support Analyst with VideoRay, offered "9 Tips for Operating in Strong Currents." Here are the first 4 tips. We'll present the other 5 in a follow-up post.Keep your tether short and controlled.
• Deploy as little tether in the water as possible, as it will act like a sail and pull on the ROV.
• Let tether out so the ROV can travel down current or up current to the target. Drag increases when working perpendicular to the current.Understand your environment before deployment.
• Fly with the current using the tether as a fishing line to control the force on the ROV.
• Use a clump weight on tether when possible to offset tether drag. This is especially helpful with surface and mid-water currents as the weight stabilizes the tether from the surface to the working depth. Lash a carabiner or small weight bag to your tether behind the ROV (safely spreading the load over at least 6 inches of tether) and leaving a short leash for the required excursion. Add necessary weight(s) to the carabiner or bag until the tether hangs straight down in the water column.
• Use natural current breaks, known as eddies, to protect the ROV from the current. Protection can be provided by a ship's hull, a structure in the water like a bridge footer, a protected area on a river, or even a wreck on the seafloor.
• If you fly from shore it is better to reposition your control box several times, rather than use too much tether in the water.
• If you use sonar, prepare for the inspection/search by pre-viewing the area first with a long-range sonar scan. This way you can identify underwater hazards like tree branches or other debris so you can plan your inspection strategically.
• Heading into the current when possible gives you the best control over the ROV. You will need to take a diagonal heading and "crab" across the current to reach your target rather than flying a straight line. Always start upstream and go downstream with a short "leash."Make sure the ROV has the thrust/power to work in the environment.
• If your ROV doesn't have powerful thrust, you are probably not going to be able to operate in strong currents. Understand the thrust you have available during operations and how to command it when you need it. A general rule of thumb is to have around twice the amount of thrust to the ROV's mass you are deploying.
• VideoRay's new Mission Specialist Defender is producing incredible results for pilots offering superior performance and maneuverability. Seven powerful thrusters provide you with six degrees of freedom control including lateral movement, pitch, and roll.
Plan the full mission in detail and have a back-up plan just in case.
• Plan the mission around tidal windows when possible.
• Time your operations as close to slack tides as possible. Don't be fooled by general tide times. Moving just a short distance from the port where the tide times are listed for can change the slack water times by 30-60 minutes, so be ready to throw the ROV in an hour before the quoted slack tide.
• Pay attention to neap tides and spring tides. Timing your operations right can add valuable time to your operational window.