In case it has not been reported, Transfer Boarding Parties can occur between ships of the same nation without the ships in question being fouled or grappled to each other.
This may be by design, but it goes against the original board game rules as stated in the Basic Game: Page 5, Section VII, "Boarding Preparation Phase", which states, "Ships which have been fouled or successfully grappled may form boarding parties if desired." The implication is that w/o the benefit of a foul or a grapple the ships are not truely connected, even if adjacent.