Boston Harbor Cruises has sailed a long way in its 93 years, from the early days of half-hour cruises on the Charles to the mighty perch it holds today as the harbor’s dominant ferry operator.

But now, the company heads into uncharted waters: ownership by an out-of-state operator, one controlled by a private equity firm. The four family members who own Nolan Associates LLC completed the sale of BHC on Tuesday to Hornblower Holdings, a Chicago ferry and cruise company, for an undisclosed amount.

The transfer comes at a crucial time as local leaders weigh expanding commuter boat options. BHC executive Alison Nolan has been pivotal in these talks, in part because her company already runs the Massachusetts Bay Transportation Authority’s ferries for Charlestown, Hingham, and Hull.

What will happen now that a Chicago company is calling the shots?

Good news, ferry fans: Nolan will stay on board as general manager. No sailing into the sunset for her. In fact, she expects nearly everyone in the nearly 600-person workforce to remain. The Boston Harbor Cruises name and logo will stay, too.

Yes, it’s bittersweet to end nearly a century of family ownership. But Nolan portrays this development as a positive one for the civic leaders who are floating plans to expand ferry service. BHC, she says, had pretty much maxed out its capacity for additional fleet and technology investments under family ownership. Hornblower, she notes, has considerable ferry experience, most notably with the massive expansion that has taken place in New York City.

BHC brought 44 Boston Harbor boats into Hornblower’s fleet, which now totals 137 vessels, post-acquisition.

(The Nolan family continues to own, for now, a dozen research and construction boats under the name Blue Atlantic Offshore.)

BHC also runs water taxis and ferries to Salem and Provincetown and provides whale watch trips and other excursions.

Hornblower already had a presence in Boston, with two dinner ships (Odyssey and Spirit) and three charter vessels, as well as boats in nearly 20 other North American cities. The private equity firm Crestview Partners, in turn, has held a controlling stake in Hornblower for more than a year.

The BHC deal had been rumored for months. But Nolan says the sale discussions date to early 2018, when she and Kenneth Svendsen, president of Hornblower Cruises & Events, got to talking at an industry conference.

Last month, the Boston Planning & Development Agency approved shifting BHC’s Long Wharf leases to Hornblower. Last week, the MBTA approved transferring the commuter ferry contract.

The sale caps a decade or so of strong growth for BHC, when it more than doubled in size after members of the Nolan family bought out the now-defunct construction company Modern Continental’s majority stake in 2006. (The family brought Modern as a partner on a decade earlier.) BHC beat out a rival operator for the Hull ferry in 2013, taking full control of all official MBTA routes on the water, and then took over contracts to run excursion boats to the Boston Harbor islands.

BHC’s upward trajectory has mirrored the city’s. The green monster of a Central Artery came down, reconnecting downtown and the waterfront. In its place, the Greenway sprang up. Luxury condos and offices replaced parking lots in the Seaport. Nolan says the company’s growth will continue — with Hornblower’s considerable backing.

That will be a relief for ferry advocates such as Alice Brown, a planning director with the nonprofit Boston Harbor Now. The organization recently spearheaded a study to din the most commercially viable ways to expand commuter service in the harbor.

The recommendations included frequent rides to Quincy, with stops at Columbia Point and a new East Boston dock that could help get commuters downtown or to the Seaport.

Work is underway on both fronts: Lieutenant Governor Karyn Polito stopped by the John F. Kennedy Library on Wednesday to talk about a dock redesign happening there. The City of Quincy applied to the MBTA last month to participate in a pilot program that would improve the city’s limited service. Lynn officials did so, as well, to revive its short-lived commuter service. Brown says she’s encouraged by the progress on plans for a proper ferry dock in East Boston. And maybe that long-awaited Seaport dock on Commonwealth Pier will finally happen, since Fidelity is rebuilding the World Trade Center.

It remains to be seen where Boston Harbor Cruises will fit among all the moving pieces. But if what Nolan says is true, a bigger company’s backing should ensure that BHC continues to make waves in the harbor for many years to come.