Whether or not you need a visa to work on a yacht depends on a number of factors, including the country in which the yacht is registered, the country in which you are a citizen, and the terms of your employment.
In general, if you are a citizen of a country that is a member of the European Union (EU) or the European Economic Area (EEA), you will not need a visa to work on a yacht that is registered in an EU or EEA member state. However, if you are a citizen of a non-EU/EEA country, you may need a visa to work on a yacht that is registered in an EU/EEA member state, depending on the specific laws and regulations that apply.
If the yacht is registered in a country outside of the EU/EEA, the visa requirements will depend on the specific laws and regulations of that country and on your citizenship. Some countries may require all foreign workers, including yacht crew members, to obtain a work visa, while others may have more flexible policies.
It is always a good idea to carefully review the visa requirements that apply to your employment before accepting a position on a yacht, and to ensure that you have the necessary documentation to work legally in the country in which the yacht is registered. If you have any questions or concerns about the visa requirements that apply to your employment, it is a good idea to discuss them with your employer or a maritime lawyer before accepting the position.