Hello,
I am a dyslexic marine ecologist and newbie to the ROV/tech world, and this is my first post here so I apologize if I am not using the right vocab and spelling to give context for my question/problem.
Does anyone here have experience or tips using the BluerRov2(BR2) to find and recover gear that they have put out and left in the sea for a while?
I will be studying deep-water kelp habitats in the Galapagos (50-70m deep) for my PhD thesis, and am be using the BR2 (BlueRov2 +heavy configuration + griper) to do video surveys. To assess long-term temperature fluctuation in this ecosystem I also am hoping to leave ~4 hobo temperature loggers on the seafloor (~48-52m deep), attached to cement mourning blocks, and I recover them again ~7 months later. Deploying these seems relatively straightforward: my sites are on a knoll 40km offshore so from a boat I plan to lower the 2 moorings, each with the temp loggers and a bright marker buoys and take the GPS position of where they were lowered. We cannot leave buoys floating in the first 6m of the water column in the Galapagos due to marine traffic (and its a local rule), so my plan is to leave the buoys floating ~10-14m above the seafloor (~40-35m deep) so that will be visible to ROV and accessible to Scuba divers that are limited to a max depth of 40m.
After ~7 months we can go back to the GPS points where they were the moorings were lowered, and then use the BR2 to find them - hoping that the buoys will be conspicuous enough to see them (visibility here varies between 5-15m). Once located we will use the gripper to hold on to the buoy rope and hold the position. A team of divers will descend following the ROV tether line down to the buoy and tie a rope to it, and then ascend which to bring it to the surface (doing appropriate safety stops and all the precautions given ROV in water). BR2 will let go of the buoy and retreat as soon as divers are close. From the boat with rope in hand will use a winch to bring up the moorings with the temperature loggers+ buoys (with my precious data!)
My main questions to you (community members and experts) are:
A) how likely/challenging will it be to find these loggers again using a BR2 (considering I have no USBL or Sonar)?
B) Do any of you have done anything like this at these depths?
C) Is Anyone doing anything like this but with help of better tech: e.g. some kind of acoustic pinger that can be attached to the mooring with loggers and the ROV has some kind of receptor or sonar that can detect it?
I welcome suggestions, feedback and questions you may have for this (crazy?!) plan I propose here, which I hope will enable me to collect temperature data that will be super interesting to understand if and how climate change-driven marine heatwaves affect these mesophotic habitats and kelp communities
Sounds like an interesting (and hopefully fun) project!
Iâd say that depends on how accurate the initial position record is, and the visibility and current strength at the time of recovery combined with the skilfulness of the operator(s).
Itâs not something Iâve personally done at those depths.
This retrieval example from @btrue may be worth a look, although your use-case is quite a bit deeper so will need lighting from the ROV to see what youâre looking for.
That may be possible, although depending on the constraints of the use-case it could be quite challenging to achieve. Hardware wise it would require at minimum a transmitter at the bottom (with the loggers) and a receiver on the ROV or the boat, but the most efficient and practical retrieval approaches would likely make use of both transmitting and receiving on each end.
Behaviour wise the main approaches I can think of are:
bottom transmitter transmits at regular intervals, and is searched for and detected by the moving receiver
too frequently could be wasteful of power, and may cause confusion for other vessels that come by if they have a sonar sensor with a similar frequency, and could potentially be disruptive to nearby marine life
too infrequently could make searching and finding slow and challenging
bottom receiver waits for a transmission, and when it detects one it transmits back so it can be detected (resulting in faster ping-ponging as the sensors get closer)
Beyond that, if you know youâll only be searching after a set amount of time, or within a particular time period during each day, then that could be used to help save power by turning off the bottom sonar while itâs not needed (albeit potentially with some extra risk, because if your control computer somehow loses track of time it may change to a range thatâs misaligned with the search time).
Technologically speaking that kind of use-case could be achieved with a couple of Ping Sonars being controlled by some Arduinos or Raspberry Pi boards or similar, although it would require custom firmware on the sonars to support the non-standard usage. At the moment we donât provide firmware source code (i.e. that would allow adding custom messages and/or logic), so unless that changes custom firmware would need to come from us.
The ~30 degree beamwidth on the Ping Sonar means detection would be possible within a radius of about 10m for an ROV 35-40m above the bottom transmitter
Thank you @EliotBR for all the info and feedback. @model14 appreciate your suggestion, which sounds a bit easier as the speed boat we will be on does have depth sounds. I will look into a what material/size of mooring buoys are needed that can give a strong return, please if you have any ideas or suggestions do share
Cheers,
@Salome Just to add a little bit since Eliot mentioned my video
In my limited experience, so far the ROV saying of âdepth is just a number as long as you stay above the implosion depthâ is accurate. The only difference between shallow dives and deep dives is the tether drag and less ambient light. The Blue Robotics tether is positively buoyant in freshwater until it gets exposed to water for a few times within short period (before it completely dries).
