Problems of the
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HAULIER and CARRIER IT is worth while, before continuing the consideration of some of the other aspects of trailer use, to translate into figures some of the formulm given in previous articles. Thereby we may gain more direct knowledge of the practical aspects of the subject. In particular, I think it important to stress the advantages of the pneumatic-tyred outfit. The pneumatic tyre is a proved boon and blessing to all branches of transport. In its application to steam wagons, however, it presents the greatest novelty, and readers will naturally be intiested to see how it compares in point
of cost. ,
I should add that its incidental advantages in 'respect of diminution of maintenance expenditure and increased point-to-point speed are already proven in the hands of users. As regards the matter of increased speed, it is worth while, too, to bear in mind that, so far as the steam wagon and -trailer together are concerned, the legal limit for speed under the Road Traffic Act is, in the case of pneumatic-tyred machines, exactly twice' that which is set for solid-tyred vehicles. The actual figures are 16 m.p.h. and 8 m.p.h. respectively.
Overlooking the Speed Limits.
Naturally, of course, the maximum difference in economy will present itself in regard to this permissible increase in speed, and it will be more evident if the conditions be such that the user has strict regard to legal limits. In deference to readers' present belief and current practice, I will in the course of this article ignore the somewhat strict limit in respect of either type of haulage unit and more particularly as regards solid-tyreel machines. .
In conformity with that condition, therefore, I shall assume that the average speeds are its follow :—Solidtyred steam wagon 16 m.p.h. ;solid-tyred steam wegon and trailer 12 m.p.h. Pneumatic-tyred steamer 20 m.p.h. and a pneumatic-tyred wagon and trailer 16 m.p.h.
The formulm for the cost of any particular journey as given in previous articles were 42 + 9.43 M for the wagon alone and SI. + 12.8 M for the combined unit, where M is the total length of the journey,: that es to say, the distance out pins the distance, home. ,This assumes an hour to be necessary as standing time for the steam wagon, that is to say, one hour is presumed to be sufficient for loading,, unloading and Other terminal delays, taking average conditions, whilst le hour is the corresponding period for the steam wagon and trailer.
Applying these formulm to the cases where the vehicle is used for a journey which occupies a whole day, a day's run for the steam wagon alone comprises 130 miles, 65 out and 65 home, and the cost, according to the foregoing formula, is £5 5s. 8d. In an ordinary working day the limit of travel of a solid-tyred steam wagon and trailer is about 90 miles and the cost, according to the formula, is £5 4s. 5d.
• The two amounts, it will be observed, are practically the same. The one machine has delivered a load of 6 tons to a point 65 miles away, whilst the other has conveyed 10 tons for a distance of 45 miles, and bath have returned. The cost per ton-mile is 3.254). in the case of the steam wagon and 2.804). in the case of the steamer and trailer.
Comparing Pneumatic-tyred Units.
Comparing pneumatic-tyred equipment on level terms, that is to say, again ignoring legal limits and assuming average speeds as set out above,the corresponding daily maximum distances are apprwcimately 100 miles and 120 miles. The formulm are somewhat modified, because of the greater average speed being 42 + 8.9 31 for the wagon alone and 81. + 11.7 DI for the wagon and trailer. In each case the total cost for a day's journey is £6 2s. 2d. for the steam wagon and £0 3s. 9d. for the wagon and trailer. In this instance the lorry carries 6 tons for a distance of 80 miles; arid the wagon and trailer conveys 10 tons for..60 miles. The cost per ton-mile is 3.26d. and 2.504). respectively.
Readers should note that, whilst in .the ease of the wagon alone the advantage conferred by the use of pneumatic tyres is not apparent in the cost per ton. mile, it is, nevertheless, markedly evident in that it permits of a greater radius of action.
The pneumatic-tyred steam wagon and trailer," on the _other ,hand, notonly offers the advantage of an increased zone .of operations within the linnts of a working day, but is also less expensive per ton-mile. The actual decision as to whether trailers,,should be used or not should be made according, to the fircumstatices of each case. If the length of haul-be beyond the capacity of the combined outfit, then further argument is needless. If not, the case must be considered On its merits, having particular regard to the-proportion of the journey which is in congested towns, to terminal delays and facilities for manceuvring at loading and unloading points.
The effect of these conditions cannot he calculated, but can be discovered --only as the outcome.of , actual experience. It is also a fact that trailers involve a need for a little more skill on the part of the driver.
An important factor,the effect or which will be demonstrated in the course of the figures and illustrations which are given later in this article, is the-waste of time occurring because the journeys are not of a length conveniently to occupy a full day. In the event of the trips being of awkward length there is sometimes waste because the vehicles return to the. base when it is too early to cease Work, yet too late'to-get out on another -journey. , This dithetilty is experienced more and more as the length of the. journey -increases, and is more evident, ia the case of the trailer combination, owing to the increased terminal delays.
Difficulties Caused at Loading Points.
The intensity of this trouble depends to some extent upon the elasticity of the hours and conditions at the loading and unloading places. If the work be mainly in connection with factories and warehouses which open and close at stipulated times the difficulty is greater.
In what follows I have taken as a basis the tradesunion day of 84 working hours. I have allowed an average of 4 hour per day for getting up steam, leaving 8 hours for working operations. The conditions already stipulated, namely, that one hour should be allowed for loading and unloading a steam wagon, and 14 hour for the same operation in connectibn with a trailer, are again assumed to prevail. As a preliminary I will set out the calculations relating to a lead of five miles, that is to say, involving a complete round journey of twice that distance.
Taking a solid-tyred steam wagon first, with an B38
average speed.of 16 tu.p:h., the,total time for the,round journey is 1 hr. 374 mins. Five complete journeys should occupy 8 hours 74 mins. If we assume thatthis 74 mins. could be made up, then the five journeys could be completed in the day anci.%30 tons .delivered at a cost of f2 18s. id. That is 'equivalent to 23.2d. per ton.
The use of the pneumatic-tyred wagon would not help.matters in this particular case, because the extra 4 m.p.h. would4not enable.another-round journey -to be completedirinside the limit of 8 hours, so that 'the cost;
in that instance would be the same. • If the' lead were of 10 miles the time for a solidtyred steam wagon would be 2i hours. It would, therefore, be possible to do three complete journeys in the first day and load up for the next day, when the .advantage of having the load all ready would permit of four journeys being completed. The work then is carried out at -the equivalent of 31 journeys per -day and the cost is 39.7d. per ton.
Four Journeys Per Day.
With a pneumatic-tyred steam wagon, however, it would be possible to do four journeys each day, thus reducing the cot to 37.6d. per ton.
Figures corresponding to these have been worked out for a variety of mileages, starting‘with a mile lead and running up to 70 miles for the pneumatic-tyred steam wagon. The figures 'for cost and the number of journeys are set out in the accodinanying table.
Further to emphasize some of theaspects to which I have referred, curves for two contrasting types of vehicle have been set out on the accompanying graph. The reader's attention is drawn particularly to the way in which -the cost per ton suddenly increases at the critical times when the number of journeys per day
has to be decreased. S.T.R.