Some crews require players to ask permission to board (often abbreviated PTB) before they board a ship. This may be considered a formality, in which case permission will be automatically granted. In other cases, there may be reasons why others might not be welcome on a crew ship. For example, a pillage might be private, or devoted to training a new officer. Ships may also be involved in events and be limited by the event rules as to how many people may be aboard at a time.