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Approved foam or alternatives for potable water?

Hi, Can anyone tell me if there is such a thing as approved buoyancy foam for potable water? We use our Bluerov2 for water tank inspections and the question came up about material testing.
In the UK we “must” have approved materials when they contact drinking water,
Is there an available WRAS or BS approved buoyancy foam available?
Has anyone used airbags instead of foam for buoyancy? is this even possible?
Any help in sourcing or using alternative buoyancy would be great, as I fear we may need to remove the Bluerov2 as a UK asset until this is rectified.

I’m not sure about material testing/approval for potable water, so I’m probably not helpful on that front, particularly if you’ve done some dives with the same ROV in non-potable water (in which case the whole ROV may no longer be allowed without explicit testing and approval after a thorough clean, regardless of the materials it’s made of).

Buoyancy works by volume displacement, and air is highly compressible so bags of air are a poor choice. Maximum buoyancy comes from minimising material weight while maximising volume, so you’d want a lightweight pressure vessel that can handle the pressures you’re going to. Some empty sealed bluerobotics acrylic tubes could do the job, although you’d need to do a mass comparison with the foam you’d be replacing to determine the viability (or technically an average density comparison of sealed tube vs foam).

The shape may be problematic, so if you’re interested in alternatives you could source (or make) some sealed boxes (at least with a flat base), but you’d need to pressure rate them to whatever depths you expect to go to. That could end up as a winning solution though, because they might not need to be as thick as the bluerobotics tubes if your water tanks aren’t as deep, so you could end up shaving off some mass that way.

Hi, Thanks for the reply, I suspected airbag’s would pose a few problem’s, I like the idea of using sealed acrylic tubes though, As our ROV only goes down to a few metres, pressure shouldn’t be too much of a problem. I may have to make some sealed polypropylene tubes, or cable tie some empty bottles onto it for testing and easy volume comparison before getting something made of approved materials. (luckily my neighbour is a fibreglass and plastic fabricator) But you’ve given me a load of ideas now, so I’m off to the drawing board. Cheers again.
Craig

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Glad I could help get the creative juices flowing. Would be cool/interesting if you could post the process/result in the Build category, and/or some testing in the Dive Log category, assuming that’s not problematic to your business use-case :slight_smile:

I’ll do that if I can come up with something useable (it also look good) We have a few modifications already that messed with buoyancy eg. top mounted ip camera, 4 extra light’s, topside power module, and gripper, but I suppose that’s why we have a Bluerov2 purely for the fact we can modify it and the support is amazing in the community.

Fair enough :slight_smile:

Do you think it would be useful for there to be a guide and/or tool to help determine buoyancy calculations and effects based on thruster placement and part shapes and densities? That’s definitely something my previous company was struggling to estimate effectively - curious if others are interested in something along those lines.

Modular, modifiable design is definitely a joy to work with, and having a community that works together to support each other’s progress is awesome :smiley:

Yes, I think you’re onto something there. A buoyancy guide would be very helpful, even with a basic weight chart of the Bluerov2 in different configurations would help, so we don’t have to weigh everything individually for quick changes, (It also makes learning things a little easier when someone like yourself explains thing’s clearly rather than having to search the net for answers that are usually wrong anyway. :grinning:)

Noted, and good idea on the ‘common configurations’. Not everyone changes things, and having some kind of known general parameters by default when starting out is likely helpful.

For a potential ‘tool’ I was thinking something like in-water mass of all the bluerobotics components already being included, so you could effectively choose parts, or create simple volumes and set their densities for custom parts, from which it could estimate the center of mass and rough guides for max speed and whatnot, as well as issues to look out for with imbalance and weight too high/low compared to thruster positions. Not sure if that’s best made into a self-sufficient thing, or if it’d be better (or at least easier) to basically provide instructions for how to determine such information from a CAD model, and interpret the results. I’ll have to have a think.

Happy to help when I can - I’m interested in how far people can get when working together. Everyone doing the same work for effectively ‘solved’ problems is wasteful and frustrating, and doesn’t mesh well with my desire for general efficiency. Also, sharing knowledge means discussions can take place at a higher level, and more meaningful contributions can be made by everyone involved after learning a bit from each other :slight_smile:

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It seems like a cheap and easy solution might be just to make floats out of short pieces of PVC pipe with end caps – pipe can be cut to any length to get desired buoyancy. Obviously PVC/cement are commonly used in potable water systems, so should have approvals.

Also if you put a threaded plug on one of the ends, I bet you could just add water to adjust buoyancy.

Not sure how deep in water a threaded fitting would work though. PVC fittings are usually rated to a decent pressure, but of course that assumes the pressure is inside.

You’re thinking along the same lines as myself, I was thinking of utilising more of the acrylic tubes as used for the electrics, especially if I move to the heavy configuration it leaves me a load of space to work with and also gives options for future integration of more sensors/camera’s etc.