WesWorld

Quoted

I think we've only really considered for capital ship to carrier conversions before. Since those were fairly thorough jobs, I think the ruling was you'd figure out the level of refit/reconstruction necessary to make your changes, then apply that cost in resources and time to what you'd already built. After that, you'd have a partial complete carrier, and would just spend the remaining tonnage/time necessary to finish her.

Quoted

Depends on what you're modifying them for, and what point has been reached in their construction. Fairly major arrangement changes shortly after keellaying, for instance, shouldn't require hardly any additional work at all - but after launching anything more than, say, AA armament changes are going to require some serious elbow grease.

Quoted

2.2.5
Incomplete hulls may be converted as an expediency measure in cases of emergencies or when treaty
restrictions make it desirable to do so. The process is nothing more than a reconstruction of the hull that
exists, followed by normal construction of the remainder of the ship in its new form. Possible conversions
include aircraft carriers built from capital ships, cruisers, oilers, seaplane tenders, or cruise liners.
Battlecruisers might be converted to battleships and vice-versa.
To convert the hull, first reconstruct the incomplete hull as described in 2.2.4. Your end-product will be an
incomplete hull of the type of ship you now wish to complete.
To then complete the hull, simply build in materials equal to the light displacement of the completed ship,
minus the light displacement of the incomplete hull. The minimum time to complete is equal to the ship’s
construction time from scratch, minus the length of time spent building the ship’s hull in its old form.
It is reasonable for a player to spend an extra one to six months just planning the conversion, before
undertaking the reconstruction. However, this is left as an option for players with a sense for realism.
Example: An opportunistic signatory of the Treaty has an incomplete battleship hull that will have to be
scrapped if not completed as an aircraft carrier. The battleship’s light displacement was to be 31,000 tons,
and would have taken 40 months to complete. However, she is currently only 25% complete - 10 months of
construction and 7,750 tons of materials so far.
Reconstructing the hull will take 75% of that - 7.5 months, and 5,812.5 tons. The navy now has an
incomplete aircraft carrier hull, with 10 months of construction and 7,750 tons of materials put into her.
As a carrier, the ship will have a light displacement of 25,000 tons and would take 34 months to build from
scratch. Since the reconstructed hull has seen 10 months of construction and 7,750 tons of construction, she
will require just 24 months and 17,250 tons of material to complete.
In total, however, the construction, reconstruction and completion of the ship has taken 41.5 months and
30,812.5 tons of materials.