Alistair W. Oag
Drilling Engineering Manager, ECA
Schlumberger D&M

The Basics

Curling is played on ice with (approximately) 42-pound (19 kg) granite stones. The size of the playing surface (a 'sheet') is 138 feet (about 42 m) long by approximately 14 feet (4.25 m) wide. The goal is, after all 16 stones are played (8 by each team), to have a stone of your team's closest to the center of the house, called the 'tee' (see below). This is accomplished by sending your stone to rest in scoring position (a 'draw'), by knocking your opponent's stones out of scoring position (a 'takeout'), and by guarding your own stones with others. The team with the closest stone, inside the house, scores a point, or more if they also have the second closest stone and so on. Each round is called an 'end' and consists of two stones delivered by each player on each four-player team. The stones are delivered from the hack on one side of the sheet to the house on the opposite side. This consists of the player pushing off from the hack with the stone and releasing it with a spin, or 'curl', which gives Curling its name.

The modern game has developed from an outdoor pursuit, played on a frozen Scottish loch; no doubt with a wee dram to keep the players spirits up, into the highly technical indoor sport it is today.

The Curling Stone

The curling stone originated in Scotland from large chunks of rock bowled across the ice, none having any particular size or shape. They evolved into what are now matched sets of fairly uniformly made stones. They are all made of pure granite, and they are amazingly hard. The best stones come from a single granite quarry on the island of Ailsa Craig, off the West coast of Scotland. Shipping is quite expensive due to weight (16 stones in a set at 42 pounds (19 kg) a piece, not including packaging), and manufacturing is expensive because of the toughness of the material, which has to be ground into it’s final shape with diamonds.

The stone is concave on both the upper and lower surfaces. On some stones, the degree of concavity is different on both sides to allow for reversing the stone for 'faster' or 'slower' ice. A handle, usually on a circular plastic disc, is bolted onto the stone through a channel running through the middle of the stone to a bolt on the other end. The picture on the right shows the stone with it’s handle, which is attached by the steel bolt passing from the underside, shown in the picture on the right.

The picture of the underside of the same curling stone shows the concave surface with the bolt in the center. The lighter circle is just beyond the actual running surface of the stone which is a ring about 1/4 inch (6 mm) wide with a diameter of 5 inches (13 cm). This allows the stone to go farther, more accurately, and pick up more 'curl' than would be possible on a flat surface.

There is a lighter-colored band in a ribbon around the curling stone. This is the 'striking surface'. In manufacturing, the entire stone is very highly polished. This surface is dulled down for the purpose of improving collisions with other stones, both so that there will be a larger contact patch in the collision and so that the stones will not chip.

The Curling Delivery

The stone is delivered sort of similarly to a bowling motion. Actually, it's not that similar, but it's the only thing that even resembles it. You start off at what's called a 'hack', or basically a block sticking out of the ice.

Your first motion is to take the stone and pull it backwards, frequently lifting it off the ice in the backswing, then you push or swing it forward into a smooth glide down the ice. However, to deliver a stone well, you should glide along with the stone as far as possible. Good curlers usually glide very close to the ice, in an odd, very stretched pose.

You must release the stone by the 'hog line'.

As you slow down, the stone glides on, to come into play on the opposite side, beyond the other hog line. If it does not cross that line then the stone is deemed out of play and is removed from the ice. See how the release looks in this short movie.

Curling