Place ham in a large dutch oven style kettle. Cover with cold water, and fill to about 2" above top of ham. Cover kettle, and bring to a boil using high heat. Turn down to med-high and let boil a few minutes, then drain water, and refill with water 2" above ham, and bring to a boil again over high heat. This method is used to make the ham less salty. (Or you may refrigerate ham overnight in water, and change water several times before cooking instead).
Once water comes to a boil, turn heat down to med. to med-high making sure it keeps boiling. Keep cover on kettle while cooking. Add peeled onions to the kettle. Cook ham 1/2 hour per pound of ham. Add some water to the kettle, when it starts getting low. Peel and cut potatoes and carrots. Wash and core cabbage, then cut into wedges. Add vegetables during the last 30-40 minutes of cooking time. Serve when veggies are tender, or to your liking.