Actually, the most reliable way to get answers to these questions for
USA waters is to ask the US Coast Guard. They are the controlling
authority and what they say is law. You may argue with them in court
if you like, but they win 100% of their cases so I wouldn't advise
it. At any rate, rule 33 has been changed and the above url is out of
date. See http://www.navcen.uscg.gov/mwv/navru...vrules2003.htm.
You are not required to have a bell on your 50' vessel. It might be a
good idea to print out the pdf of the new rule and keep it in your
rule book.
While the International Rules were changed in 2003, I don't think the
Inland rules have been changed, so a bell is still required. Also, it
would be wise to check the Canadian Inland rules also (though I think
they follow the Intl wording now).