In the website of Ministry of Foreign Affairs and Cooperation of Spain it's stated:
Seamen Visa Requirements
Only seamen who are nationals from a country which is required to have a valid visa to enter the Schengen Space need to
apply for a transit visa and if they intend to:
- join a ship that is (or will be) in a Schengen port
- land with the aim of join another ship that is (or will arrive) in a Schengen port
- land due to sickness, repatriation, holiday and so on.
So from the above reference it's clear that with a seamen' Schengen visa one can land in Schengen Area for holidays (tourism).
That being said, you don't need to revoke your Schengen visa, because with a Schengen visa (including the seamen Schengen visa obtained from a Spanish embassy) you can visit all the countries inside Schengen Area (including Germany). The states within Schengen Area are listed below:
Austria, Belgium, Czechia, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Italy, Latvia, Liechtenstein, Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, Slovakia, Slovenia, Spain, Sweden and Switzerland.
Here is the map of all Schengen states from European Commission website: