The case of Lozman v. City of Riviera Beach once seemed easy to capsulize in a single question: Is a houseboat a house or a boat?

But as oral arguments unfolded before the Supreme Court Monday, the issue became far more complicated. For one thing, was the focal point of the case even a houseboat, or was it just a floating home that should not be called any kind of boat?

Fane Lozman’s ramschackle structure had French doors on three sides and no batteries because it depended on being plugged in for its electricity, like most homes. But in the years since Lozman bought it in Florida in 2002, he relocated it several times by moving it across water, which is something boats do.

As a result, the question arose: what to do with structures like Lozman’s that are meant to stay moored, making them seem more like homes, but in fact can move people or things across water like a boat, when needed?

The court’s answer is crucial to determining whether federal admiralty jurisdiction over boats should prevail, or ordinary state laws that govern houses or land structures should apply, when things go awry. Owners of floating casinos and pricey floating homes in Seattle are eyeing the case nervously.

Advocates before the court offered conflicting ways of distinguishing between vessels and homes, drawn from court precedent: is it “practically capable” of maritime transportation, or is it “indefinitely moored;” or should a “function test” prevail?

Each test crumbled as hypotheticals flew, from Justice Stephen Breyer’s Styrofoam “floating sofa” that could transport people or things across the water, to Justice Samuel Alito’s replica Viking boat, built for display in a museum, but seaworthy enough to float in a pinch.

At one point Justice Anthony Kennedy sarcastically described Lozman’s home as a “magnificent structure” that was “mercifully destroyed” after the city, eager to define it out of existence as a vessel, imposed maritime liens for numerous deficiencies.

Stanford Law School professor Jeffrey Fisher, best known for his high court advocacy in criminal cases, argued on behalf of Lozman that federal jurisdiction did not apply, because as he viewed it, Lozman’s home was not a vessel. “This is a rectangle that sits 10 inches under the water and is not meant to be moved around,” said Fisher. Under the wrong test, Fisher suggested, even floating docks or garage doors could be labeled as vessels if they float and could carry people.

David Frederick of Kellogg, Huber, Hansen, Todd, Evans & Figel, representing Riviera Beach, pressed for the “practical capability” test, and insisted that because Lozman’s home – and other structures like floating casinos – are capable of being used to transport things over water, they are vessels.

That seemed too broad a definition for several justices. When Breyer resurrected his floating sofa example and asked if that is a vessel under Frederick’s definition, Frederick was noncommittal. “I’ve given up the absurd hypos because there is no litigation on them.”

Chief Justice John Roberts Jr. tried another tack, suggesting that one factor should be the design of the structure, not just its ability to float. “The thing that makes something look most like a boat in my view is a raked bow. That tells you that’s what they want to use it for, to move through the water.”

Frederick had a ready answer. “House barges have been vessels since the time of Cleopatra,” he said. “The fact that it is flat-bottomed … does not make it not a vessel.”

Tony Mauro can be contacted at tmauro@alm.com.