The Ultimate Guide to Choosing Marine propulsion solutions provider

Sep. 01, 2025

5 important things to consider when choosing a propulsion ...

Are you unsure of what technology to aim for in a changing maritime market? Looking to get the most out of your investment and vessel when choosing a propulsion manufacturer?

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There can be some pitfalls and showstoppers when acquiring a propulsion solution today. Designing and purchasing a vessel is a long and complex process of specification, funding, and expectations.

In short, finding the right solution for your operation is not easy. Therefore, in this article we go through 5 important things to consider when choosing a propulsion manufacturer. Some of these are even easy to overlook, so let’s dive in.

What is a propulsion solution?

When you hear the word propulsion it is easy to think only of propellers. And yes, propellers are literally pivotal in when propelling a vessel, but there is much more to propulsion. A propulsion manufacturer will consider not only the propeller, but also multiple other elements that must be tuned to reach the desired performance.

The ship’s hull and correct propeller tunnel
Appendixes, like rudder, brackets, keel, etc.
Gearbox
Main drives, like diesel engines, electric motors, etc.
Control systems
And more..

All these components fall in under the term “Propulsion solution”. What may surprise you is that propulsion manufacturers rarely supply the power systems or solutions for the energy themselves. Propulsion manufacturers should focus on efficiency, regardless of the power-source. The greatest savings are in the energy you do not use, is a saying in the marine industry. Efficiency should always come first.

So, with that in mind and the stage set, let’s go through a non-exhaustive list of things that are important to consider when choosing your propulsion system and their manufacturer. Bear in mind that each point may inform the other in some way, and they may need to be balanced against each other. It all depends on your operation and the vessels intended use.

5 important things to consider

Vessel’s region of operation and expected tasks

Depth is an important factor of geography and area of operation when it comes to a propulsion system. With some specific operational requirements, vessels may have to be able to get all the way into the shallows or even be able to reliably beach to get to those in need. Some CTVs may operate around wind farms on shallow sandbanks and must handle those conditions.

There will of course be exceptions, but if the waters of operation are very shallow, your main option is a waterjet solution. Here most of the mechanics are embedded into the ship, and with no propeller protruding out from the hull. This reduces your vessel’s draft and may affect who is the ideal manufacturer and supplier.

Read more: Why CPPs are the preferred choice for wind farm vessels

Operational profile

Exactly what your vessel will face in operation can be hard to determine, but what must be determined when finding the optimal solution is operational stability or predictability.

Examples:

A ferry going inland will have a very predictable operational profile, going between ports with short stops.
A CTV will have a very different profile, but also predictable. It will go at high intensity between land and installations/rigs, push on the wind mill for crew transfer and later it may loiter for longer periods of time, waiting for crew to return.

These bits of insight determines what the optimal power and propulsion solution is. Should you choose diesel combustion, hybrid or fully electric, and should it be paired with a specific type of propeller or waterjet? Ask a manufacturer. They are after all the experts.

Accepted TCO (Total cost of ownership)

It is not possible to speak of efficiency without talking about your TCO or forecasted OPEX. By large, it revolves around what fuel or energy cost is acceptable, a major part of your OPEX. This again depends on your industry sector, market, and available resources. Some operators may have very low fuel costs, and not focus as much on operational efficiency, while other have clear ambitions and perhaps regulatory/financial guidelines they must follow.

This is also an aspect of the industry and market that is rapidly changing, with an increasing focus on having an efficient operation and vessel.

Read more: The most valuable energy is the one you do not use

Choice of Technology

There is a lot happening in the industry with power technologies. Diesel is still a huge part of the market and can surprisingly be the most efficient and/or green choice, under certain conditions.

For example, if your region or area of operation does not have any electric charging infrastructure, or the energy supplied are coming from fossil fuels, having a hybrid vessel will often mean hauling around many tens of tons of batteries and management systems without the means of charging them at quay. On-board charging has roughly 10% power loss, from feeding electricity to the batteries from your diesel generator, and back out to the electric motors from the battery.

When designing the vessel’s hull lines, it is important with a relationship and communication between the designer and the propeller manufacturer. You must optimize the system with regards for the propeller diameter, propeller tunnel, rudder size, -position and -type. Additionally, the angle of propeller shaft related to the hull base line must be considered.

