What Happened to Lignum Vitae Bearings? The Tropical Wood Trusted Inside the First Nuclear Submarine – Transcript

00:00January 1954, Groten, Connecticut. The most advanced ship on Earth, slides into the Tempame's River. She will be driven by a nuclear reactor. And where her two propeller shafts meet the sea, they turn on blocks of wood. Not just any wood, a tropical timber so dense it sinks in water called lignum vitai. For a hundred years, it carried the propeller shafts of battleships,

00:26ocean liners, and wartime cargo ships. It steadied the turbines inside great hydroelectric dams. Then the timber yards emptied. The men who could read its grain and shape its staves grew old and the craft slipped away with them. The wood itself retreated to places almost no one ever sees. It is easy to assume that steel simply outgrew it. That wood was a primitive stop gap. Neither is true. So what pushed it aside? And why

00:54are engineers finding their way back? Every episode, we tell the story of one machine, mechanism, or maker that once ran the world and then quietly slipped out of sight. Subscribe if that kind of history matters to you.

01:08From a Victorian workshop in Greenwich to the dawn of the nuclear age. This is how one Caribbean tree came to carry the world's ships. In the 1840s, the steam ship was changing shape. For a generation, steam had meant paddle wheels, great churning drums bolted to a ship's sides. They worked, but they were clumsy. In a rolling sea, one wheel lifted clear of the water while the other buried itself. In war, a single cannonball could them. The screw propeller

01:35promised something better. Tucked beneath the stern, fully submerged, it was out of reach of waves and gunfire alike. In 1845, the Royal Navy settled the argument in public. It tied the screw sloop Rattler Stern to Stern with the paddle steamer electto and let both run at full power. Rattler dragged her rival backwards through the water. But the propeller brought a problem the paddle wheel never had. A paddle shaft crosses the hull high above

02:02the water line in the open air. A propeller shaft has to leave the ship below it. Somewhere near the stern, a spinning iron shaft as thick as a tree trunk has to pass straight through the hull and the sea has to stay outside.

02:15Two things made that possible. A packed seal called a stern gland squeezed around the shaft to hold the water back. And just behind it, a bearing carried the weight of the shaft and the heavy propeller hanging off its end. That bearing sat in the worst place on the ship. No engineer could reach it at sea.

02:33Oil and grease washed away. Salt water attacked the metal, and every harbor and rivermouth fed its sand and grit. Builders lined it with brass the best they had, and the brass was ground away.

02:46As the bearing wore, the shaft sagged. A sagging shaft no longer ran true. It shook with every turn, and that shaking tore at the stern gland. The one thing keeping the ocean out. Screw steamers like the Himalaya and the Malaca were giving trouble with their brass stern bearings, and the men who built their machinery understood what that meant.

03:08The propeller, for all its promise, was not yet fit for long ocean voyages. Then came a demonstration nobody had asked for. December 1855. The Crimean War is winding down and her majesty's ship Royal Albert is steaming from Sevastapole toward Malta. She is one of the largest warships afloat, three gun decks, 121 guns, the flagship of Admiral Sir Edmund Lions and barely a

03:33year and a half out of the dockyard. On the 29th of December, deep in her stern, the sea finds its way in around the propeller shaft. Not a trickle. Six tons of water every minute. A ship that no enemy had managed to hurt is going down in open water. From a wound in a part of the hull no one can reach. There is only one choice left. The Royal Albert turns for the nearest land. The Greek island of Ka and the pride of the fleet is run

03:59deliberately onto the shore. Her captain William Mens proposes a desperate repair. A wooden box built around the shaft deep inside the hull to choke off the flood. It works. The ship survives.

04:12A model of her stern with that makeshift box in place is still held by the National Maritime Museum in Greenwich. And here's the strange part. By the time the Royal Albert hit that beach, the cure for her wound already existed. It had been patented the year before, a few miles up river from the dockyard where she was built. The man behind it was John Penn. Born in Greenwich in 1805, the son of a milright, he had turned his

04:40father's workshop into one of the best equipped marine engine works in Britain. His firm supplied machinery for the Navy's new screw warships, the Royal Albert among them. So the failing bearings were not somebody else's problem. They were his. Penn turned to Francis Pettit Smith, the man who more than anyone had championed the screw propeller in the first place. Smith ran a long series of trials for him. Bearing after bearing was tested against a

05:06turning shaft underwater. First in one metal, then in another, then in different kinds of wood. Most of them wore or scored or seized. One did not. It was not a metal at all. In 1854, Penn patented a stern bearing lined with strips of timber. Two years later, he stood before the Institution of Mechanical Engineers and laid out the results. The timber came from a small, slow growing tree of the Caribbean, and

05:33Europe had known it for three centuries, just never as an engineering material. In the 1500s, it had been shipped across the Atlantic by the ton as a supposed cure for syphilis. It cured nothing. But the name it earned in those years stayed with it. Lignum vitai, the wood of life.

