SO30i under a 14m air draft bridge

Giving Google translate a shot before posting in English might get you more responses on this website. Posters here often discuss finer points of language as it pertains to boating, and the language they discuss and use is French.

Sounds like you're going to buy the boat, but need to figure out how to get under the bridge. Most of the time there should be no problem, but you're right to want to err on the side of caution and over-heel the boat to make sure you're always going to clear. 18º is a good bit of heel. Is there a way to observe exactly how much clearance you have when going under the bridge with that much heel? Perhaps you can get by with less. (Our VHF antenna and instruments don't add 2' to our mast's height.) In any case, you may need more than 100 kg out at the end of the boom, and, depending upon the physics, the end of the boom may have to go under water. In that case, you won't be able to use water (in buckets, for example) as counterweights, unless you pull in the boom, which reduces your lever arm and calls for additional weight to achieve the same 18º angle. Powerboat wakes may also knock your careful calculations awry. (You know that with your hull all the way over to one side as you go to heel, they will try to blast by.) It would be a good idea to actually try several different methods before you buy the boat, to make sure one will work. There are videos of people doing what you propose as they cruise down the Intracoastal, but they're specific boats that have obviously planned it all out carefully. It might be simpler to get a tide table and work around the 2-hour window, as you suggest. Safer, too.