For centuries lightvessels (or ships) have protected seafarers from our fast flowing waters and jagged coast line. Simply, these ships are floating lighthouses that sit in water too deep or dangerous to place a static beacon.
Expensive to maintain, many lightvessels were retired during the 1970s and '80s to be replaced with cheaper buoys; humans no longer required. Remaining ships and now unmanned and solar powered. Like a lot of larger boats, many lightvessels have been converted into quirky homes dotted around our coastline.
The two pictured together are at Port Werburgh, Hoo Ness (if they're still there) just east of Upnor Castle near Rochester. Floating is the East Goodwin which still guards the infamous Goodwin Sands.
The history of these craft is fascinating. Good old wikipedia has some interesting facts: lightvessels