October 21^st , Arlington, VA - Dominic Cusanelli, Naval Architect at Naval Surface Warfare Center - Carderock Division has been promoting the installation of a simple device known as a "Stern Flap" for ocean going vessels.  The flap is a relatively small plate extending off the back (aft) of the ship's hull.  Stern flaps are designed to reduce the power required to propel a ship through water. 

Cusanelli says the stern flap is a ship design many naval architects are finally taking a close look at.  The advantages are significant fuel savings and in turn direct reduction in air borne pollutants such as carbon dioxide CQ₂ nitrogen oxides NO_x sulfurous oxides SO_x and particulate matter.

Speaking to naval engineers and shippers at the ASNE Marine Environmental Stewardship Seminar on October 21^st, Cusanelli detailed stern flap modifications made on a number of naval combatant vessels.  He described the flaps as plates affixed at the transom above the propellers, not unlike a mini-platform that one could stand on, but below the water line.  They run the width of the transom and extend out the length of about 1% beyond the ship's hull.  The stern flap on one 530' destroyer runs 34' along the hull and protrudes out about 5.3'. 

Cusanelli says the flaps work by affecting afterbody flow rates and pressure under the hull, and by modifying the trailing wave systems.  Complex details about actual hydrodynamics are available.  Basically, the flaps reduce drag so that the engines do not have to work as hard for the same output of energy.

Studies show the stern flaps on one vessel saved 3,650 barrels of fuel in a single year.  This amounts to a fuel savings of about $135,000 for only one vessel.  The EPA was so impressed with stern flaps, the design was given a 1998 EPA Climate Protection Award for "Technical Breakthroughs in Ship Energy Efficiency."

Nine stern flap modifications are currently operating on US and Australian navy ships.  Cusanelli's group estimates an annual savings in CO₂ emissions of over 500 tons/year from just these nine applications.  Other hazardous emissions such as NOx are reduced by over 30 tons/year and SOx by over 16 tons/year.  Future installations, if approved and funded, for about 140 additional ships would save close to 200,000 tons of CO₂ emissions each year such ships would operate.

Stern Flaps on Merchant Vessels

Working with Cusanelli at NSWCCD, Gabor Kavafiath told CQD that future modifications to merchant vessels could result in similar achievements as those found with combatant vessels.  However, flap design must be modified to suit the typical performance characteristics of the vessel's trade.

For instance, stern flaps on navy ships are designed for ships traveling at consistently high speeds, approaching 30 knots.  Large merchant ships however typically operate at lower speeds, say 12-15 knots.  Kavafiath and Cusanelli believe stern flaps can be designed to optimize engine performance at the lower speeds, resulting in fuel savings and reduced airborne emissions.

The most likely candidates, according to Cusanelli, are fleets operating pre-specified trade route.  A consistent operating program better enables naval architects to design an optimal stern flap for each particular vessel.  An owner that knows his vessels will be cruising a set number of hours per year will benefit most since the flaps will be installed based on the most likely cruising speed.

Stern flaps are relatively simple and inexpensive to install.  Most of the vessels found the installations paid for themselves in fuel savings within a 1-2 year period, says Cusanelli.  Best of all, this modification is both economically and environmentally beneficial.  With increasing worldwide attention on ship pollutant emissions, it is great to see a simple technology that combines fuel savings with environmental cleanliness. 

Green Ship Workshop in Nova Scotia
December 9^th and 10^th, 1999, Halifax, Canada
by Jack Cole, Director, Environmental Services Canadian Coast Guard

In recent years the Canadian Coast Guard (CCG) has embarked upon several initiatives to demonstrate its commitment to safe and environmentally responsible use of Canada's waters.  These efforts relate directly to CCG's mission "to lead the way in marine safety, service and protection of the marine environment".

In support of this commitment, CCG is holding a workshop inviting participants to explore the development and promotion of a voluntary "green Ship" designation for North American vessels.  This event will take place December 9 ^th and 10^th 1999, in Halifax, Nova Scotia, Canada.

The workshop is meant to provide a forum for shipping agencies to exchange their experiences with environmental issues, to discuss the possibility of developing a Green Ship designation, and to discuss the components of such a designation.  Shipping organizations typically operate their vessels in an environmentally responsible manner.  This workshop will examine how much further we should go in this direction and what would be the costs and benefits of doing so.  We hope to provide an answer to the question "How Green should we be?".

We have already contacted several shipping organizations in North America (BC Ferries, USCG ( Canadian Navy, US Navy etc.) that expressed great interest in participating in this workshop.  We believe that the results from the meeting can bring benefits to both the shipping business and the marine environment and ultimately lead to more environmentally responsible marine transportation.