Boats taking on water

Question
I have a small 15 ft. boat, and I know that I can take on water over the rear in high waves or of course if I have an actual hole in the boat. But what I don't understand is why I see boats of all sizes, especially large ones, always pumping out water, even while at dock.  With today's materials, how do boats take on water in the hull?  Can't these be made fully sealed?

Answer
Hi Dick  (1)   Most of the bigger boats that you see are in-board powered(motor on the inside)with a propeller shaft that goes thru the hull.There is what is called a packing gland in the hull where the shaft goes thru.To keep from burning up the sealing material that is in this gland while under way, most folks leave this seal a little loose and it will drip while at dock side.(2)A lot of bigger boats have under deck air conditioners,these are cooled by pumping water thru them.(3)Also there maybe a bait well or live well on board that they are pumping water thru to keep the fishing bait alive.I'm sure that their are other reasons that you  see water running out of these boats but these three come to mind as the most common.Hope this helps--Have a safe holiday season!  Bert