Question: Does the CDC have any authority over ships coming in?

Answer passage (source: CDC):
page_title: Cruise Ship Crew Member Disembarkations
section_headers: Frequently Asked Questions
What is CDC doing to ensure cruise lines are adhering to the No Sail Order?
section_content: CDC has provided Interim Guidance for cruise ships during the period of the No Sail
Order to help inform the plans that cruise lines develop to prevent, detect,
contain, and respond to COVID-19 on their ships.
CDC is committed to the safety and well-being of crew members while onboard
and as they disembark. Crew members on ships in or intending to be in US
waters who have questions about the process for disembarkation or who have
concerns about what their ship is doing to prevent COVID-19 onboard can share
their questions or concerns with CDC by sending an email to
eocevent431@cdc.gov
CDC is also reminding all cruise lines in U.S. waters or seeking to operate in
U.S. waters of these requirements. With the assistance of its federal, state,
and local partners, CDC stands ready to direct ships that do not comply to
leave U.S. waters. CDC also reminds cruise ship operators that those who do
not comply may be subject to criminal penalties.

Reviewer feedback on this answer:
Really, only the third paragraph answers the question, that the CDC can direct ships away if they do not comply.
This answers the question fully.  It gives a good level of detail, but it also starts out with a clear and to-the-point answer.

Reviewer ratings:
Acceptable
Excellent

Answer passage (source: CDC):
page_title: Cruise Ship Crew Member Disembarkations
section_headers: Frequently Asked Questions
What is CDC’s legal authority for preventing crew who are U.S. citizens from disembarking cruise ships?
section_content: CDC is using its legal authority under the No Sail Order and 42 CFR 71.31(b),
71.32(b) to stipulate specific conditions for the safe disembarkation of crew
in a manner that will not endanger the public’s health. Having cruise lines
sign a legal attestation is one method of ensuring that these conditions have
been or will be met. CDC is not detaining crew who are U.S. citizens or
preventing them from entering the United States. We are hopeful that more
cruise lines will take the necessary steps to ensure that their crew members
get home safely in a way that will not risk the health and safety of our
communities.

Reviewer feedback on this answer:
The answer states what law authorizes the CDC to control how crew can disembark from ships, which does answer the question, though it does not go into other detail about other ways the CDC could have authority over ships.
This explains more briefly that the CDC has authority over cruise ships.  It is more to the point, but is very clear in its answer.

Reviewer ratings:
Acceptable
Excellent

Answer passage (source: CDC):
page_title: Cruise Ship Crew Member Disembarkations
section_headers: Frequently Asked Questions
Why is CDC requiring that cruise officials sign a legal attestation?
section_content: Requiring a signed attestation helps ensure that the information provided by
cruise officials as a condition of disembarking or transferring crew is
truthful and accurate. By signing the legal attestation documents, cruise line
officials certify that the information they provided to CDC is truthful and
accurate. If the information is not truthful and accurate, these officials are
subject to the criminal penalty provisions of 18 U.S.C. § 1001. It is common
to ask corporate officials in other settings to certify that statements made
to the U.S. Government on behalf of the corporate entity are true and correct,
such as in a Securities and Exchange Commission (SEC) filing or when seeking
payment reimbursement under Medicare.

Reviewer feedback on this answer:
It explains that the CDC does have some authority over cruise ships.  It doesn't get too specific in how the CDC plays a role in validating the attestation documents, but overall it answers the question well.
The answer implies the CDC has authority over ships coming in, but isn't really stating it outright.

Reviewer ratings:
Acceptable
Acceptable