Given a choice of 3 total production tiles in the beginning, say a forest/plain/hill, a forest/plain and a forest/grassland, and choosing to build a workboat first, it makes sense that forgowing food for production will be the best because the quicker you produce the workboat, the quicker you are working a 4 or 5 production tile rather than a 3 production tile. It is true that growing sooner allows another worked tile, and more production, but each extra unimproved tile adds only 1 food or production since you have to feed your citizens. The key is to work the most improved tiles the soonest.
The question with the workboat depends on whether getting the workboat out quicker is worth more than the city growth. Well, you either gotta do the math, or reload the game each way and see how you come at after X# of turns.
Here's the math on epic speed, assuming workboat first, in one case working a 3H tile, and in the other a 2F1H tile. For the 3H case, we will look at both fish and clams, as fish give 1 more food. This difference doesn't matter for the other case, because we will be done with the study when the more slowly built boat finishes. Each case will be broken down at what has been produced at turns 12, 17, 19, and 21, turns when growth happens or a WB is finished. Production is for after the turn is completed.
Case 1, work 2F1H forest grassland tile.
At each turn will have produced:
Turn 12: 24F, 24H
Turn 17: 34F, 34H (grow to size 2, work another 2F1H, resulting in 1 more hammer per turn)
Turn 19: 38F, 40H
Turn 21: 42F, 1H overflow after completing workboat.
Case 2, work 3H, have clams to improve. Will switch to 2F1H on turn 12 as that will be enough to complete the boat.
Turn 12: Complete work boat, 2F, 1H overflow, now working 4F2C tile
Turn 17: 20F, 5H
Turn 19: 28F, 7H
Turn 21: 36F, 9H plus 18C (27 if financial) (grow to size 2)
Case 3, same as above, but have fish.
Turn 12: Complete work boat, 2F, 1H overflow, now working 5F2C tile
Turn 17: 25F, 5H
Turn 19: 35F, 7H (grow to size 2)
Turn 21: 45F, 11H plus 18C (27 if financial)
So if we grow as quick as possible, when the workboat is completed, we are size 2, having produced 42 total food, and have 1 hammer additional production from overflow.
If you make the workboat as fast as possible, and have clams, after the same # of turns, you have 6 less food produced, but have produced 8 more hammers. Since a worker is the likely next build, 8 hammers is definitely better than 6 food. But we have also produced 18 more commerce from working the clams for 9 turns.
It's really a huge difference if you have fish to improve. In the end, you have 3 more food and 10 more hammers. Not to mention the 18 commerce.
It gets more interesting if you have floodplains available to work ... you will grow to size 2 quicker, and be getting some commerce. I'm not going to go into it right now.
But here is something a bit more interesting ... suppose you start with fishing and mining, and can complete BW by the time a worker is built and have plenty of forest around. By far the quickest way to grow the city is to go worker first and then chop for production. If you have enough forests, you can chop until your worker(s) have something else to do. Chop Work boats, chop a warrior, another worker, a settler.