In another post I listed Boat/US reasons for boats sinking underway.

The top reasons for boats sinking at the dock a

Where the Water Came From
:
Reason Percentage
Underwater Fittings: 50%
Rain and Snow: 32%
Fittings Above the Waterline: 9%
Poor Docking Arrangements: 8%
Other: 1%

Underwater fittings include : "In 50% of the dockside sinking claims, water
found its way into the bilge through leaks at underwater fittings. The
majority of the leaks were at stuffing boxes (12), followed by outdrive or
shift bellows (11), failed hoses or hose clamps (eight), sea strainers
(four), and drain plugs (four).

There were two sinkings each from air conditioning fittings, gate valves,
transducers, mounting bolts, and mufflers. One boat went to the bottom as a
result of a leaking speedometer impeller. It is certainly possible that more
than one fitting had been leaking. "

An interesting note concerning claims due to rainwater/snow was:

"Water falling from the sky, either rain, snow, or sleet, accounted for a
whopping 32% of the sinking claims. Everybody has seen a rowboat or two
awash, so this shouldn't be a surprise. What may be startling is that all of
the claims involved boats with self-bailing cockpits that should have shed
the water overboard."