When ranking the worlds most powerful navies we must consider "power projection" (i.e blue water capabilities). For example, the PLAN is the second largest navy in the world behind the US Navy - but China cannot project her naval power beyond on own territorial waters. So can we really consider the PLAN more powerful than navies that can?? No, not really.
Power projection (in naval terms) is the ability to exert force and influence around the world. Currently only 4 navies have that capability - The US Navy, Royal Navy, French Navy and the Russian Navy. These navies are the most powerful navies in the world, especially on the open oceans.
Navies like China, Japan and India however, can only project power on a regional scale and have little to no power or influence on the worlds oceans.
So my ranking would be:
Navies with global power projection
1. USA
----HUGE GAP----
2. UK/France/Russia
3. UK/France/Russia
4. UK/France/Russia
Navies with regional power projection
5. China/Japan
6. China/Japan
7. India/Germany/South Korea
8. India/Germany/South Korea
9. India/Germany/South Korea
10. Australia/Italy
11. Australia/Italy
Other important navies
12. Canada
13. Spain
14. Netherlands
15. Turkey
16. Norway
17. Greece
18. Brazil
19. Belgium
20. Indonesia