In a 4-quart kettle that can be used on a barbecue grill, combine catsup, water, sherry, worcestershire, onion, lemon, garlic, and butter.
Bring to a boil, reduce heat, and simmer for 30 minutes.
Arrange ribs, fat-side-up, on lightly greased grill 4 to 6 inches above a solid bed of low-glowing coals.
Baste lightly with sauce.
Cook, turning occasionally, for 1 hour to 1 hour and 20 minutes, or until meat near bone is no longer pink when slashed.
Every 1/2 hour add 5 or 6 briquets to fire, spacing them evenly, to maintain a constant temperature.
Reheat remaining barbecue sauce by placing kettle on grill.
As ribs cook, remove them from grill, cut into serving-size pieces, and place in kettle.
Cover and simmer for 20 to 30 minutes longer.
Spoon sauce over pieces to serve.
Season with salt and pepper.