Where to start depends on our goal. If trying to determine the travel time between two places, follow the steps outlined in “Ship Speeds.” You’ll need to decide on the distance first, then whether the trip is along a coast, the open ocean, or both. Then consider what sort of issues you’d like characters to face on the journey. You may need to slow them or accelerate their travel based on story needs. If trying to decide what weaponry or personnel ships have on your world, the sections on this will assist a decision. The section on ship types will help you determine the style of vessel you want, but when it comes to rated ships, it’s largely immaterial which you choose unless you intend two or more ships to go to war with each other.