What do you always check and why?

[NdN]

After a friend lost a propeller while backing away from a mooring, I now check forward and reverse while still secured to dock or mooring.

[xsboats]

I keep my ignition key clipped to the raw water intake handle after having to check my shorts following not checking the exaust for water.

[Omatako]

For coastal sailing I check (the reasons are obvious unless otherwise stated):

• the weather forecast
• tides where I am and where I'm going
• the appropriate charts are aboard and up to date
• the engine oil
• engine coolant
• fuel level
• drinking water
• the menu and related food stock
• beer, wine and coffee stock (any of these running out is a calamity)
• log a trip report with the Coastguard (radio check, origin of trip, destination, ETA and number of people on board).

Everything else can be relied on to break when it's ready and most of it won't give any visible warnings so I don't stress about it.

As another post said, an open sea voyage will get an extensive pre-trip inspection too long to list here