Yours must be a later version as in 1968 they were still listed as Cold moulded Marine ply on Mahogany frames ..... >
The above bein g the Dolphin 20 and 23 as can be seen. The other Dolphin available at that time being the Dolphin 19. Main design difference being that 19 had 2 windows each side of cabin top, the 20 having a long single window each side. The two boats being very similar outwardly apart from this.
Later part of production put to GRP