I don’t usually go heavy navy purchases as the CP until Russia falls. Once I have that Russian money and $6 from Moscow every turn then Germany can build a navy to challenge the Allies enough to force UK to buy ships, weakening its position in Africa and the Middle East and keeping its infantry out of mainland Europe.
If it gets to the point where AH or Ottomans can gain naval supremacy in the Mediterranean, the game is just about over, in my experience.