Floating Boat Bags for boats on moorings

i have seen similar on some boats round me,
but i think the only alternative to antifoul in uk waters is to dry sail.

still dont stop full fouling, our customers tend to go for copper coat, and it works the only issue is it can be a bit temramental on older boats that have already had a coating,
as for ultrasonics im not convinced, and you also hear a clicking when they are in use at night

The St mawes SB3 lift is a home made affair out of some box section for a frame and some flexi air tubes strapped underneath which are inflated using a dive bottle. This lifts the SB3 hull clear of the water with only the bulb immersed when the keel is up. Works well but it is on a very sheltered swinging mooring would not work in an exposed position. Big bonus it does not require dock side electrics to get it to work!!!

I have this idea that i can cast a mooring sinker in cement with a hole in the middle through which i shall loop and shackle the riser chain. then i will use a 1ton builders bag (filled with air bags) to float the sinker off the slip as the tide rises.

Would bin liners do as airbags?
How big a cement sinker would an air filled 1ton builders bag lift?
Would the builders bag straps be strong enough?

We used to use two oil drums tied together with a length of 4x4 on top.
The sinker was hung below the drums using a strop over the 4x4.
The sinker was carried down the beach at low water using our tractor
And the drum floater attached, as the tide came in the sinker lifted and could be towed out to position and finely positioned in place using warps to nearby moorings. When all was ready using a bread knife on the end of a long boat hook the strop was cut and the sinker dropped into position.

Another permutation of this with bilge keelers was to hang the sinker over the bow of the boat at low water and let the rising tide do the work in a similar fashion. Sometimes the boat was so bows down the prop came out of the water so a second boat as a tug was used.

Finally I have also seen it done with two inflatable dinghies side by side with a beam between them.