05:52Sailors knew it, too. Shipwrites turned it into pulley blocks and rigging fittings because it shrugged off wear and weather. And in the 1700s, the clock maker John Harrison built it into the timekeepers that would solve the problem of longitude because bearings made from it needed no oil. Now, John Penn was proposing something far more brutal. He wanted to rest the propeller shaft of a warship on this wood underwater in salt and sand for years at a time. Brass had

06:20failed there. So why would a piece of timber survive where metal could not? The answer begins inside the tree. Lenum vitai does not grow like the timber of a northern forest. It is a small tree of dry Caribbean coasts and it is in no hurry. A trunk no thicker than a dinner plate can represent many decades of growth. All that time is packed into the wood. The first thing anyone notices is the weight. A cubic foot of oak weighs

06:45around 45 lb. A cubic foot of water weighs about 62. A cubic foot of lignum vai weighs close to 80. Drop a block of it into a harbor and it goes straight to the bottom. The second thing is harder to see. In most timber, the fibers run straight up the trunk like a bundle of drinking straws. That is why a log splits cleanly under an axe. The fibers of lignum vi do not run straight. They

07:12wind back and forth as the tree grows, each layer crossing the one beneath it. An engineering journal in 1919 compared the pattern to the corded fabric inside an automobile tire. The result is a wood with almost no natural line of weakness.

07:27It resists splitting. It resists crushing. Under a heavy load, it simply holds. But density and toughness alone would not have saved a ship. Plenty of hard materials had already been tried in that bearing, and the hardest of them were metals. What sets this wood apart is what fills it. As the tree ages, the cells at its heart stop carrying sap. In most trees, those cells are left as empty space. In lignum vit, they fill

07:53with resin. A heavy waxy greenish brown resin, itself denser than water, packed into the pores of the wood from the center of the log outward. The same 1919 account described every nook and cranny of those dead cells as filled with it.

08:09This is the heart of the matter. In an ordinary bearing, the lubricant is something added. Oil or grease is spread across the surface and the surface works only as long as that film stays in place. Take it away and metal meets metal. In the stern of a ship, the sea takes it away. In lignum vite, the lubricant is not a coating. It is an ingredient. Think of the difference between butter spread on a slice of bread and the fat marbled through a cut

08:36of meat. One sits on top and can be wiped off. The other goes all the way through. As the surface of the wood slowly wears, it does not wear down to something dry. It wears down to more of the same, and [clears throat] the sea cannot rinse it out because the resin does not dissolve in water. Water does something else instead. When researchers in Poland tested lignum VD bearings in 2025, they left the wooden sleeves

09:03soaking between trials. After 2 months underwater, they found the surface coated in a slick gel-like film that clung to the wood and was difficult to remove. They could not yet say exactly what it was, but they noted that these bearings never showed the stuttering, sticking motion that troubles so many other materials at low speed. So, the worst place on the ship turned out to be the one place this timber was at home.

09:28Salt water did not corrode it. Soaking did not rot it. It only swelled a little and gripped its housing tighter. Yet, a solid block of the finest lignum vai simply clamped around a propeller shaft would still have failed. Because John Penn did not just choose a material, he gave it a shape. Picture a wooden barrel and then turn it inside out. A Cooper builds a barrel from long narrow strips called staves set edge to edge in a

09:54circle. Penn's bearing used the same idea with the wood facing inward. A heavy bronze tube was fixed into the stern of the ship. Along its inner wall, running the length of the tube, strips of lignum vtai were locked into place side by side all the way around. The propeller shaft passed through the middle and rested on the wood, but the staves did not quite touch each other.

10:17Between each one and the next, a narrow channel was left open, running from one end of the bearing to the other. Those gaps were not a flaw. They were the point. The sea flowed through them. As the shaft turned, water moved steadily along the channels and out at the stern, and it did two jobs on the way. It carried off heat because even a slippery bearing warms up under the weight of a propeller, and it carried off dirt. A

10:44grain of sand that found its way in did not stay trapped against the shaft. It was swept into the nearest groove and flushed out behind the ship. On the largest vessels, a pump pushed a gentle flow of water through from the inboard end. To keep that current moving, the shaft needed protection, too. Bare iron turning in saltwater rusts and a rusted shaft is a file. So, the section that ran inside the bearing was wrapped in a

11:09smooth brass sleeve, wood below, brass above, and the sea in between. Now, the shaft begins to turn. At first, slowly, a ship leaving harbor, engines barely ticking over. At this speed, the brass sleeve is resting directly on the timber, and the resin in the wood does the work. This is the moment that destroys most bearings, the moment of starting from rest, and it is exactly