1. Put the ham bone in a 6 litre pot with enough water to fill halfway. Heat to boiling, lower the heat to a simmer, and cover. Simmer 45 minutes.
2. Prepare the beans while the bone is simmering. Snap the stem end from each bean and pull gently along the length of the bean to remove the string. (It may not be necessary to remove the string from very young beans.) Rinse the beans in a colander under cold running water. Drain and add to the pot along with the salt, pepper, and sugar. Simmer the beans until very tender, up to 30 minutes for old tough beans or around 15 minutes for very tender young beans. Check the seasoning halfway through the cooking and adjust if necessary. Remove the bone and drain the beans. Serve hot.