well who do you think can afford to buy and maintain the ships plus keep engineer equipment on standby for these type of operations, international rescue was a TV show not real life.
as we all know these function are a secondary role to why the vessel was purchased in the first place. do you want more of your tax going to the united nation to purchase and control and refit these ships.
I think it's a great idea but generally unrealistic.
Agree with Feanor's comment regarding the UN spearheading this. UN could simply ask/assess larger membership fees to nations starting with the members of the UN Security Council.
If they become UN ships they I'd ask a further UN question, why limit them to disaster relief?
Why not set them up as a UN unit to deter potential aggression with an international force?
Float them toward the coastline as conflict arises and provide international deterrence as a negotiation tool?