As to admission for entry by the Swedish citizen upon arrival to a US port by private yacht, the Swede will need to have a B1 / B2 visa issued by the US State Department BEFORE arrival to the USA. No visa, no admittance to the USA.
Entry by private yacht requires B1 / B2 visas and is not subject to the typical ESTA or visa waiver program of arrival by common carrier airlines or
cruise ships.
The Swede should apply for the B1 / B2 non-immigrant visa at the USA embassy in Stockholm, Sweden.
A B1 / B2 visa is NOT applied for or granted from within the USA or upon arrival. It is to be processed in the country of the applicant's citizenship or permanent residence. Obtain one before boarding your boat for the voyage to the USA, or the US territories, USVI, Puerto Rico.
The wait time for an appointment at the US Embassy is Sweden is exceptionally short compared to other countries, presently only 21 business days. It will take additional time to have the visa approval process to be completed after the interview appointment. Some countries the wait time is over a year or even more than two years to obtain the appointed interview.
Obtain the visa well before departure to the USA so that one does not need to return to Sweden to obtain the visa before arriving in the USA.
The Swede will be subject to the normal length of stay criteria of the issued temporary stay visa.
A B-1 / B-2 visa is a non-immigrant visa that allows foreign nationals to travel to the United States temporarily for business (B-1), tourism (B-2), or a mix of both (B1/B2). This visa category is widely used for brief visits to the U.S. B visas are typically valid for up to 10 years from the issue date, and travelers to the U.S.
can stay up to 180 days, with the option to return to the U.S. again after that time.
A maximum of 6 months may be obtained for any B-1 / B-2 entry, with the possibility for extensions within the U.S. in qualifying cases. The exact duration varies per visa holder. Sometimes B1 / B2 visas are issued with shorter than 180 permitted duration of stay, subject to the discretion of the US State Department personnel.
The B1 / B2 visa is a multiple-entry visa, which means you can use it to enter the U.S. more than once.
There’s no set limit to the number of times you can visit the U.S. in a year, and it depends on the specific circumstances and discretion of the CBP officers who review your case each time you enter.
One may be denied reentry particularly if the reentry is a short period of time from one's departure. The reentry allowance loophole is subject to curtailment and is never assured, but residents of Sweden are not considered to be persons that will be likely to overstay their visas, so one can have confidence that if you leave within the visa requirements and then return after a reasonable period of time elsewhere or back in Sweden that you will be well received and welcome back to the States.
It’s important to remember that the B1 / B2 visa is intended for temporary, occasional visits for business, tourism, or
medical treatment. It’s not meant to be used for living long-term in the U.S. or spending the majority of your time in the country.
Depending on the type of nonimmigrant visa you have, you may be able to extend your stay in the U.S. Learn if you qualify and how to file for an extension.
https://www.usa.gov/extend-visa
How to extend your B2 tourist visa
If you are visiting the U.S. as a tourist with a B-2 visa, you may file for an extension with Form I-539. You must also:
Include your original Form I-94, which is the
record of your arrival and departure dates
Explain:
The reason for your request
Why your extended stay would be temporary
What arrangements you have made to depart the U.S.
What effect your extended stay may have on your
employment and residency in your home country
How to extend other nonimmigrant visas
Not all nonimmigrant visa categories are eligible for an extension.
https://www.uscis.gov/visit-the-unit...tend-your-stay
A request for an extension of stay (EOS) is generally filed on a Petition for a Nonimmigrant Worker (Form I-129) or Application to Extend/Change Nonimmigrant Status (Form I-539), depending upon the nonimmigrant classification the petitioner or applicant seeks to extend. The instructions for Form I-539 and Form I-129 provide detailed information regarding who may file each form. Supplemental Information for Application to Extend/Change Nonimmigrant Status (Form I-539A) or Petition for a CNMI-Only Nonimmigrant Transitional Worker (Form I-129CW) may also be filed, where applicable. If you remain in the United States longer than authorized, you may be barred from returning and/or you may be removed (deported) from the United States. Check the date in the lower right-hand corner of your Form I-94, Arrival-Departure
Record, to determine the date your authorized stay expires. We recommend that you apply to extend your stay at least 45 days before your authorized stay expires.
You may apply to extend your stay if:
You were lawfully admitted into the United States with a nonimmigrant visa;
Your nonimmigrant visa status remains valid;
You have not committed any crimes that make you ineligible for a visa;
You have not violated the conditions of your admission; and
Your passport is valid and will remain valid for the duration of your stay.
You may not apply to extend your stay if you were admitted to the United States in the following categories:
Visa Waiver Program;
Crew
member (D nonimmigrant visa);
In transit through the United States (C nonimmigrant visa);
In transit through the United States without a visa (TWOV);
Fiancé(e) of a U.S. citizen or dependent of a fiancé(e) (K nonimmigrant visa); or
Informant (and accompanying family) on terrorism or organized crime (S nonimmigrant visa).
Be sure that your passport is not subject to expiration within 6 months of arrival to the USA. Renew your passport so that it has many years of validity and your visa is honored and not shortened.