There is also a time consideration on your delivery. The electric/hybrid market is in high demand, and the major manufacturers have lead times spanning 16 months or more. Demand is high, and manufacturer’s capacity is still growing.

Read more: Efficient Propulsion in a Green Environment, What are the Options?

Manufacturers partners and established service infrastructure

This depends a lot on your region of operation vs. the manufacturer. Having to ship parts and personnel around the world for repairs and service can be a large expense and burden on your operation. Therefore, once you get a clear view of how these points affect each other, it can be recommended to look at the service needs and options for your craft.

Even though your manufacturer of choice does not have a branch in your region, they may have partners and collaborations with other companies that have the capabilities and capacity to take care of your vessel’s need for maintenance through its lifetime.

Conclusion

This is not an exhaustive list of considerations, but some key things we have found can cause friction during your acquisition. These considerations can also affect each other, and some compromises may have to be made. However, the core take away is to holistically look at your vessel, its operation, and your region. It’s a whole comprised of many important parts, just like a propulsion system. And remember; the greatest saving is the energy you do not use.

Marine Engine Selection: Vessel Propulsion System Design

Marine engine selection represents one of the most critical decisions in vessel design, directly impacting operational efficiency, fuel consumption, and regulatory compliance. The engine selection process requires systematic evaluation of vessel characteristics, operational requirements, and performance objectives to achieve optimal propulsion system integration.

Modern vessel design demands comprehensive understanding of hull resistance, propeller characteristics, environmental regulations, and economic considerations. Each vessel type presents unique challenges requiring specific engine solutions that balance power requirements, fuel efficiency, and operational flexibility.

This comprehensive guide examines the complete engine selection methodology, from initial resistance calculations through final regulatory compliance verification, providing essential knowledge for marine engineers, naval architects, and vessel designers.

❕ Important: Engine selection decisions affect vessel performance throughout its operational life. Proper methodology ensures optimal efficiency and regulatory compliance.

FUNDAMENTAL VESSEL CHARACTERISTICS

Vessel dimensions and operational parameters form the foundation for engine selection decisions. Understanding these characteristics enables accurate resistance calculations and appropriate propulsion system sizing for specific vessel applications and operational profiles.

Hull Dimensions and Coefficients

Principal dimensions directly influence resistance characteristics and propulsion requirements through their impact on hull form and operational efficiency.

Critical dimensional parameters:
► Length between perpendiculars (LPP) affects wave-making resistance
► Breadth determines stability and cargo capacity
► Draught influences submerged hull volume
► Block coefficient indicates hull fullness

Block coefficient relationships by vessel type:

Vessel Type

Block Coefficient

Design Speed (knots)

Primary Considerations

Tankers

0.78-0.83

13-17

Maximum cargo capacity

Bulk Carriers

0.75-0.85

12-15

Efficient cargo handling

Container Ships

0.62-0.72

20-23

Schedule reliability

RoRo Vessels

0.55-0.70

18-23

Operational flexibility

Load Conditions and Displacement

Vessel displacement varies significantly between loaded and ballast conditions, affecting resistance characteristics and propulsion requirements throughout operational cycles.

Displacement calculation fundamentals:
► Displacement = Lightweight + Deadweight
► Deadweight includes cargo, fuel, and consumables
► Design displacement determines propeller sizing
► Scantling displacement affects maximum power requirements

Weight distribution ratios provide operational insights:
► Lightweight/Deadweight ratio indicates vessel efficiency
► Container ships: 0.28-0.34 (high cargo density)
► RoRo vessels: 0.6-1.4 (variable cargo density)
► Tankers: 0.13-0.20 (dense liquid cargo)

RESISTANCE ANALYSIS AND CALCULATION

Accurate resistance prediction forms the basis for all subsequent engine selection decisions. Resistance calculations determine the power required to achieve design speed under various operating conditions and environmental factors.

Components of Total Resistance

Total resistance comprises multiple components that vary in importance based on vessel speed and hull characteristics. Understanding these components enables optimization of hull form and propulsion system design for specific operational requirements.

Primary resistance components:
► Frictional resistance (RF): Depends on wetted surface area
► Residual resistance (RR): Wave-making and viscous pressure effects
► Air resistance (RA): Typically 2% of total, up to 10% for high superstructures

Resistance distribution by vessel speed:
► Slow vessels (Fn < 0.15): Friction dominates (70-90%)
► Fast vessels (Fn > 0.17): Wave-making becomes significant
► Container ships: Friction may be only 50% of total resistance
► Speed increase affects resistance exponentially

Froude Number Impact

The Froude number determines the relationship between vessel speed and resistance characteristics, particularly wave-making resistance that increases dramatically above critical values.

