Are you paying for machine days you never use?
Put in the machines, the hire rates and the driver limit and get back the cheapest fleet plan. Four machine types, a hire desk that only sells whole weeks, and not enough drivers for the fleet you own. The plan every plant manager starts from buys ten days of machine it never uses.
Construction Intermediate Optimization free
After you install, this is the model to open.
Which Plant Do We Hire and Which Do We Own?
- In your spreadsheet, click the Sortia icon in the strip of icons down the right-hand edge. No strip? Click the arrow at the bottom-right to open it. You can also use Extensions, then Sortia, then Open Sortia.
- Click Start from a template and put that name in the search box.
- Pick the card with that name and click Load this template. It arrives on a new tab with real numbers already in it.
The answer
- The optimized month
- $46,425 against $49,370 for own-kit-first
- Saved
- $2,945 same 70 operator-days, redeployed
- Days paid for twice
- 10 the hand plan covered 150 days of a 140-day need
- Coverage after
- Exact 44, 20, 60 and 16 days, nothing spare
Four machines, a month of 22 working days, and two limits that fight each other. Hire comes in whole weeks with a driver, so a week is five days whether you use five or two. Your own machines are cheaper a day, but every own day burns one of the 70 operator-days your drivers can cover. The sheet opens on the plan every plant manager starts from: use all your own kit, then hire the rest.
That is 22 excavator days, 44 dumper days and 4 roller days, plus five weeks of excavator hire, four of dozer, four of dumper and three of roller, and it costs $49,370. Click Run and the optimizer returns $46,425, saving $2,945, and the way it does it is worth reading carefully. Every machine in the optimized plan is covered exactly: 44 days of excavator, 20 of dozer, 60 of dumper, 16 of roller, no waste anywhere.
The opening plan covered 47, 20, 64 and 19, so it had bought ten days of plant nobody was going to use. That is what a minimum hire period does to a plan built by hand: you use your own kit first, discover a shortfall, round it up to whole weeks, and the rounding lands on top of the days you already owned. The optimizer works the other way round.
It parks three of your own excavator days and four dumper days, because the hired weeks on those machines already cover those days and a second machine standing on the same day saves nothing while costing $385 and $240. Then it puts the seven operator-days that freed up onto the roller, taking it from 4 own days to 11 and retiring two whole hire weeks.
The driver count never changes: 70 operator-days in, 70 operator-days out, redeployed. The general rule is that with a minimum hire period your own kit is only worth running up to the point where the hired weeks are full, and the way to find money is to look for machines where you are paying twice for the same day. Two second runs. Drop the excavator requirement from 44 days to 42, which is one small resequence in the programme, and the fifth hire week disappears and the month falls to $45,230, so two days of float were worth $1,195.
Then raise the operator pool from 70 to 80: the month falls only to $46,325 and the plan uses 75 of the 80, so an operator-day is worth about $20 here and the drivers are not what is costing you money this month. What the model leaves out is the standing cost of owning the machines, deliberately, because it is the same whatever you decide this month and putting it in would push you toward running kit you should leave parked.
Replace the four rows with your own fleet, put your true running cost in the own-cost column and your hire desk's rate in the hire-cost column, and change the 5 in the days-covered formula if your minimum hire is a fortnight.
The model
It arrives on a tab called Template: Own It or Hire It, carrying these columns:
- Days needed this month
- Own days used
- Weeks hired
- Own days available
- Own cost a day ($)
- Hire cost a week ($)
- Days short
with the model computed beside the data:
| Operator days used | 70 |
| Operator days spare | 0 |
| Own running cost ($) | 19,870 |
| Hire cost ($) | 29,500 |
| Total plant cost this month ($) | 49,370 |
Once it is in your sheet
- The model arrives with real numbers in it and runs as it stands, so you can press the button first and understand it second.
- Change the numbers to yours. The sheet marks which cells are inputs and which hold formulas, and most labels carry a note explaining the row.
- Press the run button at the bottom of the panel. It is labeled for the tool you are in, and the result lands on its own tab, with a written reading of it beside the figures.
Never used Google Sheets? Start here goes the whole way, in seven steps, and assumes nothing.
Next question
- Which tenders should you not price at all?Score the Sites Before You Bid
- Do rain days really cost you money?What Moves With Cost on This Job?
- Is one estimator quietly pricing higher than the other?Do Our Two Estimators Price the Same Job the Same Way?
- What will a tonne of steel cost you next month?Where Is This Material Price Going?
- How much contingency does the job need before the budget holds nine times in ten?What contingency gives 90% odds of staying under budget?
- What happens to the reserve when costs rise together?Will the Contingency Last?
Every model like this one, and the method behind them: Optimization in Google Sheets.