They used to show their earnings on Patreon. Now it's hidden but it shows you their number of patrons. But you can use waybackmachine.org to view screenshots of their Patreon page before they hid anything. Take the money they were earning then, divide it by the number of patrons then, and multiply it by the number of patrons now.

Now you have the money from their patrons plus ads. That doesn't include the other things they sell through their website or the money they'll be making from their new charter business.

Obviously, this is all before expenses. They've got the boat, family, crew, etc. But they're subtracting from a pretty nice starting place.

All that to say, they never set out with this as the intention. This was all a side effect of following their instincts and taking risks. You can't reverse engineer this kind of success. Just follow your heart without knowing the destination.