Hauling Big Loads at Minimum Cost
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THE previous article dealt with the relative merits of a tractor and trailer or a solo vehicle of corresponding load capacity, and developed into a straight cost comparison. The outcome was that on cost consideration alone the margin between a rigid eight-wheeler and a four-wheeler and trailer was so small ds to be unworthy of consideration.
The figures for an 800-mile week were £51 4s. 2d. per week for the eight-wheeler and £49 17s. 8d. for the tractor and trailer, showing that the tractor-trailer apparently has the advantage to the extent of £1 6s. 6d. per week.
The alternative to a lorry and trailer might easily be a six-wheeler and would be so if the ,matimum load capacity required did not exceed 12 tons. It seems, therefore, that the next step on the solution of this problem must be the consideration of the cost of the six-wheeled rigid type operating under the same conditions.
Depreciation Calculated First Proceeding along the same lines as previously I take first the primary cost. A good average figure is £2,300. Assuming the tyres to be 36 in. by 8 in. all round, the cost of a set is £200 and deducting that from £2,300 I get £2,100 as the net value of the vehicle. I assume, as in the case of the eight-wheeler, a life of 300,000 miles and take £210 as being the residual value, that is to say the price obtainable for the vehicle second-hand after it has completed that mileage. Deducting £210 from £2,100 I get £1,890 and spreading that over 300,000 miles gives me 1.51d. for depreciation.
As before, I regard that as a basic figure, subject to correction according to the annual mileage, using the formula which provides that for every 2,000 miles per annum that the mileage falls below 50,000 there should be an addition of 5 per cent. to the basic depreciation as calculated.
In this case we are assuming the annual mileage to be 40,000, so that we must add 25 per cent. to that 1.51d. to get the real amount for depreciation. Twenty-five per cent. of 1.51d. is .38d. so that our depreciation is 1.89d., say 1.9d. per mile.
The other item calculated from the first cost is interest and 4 per cent, per annum on £2,300 is £92, which is £1 17s. per week.
The tax, in the case of the six-wheeler, may be a little less than that of the eight-wheeler, say £1 16s. per week. Wages are, as before, £16. Garage rent I take at 12s. Insurance is slightly less, £2 2s. instead of 12 5s. and the interest is as just stated so that the total of standing charges of a six-wheeler is £22 7s. per week.
Now for the running costs. A good average figure for fuel consumption is at the rate of 111 miles per gallon
and at Is. 8d. that is 1.73d. Lubricants I take at 0.2Id. A set of tyres at £200, running 24,000 miles per set, is 2d. per mile. Maintenance, according to "The Commercial Motor" Tables of Operating Costs, is 1.76d. per mile. Depreciation is 1.90d. and the total is 7.60d. per mile.
To get a total weekly cost we multiply 7.6d. by 800, which gives us £25 6s. 8d. Add the standing charges, £22 7s., and we arrive at a total of £47 13s. 8d. per week, compared with the two figures already quoted of £49 17s. 8d. for the vehicle and trailer, a difference of £2 4s. per week in favour of the six-wheeler, and £51 4s. 2d. for the eight-wheeler, which is thus 13 10s. 6d. per week more expensive than the sixwheeler.
The objection may be raised that there is no point in comparing the operating cost of a six-wheeler with an eightwheeler inasmuch as the load capacity is not the same.
Comparison with the vehicle and trailer is, however, permissible since the load capacities in that case might be assumed to be comparable and I will work out a cost per ton-mile on the assumption that the vehicle is always fully loaded. I will take the capacity of the tractor and trailer to be 13 tons in which case, in covering 800 miles, the ton mileage will be 10,400 and the cost per ton-mile, on the figures above quoted, 1.15d.
The six-wheeler with a maximum load capacity of 12 tons will achieve only 9,600 ton-miles in a week and the cost per ton-mile will thus be 1.19d.
