Browse Projects > Detailed View

Methodologies for Tugs and Cruise Ships


To estimate propulsion load, certain assumptions are made about the relationship of vessel speed to power; generally, it is assumed that as vessel speed drops, the power demand declines. But for tugs, slower speeds could also indicate increased operating load due to an increase in the number of barges being towed or while docking or undocking larger vessel. On the other hand, vessels equipped with distributive diesel electric systems, such as cruise ships, are able to shut off engines when the vessel is operating at slow speeds to ensure that the remaining engines continue at an optimum load, such that vessel speed and engine operating load is not correlated. The application of distributive power also makes it difficult to differentiating auxiliary and propulsion applications as each engine is a power source for any electrical equipment connected to the vessel’s electrical system whether for propulsion or for auxiliary power. These two cases, tugs and cruise ships require a different approach to estimate fuel consumption and emissions than those developed for other ship types.


To investigate and develop alternative methods to estimate engine operating loads for tugs and cruise ships.


These two vessel types are considered significant emission sources though for different reasons. The U.S. domestic fleet is composed of 5,844 push boats as reported by the USACE in 2017; represent approximately 62% of all U.S. flagged vessels. Unlike larger ocean going vessels that tend to operate out of coastal ports, tugs can be found operating in nearly all navigable waters throughout the U.S. adjacent to waterfront communities. Though there are considerably less cruise ships in operation than tugs, they tend to be equipped with some of the largest marine engines (for example the Symphony of the Seas has a total power of 96,000 kw). Being able to more accurately estimate the operating load for these two vessel types will provided for more accurate fuel consumption and emission estimates.

Related Research:

A search of TRB publications did not identify any research on these topics.


Because the issues related to estimating engine load are different for tugs and cruise ships the approach to develop alternative methods need to be occur in separate phases.

Phase 1 – Tugboat operating load methods

· Assess possible studies or data source that evaluate tug operating loads, volume of cargo moved and direction and magnitude of current.

· Evaluate compiled data to discern operational patterns that could be useful in quantifying engine loads. It may be helpful to team with some tug boat operators to insure that identified patterns are typical.

· Apply the operational patterns identified above into sample AIS data to see if the estimated engine loads seem reasonable.

· Distill the lessons learned in this exercise into a methodology that can be used by others to estimate tug propulsion operating loads.

Phase 2 – Cruise ship operating load methods

· Compile and evaluate existing studies of cruise ship power demand for different phases of their operations (dockside / anchorage, evening cruise, daytime cruise).

· Using the compiled data, develop power profiles for each operational phase – it may be that the engine load can be assumed to be optimum, but the fraction of the total power will change for different operating modes and time of day. It should be helpful to partner with staff from cruise ship lines to ensure that the power profiles are reasonable.

· Apply the power profiles developed above into sample AIS data to see if the estimated power seem reasonable.

· Distill the lessons learned in this exercise into a methodology that can be used by others to estimate cruise ship power demand.

Phase 3 – Dissemination

· Compile the methods into a draft document for external review and submit to reviewers.

· Update draft report based on responses from reviewers.

· Consider posting the final report on TRB website.


Port authorities, cruise lines, towboat companies, international, state, regional and Federal agencies such as the IMO, the U.S. EPA, CARB as well as research institutes, NGOs and consultants may find the development of these methodologies useful in creating future emission inventories.


To better understand local and regional air quality issues, it is critical that accurate emission inventories be developed particularly for communities adjacent to waterways that are regularly used by tugs and cruise ships. This requires a better methodology to quantify tug and cruise ship operating power demand. Such methods would be incredibly valuable to ports, cruise line, tug boat companies, state, regional, national and international agencies as well as scientist and engineers involved in developing marine vessel emission inventories. The provision of more accurate emission estimates allowing for more cost effective prioritization of emission reduction initiatives.

Sponsoring Committee:AW030, Marine Environment
Research Period:12 - 24 months
Research Priority:Medium
RNS Developer:Richard Billings
Source Info:Boyd, Elizabeth and Donald Macpherson, Using Detailed Vessel Operating data to Identify Energy-Saving strategies, ITS 2014 Conference Hamburg, Germany

Den Hertog, Vince; Ken Harford; Robin Stapleton, Raptures: Resolving the Tugboat Energy Equation, Tugnology 2009 Amsterdam, the Netherlands

Guangrong, Zou, Ship energy efficiency technologies – Now and the Future.

Nitonye, Samson; sedum Adumene, Ukpokpo Umorami Howells, Numerical Design and Performance Analysis of a Tug Boat Propulsion System

Waage, Rune; Roald Myhre; Joost van Eijnatten; and Corinna Nones, Wartsila HY TUG Propulsion System 2018
Date Posted:11/01/2020
Date Modified:01/19/2021
Index Terms:Tugboats, Cruise ships, Propulsion, Fuel consumption, Pollutants, Engines, Speed,
Cosponsoring Committees: 
Marine Transportation
Vehicles and Equipment

Please click here if you wish to share information or are aware of any research underway that addresses issues in this research needs statement. The information may be helpful to the sponsoring committee in keeping the statement up-to-date.