Babington's Treasure Map

Young Timothy Ignatius Merriweather had spent several years in the company of his aging grandfather, who shared the same name.
Some of the stories which he told were quite hair-raising but one of them seemed to stick in young Tim's mind and he often questioned his grandfather for more detail.
It turned out that his grandfather was in the Royal Navy and after beginning as a cabin boy aboard HMS Vertigo, used his promotions to work his way up the navy ladder.
His grandfather told him of his background on that British warship, that had rescued several sailors from a sinking ship and recovered much of the cargo from that ship and because they were unable to carry the bulk of it back to England, some was buried on an island. Some of these secrets are stored in his grandfather's old sea chest.
Young Tim joined the navy as cabin boy too on HMS Vigilant and was instructed to not open the hiding place of the map in the sea chest until his 21st birthday.
An accident at sea caused a lot of damage to the Vigilant, which needed to be moored near the Australian coast, south of where the town of Port Hedland was to be, when a natural disaster destroyed the ship and its crew, except for the cabin boy and his sea chest.
The sea chest held many of the old captain's documents, possibly even some detail of where some treasure was buried. There was always the mention of the telescope case and some secret which it held.
The map recovered from the telescope case was coded and that took a number of years to decipher. All Tim had to do now was follow the directions to find out if his deciphering was accurate.
If all goes well, they can recover the treasure.