You have to convert some of the workers to thieves, which can be transported by a ship to
en island. Remember to covert them back to workers when they are on the new island. The
thieves can carry goods and bring the goods to the new island.
Hope it helps. :-)

what you do is send some pioneers, thieves and geologists so that you can one, use the
thieves to convert to workers and convert the pioneers to diggers and the geologists to
builders you then build a harbour on both islands and transport some wood and rocks and
maybe some spare tools, should work

http://settlersgang.websettlers.de/walkthroughs.htm

This link will tell you everything you need to know have fun x