Notes on the relative energy efficiency of ferries, cars, busses and trains

 

There are several ways to calculate fuel efficiency of a transit vehicle. Power can be measured at the engine flywheel, at the propeller or wheels, or as the chemical energy of the fuel consumed. Passenger-miles can make any one of several assumptions about load level or the overhead of deadheading.

 

For this analysis, BTU/passenger mile is based on the chemical energy of the fuel, approximated as 17,500 BTU/lb or 140,000 BTU/gallon for all liquid fuels. For diesel engines, a fuel rate of 0.35 lb/hp-hr is assumed.

 

Passenger loading for a commuter ferry, bus or train is assumed to be 50%, allowing for less then full passenger loads in the commute direction and very low passenger loads in the "reverse commute" direction. Home porting strategies can reduce the number of reverse commute runs, but this is offset by light passenger loading during mid-day service.

 

Single-occupancy car:

7,000 BTU/pax-mile

(assuming 20 MPG and 140,000 BTU/gal)

 

AC Transit Bus:

660 BTU/pax-mile one-way with 56 passengers

1,320 BTU/pax-mile at average 50% load.

(from http://www.watertransit.org/pubs/eir/Section3.13_Energy.pdf)

 

Light Rail

91 BTU/pax-mile, full passenger load

182 BTU/pax-mile, 50% load.

(from http://www.watertransit.org/pubs/eir/Section3.13_Energy.pdf)

 

BART

68 BTU/pax-mile, full passenger load

136 BTU/pax-mile, 50% load

(from http://www.watertransit.org/pubs/eir/Section3.13_Energy.pdf)

 

 

Ferries currently in service between the East Bay and San Francisco

 

"Peralta" - 3200 HP, 26 knots, 331 passengers

2,280 BTU/pax-mile, full passenger load

4,560 BTU/pax-mile, 50% passenger load

 

"Encinal" - 3600 HP, 24 knots, 388 passengers

2,370 BTU/pax-mile, full passenger load

4,740 BTU/pax-mile, 50% passenger load

 

"Bay Breeze" - 1285 HP, 26 knots, 250 passengers

1,210 BTU/pax-mile, full passenger load

2,420 BTU/pax-mile, 50% passenger load

 

"Express II" - 850 HP, 28 knots, 149 passengers

1,250 BTU/pax-mile, full passenger load

2,500 BTU/pax-mile, 50% passenger load

 

 

Historical:

 

Ferry "Berkeley" (1889) - 1250 HP, 12 knots, 1700 passengers

536 BTU/pax-mile, full passenger load

1,072 BTU/pax-mile, 50% passenger load

(assuming fuel rate of 0.5 lb/hp-hr)

 

Proposed:

 

New design based on "Express II" with maximum speed 20 knots:

640 BTU/pax-mile, full passenger load

1,280 BTU/pax-mile, 50% passenger load

(Reducing fuel consumption by square of speed ratio.)

 

 

Specifications for ferries now in East Bay service:

from http://www.ci.alameda.ca.us/home/pdf/f_combined_costplus.pdf

Alameda Oakland Ferry Service

Vessels Peralta Encinal

Built: 2001 1985 (Rehab 2003)
Builder: Nichols Nichols
Material: Aluminum Aluminum
Length: 107.3 Feet 86.4 Feet
Engines: Cummins Detroit Diesel 12V4000
Horsepower: 3200 3600 (Re-power 2003)
Max Speed 26 knots 24 knots
Fuel Usage (1500RPM) 125 Gal/Hr (Total) 125 Gal/Hr (Total)
Passengers: 331 388
Crew: 200 or less Pax 1 Master, 2 deck hands 1 master, 2 deck hands
Crew: 201 or more Pax 1 Master, 3 D/Hs 1 Master, 3 D/Hs
Decks: Two (2) Three (3)
Galley: Yes Yes
ADA Compliant: Yes Yes
Hours Used Per Week: 75 40
Draft: 7 Feet 7.5 Feet
Width 31 2 31 6
Registered Tonnage Gross 96 Gross 99
Market Value (4/1/03) $5.2 million $3.0 Million
Replacement Value $5.5 million $5.0 Million

Alameda Harbor Bay Ferry

Vessels Bay Breeze Express II

Built: 1994 1985 (Rehab 2003)
Builder: Nichols USA Catamarans
Material: Aluminum Aluminum
Length: 82.2 Feet 71.2 Feet
Engines: 2 2
Horsepower: 1285 850
Max Speed 26 knots 28 knots
Fuel Usage (1500RPM) 55 Gal/Hr (Total) 55 Gal/Hr (Total)
Passengers (exc crew): 250 149
Crew: 200 or less Pax 1 Master, 2 deck hands 1 master, 2 deck hands
Crew: 201 or more Pax 1 Master, 3 D/Hs N/A
Decks: Two (2) One (1)
Galley: Yes Yes
ADA Compliant: Yes Yes
Hours Used Per Week: 40 Backup
(current schedule)
Draft: 6.0 Feet 6.0
Width 32.0 22.0
Registered Tonnage Gross 99 Gross 30
Market Value (4/1/03) $2.5 million $1.0 Million
Replacement Value $4.0 million $2.0 Million