Froude number formula: Fn = V / √(g × LWL)

Critical Froude number ranges:
► Fn < 0.15: Friction resistance predominates
► Fn 0.16-0.17: Wave-making resistance begins significant increase
► Fn > 0.2: Wave resistance becomes dominant factor
► Higher Fn requires exponentially more power

❔ Did you know? Increasing vessel length reduces Froude number for given speed, but increases wetted surface area and frictional resistance, requiring optimization balance.

Environmental Factors

Operating conditions significantly affect resistance characteristics and required propulsion power beyond calm water calculations.

Shallow water effects:
► Becomes significant when depth < 10 × draught
► Increases wave system and pressure resistance
► Causes squat effect reducing under-keel clearance
► Requires higher power for same speed

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Weather resistance additions:
► Wave-induced motions increase resistance
► Wind effects on superstructure
► Current and drift considerations
► Sea margin accounts for adverse conditions

PROPULSION SYSTEM REQUIREMENTS

Propulsion system design bridges resistance requirements with engine capabilities through propeller optimization and efficiency considerations. Systematic propulsion analysis ensures optimal power transmission from engine to vessel propulsion.

Propeller Design Considerations

Propeller characteristics directly impact engine selection through power and speed requirements that must match available engine options.

Propeller sizing constraints:
► Maximum diameter limited by draught in ballast condition
► Minimum submersion requirements prevent cavitation
► Number of blades affects efficiency and vibration
► Blade area ratio influences cavitation characteristics

Efficiency factors affecting propulsion:
► Hull efficiency (ηH): Wake and thrust deduction effects
► Open water efficiency (ηO): Propeller design optimization
► Relative rotative efficiency (ηR): Behind-hull flow conditions
► Shaft efficiency (ηS): Transmission losses

Light Propeller Curve Development

The light propeller curve establishes the fundamental power-speed relationship that determines engine sizing requirements for the vessel.

Curve development process:
► Calculate calm water resistance for design condition
► Apply propulsion coefficients and hull efficiency
► Determine propeller characteristics from series data
► Plot power requirements versus shaft speed

Typical propeller design examples:
► 50,000 DWT tanker: 6.8m diameter, 4 blades, 88.2 rpm
► 19,000 TEU container: 10.7m diameter, 5 blades, 76.7 rpm
► RoRo vessel: 6.1m diameter, 4 blades, 117 rpm per shaft

MARGIN CALCULATIONS AND POWER REQUIREMENTS

Propulsion margins account for operational uncertainties and ensure adequate power reserves for varying conditions. Proper margin application prevents under-powered vessels while avoiding excessive engine sizing that increases costs.

Sea Margin Requirements

Sea margin compensates for adverse weather conditions, hull roughness, and propeller fouling that increase resistance above calm water calculations.

Typical sea margin values:
► Tankers and bulk carriers: 15-20%
► Container ships: 20% (schedule critical)
► RoRo vessels: 25% (fixed schedules)
► Factors: route conditions, operational profile, schedule importance

Engine Margin Application

Engine margin provides reserve power for engine degradation over time and ensures adequate power availability throughout vessel life.

Standard engine margins:
► Typical application: 15% above required power
► Accounts for engine deterioration over time
► Provides flexibility for operational variations
► May be reduced for EEDI compliance (12%)

Light Running Margin

Light running margin accounts for increased resistance in heavy weather conditions when vessel operates at reduced displacement.

Light running margin considerations:
► Typical values: 4-7% depending on vessel type
► Lower for slender hulls (container ships: 4%)
► Higher for full hulls in severe weather areas
► Not required for controllable pitch propellers with independent pitch control

Combined margin calculation:
► SMCR = Light propeller power × (1 + SM/100) × (1 + LRM/100) / (1 - EM/100)
► Example: 6,570 kW × 1.15 × 1.05 / 0.85 = 8,900 kW

ENGINE SELECTION METHODOLOGY

Engine selection involves systematic evaluation of available engines against vessel requirements, considering efficiency, costs, and operational characteristics. The selection spiral methodology ensures comprehensive evaluation of all relevant factors.

