Complex Naval FAQ
A bug occurs when galleys are lost to the high seas (i.e. not by battle, disbanding, nor by movement or supply attrition). Galleys lost in this way are considered to be lost warships and are reported as such in the ledger for the remainder of the game. Military support for the galleys continues to be paid until the effect is cleared by a save and reload. If a number of warships are still around, maintenance for warships is reduced because a number of warships are considered to no longer exist as far as maintenance is concered. The number of warships considered lost are at most the cumulative number of galleys lost to high seas since the last reload, and no more than the total number of warships possessed at the time the galleys were lost.
So it is possible to reduce naval maintenance of warships and instead pay maintenance for galleys. Build 10 warships and 10 galleys. Lose 10 galleys to high seas. Build 10 more warships and 10 more galleys. Lose 10 more galleys to the high seas. You only pay support for 20 galleys although you actually have 20 warships. If you lost a warship and built a new one, you would pay maintenance for 1 warship and 20 galleys. If you built a warship before one was lost, you would still be paying maintenance for only 20 galleys.