Being kind he might have had a bit of engine trouble? - probably not though, just assumed it would stay empty.....IMO a week and also not telling the Marina (and giving them a key) is taking the p#ss.
Tricky one when it is neighbours - I would have a polite chat with him to find out what the "problem" was and point out the inconveniance caused.....if he is an a#sehole, buy some bolt cutters.