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Voluntering on board of a cargo ship can be hard as Henning wrote in a comment. On some cargo ships however once can rent a passage. I for instance found this German prospectus with a ship touching Haifa: https://frachtschiffreisen-pfeiffer.de/reisedateien/programm/Pfeiffer-Programm-Suedeuropa.pdf (2nd entry on page 4) If one can join in Haifa or only Hamburg I don't know, you might send them a message. With cargo ships however mind that the routes can change while traveling depending on business needs. Cargo has way higher precedence over passengers.
Volunteering can be simpler on sailing yachts. Find a Crew is a site collecting such offers. Typically however skippers prefer to have people for the complete turn and those are smaller boats, thus it's more likely to become seasick.