The New Zealand Railways Magazine, Volume 2, Issue 5 (September 1, 1927)
A Notable Rail Motor Service
Inaugurated in 1926, the Frankton-Thames night passenger service which leaves Frankton at 10.35 p.m. and returns from Thames at 3.15 a.m., has proved to be one of the most popular trains ever introduced by the Department.
It is notable in more respects than one. First of all it provides one of the very few instances to be found on any railway of what is practically a main line night passenger train service maintained by a rail motor. Usually, when it is found necessary to run a passenger train during the dark hours over a long distance, this important duty is assigned to an ordinary locomotive and train. Only in rare instances, and they are hard to find, can a rail motor be found successfully fulfilling all needs on such a service.
The “Sentinel-Cammell” rail coach which operates on this route owes its origin to the activities of a well-known British firm of steam road wagon manufacturers.
Finding their steam road wagons, of which several thousands are now in use, to be both economical and successful in competing with the petrol driven motor lorry, this enterprising firm did not see why a similar vehicle made to carry passengers should not be built to run on the railway. The “Sentinel-Cammell” rail coach, one of the most successful of modern innovations in railway working, was the outcome of these deductions.
It is only at Christmas and Easter, and during exceptionally busy holiday periods, that the rail motor is replaced by an ordinary engine and car (or cars) and guards' van. This is necessary owing to the popularity of the service, offering as it does quick transit to and from stations on the Thames branch to Auckland city. On the up journey, connection is made at Frankton with the 7.10 a.m. (from Frankton) Wellington to Auckland “Limited,” arriving in Auckland at 9.38 a.m.; in the opposite direction passengers leave Auckland on the 7.45 p.m. Wellington express, arriving at Frankton at 10.24 p.m., the rail motor departing from Frankton at 10.35 p.m. for Thames and intermediate stations. Occasionally, through breakdowns or the need for overhaul, the rail motor is replaced on one or two trips by an ordinary train and locomotive.
It is not surprising, indeed, that any rail motor vehicle, however perfect, should give trouble in such strenuous work-running a double trip of approximately 126 miles every 24 hours, often with capacity loads for a great part of the distance, and with over forty stops to be made en route.
This rail motor, the only one of its kind at present in New Zealand, originally started on the Petone-Wellington suburban run. Owing to the need for all trains to work the track circuit controlling the automatic signalling on the section, the wooden centres of the wheels where removed at the time and replaced by solid steel disc wheels. These are still in use, and may account for the rather bumpy riding experienced when the rail motor is running empty or only partially filled.
In order to economise, the Frankton-Thames night service is run entirely without tablet and signals between these two points. Tablet working is, however, in force for the up train between Hamilton and Frankton. Thus it is possibly one of the best paying passenger trains in New Zealand. The cost of operation is very low, there being no station staffs (with the exception of Hamilton and Thames, at each of which a porter remains on duty, to switch on lights, attend to luggage; and at Hamilton, to operate the level crossing warning bells for the down train, and, at Frankton, where the staff would, in any case, have to be on duty to attend to other trains) required to run the service.
Perhaps at this stage, a few particulars regarding the rail motor will be of interest.
The seating capacity of the rail coach is for 56 passengers; (other types, however, are made which seat considerably more people). The unit is not, as many of the travelling public (to the writer's own knowledge) believe, electrically propelled, but is entirely steamdriven. Why so many people should imagine it to be electrically driven is hard to understand, unless the total absence of the usual boiler, outside cylinders and exterior motion and valve gear, can have some effect in causing the misunderstanding. Strange to say, it is a good fault rather than a bad one. Many elderly and nervous people have expressed great surprise and even regret when told it was a steam driven vehicle they were going to travel on!
As the rail motor is not intended to be run on trains, great saving in weight is effected.page 43
In ordinary coaches much additional dead weight is added solely to provide sufficient strength and resistance to train stresses and shunting shocks. With the self-contained rail motor coach all this is obviated and the complete car can be very light in comparison with the ordinary coach. Springing presented a difficult problem for the builders, low tare weight per passenger making the weight when empty and fully loaded vary as much as 22 per cent., instead of 11 per cent. as in an orthodox railway coach. Spacious windows are provided, and at night electric light is used for both interior and exterior (running lights)on the rail motor.
The driving power is supplied by a patent two cylinder vertical steam engine of the totally enclosed type as used on motor car engines. The only difference, speaking from the laymen's point of view, is that the engine has piston rods and connecting rods, whereas the motor car engine has the connecting rods, coupled up straight to the pistons. Otherwise, the engines are very similar, poppett valves and cams of the usual petrol engine type, being used.
The normal maximum speed of the engine is 500 r. p. m. The drive from the engine to wheels is by chains. One chain on the left hand side of the engine drives on to the leading axle, and a chain from the right hand side of the engine drives on to the second axle.
One of the greatest differences between a “Sentinel-Cammell” rail coach and an ordinary steam-driven rail motor is in the type of boiler used. Usually this would be of the horizontal locomotive pattern; in the “Sentinel” it is a vertical water tube boiler of uncommon design. Firing is performed through a chute in the top of the boiler. The boiler pressure is very much higher than commonly employed on railway work, a steam pressure of 275 lbs. per square inch being used.
Control can be effected from either end. In the case of the rail motor used on the Thames-Frankton service it is not found necessary to use this feature as it is possible to turn the vehicle on the turntables provided at Thames and Frankton respectively.
The cost when new of a “Sentinel-Cammell” steam rail motor coach is approximately £4,000 in New Zealand. The running costs may vary according to the service on which the vehicle is employed, whether hilly country is traversed, and other factors. The running costs of the rail motor employed on the Thames branch may safely be covered by a 1s. a mile inclusive of driver, firemen and guard's wages, which is very low in comparison with a steam locomotive and train of normal type to carry 56 passengers.
In some countries abroad only two men suffice to run one of these rail motors. At first only two men were employed when the vehicle was running on the Petone line. Owing, however, to the need for greater vigilance because of the numerous level crossings and sometimes stray cattle encountered on the Thames branch, a driver and fireman and guard, are now employed.
Second class fares are charged, all tickets issued en route being made out by the guard on P-9 tickets. Small quantities of hand luggage, and bundles of newspapers, notably the “Auckland Star” which was indirectly responsible for the inauguration of the Frankton-Thames rail motor service, are carried.
Checked luggage, bicycles and excess belonging to passengers who may be travelling on the rail motor is not carried, but is forwarded by the first available passenger or mixed train to destination station.
It is interesting, in view of the success of this service, to note the tendency to introduce night trains in the Auckland district. Only recently the Department has introduced a night train to Whangarei, and it is to be hoped this commendable enterprise will meet with equal success.