It wasn’t just the caravel that allowed the Portuguese to take their ships around the Cape of Good Hope. When it comes to traveling, it’s not enough to have an appropriate means of transportation. You have to either know, or have the ability to figure out where you are at, and how you plan on getting to where you wish to be,
Navigators of the world, specifically nautical ones, relied upon an item called the mariner’s astrolabe. This item could and can help measure the distance of objects off of the horizon, things such as Polaris, the moon, and other celestial items in the sky, Based off of the planispheric astrolabe, its purpose was to, through the use of charts, tables, and triangulations, determine where one was at in relation to a map of some sort.
Getting an astrolabe to be effective on a ship, what with its rolling decks and unstable bases, was a bit of a trick. This is the first area where the Portuguese come into the picture, for it was an unknown mariner who determined that if you held the astrolabe from the top, and pointed it out to the horizon, it wasn’t necessary to place it upon firm ground. From there, they could then swivel a connected plane (called an alidade) at the celestial item and then determine the degrees from which it existed from the horizon.
But this wasn’t the only things that the Portuguese did. As odd as it sounds, they were the first to make an astrolabe out of metal. This was rather important, because this did two things.
One, it gave more precise measurements. Wood, which was the material used before metal, has a propensity to do three things – expand, contract, and…well, I’ll hold on to the third thing for a moment. Materials that expand and contract give inexact measurements. Metals, (which expand and contract at a much lesser degree than wood) could be relied upon to give better measurements, and thus give the mariner a much better idea upon where they were.
The third thing that wood does is rot. And for mariners who were to measure the length of their journeys, not in weeks or months, but in years, it was important to have tools that could last. Being stuck in the middle of the Pacific Ocean, with no means of determining where you were in it, was almost certainly a death sentence.
These two items – the mariner’s astrolabe, and the making them out of metal, were both Portuguese innovations that occurred sometime during the life span of Vasco da Gama. The Portuguese, by roughly 1500, had the better ships, and the better means of navigation. It’s no surprise that they, at least until Spain started rolling in the gold and silver from Mexico and Peru, were the ones who first established and controlled the Nautical spice routes to India and Indonesia.
(Note: Pictures of the Mariner’s Astrolabe are rare, as most have been lost to the ages. The picture above comes from the Adler Planetarium.)