Naval treaties based on hull count instead of tonnage

How would naval treaties change if they limited hull numbers rather than tonnage?

Designs would grow to maximize each slot, and the system would suit British procurement habits better than American ones.

Limiting numbers rather than total displacement changes the value of every permitted ship and encourages navies to maximize each hull. The Royal Navy's traditional way of asking Parliament for a number of ships would fit the system more comfortably. The United States would face a less congenial constraint because Congress separately authorizes force structure and appropriates specific construction. A hull-count limit therefore changes both design incentives and the political machinery through which navies seek their fleets.