Shipbuilding is stellar. Marcin Ryngwelski on the Kort nozzle and precision installation at the yard

In modern ship propulsion, every knot matters, and every bit of thrust counts. That’s where solutions like the Kort nozzle come in—a deceptively simple piece of engineering that continues to make a major difference, especially in vessels requiring high maneuverability and pulling power. Put simply, the Kort nozzle is a structural element that enhances the performance of a propeller, particularly at low speeds. It's a concept that has stood the test of time.

Kamil Kusier executive editor 03.08.2025, 14:21 Reading time: 2 min

Kort nozzle around a ship propeller under a red painted hull in a shipyard — dysza Korta fot. Wikimedia Commons

In brief

Marcin Ryngwelski, president of the management board of PGZ Stocznia Wojenna, describes the Kort nozzle as a structural element that supports the propeller and increases its efficiency. The solution was patented in the USA in 1936 by German engineer Ludwig Kort, and propellers in Kort nozzles were used on the vessels ZODIAK and PLANETA built for the Maritime Offices in Szczecin and Gdynia. Assembly takes place in the shipyard's Mechanical Department, and the thruster well must meet tolerances measured in millimetres with components weighing up to several dozen tonnes. A leak test is carried out after assembly.

dysza Korta fot. Wikimedia Commons

Ludwig Kort – the engineer who changed the flow

The invention takes its name from Ludwig Kort, a German engineer who dedicated years to studying hydrodynamics and the efficiency of jet propulsion systems—not only in maritime applications but also in aviation.

In 1936, after extensive research, Kort patented the design in the United States. His idea—to enclose a propeller inside a hydrodynamically optimized nozzle—proved revolutionary. To this day, Kort's name is synonymous with improved propulsion in high-resistance, low-speed maritime operations.

Real-world application: from theory to steel

Though modern vessels increasingly rely on azimuth thrusters and hybrid-electric solutions, the Kort nozzle still has its place—particularly in vessels like tugboats, pushers, and utility ships, where responsiveness and thrust are mission-critical.

A fun fact? Kort nozzle-equipped propellers have been installed on ZODIAK and PLANETA, two state-of-the-art vessels built for the Maritime Offices in Szczecin and Gdynia, Poland. They are used in hydrographic and support roles where precision handling is essential.

Installation at the yard: it’s not just plug-and-play

Installing a propulsion unit with a Kort nozzle is a job for experts—this is precision mechanical work involving multi-ton equipment, tight tolerances (often down to millimeters), and specialized tooling.

At Polish shipyards, these operations are typically handled by the Mechanical Department, often in coordination with third-party specialists. The process starts with a Technology Instruction Manual issued in accordance with the manufacturer's guidelines.

Before installation, the nozzle well ("propeller tunnel") must be perfectly prepared, ensuring exact dimensions and cleanliness. Once mounted, sealing tests are conducted to ensure complete watertightness during operation. There’s no room for leaks—or mistakes—when dealing with main propulsion.

Note: The Kort nozzle is not a standalone element installed separately by the yard. It’s an integrated part of the entire propulsion unit.

Bottom line? Shipbuilding is stellar

The Kort nozzle remains a great example of how legacy engineering can still power the future. In today’s advanced maritime sector, proven solutions continue to earn their place—especially when paired with skilled workmanship, precise installation, and deep domain expertise.

Source: Gazeta Morska · Compiled by: Kamil Kusier