I would just copy one of Cooks voyages. Have your voyages meet the same weather at the same time making the same distances even going the same places.
The goal should be to make money, that was always the goal.
More info can be found here:
Daily Life Abaord Ship in 1700s menu page
Have faith that the oceans are going to rise and flood the world, that plague and pestilence brought on by Climate Change is going to punish us for not believing. Please do as they say it is our only hope. :P