Over 120 Dives!

At first we were nervous about such an inexpensive and user created platform such as OpenROV for performing oceanic research. Comparable systems cost 10 times the price, but are unfortunately out of the reach of our funds. The OpenROV 2.6 units had a lot of problems with the motors, and we had concerns with durability. The new 2.7 unit has been so much more robust in just about every arena and has been a great tool. With just a few tweaks we have repeatedly and consistently collected data.

The team is finally getting settled back into repair, design and build mode after spending a combined three weeks deploying ROVs on Santa Rosa Island, where our Research Station is located. The total combined deployments has given us a total of over 120 dives. We are working on two research projects, a Marine Protected Area health study, and a subtidal/intertidal ecology study. The majority of the dives were done with our two transect duty 2.7 OpenROVs: The Remote Underwater Mariner (RUM) and The Black Pearl. We’ve learned quite a bit from using them on such regular intervals.

Lessons learned:

• The motors need to have a strain relief on the copper windings to prevent breakage of the wire and subsequent shorting.
  • We used hot glue to better attach the windings to the rear of the stator, avoiding getting glue on the rotor and interfering with the motor mounts.
• The ROV should always be slightly positively buoyant, we use the hold depth function which works great for running transects.
  • On one of the last 60 meter transects, our ROV’s tether became completely and utterly tangled in kelp due to heavy surge. Harsh conditions and attempts to pilot out of the tangled mess resulted in the tether being severed at 30 meters from the launch site, because the ROV was slightly positively buoyant, we were able to retrieve the ROV!
• The out of the box balancing of our ROVs needed to have some ballast adjustment because of the tendency to pitch forward on straight transects.
  • The video transects we perform require a higher quality video, so we use two GoPro cameras, a forward one and a downward facing one. We mount them on a 3D printed rail system that Paul designed, with PVC skids for protection (the side outrunners are for the intertidal system.) The rail allows for adjustment of position for balance and ballast. Some additional high density closed cell foam floats from fishing nets were used to offset the weight, and provide more buoyancy in the rear.

• The topside adapter boards need to be fully sealed off. One of ours died due to corrosion from sea water splashes, and moist conditions.
  • We have a small pelican box with a battery powered wi-fi access point, the wires pass through holes we drilled and then filled with hot glue. This enables us to connect by wi-fi using our toughbooks, with all of the ports sealed.

Two absolute necessities for repeated deployments are a tether management reel (a commercially available slip ring works well to allow the spinning) and if working in uncovered areas, a laptop shade!