Sunk at dock but no leaks, no rain?

Woke Up this AM with a call the neighbor's 28 Tiara was sitting on the bottom of our canal. By late afternoon she was again floating but obviously it will be a long long time with repairs. No leaks could be found so it's really strange. Not had any rain; she had all new batteries just a month ago and 3 bilge pumps on auto switches. The mechanic he brought over to help out suggested he install a high water alarm. Anyone have a specific one they would recommend ?

Impressive system, especially all of the wireless accessories.

Not for mine and maybe in his future. Boat was refloated, no source of the water found, and today they plan to start with getting the motors running. Neighbor has been in the boat business 40 plus years; buying fixing up, selling but this is one he kept for personal use and has spent a lot of time upgrading. I've never found him to be stumped on the cause for an issue but so far this is a first. Why would you advise an attorney? He has no insurance.

I learned it was plugged into 30 amp shore power and after speaking to the delivery captain of Ocean's 2nd 40 ft. spt. fish ages ago learned hull #1 sunk after being pinned under a concrete dock on the way to a Florida boat show, so we explored that and ruled it out.

The homes camera system failed to record that night; doesn't that figure. No leaks all last night. Current theory is the stern line from the far from dock cleat became loose enough at the high tide to get under and catch on the swim platform and as the tide dropped held one aft side up and the other down and water flooded into one scupper, ran into the bilge and to the bow where it overwhelmed the forward pump and then flooded the nearly new batteries, that had burn marks on their positive terminals. Evidently the "one way" rubber scupper flaps will not work underwater. Of course the above is all theory and he will probably never know for fact.