Friedrich Krupp Germaniawerft is a minor decision for 
Prussia, 
North German Federation, and 
Germany.
Germania Werft was a German shipbuilding company located at Kiel. Founded by Lloyd Foster in 1867, the idea for this company was to build war and commercial ships. Friedrich Krupp took over the company after the original company went bankrupt. After Krupp took over, the company grew to become one of the most important U-Boat builders. They were dismantled after the end of WWII.
First you'll need to own Kiel (by the start of the game owned by 
Holstein, obviously, then you'll need to research Steel Steamers to enact it. This will give you 50% ship repair and -5% ship build time in Kiel, and also 1 prestige.
There are no downsides to this decision.
Make sure Kiel has naval bases to make the decision more effective.
Ingame description
The Germaniawerft (Ger. Germania Wharf), was a major German shipbuilding wharf in Kiel, North Germany, which was responsible for constructing many of the German U-boats deployed by the German Kriegsmarine during WWI and WWII, as well as Kaiser Wilhelm II's personal yacht. Originally founded as the Norddeutsche Schiffbau-Gesellschaft in 1867, the wharf was bought by renowned German industrialist Friedrich Krupp in 1902, and renamed the Germaniawerft. By constructing the Germaniawerft in Kiel, we can ensure that the Fatherland never lacks the ships it needs.