I think you misunderstand the situation. There are two ways to "register" a boat, state and federal. A boat showing ownership
in Delaware does not have to have a Delaware state registration. Not finding a recent state registration renewal does not mean anything.
Bird of Passage has a federal registration called Documentation
which is done with the US Coast Guard. The US government
web site shows that the federal documentation
with the USCG for Bird of Passage was renewed Jan 6 2010, expiring Jan 6 2011.
A vessel that is USCG documented is not required to have any state registration. Some states may also require that you pay a state registration fee (it is a revenue source for the state) in addition to the federal documentation but only if the boat is docked in that state.
It is very common for boat owners in other states to set up a cheap
corporation in Delaware for tax purposes to show ownership
there. In many cases neither the boat nor the owner are in Delaware. If that is the case then there will not be registration in Delaware.
The official owner of the boat is a company named Hobo Co at the address in Delaware. That address in Delaware is the office of Delaware Registry, Ltd. Delaware Registry, Ltd is in the business of setting up Delaware corporations for individuals and companies that want a Delaware corporation, usually for tax reasons.
So Delaware Registry manages the paperwork and provides the Delaware mailing address for Hobo Co. If you want to find the owners of the boat you need to find out the owners of Hobo Co. Since Delaware Registry, Ltd is handling the paperwork for Hobo Co you should ask them the name of the corporate officers or actual owners of Hobo Co. who will then be the owners of Bird of Passage.
I believe corporate ownership is considered public information to prevent people from setting up dummy companies to avoid taxes
and liabilities so I think the names is should be available. If Delaware Registry, Ltd will not tell you the names you might be able to get it from the state.