the sand on the sea bottom, this stuff was under the sand. >> jaco boshoff: under the sand. >> pelley: so you're in how much water? >> boshoff: about five meters of water. >> pelley: about 15 to 20 feet of water? >> boshoff: that's correct. >> pelley: and then these are two feet under the sand below that. >> boshoff: that's right. >> pelley: turns out shallow water only makes the work harder. surf tosses the divers. and sand, vacuumed away, settles back within hours. but, after more than 300 dives, this is what they've recovered these are nails that pinned sheets of copper over the hull for protection. what looks like a lump of concrete is marine growth on a wooden pulley block, similar to this one used to hoist sails and cargo. this x-ray shows the two white spaces where rope was threaded around the wheel. the divers discovered wood that a lab would later trace back to mozambique. anis revealing artifact of all-- masked by two centuries under the sea, x-rays show a shackle, similar to this, used to bind slaves. >> boshoff: so there's a long bar running through. and shackles had... of