Installing prefabricated structure
This is an important step in the building process, and in the sixteenth century it was the biggest prefabricated element made during the construction of a ship. This sturdy structure four meters wide and nearly six meters high should be strong enough to withstand the impact of the Atlantic waves. The great timber that runs from top to bottom in the middle of the structure is the sternpost; the spintles supporting the rudder will be added to it on a later phase.
The lower end of the flat transom is fitted into the notch created by the heel and the sternpost knee. Thick nails one foot long and sturdy iron bolts make sure the union is solid enough.
An improvement in shipbuilding
At the time of the San Juan most ships had a flat transom. However, that wasn't the norm a hundred years before. Back then it was an innovation that would transform shipbuilding. Up until the second half of the 15th century both the front and back ends of a ship were built in quite a similar way. The forward end of the side planks of the hull were nailed to the stem and the back end on the sternpost, the main difference being that the stem was curved and the sternpost was straight.
Creating a flat surface on the back of the ship (called a flat transom) made the construction easier, and the inner volume of the hull became bigger. Having a flat transom was an important improvement for Basque ships that had to go through the Atlantic carrying great loads.
Mounting the flat transom in place
The means available in the 16th century for lifting and putting the flat transom in its precise location were rudimentary: wooden cranes, block and tackle, and the effort of men and oxen. Instead, we will use a modern crane. Just trying to imagine the organizational effort needed to make it the old way makes us –once more– appreciate the skills of the technicians of that era.
More pictures of building process here