How can it be non VAT if it is UK registered and in an EU nation? That is not physically possible from my understanding having been through the VAT situation when Croatia
I would suggest you double check the documentation
is it may have been that the vessel was rated as "zero" for VAT due to age. However this is Greece and it has become clear how lax they are at collecting VAT recently.
If you do have to pay VAT then it will be at the rate of the nation state the vessel is purchased or imported into. So you will have to pay Greek VAT on the value perceived at the time by the authorities.
If you subsequently leave the EU for more than 3 years you will then be subject to VAT on your return so it is well worth planning any long trips around this fact. For those planning on going to the Caribbean
it is worth noting that Guadaloupe and Martinique
are both considered part of the EU as they are "Domaine Outre Mer" territories and part of metropolitan France
. Therefore you are enetering French national waters.