In a double takeout one throw removes two opposing stones. Prerequisites, geometry, speed, risk and rules, honestly classified for ambitious players.
The honest answer: a double takeout is a throw that removes two opposing stones from play. That is how the world federation's glossary defines it [1]. A media glossary specifies: two stones from the house [2]. The rulebook also knows the raise take-out, in which your stone hits a stationary stone, which then knocks a third stone out of play [1]. That is the basis of many doubles.
I classify the double takeout as pro because it demands more than a good hit: you need speed, contact and a feel for the layout at the same time. One teaching resource names double and triple takeouts as examples of heavy weight [3]. That is no study, only a hint.
How hard is it? It builds on a reliable takeout. There is no timeline, and no source material I read gives a success rate.
Two stones must lie on a line your stone hits, or one stone must slide onto the second after contact. The picture in your head is like billiards: the first stone hits, the second moves. That is an explanatory aid, not a measurement from a source (practice).
Milestone: For a given layout you can explain which stone you hit and where the first stone goes.
The first stone is hit so that it takes the right path. A coach's essay describes two "noses" for stones lying together: the nose of the front stone and the "nose of the tandem" (the line through both stones) [4]. If you hit the tandem on the wrong nose, the second stone can run past the target [4]. The principle helps you read tight layouts. It is an essay, not a study.
The double needs more speed than a simple hit because both stones are moved. In elite curlers, push-off duration was shorter and velocity higher in takeouts than in draws [5]. For heavy throws you start the push later [6]. With more speed, the risk of tipping the end rises too; the skip sets the speed.
Milestone: Your simple takeout hits the target stone cleanly in four of five cases before you try doubles (practice measure).
The US material advises clarifying before the throw what is desired, what is acceptable (a "pro" miss) and what is unacceptable (an "amateur" miss) [7]. In a double, a pro miss is usually: the first stone goes out, the second stays. That is still a takeout.
A stone your throw sets in motion may be swept by the team it belongs to, anywhere in front of the tee line at the playing end [1]. So opposing stones are swept by the opponent. You yourself sweep others' stones only behind the tee line and only once they have reached the tee line at the playing end [1].
Don't do the opponent's work. A throw that pushes the stone at the front of the house against yours tips the end in their favour [7]. That also applies to the double.
Observational data from the 2022 Olympics (34 games, men) show: medal-winning teams had more tactical diversity and better success rates in key shots than the Chinese team [13]. That doesn't mean you should play more doubles, but that you should master several shot types reliably. A double is an option, not a goal.
A throw that removes two opposing stones from play [1]. A media glossary describes it as a takeout that clears two opposing stones from the house [2].
In a raise take-out your stone hits a stationary stone, which then knocks a third stone out of play [1]. In a double takeout your throw directly removes two opposing stones [1]. In practice, the line is blurry.
More than a simple hit; according to one teaching resource, heavy weight [3]. Takeout speed comes from a short, fast leg push-off that starts later on heavy throws [5][6]. The skip sets the speed.
Only if the risk is right. US material advises calling the higher-percentage shot first and weighing risk against reward [7]. If the single is safe, play the single.
Curling for Beginners: Can Anyone Really Learn It — and Is It a Real Sport or Just Cosy?