What is the best tournament format for Cripple Mr Onion?
Totally missed when you gave the link to the rules.  That helped out a bunch.  As I understand it, Cripple Mr. Onion plays out much like Blackjack in that each player bets individually against the dealer.

There is a difference in that the dealer is a player too and the position of dealer is bid for each round.  I don't think that makes a ton of difference to what I'm proposing.

If you end up with 7 or less people you should do one table and one round.  At the end of the time, players are ranked by the number of chips that they have.

If you have more than 7 people you will need 2 rounds.  


Divide the players up into X groups of Y people.  X and Y should both be between 3 and 7 (inclusive).
Split your available time in half, reserve 10 minutes for a break during which the chips will be counted.
At the end of the first time period, the person with the highest chip count at each table will move on to the finals.
For the finals, collect all the chips and redistribute them evenly.  (You don't want someone who had an extremely weak first table having too much of an advantage in the finals)
At the end of the finals, players are ranked by the number of chips that they have.


Example, you have 20 people.  The first round will be 5 tables of 4 people.  The finals will then be one table of 5 people.