Matt here is a copy of entry rules.

2 Selection of Teams
2.1 Area Eliminations – There will be Area Eliminations to select the teams that will represent the Areas at the National Championship. The Area Elimination events must not include ineligible teams in the same start or fleet with eligible teams at regattas that are hosting multiple fleets. Elimination events must consist of at least three (3) races and have five (5) or more competitors for its results to be considered valid.
2.2 National Championship, Eligible Teams (20):
a) Area Eliminations (11) – the first place team, or the second or third place team if the first place team is unable to attend, from each of the ten (10) US SAILING Area Elimination events. One (1) additional position is reserved for a second team from the largest participated Area Elimination.
b) Additional Teams (9):
• One representative from the Hobie Class Association, selected by the Hobie Class Association of North Amereica Chair.
• One representative from the classes manufactured by Performance Catamarans/NACRA and selected by Performance Catamarans/NACRA.
• Two representatives from different classes, being the respective class North American Champions. The classes shall be selected by the U.S. Multihull Championship Committee – these are designated the “rotating” class.
• One representative from the Tornado Class, selected by their National Class Representative.
• Three teams selected from Open Petition by the US multihull Championship Committee.
• The returning U.S. Multihull Champion from the prior year.
2.3 Selection Guidelines:
a) Class representatives are encouraged to select their designated representatives according to the following guidelines:
i) Where a Class Association represents multiple one-design classes, their representative(s) should be from their largest class(es).
ii) A current or last year’s National Champion or leader in the class’ national ranking system.
iii) A current or last year’s National runner-up.
iv) A representative deemed suitable by virtue of outstanding sailing accomplishments in that class.
b) The U.S. Multihull Championship Committee shall invite petitions from a double-handed or single-handed one-design or formula class. The Committee may give precedence initially to the classes which:
i) Have the largest participation in Area Eliminations.
ii) Have the largest participation in their most recent national-level event, and
iii) Have a national-level champion or ranked sailor willing and committed to attending this Championship.
In each succeeding year, the committee may rotate the awarding of this invitation amongst the various classes, with the intent to eventually involve all supporting classes directly in this Championship.
c) The U.S. Multihull Championship Committee will evaluate Open Petitions based on completeness, accuracy, and content of a submitted online Petition and Sailing Résumé. Petitions will first be awarded to teams that competed in their Area Elimination. If a petitioning Team did not compete in their Area Elimination, the reason should be explained in the letter of Petition and leniency may be considered.
d) The U.S. Multihull Championship Committee may, after an appropriate registration deadline, fill any vacancies with the second then third place teams from the Area Eliminations in order of the largest attended events and then through additional Open Petitions.
2.4 Once a team has qualified for this event, standings in subsequent qualifying events are void for this selection process. Open Petition may not select previously qualified teams.
2.5 If an Area fails to send a team, the U.S. Multihull Championship Committee shall fill such vacancy with the second or third place team from the Area Elimination with the largest eligible participation, then the next largest, and so on. If no alternate is able to attend, the vacancy shall be filled through Open Petitions of teams that participated in an elimination event and if need be, teams that did not participate in an elimination event.
2.6 Competitors are expected to compete in the area in which they normally race and may only compete in one area qualifier per year. If they cannot make the area qualifier in the area they normally race, they may attend another area qualifier by petitioning the US Multihull Championship committee to do so in advance.
2.7 The U.S. Multihull Championship is open to US Citizens, and permanent residents. Members in good standing of a yacht club that is a member of US Sailing are also eligible to compete. Per US Sailing regulations, the Trophy be not be allowed to leave the continental United States.

3 Alternates and Substitutes
3.1 Once a team’s entry is accepted in any Area Elimination or in the Championship, there may not be any substitution for members of the team except as provided below.
3.2 If a crewmember is unable to attend the Championship or continue in an event in progress due to sickness, accident or other emergency, a replacement crewmember may, with the approval of the Organizing Authority, be substituted for the crewmember for one or more of the races. If the substitution occurs at the Championship, the substituted crewmember must be eligible to compete, and must be of a very close approximate weight to the substituted crew. The representative of the Organizing Authority (typically the Committee Chair) will have the sole responsibility for determining if the reason for the substitution and the proposed crewmember are acceptable.
3.3 If a helmsman is unable to continue an event in progress due to sickness, accident or other emergency, the other crewmember may, with the approval of the Organizing Authority, become helmsman. If a crew with a replacement helmsman wins an event, the team is eligible to advance to the next event with either the original skipper or the replacement helmsman subject to the approval of the Protest Committee of the event just completed or the Organizing Authority.
3.4 It is the expressed intention of the U.S. Multihull Championship Committee to review the results of the Area Eliminations and the eligibility of teams submitting registration to the Championship. Substitution of a team member after the Elimination event must be adequately explained by the qualified helmsman and accepted by the Organizing Authority. “Poaching” of talent after the Elimination event for the purpose (in whole or in part) of relinquishing helmsman responsibilities will not be permitted. This shall be interpreted as the “Anti-Ringer Rule.”