I just watched a video of a big military boat going over HUGE waves. How the hell did we send wooden boats across the ocean without them being completely destroyed?
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Wooden boats can be built quite strongly, and they have an advantage over metal boats in that the stuff they’re made of is typically itself inherently buoyant. This doesn’t make a huge difference in most circumstances, but when you’re frantically bailing because you’re about to sink, and throwing cargo overboard, it helps.
More important than that, though, is that you have to keep in mind that wooden ships were generally quite a lot smaller than modern cargo or military vessels. The Santa Maria, one of the vessels that was part of Columbus’s expedition across the Atlantic, was about 70 ft long. Modern cargo or military ships are typically hundreds of feet long, with some being a thousand feet long or more. And wooden ocean going ships often were much narrower as well. In some ways this helps the modern ships, but in some ways it hurts them.
The time of the most stress on a ship isn’t typically at the bottom of the trough of the wave where it starts ramming into the water, which is what you might think. After all, cutting into the water is what the ship is always doing and so it has to be built naturally quite strongly for that. Instead, the ship is in most danger when it is cresting the wave and some of the front part of the ship is not supported by the water anymore. In some sense it is hanging off of the back of the ship. That means the ship has to be strong enough to support all of that weight. In general, it’s easier to build structures that are always going to be pushed together than to build structures which can survive being pulled apart. And as the ship crests the wave, the front is pulling on part of the back half of the ship.
The reason size matters is that, obviously, the longer the ship is, the more the front of the ship can possibly overhang a really large wave. That means there’s more stress on the rest of the ship. First that’s just because there’s more ship, and more weight to support. Second, and worse yet, it’s not just because a longer ship has more weight on average, but because the stress increases with both the weight of the ship and the distance from the pivot point, which is the crest of the wave. If you think about something very small like a leaf or a cork bobbing on the surface of the water, it doesn’t really care what the waves are doing until the waves get so severe that they start washing over it. It just goes up and down because it really isn’t any way that it could tip over, because all of it is always being supported by the water. So, in some ways, the reason we could build ocean going ships out of wood is because they were smaller. But there’s another, more obvious reason.
Namely, ships used to be destroyed by bad weather on the ocean all the time. It was unknown hazard, and obviously people tried to learn lessons from ships that had passed through many severe storms and survived, and also tried to learn lessons from ones that didn’t. Over time, the designs of ships were refined through experience, and eventually they evolved to a state where people would accept the balance of risk and reward. But they did get better over time. Very early wooden ships would never have survived a trip across the Atlantic or Pacific Ocean. For a very long time, ships were basically just a way to travel along the coast (and move goods), or up and down a river, much more quickly than walking or riding. Those Greek and Roman warships you may be familiar with, like triremes, practically always stayed within sight of the coast and practically always had to put in at shore every night. That’s because they were so small that they couldn’t carry enough supplies for long journeys, and they absolutely dreaded bad weather. Many sank when they ran into an unexpected storm. It took literally thousands of years of shipbuilding experience for people to be able to successfully build wooden ships that could travel long distances over the ocean.
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