Harvesting

There are many different models and sizes of combines for harvesting grain and several dif­ferent models and sizes of cotton harvesters. In like manner, there are a number of different machines for harvesting sugarcane. The manufacturers of harvest machines all state that the capacity of their machine (t/hour), averaged over a day’s operation, is dependent on the infield hauling operation, and, in the case of grain and sugarcane, it is also dependent on the cycling of the highway hauling trucks. This is a key point when the performance of a system of equipment is simulated. Capacity of a “middle” unit in the system depends on the “upstream” unit and the “downstream” unit. Often an advantage can be obtained by uncoupling the harvest operation from the infield hauling operation (sometimes not possible) and by uncou­pling the highway hauling from the infield hauling (sometimes not possible). Let us see how this works when we compare the grain, cotton, and sugarcane systems.

A grain combine has an onboard grain tank. When this tank is full, an infield hauling unit (truck, trailer, or wagon) must come alongside so the grain can be unloaded or the combine must stop and wait. An obvious point must be emphasized. Capacity of the most sophisticated (and expensive) combine is 0 t/hour during the period when it is not moving.

The cotton harvester also has some onboard storage capacity. When this chamber is full, a side-dump trailer must come alongside to receive the seed cotton, or the harvester must stop and wait, thus reducing its average capacity (t/hour).

The sugarcane harvester is an even more dramatic example of the linkage between harvest­ing and infield hauling. The sugarcane harvester, like a forage harvester, has no onboard storage. An infield hauling unit must be alongside to catch the harvested material or the harvest operation stops. Cycling of the infield hauling units is the key to sugarcane harvest­ing. Remember that the infield hauling units must be able to dump at the truck loading station in order to cycle back to the harvester. Now there is a direct coupling of the infield hauling and the highway hauling. When all operations are under central control, like with the sugar mill, an inter-connected logistic system like this can be the most efficient option. Unfortunately, there are few locations, other than the sugar industry (Florida, Louisiana, Texas), where it is practical.

It is appropriate to define a “harvesting unit.” This unit is defined as one (or more) harvester(s) and the pieces of equipment needed to haul material at a rate that keeps the harvester(s) moving. Excess infield hauling equipment and over-the-road equipment (each unit spends time waiting for the harvester) is generally not the most cost-effective organiza­tion of the unit. Trade-offs are always used in organizing a unit. In a commercial operation, each piece of equipment will spend some time waiting—scheduling is never perfect. Because the harvester costs more to operate per hour, it is generally best to minimize harvester wait time.

The harvest units described below are given to provide a reference point. They are not offered as an optimum solution.