Engine Layout Diagram Analysis

Engine layout diagrams plot SMCR requirements against available engine options, enabling comparison of different engine configurations.

Layout diagram evaluation:
► Plot SMCR point on engine layout curves
► Compare multiple engine options
► Evaluate derating levels and efficiency
► Consider engine dimensions and weight

Derating considerations:
► More derated engines offer lower fuel consumption
► Higher initial cost and larger dimensions
► Better reliability and longer service life
► Reduced maintenance requirements

Fuel Consumption Optimization

Specific fuel oil consumption (SFOC) varies significantly with engine load and emission control systems, directly impacting operational costs.

SFOC influencing factors:
► Engine load: Optimal efficiency typically 75-85% MCR
► Emission control: EGR vs SCR system selection
► Fuel type: HFO, MGO, or LNG considerations
► Engine size: Larger engines generally more efficient

EcoEGR benefits:
► Reduces Tier II SFOC by 3-5 g/kWh
► Available with existing EGR systems
► No additional urea consumption
► Supports EEDI compliance efforts

Barred Speed Range Considerations

Barred speed ranges require rapid passage to avoid dangerous vibration levels that could damage engine or vessel structures.

BSR management strategies:
► Calculate BSR power margin: (PL - PP)/PP × 100
► Minimum 10% margin recommended
► More cylinders provide better BSR characteristics
► Location relative to SMCR affects passage difficulty

Do ✔ verify BSR margin exceeds 10% minimum
Do ✔ consider cylinder count for BSR characteristics
Do ✔ evaluate BSR location relative to operational speeds
Don't ✘ ignore BSR considerations for engine selection
Don't ✘ assume BSR passage will always be quick
Don't ✘ overlook vibration analysis requirements

REGULATORY COMPLIANCE AND ENVIRONMENTAL CONSIDERATIONS

Modern engine selection must address increasingly stringent environmental regulations affecting NOx emissions, SOx compliance, and energy efficiency requirements. Regulatory compliance often drives final engine selection decisions regardless of other performance factors.

Emission Control Area Requirements

Vessels operating in emission control areas face additional requirements that affect engine and aftertreatment system selection.

NOx ECA compliance options:
► Exhaust Gas Recirculation (EGR) systems
► Selective Catalytic Reduction (SCR) with urea injection
► Dual-fuel engines with natural gas
► Each option affects SFOC and operational costs differently

SOx compliance strategies:
► Scrubber installation for continued HFO use
► Low-sulfur fuel oil consumption
► Cost comparison depends on operational profile
► Installation space and weight considerations

Energy Efficiency Design Index (EEDI)

EEDI requirements limit CO2 emissions per transport work, directly affecting allowable engine power and vessel design.

EEDI calculation factors:
► Main engine power and SFOC at 75% MCR
► Auxiliary engine power consumption
► Reference speed for specific vessel type
► Phase implementation affects required reduction levels

EEDI reduction strategies:
► Power Take-Off (PTO) installation
► EcoEGR for improved SFOC
► Energy saving devices (Kappel propellers, rudder bulbs)
► Alternative fuels (LNG) with lower carbon factors

Minimum Propulsion Power Requirements

MPP regulations ensure vessels maintain adequate power for safe operation in adverse conditions.

Assessment levels:
► Level 1: Simple formula based on DWT
► Level 2: Comparison with similar vessels
► Container ships exempt from current requirements
► May affect EEDI optimization strategies

VESSEL-SPECIFIC SELECTION EXAMPLES

Different vessel types require tailored approaches to engine selection based on their unique operational requirements and constraints. Examining specific examples demonstrates practical application of selection methodology for various vessel categories.

Medium Range Tanker Example

A 50,000 DWT MR tanker demonstrates typical selection process for conventional cargo vessels prioritizing fuel efficiency over speed.

Vessel characteristics:
► Principal dimensions: 185m × 32.2m × 12.8m (scantling)
► Design speed: 14.5 knots (Fn = 0.18)
► Block coefficient: 0.82 (scantling), 0.81 (design)
► Propeller: 6.8m diameter, 4 blades

Power requirements:
► Light propeller curve: 6,570 kW at 88.2 rpm
► Margins: 15% sea, 15% engine, 5% light running
► SMCR: 8,900 kW at 93 rpm
► Selected engine: 7G50ME-C9

Regulatory compliance challenges:
► Initial EEDI: 5.38 (Required: 4.97)
► PTO installation: Improves EEDI to 5.04
► EcoEGR addition: Achieves EEDI of 4.90
► Alternative: Reduce engine margin to 12%

Large Container Vessel Application

A 19,000 TEU container ship illustrates high-power applications with significant electrical loads requiring PTO integration.

