Reading the grade
As with the modern scheme, the key limits that defined a grade were gross tonnage and propulsion power (in kilowatts). A lower grade authorised smaller yachts and lower power; each step up extended the tonnage and power the holder could take charge of, and moved from an operator role toward officer-of-the-watch and then chief-engineer responsibility. Knowing a holder's grade tells you the size of vessel and the level of responsibility they were certified for — which is exactly how any engineering certificate, legacy or modern, is read.
TIP — Tonnage and kW are the key When comparing any engineering certificate — legacy or modern — look first at the gross-tonnage and kW limits and whether it is an operator, watchkeeping or chief-engineer grade. Those three facts place almost any ticket.
NOTE — The same logic as the modern scheme The Y-series was structured by tonnage, power and responsibility — exactly the logic of the modern SV scheme (MEOL(SV), SV EOOW, SV Chief <500 and <3000). That parallel is what makes the mapping between them possible.