I would like to know if any kind of object of design can be protected by the Vessel Hull Design Protection Act, or if it is just to vessel hull objects.
Nope, just vessel hulls. The Congress passed the act in response to a Supreme Court case that said the State of Florida preempted the patent laws by filing a similar law. http://floridaiptrends.com/2009/02/23/vessel-hull-design-protection-act-what-the-hull/
Other types of designs are potentially patentable in a design patent.
The statute begins with an original platitude about protecting design rights through the copyright regime:
17 U.S.C. 1301. However, later the statute defines "useful article" as being limited to a boat hull or deck.
The statute was intentionally structured in this manner. The idea is that the law can be easily expanded by just altering the definition of useful article to include other types of articles. Although it did not pass, a bill was proposed in Congress that altered the definition to include clothing.
Just as a point of background. Copyright is not generally available to protect useful articles (such as boat hulls or clothing) unless the original design is at least conceptually separable from the function. The Copyright Office has a circular on this.