It seems the structural damages are mostly above waterline and involve several watertight bulkheads ending at the main deck … subject to diver inspection. Another question is if HI had a double or single bottom. A 2 m deep double bottom would not have been damaged and would provide plenty buoyancy.
And it had guaranteed structural resistance to a missile impact, whatever that means.
The square, flat stern like a box is very ugly but probably very easy (=cheap) to weld together. Most yachts today have a platform welded on the outside of the stern today to simplify boarding.
We are told that the HI deck house is gas tight but there are big air intakes on both the forward and aft funnels so that the engines can run! Maybe they can be closed from inside? Anyway, no ship floats on its funnels.
My ferries have permanent, horizontal steel fenders fitted at main deck level for protection when moored along side. Maybe it was too costly to fit anything like it on HI? Doesn’t a ship like HI spend most of its time in port?
Anyway, pushing HI against the shore submerging the side damage allowing progressive flooding was a mistake. They should have turned it around and pushed it so the hole was above waterline.