No boatbuilding material is perfect. I am not sure stainless steel
is a great material for a yacht hull
There are a few stainless yachts. I had dinner many years ago on an all stainless yacht (sorry I forget the manufacturer, but it was a large Dutch? custom motor
sailor). Interestingly, the company produced about half their models in mild steel
and half in stainless steel.
The other guest at dinner owned a near identical mild steel version of the yacht. The two owners were good friends and there was a constant friendly banter all evening about which material was better.
The steel owner pointed out he had experienced fewer hull
problems than the stainless owner. It was an interesting evening.
In terms of cost, while stainless is dearer, the bare hull is only about 1/3 the total cost of the boat. So increasing the cost of material will not have as much impact on the final cost as might be expected.