well, we are working the forest right now, so we have +2fpt and +2 hpt. When we grow, we can work the corn for +3fpt or the fish for +2fpt. the workboat will add +3fpt to the fish (making it a 5fpt tile), so we'll actually lose 6f, not 4, by trolling around in the fishing boat if we work the fish tile on growth. If we work the wheat, we'll only lose 4f, but we'll also lose 6g towards the next tech.edit: wheat is on plain, so it's 2fpt/1hpt. Plus, it'll cost 36 food to grow from size 2 to 3, so it could add a few turns (probably 3) to the time it takes to grow, thus compounding the gold loss.
just trying to weigh effect of not getting that food for a few tiles of exploration.
edit2: also, moving the boat will probably be as follows: T1 to fish, T2 2T E, T3 back to fish, T4 cast net. Therefore, we lose 3 turns, not 2, so the food effect is -9f. It think...