The most important safety system on your boat, after the structural integrity of your hull, is your bilge pump system.
Why? Well, what if you’re offshore when a thru-hull fitting fails, or you lose your prop shaft. In either case you now have a one and a half inch diameter hole in your hull about 3 feet below the waterline. This hole will let about 4,500 gallons of cold ocean per hour.
Your bilge pump system is unlikely to be able to keep up with this inflow, but if it’s of an adequate size, it will give you time to find the leak and plug it
However, if all you’ve got in the bottom your boat is a little Rule 500 gallon pump, you don’t have a bilge pump system – all you’ve got is a way to pump out your bilge when your hatches leak.
A good rule of thumb is that a sailboat should have a minimum rated pump capacity of 100 gallons per hour for each foot of overall length. So a 30 footer should have a minimum total rated pump capacity of 3000 gallons per hour, a 40 footer should have 4000 gallons per hour.
Find the full article on how to select a sailboat bilge pump.