With three big construction projects underway — a truck tunnel, a deep dredge and a rail link — the Port of Miami is steaming ahead to sharpen its competitive edge.

But those pricey upgrades are just the start, as downtown Miami’s little island port dreams big about its future.

A new 25-year master plan reveals ambitious ideas, like a mega-yacht marina facing downtown’s Bayside Marketplace with grandiose aspirations of rivaling the waterfronts in Monaco, Cannes and Nice.

While its main goal is growing its cruise and cargo business, the port is eyeing commercial development on prime waterfront property on its southwest corner, including a hotel and office tower within the next few years and up to five office buildings over the long haul.

The hotel would cater to cruise passengers and business travelers involved in port trade. Office space would target international trade and commercial interests, according to port director Bill Johnson.

“The southwest corner is some of the most valuable real estate in our community and in the entire state of Florida,’’ said Johnson, the snowy-haired executive known for his sometimes-manic energy and loquacious style. “I hope to be one of the top ports in aesthetics, sustainability and one that is integrated into the downtown community, not some industrial dirty port.’’

The preliminary plans are “just a conversation starter’’ to be molded with input from the community and the port’s stakeholders, Johnson said. The goal is to find a new revenue source for the debt-laden port, which is a self-sustaining enterprise of Miami-Dade County that operates without county tax dollars.

New revenue from a hotel, offices and a mega-yacht marina could boost the port as it shoulders the hefty costs of cruise and cargo upgrades that are the meat-and-potatoes of the master plan, said Kevin Lynskey, assistant director for business initiatives for PortMiami, the port’s new name.

On the drawing board are a slew of efficiency-driven upgrades, including new cranes and cargo security gates, which along with the dredge, rail and tunnel are aimed at enabling PortMiami to double cargo business by the end of the decade on the same tight space it occupies in Biscayne Bay.

The dredge project, uncertain pending the outcome of a legal challenge by environmentalists, seeks to deepen the port to 50 feet for the larger container ships expected in 2014 when the widening of the Panama Canal is complete. Johnson has been aggressively wooing Asian shipping giants in hopes of landing at least one line.

And as the world’s largest cruise port in passenger numbers, PortMiami anticipates growing to 5.9 million passengers in 2035 from 4 million in 2011, potentially with a new super terminal, more berth space for the sleek mega cruise ships and a multimodal transit center for taxis, busses and rental cars.

Late this year, the Disney Wonder will begin sailing from the port, as will three newly built ships: the Carnival Breeze, Celebrity Reflection and Oceania Riviera.

But the new idea for commercial development is the sexy part of the blueprint.

The master plan envisions retail shops and restaurants and an inner yacht harbor, mirroring Bayside. The port is considering restoring an old bridge to the mainland that could serve as a pedestrian walkway and link to a future bayfront promenade as the downtown area is transformed by two new museums — the Miami Science Museum and the Miami Art Museum.

The concept of a promenade along Biscayne Bay is echoed in other big plans for the bayfront, including Malaysian casino giant Genting Group’s plans for a resort complex, with or without gambling, on the site of The Miami Herald building.

The port would likely lease the land on its southwest corner to private developers in exchange for rent and a cut of revenue, a public-private partnership, port officials say, although nothing has been firmed up.

The office space could provide a new home for the World Trade Center, currently housed in aging quarters on port property, while serving as a magnet for international trade and commerce-related tenants, such as attorneys, freight forwarders and other international-trade types.

The World Trade Center has hired a marketing consultant to gauge interest in a port hotel and office space in the southwest corner, sprinkled in around the leased headquarters of Royal Caribbean Cruises Ltd., a major port tenant through at least 2021.

“We hope in six to eight weeks to know what the market is and the desire of trade-related organizations [for space,]’’ said assistant port director Lynskey. The marketing analysis won’t address the mega-yacht marina idea.

The next step would be to take the idea to Miami-Dade Mayor Carlos Gimenez and the County Commission to seek approval to shop the ideas with private developers.

Luis Ajamil, chief executive of Bermello & Ajamil & Partners, which did the master plan, emphasized the preliminary nature of the commercial and yacht marina concept.

“It’s to say ‘Here is an idea.’ Not more than that,’ ’’ Ajamil said. “As the port yearns to be more integrated to the downtown, there seems to be an opportunity to look at this concept. The vision of an inner harbor comes.’’

The waterfront area in question isn’t suitable for either cruise or cargo ships, port officials say.

Johnson floated the idea for commercial development in December to port stakeholders, stressing that it is conceptual. Among them were officials of the Downtown Development Authority, some of whom are concerned at first blush about potential competition from the port for coveted office tenants.

The DDA, which promotes economic growth in the downtown urban core, will dissect the port’s ideas at a meeting Thursdayof its urban design committee.

“The concern is, are you going to be duplicating what is going on in the urban downtown area?’’ said Alyce Robertson, executive director of DDA.

“Generally speaking, the DDA has a very good relationship with the port. We’ve been supportive of the railroad, the dredge and the tunnel, so I wouldn’t pre-suppose how DDA will react to it.’’

Marc Sarnoff, chairman of the DDA and a Miami city commissioner, confirmed the port’s aspirations for commercial development are being met with a degree of ambivalence from downtown interests. “Everybody has a concern,’’ he said.

Sarnoff said a port hotel and offices could have price advantages over others in downtown. Still, he recognizes the port as a key economic engine and finds the ideas of a mega-yacht harbor and baywalk alluring.

“I’m very excited about the port’s ability to have yachts,’’ he said. “I think it’s great. The more walkable and the prettier the area looks, the more you attract people.’’

Pamela Weller, a senior general manager for General Growth Properties, which owns Bayside Marketplace, said she has seen only a preliminary PowerPoint presentation of the ideas for the southwest corner, which faces the Bayside shops and restaurants. Her initial reaction is positive.

“Anything that brings people and economic development to the downtown area would be beneficial to everyone. We’re not looking at it as competition,’’ Weller said.

Her company doesn’t operate the Bayside marina, but she knows the waiting list for boat space is long. The area, she said, “could use more marina space.’’

And Royal Caribbean, for its part, is upbeat about the port’s ideas for commercial development.

“The idea of having a world-class hotel property on the port is a positive for the cruise lines operating ships here, since it will give us another option for our guests to stay close to the departure of their respective vessels,’’ Royal Caribbean spokeswoman Tracy Quan said.

“Many ports around the world have incorporated or are planning to incorporate mega-yacht marinas into their ports, and we think the addition of a marina is also a positive development for the city.’’

The push for a new revenue source comes as the port, already shouldering a massive $616.9 million debt as of Sept. 30, prepares to borrow another $384 million for its share of the tab for infrastructure improvements and other upgrades.

Port officials expect those investments to make the port more nimble and improve its capacity, ultimately paying big dividends. But in the near term it faces an increasing mountain of debt as it works on growing new revenue.

“From now until 2020 is a debt hump,’’ Lynskey said. “We’re running a very tight ship until 2020. After that, our financials look great’’ as projections for revenue growth provide a stronger cushion.

“We realize that nothing is going to come from downtown [County Hall] in the way of taxes for the port,’’ he said. “This has the opportunity of bringing in new revenue.’’