900ft tether against 2kt current. Will it work?

General Discussion
1

Hello All!

Scope: Inspect 1800 feet of 60 inch inner diameter pipe (interior pipe inspection) with the BlueROV2. There will be a maximum of 1.5 knots (2.6f/s) current of clear water inside the 60 inch pipe and the ROV will be traveling against this effluent. The longest span will be 920ft. For the final leg, the pipe steps down to 48 inches for 200ft where the current rises to 2kts.

Several Questions:

  1. Thrust: If we opt for the 30 degree thruster configuration, will it provide enough power to pull the
    7.5mm tether 920ft through the pipe with a 1.5kt head current?
    Theoretical: 920ft Fathom 7.5mm weight in air: 26lbs. 30 degree forward bollard pull: 24lbs.
    Unknown: Tether Friction through water being neutrally buoyant.

  2. Power: What kind of run time am I looking at with this set-up? 2.5hrs? Will be using 4 Lumen Lights.

  3. Tether: Is the maximum length for the Slim Tether 200m? For this project I could really use the Slim
    with it’s lower drag coefficient (assumed) if it is available in 300m. Would a 1000ft roll of CMX Cat5e
    or Riser cable work solely for this job with the Binder 770 connectors? (I would be purchasing the
    BlueROV2 but would not need the 300m tether for every situation and would purchase a 150m
    tether with reel to get started). Main Question would be if the BlueROV2 would be able to pull the
    Fathom 7.5 920ft against the current.

  4. Control: I assume that under full power, the controls will be a bit touchy! I hope to mitigate this with
    the 30 degree thruster mounts as I would not need so much the strafing actions. Just forward
    through the pipe while recording video is about all the maneuvering I will be doing.

I have used the 12mm neutral VideoRay tether and it is quite bulky. I have 125m of the ~4mm Deep Trekker tether which is nice all around. Seems the Fathom 7.5mm would be a great in-between.

I’m enjoying the forums so far, thanks to everyone out there.

-Adam

2

Hi @DiverJay,

Thanks for your questions! Blue Robotics hasn’t done any testing of the BlueROV2 in pipes, so there are a lot of unknowns. I have seen some of our other customers post pipe work pictures on their social media accounts, so you may want to look around at our Twitter, Facebook and Instagram pages. I don’t have any image links off hand.

Thrust: If we opt for the 30 degree thruster configuration, will it provide enough power to pull the
7.5mm tether 920ft through the pipe with a 1.5kt head current?

Unknown. We have only operated in 0.5 knots of current here off Southern California and I don’t believe we have ever let out a full 300m of standard Fathom Tether. It is going to be a lot of drag, but it might be doable.

Power: What kind of run time am I looking at with this set-up? 2.5hrs? Will be using 4 Lumen Lights.

2-3 hours should be reasonable with a standard configuration BlueROV2. The run time will be less with the Heavy Retrofit kit.

Is the maximum length for the Slim Tether 200m? For this project I could really use the Slim
with it’s lower drag coefficient (assumed) if it is available in 300m.

200m is the maximum communications distance we have seen with our current interface boards so that is why we only make the ROV-ready Tether that long. You can order more (by the meter) and put on your own connectors, but no guarantees on the communications stability at longer lengths.

Would a 1000ft roll of CMX Cat5e or Riser cable work solely for this job with the Binder 770 connectors?

A few of our customers have used coax cable before.

Control: I assume that under full power, the controls will be a bit touchy! I hope to mitigate this with
the 30 degree thruster mounts as I would not need so much the strafing actions.

The 30 degree mounting locations will definitely help along with Stabilize mode to keep a constant heading (I don’t think Depth Hold will help you here). I think piloting into a current will still be a fun experience.

Let us know if you have further questions!

3

Kevin,

Thank you for the input and recommendations. Now comes the battle of getting a unit ordered and here (South Carolina) within the next 30 days or sooner if possible. Looks like the 300m tether is on backorder along with a 3 week lead time on the ROV itself. I submitted a quote request to you today. Thanks!

-Adam

4

Hey Adam

Something to consider is changing your system to fibre optic. That way you can easily handle long distance with minimised drag effects as the FO tethers are typically in the ball park of 3-4mm diameter. BlueROV can handle over 500m of this tether in the water as it has very minimal mass in open water. Its easier in a pipe if the pipe is straight. No reason for a pipe job that you cant add 2 more rear facing thrusters to get you extra pulling power if needed.

Unfortunately its not something you can do quickly as typically it takes time to get the tether ordered.