Final answer:
Insurers use the deviation clause to avoid penalizing the insured when there is a necessary change in the vessel's course that leads to losses in non-customary waters.
Step-by-step explanation:
The clause insurers use to avoid penalizing the insured when losses occur in waters not normally considered to be the most direct or customary route for the voyage is the deviation clause. This clause provides flexibility for unforeseen or necessary changes in a vessel's course without immediately voiding the insurance contract. Such changes might include avoiding bad weather or hazards, conducting rescue operations, or complying with mandatory shipping route regulations. When a deviation occurs for a reasonable cause, and without the fault of the insured, the insurer remains liable for any loss, despite the variance from the agreed voyage plan.