What does a Lloyd's Register Approval in Principle mean?

A Lloyd's Register Approval in Principle is a formal assessment by the classification society Lloyd's Register confirming that a vessel design or system has been reviewed against applicable safety criteria, in this case under IMO MSC.1/Circ.1455. Voltic Shipping, a Boston-based company spun out of MIT's Ocean Engineering department, holds such an approval for its patented power system used in zero-emission, fully electric retrofits of existing cargo ships.

IMO MSC.1/Circ.1455 is a set of guidelines published by the International Maritime Organization for approving alternative and equivalent designs, meaning systems or arrangements that do not follow a ship's prescriptive regulatory requirements exactly but are shown to provide an equivalent level of safety. This pathway is generally used when a technology or configuration falls outside standard, pre-existing rules, since new categories of equipment do not always have direct prescriptive requirements written for them yet.
An Approval in Principle from a classification society like Lloyd's Register indicates that the society has evaluated the design against this alternative-design framework and found it consistent with the required safety standard. For Voltic, this approval applies to the patented system that adds solar collection area well beyond what a ship's deck can hold, attaching to an existing vessel without replacing legacy infrastructure.