Steam Locomotive Tenders
By the mid-1800s most steam locomotive tenders consisted of a fuel bunker
(that held coal or wood) surrounded by a "U" shaped (when viewed from the
top) water jacket. The overall shape of the tender was usually rectangular.
The bunker which held the coal was sloped downwards toward the locomotive
providing easier access to the coal.
The ratio of water to fuel capacities of tenders was normally based on
two water-stops to each fuel stop because water was more readily available
than fuel. One pound of coal could turn six pounds of water (0.7 gallons)
to steam. Therefore, tender capacity ratios were normally close to 14
tons of coal per 10,000 gallons of water. One exception to this were the
NYC tenders which were designed to pick up water at speed from track pans.
These tenders had a much larger coal to water ratio.
Other factors which determined the size of tenders were turntable length.
Some railroads bought large locomotives with small tenders so that they
could still be turned on their existing turntables. In many cases, these
tenders were replaced with larger ones as larger turntables became available.
Construction styles also determined tender size. In 1927 the first solid
steel cast tender frame made it possible to attach a single large tank
called a "water bottom". These tenders could hold 1,500 to 2,000 more
gallons of water then previous tenders could.
There were a number of variations of tender design. This page will describe
a few of them.
Typical switch engines spent as much time waiting as they did switching.
They didn't require large tenders. Tenders for such locomotives
were designed with a sloping rear -- reducing the capacity for water,
but allowing better visibility to the rear. The Pennsylvania Railroad
(and many others) had many switchers with slopeback tenders.
Whale Back Tenders
During the early days of Mallet and articulated locomotives, whale-back
(sometimes called "turtle back") tenders were used. Whale back tenders
consisted of two separate tanks (the leading one for oil, the aft one for
water). They had greater capacity than the old square tanks. They looked
like a half cylinder laying on its side. They were some of the ugliest
tenders. Many early Southern Pacific cab-forwards used whale-back tenders.
A round tank has several advantages over a rectangular tank.
- A round tank holds more than a rectangular tank of the same surface area.
- A round tank (a cylinder) is stronger than a rectangular tank (a box).
- A round tank is lighter than a rectangular tank of the same capacity (partially
because a rectangular tank requires a great deal of internal bracing).
On May 31, 1901, a patent was issued to Cornelius Vanderbilt for a tender
with a cylindrical water tank (Cornelius was the great grandson of the
Commodore). Some railroads went for Vanderbilt tenders in a big way.
Others did not. Railroads that adopted the Vanderbilt style tender for
many of their steam locomotives include:
- Baltimore & Ohio
- Canadian National
- Grand Trunk Western
- Great Northern
- Southern Pacific
- Union Pacific
Seven of the B&O T-3 class 4-8-2s, built by the road between 1943 to
1948, were retro fitted with large vanderbilt tenders, mounted on six
wheel trucks. It is conceivable that these tenders were salvaged from
scrapped locomotives. The B&O was a large user of Vanderbilt tenders.
They had some very odd ones which had three four-wheel trucks, rather than
two six-wheel. These may have been applied to 2-8-8-0 engines.
Long Haul Tenders
The PRR made good use of "long haul" tenders. The PRR long haul tenders
generally had two 8-wheel trucks. The T class 4-4-4-4 duplex locomotives
were equipped with Class 180-P-84 tenders that carried 19,200 gallons of
water and 42.5 tons of coal (221 tons total weight). The S-1 class 6-4-4-6
duplex locomotive was equipped with the same class tender but with 24,230
gallons of water and 26 tons of coal capacity.
The AT&SF 2900 Class also used long haul tenders with 8-wheel trucks.
Their tender capacity was 24,000 gallons of water and 7,000 gallons of fuel
The centipede tender was introduced in the late 1930s. What gives this
style of tender its name is the number of wheels it uses. A centipede
tender is rigidly mounted to five axles (ten wheels) which are allowed to
move laterally. There is also a four-wheel leading truck that is able to
swivel, for a grand total of 14 wheels.
This tender is also sometimes referred to as a "pedestal" tender because
of the shape of the frame holding the container -- slightly smaller at the
bottom which had a "pedestal" frame supported by the five rigid axles.
The actual shape of the tank was semi-cylindrical. This design takes
advantage of both rectangular and cylindrical tank shapes, with a rounded top
and bottom of the tank sides maximizing strength and reducing materials
The centipede tenders used on the Big Boys used a Nathan DV-7 mechanical
lubricator that was driven by the stoker engine. It was used to lubricate
various points of friction including the axle bearing box pedestal wear
faces and the front truck center pin. The box for the lubricator and other
related accommodations fit entirely inside the stoker engine compartment.
