Cut the oranges in half and juice each one. Pour the juice into a jug and set aside.
Scrape the white pith out of the skins and discard. Sit the orange halves on a tray (you may need to cut a little off some of the bases without cutting through the skin to help them sit evenly without wobbling).
Break the jelly into pieces and place in a measuring jug. Pour over boiling water up to the 250ml mark.
Stir in the reserved orange juice along with enough cold water to make it up to 500ml.
Divide the fresh fruit among the orange halves and then pour over the jelly until it almost reaches the top.
Place the tray in the fridge to chill for 3 hours or until the jelly is set.
Before serving, decorate each boat with masts – we used drinking straws – and let the toddlers decorate triangles of paper for the flags.