Assessing Ton-mileage Costs
The figures are there for anyone raising the point. My own reaction to the situation would be, what is the use of assessing ton-mileage on the basis of 13-ton loads when there will presumably never be a 13-ton load to carry, the maximum being 12 and the load itself being more usually somewhere between 10 and 12. It should be remembered that it is because the load is not to exceed 12 that I suggested taking out figures fur the six-wheeler.
The upshot of this calculation is obviously that unless one of the special reasons for using a trailer, mentioned in the previous article, is present, the rigid six-wheeler is the more economical proposition.
It may now be useful to consider the economics of the
problem assuming some of those special conditions to apply. The one which I would like to take first, arises when a haulier is in the habit of conveying loads regularly for a particular customer, the maximum load as a rule being in the region of 7 tons or 71tons, so that it can be comfortably accommodated on the ordinary maximum load four-wheeler. Occasionally, however, probably as the effect of some seasonal fluctuation in the demand for the commodity carried, the operator is expected to carry loads of from 10 I S
to 12 tons. It was pointed out in the previous article that where those conditions apply it is useful to have the trailer in the background, so as to be able to take the increased load as and when required without bringing another vehicle into service. That was one of the conditions I mentioned as being strongly favourable to the use of a trailer.
I propose to take it that when the vehicle is used solo one man only is engaged; that when the vehicle pulls the trailer a second man travels, but that there is work for him to do otherwise, so that we need to take his wages, etc., into consideration only when he is actually on the vehicle. The first thing to do is to get down to some figures of cost of the solo machine. The simplest and most direct way, having in mind the figures already set out, is to reduce the wage bill of £16 by the wage of the second man, £6 4s. and £1 for subsistence and expenses. That reduces the total of the standing charges from £22 7s. per week to £15 3s. The.other items of standing charges remain the same, for the licence has to be taken out to cover a trailer, so that no reduction in that item can be made. So also with the insurance premium, with the garage rent, and with the interest on first cost. None of these is reduced simply because the trailer is sometimes left at home.
The running costs are likely to be as follow:-Fuel, assuming 13 m.p.g. and Is. 8d. per gallon as before, 1.54d. per mile. Lubricants, 0.18d.; tyres at £120 per set and assuming 24,000 miles per set, 1.20d.; maintenance, 1.41d.; depreciation, 1.90d.
The fact that depreciation is apparently the same as with the six-wheeler is due to the fact that a shorter working life is assumed for this four-wheeler, which is expected fairly frequently to be hauling a trailer.
Running Costs for Solo Vehicle
The total of the running costs is 6.23d., and at 800 miles per week that is equivalent to £20 15s. 4d. per week. Add the £15 3s. for standing charges and we get a total cost of £35 18s. 4d. per week, which is equivalent to 10.8d. per mile.
There is no point in comparing these figures with any that have been given previously. What we have to do now is to link these with the other figures for tractor and trailer to see what the saving in cost is likely to be, as against using a solo six-wheeler all the year round to cater for this traffic. The more the trailer is in use the less chance there is of the vehicle and trailer outfit showing to advantage. There comes a point in the proportion where the two sets of cost figures balance.
It has occurred to me that this point can be determined by one of those simple equation problems we used at school.
Let us work it out in the form of a percentage. The two will become equal when the time the solo vehicle is used multiplied by the cost, plus the time that the vehicle and trailer is used by the cost of the vehicle and trailer is equal to the cost of the six-wheeler for the whole time.
Let us call the percentage of time in which the solo vehicle is used x. In that case the time the chicle and trailer is used is 100 • x. The time the six-wheeler is used is 100.
Comparison of Weekly Costs
Let us recall the figures of cost per week. The solo vehicle, £35 18s. 4d.; cost per week of the vehicle and trailer, £49 17s. 8d.; cost per week of the six-wheeler. £47 13s. 8d.
Now, x multiplied by £35 18s 4d. plus (100 x) multiplied by £49 17s. 8d. will thus be equal to 100 multiplied by €47 I3s. 8d.
