It's just odd that 80% of all boat sinking happens at the slip. I find that rather odd. Maybe it's just poor upkeep that causes this.
You're missing half that sentence... 80% of all boat sinking happens at the slip
when no one is aboard.
Head seacocks left open are a leading cause of boats that have no vented loop in the head intake to protect against leaving the toilet in the wet mode or wet/dry valve failure sinking in their slips....water outside the boat overflows the bowl and keeps on seeking its own level inside the boat till it succeeds.
Failed hose connections are another major reason why boats sink in their slips...old hoses that have become so dry and brittle that they crack open, failed hose clamps (which is why all below waterline connections should be double clamped.
Dock water hoses left connected with the water on the dock left accounts for an increasing number of unattended sinkings. Boats sink in their slips because no one is aboard to notice that their feet are wet when they go below and do something about it while there's still time.
And btw, contrary to most people's belief, most boat fires are not caused by fuel--gasoline, propane, alcohol stoves--but by faulty electrical connections...worn frayed wiring, and bad decisions due to ignorance.