Neither the tax residency or the flag of the
boat is the issue.
Insurance is a
contract between an Insurer and you (ie, personally or company, etc...). The
contract will specify which country laws it
references in it's drafting.
Whether any Insurer elects to insure you will be more based on their internal rules, than the laws of any particular country. (eg, Australian Insurers are often using international underwriters who may prohibit them from taking on risks outside Australia).
For example, I am an Australian & UK citizen, with 44 ft sailing cat which has been based in the
Med for many years, and has never paid VAT in the EU (just ensure the
boat leaves the EU at least every 18 mths).
The boat is flagged in Langkawi,
Malaysia but has never sailed there.
The boat is insured via a UK
broker with
marine insurer Yachtline although they are not the underwriter. The policy is written under the laws of
England & Wales and governed by the FCA (Financial Conduct Authority).
In Oct.2011, I made a claim after a Delaware
USA flagged superyacht dragged
anchor and came onto me in a storm whilst we were on a
mooring. The superyacht was Turkish owned and crewed. It was a tricky claim, because the damage to my boat was less than the $20,000 USD excess of the superyacht's
insurance, and the Turkish owner was less than honourable. A prick who refused to fully compensate for the damage, but instead offered a sum less than half the cost of the
repairs.
Yachtline fully compensated me, but I think ended up accepting the Turks offer because it wasn't worth the
legal fight with this Turk through the Turkish courts.
From all this, I say it doesn't matter who owns the boat or where it's flagged, just who's the Insurer and do they stand behind the contract as it's written. So you don't have to attempt to sue your Insurer (on top of everything else) to get what you believe the insure contract entitles you to.