As you already told Ricky, you entered the ship and fight the crew.
You have to be clever to defeat the other captain. Use your sword on the rope behind you. The pirate will fall and make the other captain loose his balance. Use your sword on him to kill him and get the MAP.
Use the palm tree on the map to go to the beach. Near the sea is a small ROCK. Pick it up. Use the coconut in the palmtree to let it fall out. The pick up the COCONUTpieces.
Look at the map in your inventory and use the X on the map, in the center of the island. You find Bill there. But no Ricky. Ask Bill about Ricky twice and he’ll tell you what happened. Aks Bill for Ricky’s HAND. Use the hand with the coconut and put both in the water to catch the deadly FISH.
Look at the map again and this time go to the lighter forest, to the left of the X. Look at the little trees. The one on the right might be a bit too big but the little one on the left can be picked up. So take the TREE. Walk to the vines around the tree on the right and use the fish on the vines to eat it’s way through. Once the opening is big enough step through the split tree.
On the other side you find… the X. But how to dig? Take the longer GRASS on the left and use it with the tree. Now tie the rock to the tree with the longer grass and you have a shovel. Use the tree on the X to dig for the treasure. But should you be happy with your find?
Game source: A copy of the game was found here on the internet.