What Makes a Ship's Propulsion System Tick? Diesel, LNG and Electric Motors Explained ⚙️🚢

My name is Davide Ramponi, I am 20 years old and currently training as a shipping agent in Hamburg. On my blog, I take you with me on my journey into the exciting world of shipping. I share my knowledge, my experiences, and my progress on the way to becoming an expert in the field of Sale and Purchase – the trade with ships.

When people think of ships, they often picture towering hulls, colorful containers, and endless ocean views. But one of the most fascinating questions usually lies below deck: What actually makes these giants move?

The answer lies in the ship’s propulsion system—a complex network of engines, fuel systems, transmissions, and propellers. While diesel engines have long been the go-to solution, the tides are shifting. With environmental regulations tightening and technology advancing, alternatives like LNG, hydrogen, and electric propulsion are gaining ground.

In this post, we’ll explore what powers ships today, how traditional diesel propulsion compares to modern alternatives, and what innovations are pushing maritime mobility into the future.

The Backbone of Shipping: Traditional Propulsion Systems ⚓

Let’s start with the classic: the diesel engine. It has been the powerhouse of commercial shipping for nearly a century—and for good reason.

🛠️ How Diesel Engines Work

Diesel ship engines operate on the compression ignition principle. Unlike gasoline engines that use a spark plug, diesel fuel ignites when compressed under high pressure.

Here’s a simplified step-by-step:

1. Air is compressed in the engine cylinder, heating it up.

2. Diesel fuel is injected into the hot air.

3. The fuel ignites, causing an explosion.

4. The force drives a piston, which turns a crankshaft.

5. The crankshaft turns the propeller—moving the ship forward.

Diesel engines can be two-stroke or four-stroke, with two-stroke engines preferred for large vessels due to their high power output and efficiency.

✅ Why Diesel is Widespread

• High Energy Density: Diesel fuel packs a lot of energy per liter.

• Reliability: Proven tech with mature support networks worldwide.

• Efficiency: Especially in slow-speed, long-haul operations.

• Range: Ideal for ocean-crossing vessels that need endurance.

From container ships and tankers to bulk carriers and ferries, diesel still dominates global fleets.

Modern Challenges: Emissions and Regulation 🌍

Despite its strengths, diesel propulsion has a major downside: emissions. Diesel engines produce:

• CO₂ (carbon dioxide)

• NOₓ (nitrogen oxides)

• SOₓ (sulphur oxides)

• PM (particulate matter)

To combat this, regulations such as IMO 2020 (sulphur cap) and the upcoming IMO EEXI and CII standards are forcing shipowners to rethink propulsion.

That’s where alternative systems come into play.

Alternative Propulsion: LNG, Hydrogen, and Electricity ⚡💨

Let’s explore the front-runners in future propulsion technology—and how they compare.

1. LNG (Liquefied Natural Gas)

LNG is methane cooled to -162°C, stored as a liquid, and burned in dual-fuel engines or gas turbines.

✅ Pros:

• Lower CO₂ emissions (20–25% less than diesel).

• Near-zero SOₓ and particulate emissions.

• Mature technology with growing infrastructure.

❌ Cons:

• Methane slip (unburned methane escaping into the atmosphere).

• Cryogenic storage requires complex onboard systems.

• Still fossil-based.

🚢 Real-World Example:

CMA CGM Jacques Saadé, one of the world’s largest LNG-powered container ships, runs on dual-fuel engines and complies with strict emission standards across global routes.

2. Hydrogen Propulsion

Hydrogen can be used in fuel cells to generate electricity or combusted directly in engines.

✅ Pros:

• Zero emissions at the point of use (only water vapor from fuel cells).

• Renewable hydrogen (from electrolysis) has major sustainability potential.

❌ Cons:

• Low energy density requires large storage space.

• Production is still energy-intensive and costly.

• Infrastructure is extremely limited.

🚢 Real-World Example:

Hydroville, a passenger ferry in Belgium, uses hydrogen in an internal combustion engine—a small but meaningful step in commercial adoption.

3. Electric Propulsion

Electric systems use batteries or hybrid power (often combining diesel with electric motors).

✅ Pros:

• Quiet, low-vibration operation.

• No emissions at point of use when battery-powered.

• Ideal for short routes and coastal areas.

❌ Cons:

• Limited range and power due to current battery limitations.

• Heavy batteries reduce cargo capacity.

• Requires frequent charging or hybrid configuration.

🚢 Real-World Example:

MS Ampere, a fully electric ferry in Norway, charges between crossings and has cut emissions by over 95% compared to diesel.

Side-by-Side Comparison: Traditional vs. Modern Propulsion 🆚

Feature	Diesel Engines	LNG	Hydrogen	Electric/Battery
Emissions	High	Medium-Low	Very Low	Zero (locally)
Fuel Cost	Moderate	Low to Moderate	High	Low (if grid-connected)
Tech Maturity	High	Medium-High	Low	Medium
Range	Very High	High	Medium-Low	Low
Maintenance	Moderate	Higher	High	Low

Strategic Outlook: Which Propulsion Suits What?

Each system has its strengths—and its ideal application.

• Diesel: Still the best for long-haul transoceanic shipping with current fuel logistics.

• LNG: Suited for large vessels operating in emission-controlled areas (ECAs).

• Hydrogen: Promising for ferries, cruise ships, and regional services—once infrastructure improves.

• Electric: Ideal for short-distance, frequent-stop routes like fjord ferries or harbor vessels.

💡 Tip: Some future ships will likely combine multiple systems in hybrid setups to optimize performance and sustainability.

How the Industry is Adapting ⚙️🚀

Maritime propulsion is in a state of transition—driven by innovation and regulation. Here's what we're seeing:

🔧 Shipbuilders

Designing dual-fuel and flexible propulsion systems to accommodate future retrofits.

🌐 Port Authorities

Investing in shore power and LNG bunkering infrastructure to support clean energy.

🧠 Shipowners

Exploring retrofitting programs and green financing to upgrade propulsion systems sustainably.

Conclusion: The Future is Propelled by Choice 🌊

Ship propulsion is no longer a one-size-fits-all decision. Between tightening environmental rules and a fast-evolving energy landscape, choosing the right propulsion system is both a technical and strategic challenge.

Here’s what we’ve covered:

• Diesel engines still dominate for their reliability and efficiency—but have high emissions.

• LNG and electric motors are leading the shift toward cleaner operations.

• Hydrogen is a powerful wildcard with potential—but needs infrastructure.

• Each system has its place in a diversified and sustainable maritime future.

🌟 Whether you're planning a newbuild, managing a fleet, or just curious about what drives a ship—understanding propulsion is key to understanding the industry itself.

Which propulsion technology do you find most promising? Are you working on or sailing a vessel with alternative power?

💬 Share your experiences and thoughts in the comments—I look forward to the exchange!

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