## Washington State Ferries

by Captain Dan Twohig

I am one of the Deck Officers working for the Washington State Ferries. I am currently assigned to the Wenatchee.

**The following estimates are derived from the “Jumbo Mark II Underway Basic Fuel and Emission Information” report that was put together to support running the ships on two engines vs. three. This data is available in amazingly great detail from the WSF Port Engineer’s office. WSF has saved considerable fuel dollars by shutting down one engine while running across the sound but this original study seems to be focused on maintaining our 18.5 knot cruising speed. We can do better…**

**If you slow a Mark II down from 18.5kts to 16kts while running on two engines, the additional fuel savings can be in excess of two million dollars per year (per ship…). Slowing the boats down to 16kts adds about 3-4 minutes to a 30 minute crossing.**

**I used the following formulas and assumptions to arrive at these figures.**

**A Jumbo Mk II burns 389 gallons/hr at 18.5kts on two engines (165 shaft RPM).
This same ship burns 266 gallons/hr at 16kts on two engines (140 shaft RPM).
This is a fuel savings of 123 gallons per hour.**

**Ships on the Bainbridge run operate an average of 19 hours per day, about 340 days per year. In order to be conservative with these estimated numbers, I used 16 hours per day running time to compensate for in-port time “pushing the dock” for loading, speeding up and slowing down. I realize that the data is available to be more accurate but I am using these estimates for demonstration purposes only. This is a rough analysis. A more comprehensive report can be requested from the WSF Port Engineer’s Office.**

**123 gallons saved per hour X 16 hours/day X 340 days/year = 669,120 gallons/year.**

**At $3.00 per gallon, fuel savings = $2,007,360 per ship, per year.
At $3.25 per gallon, fuel savings = $2,174,640 per ship, per year.
At $3.50 per gallon, fuel savings = $2,341,920 per ship, per year.**

**Although we have no way to predict exactly where fuel prices will go this formula demonstrates that for every $0.25 bump in price, slowing these vessels down to 16kts creates an additional $167, 280 in fuel savings.**

**A Jumbo Mk II produces 8,786lbs of greenhouse gasses and particulates per hour at 18.5kts. The same ship produces only 6000lbs at 16kts. Using the same formula and assumptions as above, this is a reduction of 2,786 lbs of greenhouse pollutants per hour or 17,997,560 lbs per ship, per year.**

**To make this number easier to understand, 17,997,560 lbs/2000 lbs = 8999 MT (Metric Tons) of greenhouse gasses and airborne particulate pollutants not released into the atmosphere of Puget Sound.**

**If we were to slow the ships down to 16kts, have departures from Bainbridge and Seattle every hour on the hour, during non-peak times we would continue to provide the needed commuterservice, make better use of the capacity that we have, save the state millions of dollars per ship per year and reduce the level of pollutants pumped into the atmosphere of Puget Sound by tens of thousands of Metric Tons per year.**

**This savings estimate is just for the Jumbo Mk II class ships . There are three of them (Wenatchee, Tacoma, Puyallup). Multiply the above savings by three then ask yourself, “what data is readily available for the other classes of ferries?”**

As for the accuracy of my numbers, they were derived from a report written by the WSF Port Engineer’s office. My rough fuel savings numbers were designed to be conservative. I am not an engineer and do not have the nuanced statistical mind to verbalize fuel consumption curves while accelerating and decelerating. A more accurate report containing charts and graphs “with circles and arrows and a paragraph on the back of each one” is probably available from WSF but it might not be easily grokked by the layman. The bottom line is that those last two “top-end” knots of speed are very expensive.

**Captain Dan Twohig**