Couple of things, I presume neither of you are tax residents of any EU state, irrepective of your passport. If you any of you are travelling using an EU passport, you will have trouble with the 18 month VAT exemption as you will good proof that you are not a tax resident.
Secondly you but most certainly your wife will be suject to the Schengen Visa Wavier tourist rules, thats 90 days iin 180 in totalled across all the schengen countries you visit. ( ALL of the EU including Norway). That boat can stay for 18 months the crew cant.
oops sorry I see your based in Norway,that might explain.
A better suggestion by the way would be to take the boat to Ireland
is not in the Schengen area, its meets the requirement to take teh boat out of teh UK for VAT reasons and is closer. Norway will be very cold and difficult to get to anytime outside the high summer.
We're probably looking at buying used VAT paid
so the 18months VAT relief has no impact in you anyway
Give it more thought.