Raising the "Mary Rose" meant overcoming a number of delicate problems that had never been encountered before. The raising of the Swedish warship "Vasa" 1959–61 was the only comparable precedent, but it had been a relatively straightforward operation since the hull was completely intact and rested upright on the seabed. It had been raised with basically the same methods as were in use in Tudor England: cables were slung under the hull and attached to two pontoons on either side of the ship which was then gradually raised and towed into shallower waters. Only one third of the "Mary Rose" was intact and she lay deeply embedded in mud. If the hull were raised in the traditional way, there was no guarantee that it would have enough structural strength to hold together out of water. Many suggestions for raising the ship were discarded, including the construction of a cofferdam around the wreck site, filling the ship with small buoyant objects (such as ping pong balls) or even pumping brine into the seabed and freezing it so that it would float and take the hull with it. After lengthy discussions it was decided in February 1980 that the hull would first be emptied of all its contents and strengthened with steel braces and frames. It would then be lifted to the surface with floating sheerlegs attached to nylon strops passing under the hull and transferred to a cradle. It was also decided that the ship would be recovered before the end of the diving season in 1982. If the wreck stayed uncovered any longer it risked irreversible damage from biological decay and tidal scouring.