Each fleet contains the number of workers that you have assigned to it, contracts must be paid to each of the workers that are in your fleet, your fleets need to be hired for a minimum of 7 days, but you can also hire them for 15 or even 30 days. Once their contract expires, you must hire them again if you want to be able to go on expeditions.
Your fleets need to be contracted in order to be eligible to attend expeditions. At the same time, it is important to know that it is not possible to dismantle fleets with an active contract.
When trying to add workers to a fleet with an active contract, you must pay the equivalent of the remaining contract days in the fleet to be able to join it. For example, if you have a fleet with 3 active contract days, and you add a new worker, this worker must pay 2.1 WCRUX (3 contract days) in order to join that fleet and be able to go on explorations.
The daily cost of hiring your fleet is 0.7 WCRUX for each worker in it, obtaining a small benefit if you hire it for more days:
All examples are done with Skylight at 2$ for ease of reading.