The Big Boy centipede tenders were designed so that they could haul a 3600
ton train from Ogden to Echo (40 miles) without stopping. This required
24,000 gallons of water and 28 tons of coal. The second series of Big
Boys were equipped with 25,000 gallon/28 ton tenders which were originally
designed for the 1942 Challengers. The difference between the 25-C-1
(nominal 25,000 gallons, C=cylindrical) and the 25-C-2 through 5 tanks was
where the fuel bunker side slope sheet joined the outer skin. With a
sufficient number of photographs one can see that the early tank had that
side slope sheet joining the tank outer skin about 2-feet below the upper
radius of the bunker. On the later tenders that slope sheet joined the
side sheet immediately below the bunker top radius. Adding a little to
the confusion for many about the Big Boy tenders was the fact that 25-C-1
and 25-C-4 tenders were completely interchangeable and were traded between
both groups of Big Boys, for convenience. The rivets used along the top
edge of the slope sheet had a large button head and are fairly easy to
see in photos that were typically taken from a forward angle.
Centipede tenders were used on locomotives that had enormous fuel requirements.
These locomotives included:
- Boston & Maine Mountains
- Denver & Rio Grande L-97 Challengers
- Duluth, Missabe & Iron Range Yellowstone
- Clinchfield E-2, E-3 Challengers
- Great Northern Z-6 Challengers?
- New York Central Niagaras
- New York Central Hudsons (Class J-1a 5266-5274 at times, Class J-3a after 1944, 5426 photo, more photos)
- Northern Pacific A-5 Northerns
- Northern Pacific Z-7 and Z-8 Challengers
- Spokane, Portland & Seattle Z-6 Challengers?
- Union Pacific Big Boy
- Union Pacific Challenger
- Union Pacific FEF-2,3 Series
No Tenders (Tank Locomotives)
Small switch engines that were only operated in a yard close to a fueling
site didn't need a tender. Instead, they carried a "U" shaped water tank
that was draped over the boiler and a small bunker behind the cab for
coal or oil. These were called tank engines. Sometimes the water tank
was split in two and were on either side of the boiler.
A "T" is added to the Whyte system of wheel classifications to denote a
tank locomotive. For example, an 0-6-0 would be a normal switch engine
with a tender. An 0-6-0T would be a switch engine with a "tank" instead
of a tender. Sometimes 0-6-0ST was used. The "ST" stood for Saddle Tank.
Sometimes, a tender was added to a tank engine to provide extra range.
This type of configuration was denoted by 0-6-0T-T.
Forney or "rear tank" type locomotives sometimes went under the designation
of 0-4-4RT. The "RT" of course stood for Rear Tank.
There is another type of tank engine arrangement not typically found on North
American built engines (but very common on European built ones). This would
be a "Well Tank" locomotive. The water was carried in a tank built into
the frame of the locomotive. Usually these were small narrow gauge
switchers. An 0-4-0 example would carry the designation 0-4-0WT. The
popular LGB German 0-4-0 G scale engine is a model of one of these Well Tank
- Saddle Tank Locomotives
- Saddle Tank + Tender Locomotives
- Rear Tank Locomotives
- Well Tank Locomotives
- The Elegance of Edwardian Railways by Geoffrey Williams, Oxford
Publishing Company, 1994
Normally, freight operations required both a head-end brakeman and a
brakeman at the rear of the train. Often, there wasn't a lot of extra room
in the cab. The fireman didn't always like to share his seat with the
brakeman and there wasn't really enough room to stand without getting in
the way of the fireman. By 1937, new locomotives were built with enough
room to seat the head-end brakeman in the cab. Older locomotives were
modified during shopping with a small cabin on the top of the tender for
the head-end brakeman. This was called a "doghouse".
Auxiliary tenders or canteen cars, used to supplement water capacity
on road locomotives and were reasonably common during the steam period.
One of the best examples of their use is behind N&W class A locomotives on
the generally down grade run between Williamson and Portsmouth. The use
of these cars enabled the N&W to bypass two water loading points where
the start would have been made on an upgrade, thus enabling the N&W to
run substantially heavier trains.
Auxiliary tenders are also commonly used in excursion service by today's
surviving steam locomotives. Often, it is only the "mainline" operations
that require them to increase the distance between watering locations.
Sometimes a tender is converted to carry the extra water. In the case
of 3985 and 844, a "Big Blow" tender was converted for this purpose.
The auxiliary tender for the SP&S 700 is from a Great Northern S-2 4-8-4.
It was built to hold 17,500 gallons of water and 5,600 gallons of fuel.