Replacement of broken parts for a foreign "yachts in transit" is duty free but two customs applications are required: one when the item arrives and another when the yacht leave FP. This “duty free” exemption does not apply to any new items on your vessel only replacement parts, therefore you need to be ready to prove “replacement” when you leave FP although by keeping the old part (I doubt this is rigorously enforced.) This double customs applications also double the charges of the customs brokerage. We have heard of yatchs having to pay a customs agent to come to the boat and observe replaced sails being destroyed. On the other the other hand we personally know two yatchs who recieved new sails without any hassles.
You are allowed to receive goods valued up to $200, including the shipping cost, duty free without requiring any duty or application to customs. Putting your yatch name on the parcel will insure you will not recieve the item without expensive customs agent fees. Using an address which is not a marina may also help avoid having to pay for an agent. We have recieved two parcels this way without requiring an agent.