How to pickup objects on seabed using suction and power needed and counterbalancing this thrust

I want to pickup a plate-shaped object (analogous to a seashell) from the seabed using suction and then retain it and collect more.

What I am thinking is put a pipe orientated vertically, with a blue T200/500 thruster on the top end, and suck the shell into the pipe . Once the shell is in the pipe, I have a method to extract it, it’s only the process of getting it into the pipe I need help with.

I am not sure

  1. What power of motor is needed - if the T200/500 is over/underkill? The shells have diametre of 120mm typical, and negative bouyancy of 20g. Would a T500 be able to generate enough suction to pickup one of these sitting on seabed, given a 200mm ID pipe perhaps 500mm long? Lets assume the shell is on the seabed, and the pipe entry is 5cm from it.

  2. How would a T500 hold up to this kind of work? Given that we’ll also be sucking up a lot of sand/gravel at same time by accident.

  3. I know using the thruster will pull the whole ROV down - we’ll only just turn it on for collection, and then turn off shortly after.

Thanks all

Hi Calum!
I’ve used a single t200 to suck and then discharge dead fish from a box about the same dimensions as the Blue Robotics payload skid. For a given flow, it’s the open area (your pipe size) that’s going to determine flow speed/pressure to suck things up.
Ideally you wouldn’t expose the T200 or T500 to sand and gravel - especially if the sand has a high amount of magnetic iron fines in it- I’ve found this to be the case int he SoCal area. Maybe if your vertical pipe long enough, and the flow speed low enough, you can produce the suction without the heavier particles being lifted to the motor?
Best of luck!

Hi @coinman66,

One could use an ejector / jet pump :

That way you wouldn’t expose the T200 or T500 to any sand or gravel.

Another option without suction (less destructive
for the seafloor life) would be to use a mechanical claw/manipulator and a negative buoyancy basket with a rope/buoy to lift the basket when full from the surface.