How is average draft calculated from three draft readings at the same location?

Average draft is calculated by taking multiple draft readings at the same location to obtain a singular representative value that reflects the vessel's draft. The proper method for determining the average draft involves adding together all the draft readings collected and then dividing that sum by the number of readings taken—in this case, three.

By using this method, you ensure that all draft readings contribute equally to the final average, allowing for an accurate representation of the overall draft at that location. This is particularly important in maritime contexts, where variations in draft can signify different vessel conditions such as weight distribution or water levels.

The other choices do not conform to the standard procedure of calculating an average. Taking the highest reading and subtracting the lowest does not provide an average but rather gives a range, which can be useful in some analyses but not for calculating an average draft. Summing all and dividing by two or by six are mathematically incorrect methods for averaging three values, as they misrepresent the proper mathematical relationship necessary for an average. Thus, the methodology of adding all the readings and dividing by three is the correct and standard approach to calculating average draft.