All our boats are unsinkable.
Filled with water, they stay on the surface of the water in a horizontal position.
This result is achieved by adding custom-cut EVA (Ethylene Vinyl Acetate) foam rolls inserted between deck and hull and freeboard. EVA high density foam is completely waterproof and rot-proof; in 5 years, your boat will not weigh 100 kilos more, and the foam will always be there, entirely.
It would be much easier to inject polyurethane foam, but it absorbs water and holds it, and breaks down in time, and imagine the work to intervene under the bridge ...
With Morningstar, if one day you had to pass a new wiring or intervene on the hull, you would just dismount the riveted bridge, just take out the foam bread, do your work and then reassemble all. Simple, easy, effective.