Hereâs an example at 250â when the tether âaggressivelyâ pulling my ROV backwards at 17:40:
I would need to give the ROV constant thruster input just to hold position.
@Salome The best advice I can give you is to locate the buoys over a seabed that you can distinguish with the depth sounder/fathometer. Air, as in a fish bladder, gives a good return, as does hard material that reflects the sound. Styrofoam, as you may be using for the buoy absorbs the sounder ping and gives a poor return. When you have your instruments in place try and chart the surrounding bottom and get some pictures from the sounder/fathometer screen. Donât be mistaken, what you are trying to accomplish will be difficult! I have a lot of fishing experience trying to return to the same location using GPS at 100-150 feet depth, and it can be quite difficult. Before your drop those instruments give it a lot of thought. Give us your ideas and we can help you ferret the best ones out.
Hey @Salome, Iâve done quite a bit of this sort of thing and am reasonably experienced with BlueROV. While I love the latter (makes fish ecology surveys at depth a real possibility for us), I wouldnât use it for your purposes. A few people have suggested using the boatâs depth sounder to look for the buoy which can work. In the depths you are considering I would use the sounder in conjunction with a very good GPS mark/waypoint (worth investing in a decent unit). Once youâve turned up on site and located the mark, I would drop a shot line to the bottom so that you a) have a surface visual reference of where the position is and b) have a line that you can descend on. Is there any reason why you want your buoy so deep? If the depth limit for legal/marine traffic purposes is >6m, then personally I would have your float system as shallow as possible, at say 8-10m. You can then descend the shot line to ~12-15m and conduct a search pattern (circular, attached to shot line) looking for the bouy and or the line to the logger on the bottom. You could use the BlueROV for this part of the job but I would still have that float as shallow as possible, conditions dependent. And of course, all of this is dependent on conditions: if you have strong currents at your surface site itâs going to be very difficult to make any of the suggestions here work! In regard to your Question C about alternative tech - if you have the funds you could look at acoustic release options but they do tend to be quite pricey. All in all, I think itâs very doable and Iâm interested to see the results of your research! Good luck!!
I was looking through my old phone pictures and I found some pictures from that dive and it reminded me of this post. I know this isnât very useful to most people, but I think it help explain the large tether tension other than the usual dragging through the water. It will bump this topic on the recent posts if nothing else. The positive buoyancy of the tether creates a lot of tension that increases with ROV depth. I donât think that excess floating tether has a real effect on ROV handling.
All 150m (492â) deployed to get me to 250â. I think the reason why I stopped at 17:40 in that video was because I took this picture.
Thanks, @bjcresswell , your suggestion of using shot line for a surface visual reference and descend line is such a helpful tip that did not occur to me. Do you have any resources or suggestions for the best setup (type of anchor weights, rope, and float you use) for a place where surface currents are between 1-3 knots down to 10 m depth, to wonât get dragged away (or at least hold position for the first 30 minutes!)
No worries @Salome! Iâm not sure I know of any reference manuals that go into the details of site setup and relocation, but I work and have worked with a number of organisations (Australia) and the collective approach is pretty similar across them all. With 1-3knots current you should be ok with the shot line approach, although 50m depth is probably the deepest youâd want to go (imagine how much the shot weight can drift off the mark as it descends through the water column). Specifically:
Shot/weight: Because of the depth Iâd use as heavy a weight as possible. You can use an anchor as your shot if youâre worried about dragging, however anchors tend to drift more on the way down so Iâd use something very heavy and compact (for deeper stuff Iâve used solid steel bars ~10kg, very unlikely to drag if youâve just got a lightweight float on the surface and go down quickly through the water column. If youâre short on options then a bunch of diveweights cinched and locked in on a dive belt would work alright.
Line: Any marine rope would be fine but donât go too thick (drag). Youâll want to use a line that is probably ~50% longer than the max depth of your site location, so at 50m youâd need 75m of line, but as you get more experience with your study site youâd be able to fine tune that (you actually want as short a line as possible that isnât going to drag the surface float underwater).
Float: Literally anything would be fine for your purposes I think. If you were going to experience strong currents then I would say to use a higher buoyancy float to prevent getting dragged under but I imagine you wouldnât even be attempting this in high currents anyway (and as an extra point I would advise planning your fieldwork around slack water (high/low) or any other known periodicity of currents, where possible).
