Re: 6 month insurance contract?
My boat is also in a charter fleet and covered by my policy through the charter companies plan. I assume that you are paying for the plan even though it is through the charter company ( in some way anyway). I also would assume that the boat is insured year around with a lay up clause of some sort. In the Great Lakes we do have lay up clauses because the water gets a little to hard in the winter.
I would be surprised if the company covering the liabilities on the charter would not have a way to decrement the policy for owners use only in the off season, unless they are adamant from a liability standpoint about lay up off season.