Who you deal with
The natural resources and maritime services directorate handles the flag, technical matters, registration and certification. The national maritime authority and the local captaincies handle surveys and crewing. Operators register with Turismo de Portugal.
At twelve passengers
This is the easiest route on this list. Recreational craft are named outright as an admitted vessel type for maritime-tourist activity, and the EU Declaration of Conformity itself satisfies the survey requirement. What remains is an annual inspection, a tourism plate, and the operator's own licence.
At twenty passengers
If the reading of the crewing provision holds, Portugal stays a light route above twelve as well, which would make it the easiest twenty-passenger market in Europe. If it does not, it becomes a national survey.
Who may drive it
For tourist operation up to twelve people excluding crew, a recreational navigator's certificate appropriate to the vessel type and navigation area is enough. That is a notably light qualification bar for commercial passenger work.
Hiring it out without a crew
Expressly lighter. Recreational craft hired out without a crew observe only the recreational boating regime, not the maritime-tourist regulation.
Where the engine matters
We found no ban and no power cap anywhere in Portugal, which makes it the cleanest propulsion answer on this list. Two caveats we could not verify. The Ria Formosa is a natural park whose own rules will set access and possibly engine conditions, and the Douro is administered by a port authority that conditions the vessel's certificate on an adequate base berth and on AIS.