Invasive Species documentation

Hello fellow Open ROVers,
We are currently running a research project in the southern coast of Crete and made a bit of an update video
Now I was wondering if others are running full on transects with their open ROVs?
I generally like to pull the cable out (away from shore) on the surface until the end (from the boat that is) then dive down to the bottom (usually around 50-70 meters) and head straight towards shore on the slowest prop mode on full speed, trying to keep a straight heading and following the bottom in about 1 meter distance.
It seems to work well without disturbing the wildlife too much. Curious what you guys think or if someone has an idea for improvements!

Really great work so far, I’ve checked out a few of your YouTube videos.

I’m a PhD student here in Hawaii looking to do similar benthic surveys, Trident should be in the mail soon I hope. We’re surveying mesophotic corals in the 60-80 m range and one of the tasks will be doing belt-transects or full-on benthic photogrammetry.

  • Relatively constant altitude above the seafloor

  • A bottom-facing camera, taking photos at a set interval (or constant video)

  • Fairly constant transit speed by the Trident during the belt-transect

For our application I’m planning on using a clump weight located 80 m down the tether, with 20 m of free tether between the clump weight and Trident. That should allow up to a 20 m transect (ours are normally 10 m). Much shorter than yours!

In your experience are you able to keep the Trident flying at a fairly constant distance above the substrate?

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sounds like you already thought the process through!
The weight after 80m will certainly make your life easier! With the long transects the drag of the cable makes it tricky to stay in a straight line and keep a constant speed, with 10m transect length or 20 even it should be easy!
The distance from the substrate is fairly easy if the bottom structure is not too complex. For the transects I find it easiest to switch the motors to the lowest power and go at full throttle - gives you a constant speed you. can work with, also if you do it on top of a known length ones you can actually work out the distance from the time!
low speed transects only works with little drag of cable though so in our case I can pull out the cable first and on the way back go low speed, if I make a perpendicular run the wind on the surface will pull on the 100 meters enough to make for a jerky ride…

I manage to fly close to the substrate using one kg diving weight attached to the theater 40 cm from the Trident and dragging it through the bow with a zodiac. The good thing of doing this is that if you manage to leave the ROV just below the boat you can gps track the transect. It was useful for shallow and flat bottoms (see video). In the photo you can see how I attached the weight (1kg) to the cable, in this case to send the cable directly to the bottom but I used the same weight attached ~40 cm away from the TRIDENT to drag it and perform the transects.
TRIDENT TRANSECT VIDEO