Selecting expendable hulls constrained seaplane-carrier conversions

What bottlenecks constrained seaplane-carrier construction in World War I?

The main constraint was choosing a viable hull that was useful enough to convert but expendable in its existing service.

The conversions did not face a specialized industrial bottleneck comparable to later purpose-built carrier construction. Planners instead searched for hulls that were serviceable enough to convert but not so valuable that the war effort would miss them. Older Channel and Isle of Man ferries fit that compromise better than the newest civilian ships. Retired naval constructors could inspect candidates and determine which offered the best conversion value.