Final observations: all the above is just to get you accurately onto your site(s). It wonât work without a very good GPS mark (youâll just be dropping your shot into some random spot and setting yourself up for failure!) and as other people have noted you can combine with the depth sounder to help orientate yourself to the benthos. Once youâre on your mark, I would then motor up current/wind and drop anchor so that your boat âhangsâ back near the surface buoy and from there you can roll with the rest of your site location activity, either ROV or diver. As others have observed itâs going to be challenging and might be worth practicing in some shallow/benign environment before you go live with the real thing.
You should look a bit more into acoustic release system. So call pop-up boys. With these system you past near your mooring with a boat and send specific ping in the water. The mooring will release a boys that will move up to the surface. Then you have to find it and pull on the rope to retrieve your equipment. These device are made to last and operate on internal batteries. Not fun like driving a BR but straigth forward en efficient. You just need to make sure the pinger can listen at the desired depth.
Iâve piloted a couple ADCP deployments/recoveries, helped release âfrozenâ acoustic releases for acoustic fish-tag loggers, recovered 1 ton cement anchors, and monitored a Wire Walker deployment with a BROV2 Heavy configuration, at depths of 45-50m, ~ 3+ months after initial deployment. Tether drag and consistent vessel positioning / tether management in the dynamic ocean is always a challenge. Tossing a weight with line and surface float, ~ the expected depth in length can not only give your boat operator a reference point to hold position relative to (assuming itâs not dragging along the bottom in high current.) It also gives the ROV operator a line to follow down that puts them in the approximate area - the trick is dropping the weight right as you pass over the gps point!
Being able to check that a deployed ADCP is correctly oriented can be quite helpful - something you might wonder about for duration of deployment if only an acoustic release is used!
Great video @btrue thank you - very useful. I think the drag you experience would be compounded by having to launch from the shore. Iâm definitely no expert but suspect that as the tether becomes less positively buoyant the weight would pull the ROV back towards the tether as the whole length sinks. Presumably would probably make 180 degree turns quite difficult? The effect would get stronger the longer the tether but suspect it would not be a problem if deploying from a boat where you can be directly above the ROV.
Iâm a new BlueROV user and wondered if you were using the heavy configuration in this video and also how you get that excellent info to appear on the bottom of the screen? Any advice greatly appreciated.
Cheers
Great videos Tony - do you think there is much risk of damaging the BlueROV tether with the sharp blade as have thought about adding something similar to the Newton Gripper.
Hi Bill !
You can get the info to show on the video by opening the video with VLC media player, with the .ass file that QGC creates when recording in the same directory. You can âburn inâ the info to the video by specifying the .ass file as a subtitles file in a video transcoding program (free) called Handbrake.
As for the tether, and recovering things from shore vs. a boat - the longer the tether, the tougher to drive the ROV, period. Iâd be less concerned with the buoyancy of the tether, as it stays slightly positive to neutral no matter what. However the buoyancy of your recovery line may impact operations.
I believe most of the videos I shared were with a non-heavy configuration BROV2, but some of the later dated ones were likely the heavy, as Iâve pretty exclusively switched to those in recent years.
The tether jacket is quite abrasion resistant, but a sharp blade can for sure damage it. The newton gripper could be used to grab things, and the tether with kevlar is fairly strong, you could probably recover a ~10-15 lb object easily in this manner? Not sure of your application.
Thanks Tony - been meaning to get back to this. Is there a way to display all that info live in QGC or can only be added to the video after? Apologies for the newbie question but I can only find how to display a couple of basic parameters to live in QGC so was wondering how to include the more comprehensive info in the above video.
@BillyBudd
I do use Handbrake to burn in the subtitle track while also converting the video file to .mp4 so I can use it with my video editor.
I bought the heavy configuration with the ROV, so I have never used the standard configuration.
Yes, The drag is caused by the positive buoyancy putting upward tension on the tether. The tether is so positively buoyant that it never seems to become neutrally buoyant so thereâs always some upward force. A part of the problem is that I usually use the ROV to pull the tether from the spool. It does help to drive the ROV out on the surface first to get some extra tether floating directly above the target area.
Most of my dives are in about 30â of water near the shore so the regular drag through the water isnât a huge issue. It starts to become noticeable as I get deeper.
Hereâs a good example of me fighting the drag from the tether and spool around 2 or 3 minutes into this video on the descent down the slope. In future dives I will probably take the time to get some tether out in the water to significantly reduce this early drag, plus it would also allow me to use the Ping echosounder to get a preview of the bottom slope and depths.
have had precious little time to spend on familiarising myself with this so far so appreciate the heads up.