Trying to Solve a Problems Taking into Consider
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Problem of the Choice ation the Difference of
of a Vehicle of the Permissible Speed HAULIER and CARRIER 0 NE factor which was not taken into account when making the calculations quoted in the previous article was the proportion of standing and run'fling time. New readers should note that I am discussing the choice of vehicles to replace older types, which are being 'discarded because they are heavy and, therefore, are not so well adapted for operation under the new conditions as are more modern vehicles. In particular, I am keeping in mind the fact that licences under the new Act are awarded on a basis of unladen weight and that new types of machine for a given unladen weight have greater load capacity.
This consideration of the proportion of standing and running time is particularly important in comparing vehicles of medium capacity (those which weigh less than 2i tons unladen and may, therefore, travel at 30 m.p.h.) with larger lorries which are limited to 20 m.p.h. In the previous article I chose as examples a rigid 4-ton six-wheeler of 29 tons unladen weight and a 6-ton fourwheeler of orthodox design.
Acceptance of the factor of terminal delays as being important in connection with the choice of a vehicle at once makes it clear that almost every case must be decided on its merits, for the proportion of running and standing time varies with distance, as well as with the character of the load, and both of these differ according to the class of work. I should point out that I am, in this discussion, leaving out any consideration of cases in which there is a. minimum load. If, for example, the minimum load be six tons, the question as to whether a 4-tonner may be used clearly does not arise.
A 4-ton Six-wheeler or a 6-ton Four-wheeler?
The class of work which must be considered, therefore, is that in which a given tonnage is available for conveyance daily, leaving the choice of the vehicle to the operator, thus allowing him to decide whether he will use a small machine and make a larger number of journeys per day, or a bigger lorry covering fewer journeys. Again I propose to take as examples a 4-ton six-wheeler and a 6-tonner.
A typical example of the class of work to which this problem particularly applies is the haulage of road material, sand and gravel, and the like. In such work, loading often takes place by means of a chute. Some delays usually arise in awaiting a turn at the chute, but the size of the load does not affect the matter to an appreciable extent. An average time of 15-20 minutes usually suffices. This allows for occasional prolonged delays, because 10 minutes are sufficient when no waiting is necessary.
.t■ or the sake of simplicity, I will also assume that the load is to be delivered in one consignment at a building site, or where a new road is being constructed. The time needed for unloading in these circumstances will be about the same as that for loading. The delivery may have to take place over a variety of distances. For the first calculation I will take a lead of 10 miles. This is, I think, a t3ftpical case.
It will be reasonable to take the maximum legal speed as the average. (This, I know, involves exceeding the legal limit a little, but hardly enough to cause trouble.) The time taken for a round journey with the small machine will thus be 70 minutes, comprised of half an hour for terminal delays and 40 minutes' travelling. Probably seven journeys will be completed in a day. The daily mileage will thus be 140 and the ton nage 28. The actual time occupied will be approximately 81 hours.
In a week, 37 round journeys should be completed, which is equivalent to a total of 740 miles and allows of the conveyance of 148 tons. The total cost will be 219 9s. ed., which is equivalent to practically 2s. 8d. per ton.
The e-tonner will take longer over each journey, averaging 20 m.p.h. The time occupied on the round trip will actually be 1 hour, of which half an hour will be spent at terminals. It will thus be pos rible to complete only five journeys per day, without overtime. The daily mileage will be 100 and the tonnage 30. In a week, 27 journeys will be completed, equivalent to total tonnage of 162, 540 miles being covered.
The total cost will be £20 3s. 4d., or 2s. 5d. per ton. For that work the 6-toriner shows to advantage.
Now let us take an example involving a lead of, say, 40 miles, but assuming that loading and unloading occupy 15 minutes each, as before, and that the average-speeds are 30 m.p.h. and 20 m.p.h.
The total time necessary for the smaller machine to complete the round journey will be 3 hrs. 10 tains. It will not, therefore, be possible to cover more than two journeys per day, In the course of a week 11 journeys will be completed, conveying a total tonnage of A Ind covering 880 miles. The total cost will be 222 5s, ed., or 10s. 1d. per ton.
The 6-tanner will need eight hours for travelling alone. It will be able to make only one journey each day and will do nothing on the Saturday. The total mileage during the week will be 400 and the tonnage 30. The total cost will be 216 13s. 4d. per week, or us. ld. per ton, . On long-distance haulage, the smaller machine has the advantage owing to its higher speed. If speeds were the same in both cases the heavier machine must inevitably be the more economical. Hitherto, owing to the legal limitations on speed having been largely ignored, the larger machine has had the advantage, particularly on long-distance haulage. Now, as the speed limits are to be enforced more strictly, there will be a tendency to favour the smaller vehicle.
If the times for loading and unloading be proportional to the weights carried, the difference between the two machines over the short hauls is not so evident. The 4-tonner may be assumed to need 45 minutes for each operation and will thus require 2 hours 10 minutes for a complete round journey. At that rate it will be able to complete only four journeys per day, say 22 in a week, conveying a 'total of 88 tons and covering 440 miles, The cost will be 213 10s., or 3s. ld. per ton.
The 6-tonner will take an hour each for loading and unloading and three hours for the full journey. It may be able just to complete three journeys per day and one on Saturday morning, that giving a total time of 48 hours. The total tonnage per week will amount to 96, for which, as 16 journeys have been made, the distance will be 320 miles, which works out almost to 3s. per ton.
On the long haul the small machine will still be able to complete its two journeys per day and the cost will be as before, 10s, id. per ton.
The larger machine must now obviously be more expensive than before, because, under the previously assumed conditions of loading, it could only just complete one journey per day. Now a certain amount of overtime will be necessary.
In conclusion I should emphasize that the foregoing statement referred only to the cost of operation of the vehicle. S.T.R.