The information provided is for a 2002 Duffy 18' Classic. Many systems and components are common across models and years.
It is up to you to determine if this information applies to your boat or not.
The original part is a Perko 1310DP0CHR, which uses a 12V double-ended Festoon base bulb (Perko 0071DP0CLR). There are LED replacement bulbs and fixtures, some of which offer the same footprint and fastener spacing.
The stern light is integrated into the stainless steel frame supporing the Duffy canopy and it uses standard parts.