Acho que você está falando sobre a série Buccaneers por Sheila K. McCullagh.
When Nicholas looks at the picture Great Uncle Jeremy left him, he finds himself climbing through the shining ring to the land of Ramir and the buccaneers on the The Silver Dolphin. Can he help Captain Harken and his crew in their fight against the Dragon Men...?
Eles eram muito curtos, cada volume apenas 60 páginas ímpares.