How about a specific number of supplies per ship? For example 4 for the CV, 3 for the cruiser, and 2 for a destroyer (the first 4 would automatically go to the CV, the 5th would automatically swich to the cruiser). After 15min only the ships that were resupplied respown. Then you would have another 15min to bring the supplies for the other ships, but they would only respown if the task group stays near the port.