Charters are a financial deal between two private parties... you can buy insurance for that from lots of providers.
Borrowed boats are covered under the US Sailing burgee program package (assuming they buy it). Borrowed means borrowed... the owner does not get paid. It's used to borrow somebody's boat for marks. etc... It has been used to borrow cats to lend out... which is a bit of a stretch but seems to fly by the company.
