For the avoidance of duplication here and hopefully on Flikr and the Facebook group where the question comes up occasionally.
Hull Identification Numbers (HINs) are a structured number identifying the maker of a boat and some other information (see below). It was introduced after the Achilles boats were made and was not mandatory until 1998. Butler would never have had a makers number etc so the boats can not have a formal HIN.At the factory hulls were not generally identified the original sail number being the hull number.
The Google AI description looks to be correct:
A boat's Hull Identification Number (HIN) is a unique 12 or 14-character code that serves as a serial number for the boat, similar to a Vehicle Identification Number (VIN) for a car. It's used to identify the boat and track it for various purposes, including registration, defect notifications, and sales.
Key aspects of a HIN:
Permanent Marking: The HIN is permanently etched or molded into the boat's hull, typically on the starboard side of the transom and also hidden elsewhere on the boat.
Structure: The HIN typically includes a manufacturer's code, a unique serial number, and sometimes details about the year and place of manufacture.
Historical Context: HINs were introduced in the US in 1972 and in the EU in 1998.
Relevance to Recreational Craft Directive (RCD): The RCD requires all boats built after 1998 to have a HIN, which helps in ensuring compliance with safety and environmental standards.
Manufacturer's Identity Code (MIC): For boats built in the UK, the MIC is a unique three-letter code identifying the manufacturer, registered with British Marine.
Uses: HINs are used for registration, tracking recalls, and facilitating boat sales.
My note: usually asked for by insurance companies, the SSR and others but like all vintage boats there is nothing to give.