I have laboriously worked this equation out (I do not propose to put the details down here), and I have found that if the solo vehicle is used as little as one journey in every six, the cost will be equal to that of using the six-wheeler all the time. Since it is unlikely, under the conditions I have set out, that the trailer will be used anything like so much as that, the conclusion is that in nine cases out of 10 the vehicle and trailer will be the more economical proposition when the trailer used is more or less occasionally and not regularly: that is, always provided that one man only is employed when the solo vehicle is used.
The other case in which I suggested it would be profitable to use a vehiele and trailer is when the conditions are such that on a longish journey the trailer with its load can be dropped to be unloaded, while the vehicle proceeds solo to the end of the journey. In this case two men will be c employed all the time, so that we are not so much concerned with cost figures as with time. .
Assume that the journey is one of 204 miles. It does not matter where the trailer is dropped, but to simplify the following figures I propose to assume that it occurs half way along the journey, that is to say at 102 miles from the start.
First, let us plan the route for the six-wheeler. Assume that the vehicle starts work at 7.30 in the morning and is loaded by 10.30 a.m. From 10.30 a.m. to 1 pin, and from 1.30 p.m. it is travelling and by 5 o'clock has covered 102 miles, where the first stop is made. It takes l hrs. to off-load the 5-6 tons which are to be delivered here. That means that work will be finished at 6.30 p.m. and the driver may run a little further or he may stay where he is for the night. That does not matter. Assume he stays where he is for the night and therefore registers 101 hrs.
Next morning he sets off again at 9.30 a.m. and by 2 p.m. has reached his destination. From 2 p.m. to 4 p.m. the rest of the load is taken off and the total time on that second day is 8 hrs., so that altogether 181 hrs. have been spent on that journey.
Time Schedule for Trailer Work
Now take it that a vehicle and trailer be used. The outfit takes the same time to load, so that if he starts at 7.30 a.m. he is ready to leave at 10.30 a.m. From 10.30 a.m. to 1 p.m. and from 1.30 to 5 p.m., as on the previous day, is the time taken tc; reach the first unloading point, 102 miles away.
It takes a quarter of an hour to drop the trailer, and by 7.15 he has travelled another 30 miles making 132 in all and leaving 72 to be covered the next day.
He does that 72 miles by 11.45 the next morning and has completely off-loaded by 2 p.m., taking altogether 6 hrs. He has taken 11 hrs. the first day, so that the total time for the journey is 17 hrs., showing a saving of 1 hrs.
The story is not quite finished. Some figures are needed to supplement what has already been related. The result is surprising.
What I propose to do is work the cost of the above journey out on the basis of time and mileage charges. The standing charge for both vehicles is the same, namely, £22 7s. per week. Add £5 13s. to that for establishment costs and we get £28 a week, and that was for 52 hrs, It is thus equivalent to 10s. 9d. per hour. The running cost of the .six-wheeler is 7.6d. per mile and for the vehicle and trailer 8.26d. per mile.
The six-wheeler takes 18i •hrs., and that, at 10s. 9d. per hour, is £9 18s. 11d. Add for 204 miles at 7.6d., £6 9s. 2d., and the total is £16 8s. Id.
Little Difference
Now for the vehicle and trailer. It takes only 17 hrs., and that, at 10s. 9d. per hour, is £9 2s. 9d. For the 204 miles at 8.26d, per mile the cost is £7 Os. 5d., so that the total cost is £16 3s. 2d. Again the difference is so slight that I for one would not attempt to justify one against the other.
. The conclusion, after all this, seems to be that the use of the trailer is governed by convenience and conditions alone. So far as cost is concerned there is little to choose between the rigid-type vehicle and the vehicle and trailer. The only exception to this, one already dealt with at some length, is where, for a reasonable proportion of the time, the capacity of the solo four-wheeler is sufficient for the load to be carried and where rarely, or even frequently, there is an extra load which can be put upon a trailer. That is the particular condition under which the trailer shows to great advantage. S.T.R.