One of the issues raised before has been 'what is an acceptable ratio between dry docks and ships in service for maintenance requirements'? Here is some research on one particular real world case.
The Kaiserliche Marine had grown to be the second largest Navy by 1914. It was built by a collection of private yards with some construction by the three Navy operated yards; Wilhelmshaven Naval Dockyard, Kiel Naval Dockyard and Danzig Naval Dockyard. Of the three Danzig was the smallest and focused on small craft upto cruisers and uboats.
It turns out that all refits, repairs, maintenance, etc. was carried out by the Naval Dockyards, the private yards were only involved in building the ships. From this we can narrow down the proportion of tail to teeth in a modern navy.
By 1914, Wilhelmshaven had a workforce of 11,500, carried out 40 dockings per year and had 8 graving docks, 1 large floating dock, 5 smaller ones and 4 ones for TB. Kiel had a workforce of 10,500, carried out 36 dockings per year and had 6 Graving docks and 2 large floating docks.
In 1914, the KM had 22 pre-Dreadnoughts, 8 Armoured Cruisers , 17 Dreadnoughts and 6 Battlecruisers.
Pairing up 14 graving docks and 53 ships;
3 of the BC had only 2 docks to fit them (both at Wilhelmshaven)
2 of the BC could fit in 5 docks (all at Wilhelmshaven)
the last BC and 17 Dreadnoughts had 7 docks available (all at Wilhelmshaven)
The 30 pre-Dreadnoughts and Armoured Cruisers could fit 8 docks at Wilhelmshaven and 2 at Kiel. The other 4 docks at Kiel were smaller.
The ratios are 3 ships to 1 dock for PD/AC, 2.5 to 1 for BB/BC, 1 to 1 for large BC
On average a dock will handle 5 ships per year. If we made allowance for floating docks perhaps we could suggest that you would need to have 1 drydock available for 4 or 5 ships in your fleet and that this drydock can't be used for construction purposes.
Thoughts?
Cheers,