Vessel specifications:
► Dimensions: 400m × 58.5m × 16m (scantling)
► Design speed: 21 knots (Fn = 0.175)
► Block coefficient: 0.65 (scantling), 0.63 (design)
► Propeller: 10.7m diameter, 5 blades

High electrical demand:
► Container refrigeration: 6 MW PTO required
► SMCR increased to 52,350 kW for PTO capacity
► Selected engine: 10G95ME-C10-EGRTC
► 3% lower SFOC than 8-cylinder alternative

RoRo Vessel with Alternative Fuels

A 6,000 lane meter RoRo vessel demonstrates controllable pitch propeller applications and LNG fuel benefits for EEDI compliance.

Unique design features:
► Twin CP propellers for maneuverability
► High electrical load from reefer containers
► LNG fuel for emission compliance
► Variable RPM operation with power electronics

Environmental performance:
► EEDI with MDO: 12.19
► EEDI with LNG: 9.42 (23% improvement)
► Required EEDI: 11.23 (Phase 2)
► LNG enables compliance with future Phase 3 requirements

PRACTICAL CONSIDERATIONS FOR ENGINE SELECTION

Beyond theoretical calculations, practical factors significantly influence engine selection decisions and long-term operational success. Considering these practical aspects ensures realistic selection that meets actual operational requirements.

Installation and Space Constraints

Engine room dimensions and vessel layout impose physical constraints that may override theoretical optimization.

Dimensional considerations:
► Engine length affects machinery space arrangement
► Height restrictions in low-profile vessels
► Weight distribution impacts vessel stability
► Access requirements for maintenance

Economic Analysis

Total cost of ownership includes initial purchase, installation, fuel consumption, and maintenance costs over vessel lifetime.

Cost factors:
► CAPEX: Engine cost, installation, modifications
► OPEX: Fuel, lubricants, maintenance, spares
► Lubrication oil consumption increases with cylinder count
► Derated engines offer substantial OPEX savings

Operational Flexibility Requirements

Different vessel operations demand varying levels of propulsion system flexibility and reliability.

Flexibility considerations:
► Fixed vs controllable pitch propellers
► PTO capability for high electrical loads
► Fuel flexibility for global operations
► Maintenance accessibility in remote locations

❔ Did you know? Container ships often require oversized engines to maintain schedule reliability, making fuel efficiency secondary to power availability for schedule recovery.

MARINE ENGINE SELECTION INSIGHTS

Froude number threshold significance: Wave-making resistance increases dramatically above Fn = 0.16-0.17, making length optimization critical for fast vessels to maintain reasonable power requirements.

Block coefficient correlation: Slow vessels (tankers, bulkers) use high block coefficients (0.75-0.85) for maximum cargo capacity, while fast vessels (containers) require low coefficients (0.62-0.72) for wave resistance reduction.

Propulsion margin optimization: Sea margins vary from 15% (protected routes) to 25% (severe weather, schedule-critical), directly impacting engine size and fuel consumption throughout vessel life.

EEDI compliance strategies: PTO installation typically provides the most cost-effective EEDI reduction, improving efficiency while reducing reference speed through power allocation.

Derating efficiency benefits: More derated engines achieve 3-5% lower SFOC at typical operating loads, providing substantial operational cost savings despite higher initial investment.

EcoEGR fuel savings: This technology reduces Tier II SFOC by 3-5 g/kWh without additional consumables, making it attractive for EEDI compliance and operational cost reduction.

Barred speed range management: BSR power margin must exceed 10% for safe passage, with multi-cylinder engines providing better vibration characteristics and faster passage capability.

LNG fuel EEDI advantages: Natural gas fuel provides 23% EEDI improvement over conventional fuel, enabling compliance with future Phase 3 requirements without major design modifications.

Container ship electrical demands: Modern container vessels require 6+ MW PTO capacity for refrigerated containers, necessitating engine sizing above pure propulsion requirements.

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