Machines fail, and on an island the failure costs you a day of a whole crew rather than a day of a machine.
So the rule is simple. A machine that stops through no fault of the site is not charged for that day, and we get a replacement onto the next barge at our cost. A mechanic travels with anything over thirteen tonnes on a job longer than a fortnight.
If a machine stopped because it was worked outside what the quotation described, we will say so with the site diary open rather than send a bill and hope. That has happened four times in nine years and three of them were settled in the customer's favour.