What does double mean in 29?

A defender says double, meaning they do not think the bidder will make the bid. If the bidding team makes it, they gain two game points. If not, they lose two.

Can a redouble be answered?

No. There is no re-redouble. The hand is worth four game points either way.

A player from the opposing team, when they believe the bid will fail.

The bidding team's reply to a double, saying they are sure the bid will be made. It raises the stakes again.

Does doubling change the bid?

No. The bid stays the same. Only the points at stake change.

Why would a team double?

To raise the reward for a correct guess. A double is a risk, so it works best when the defenders can count the points left in play.

Double and redouble in 29: raising the stakes on a bid

A plain hand of 29 is worth one game point. Double and redouble turn it into a four-point hand, which in a race to six is most of a match.

Double

After the bid is settled and the trump is chosen, either defender may say double. The message is "we do not think you will make it". If the bidding team makes the bid, it gains two game points. If the bidding team fails, it loses two.

A double is a challenge. It does not change how many points the bidder needs. It changes what the hand is worth.

Redouble

After a double, the bidding team may answer redouble. The hand is now worth four game points either way. Only the bidding team can redouble, and only in answer to a double. There is no answer to a redouble.

The arithmetic of a race to six

Game points run from −6 to +6. A redoubled hand can move one team four points at once. From zero, a successful redouble puts the bidders at +4 and the defenders at −4. One ordinary hand more and the match is over. That is why good players treat the double as a weapon to use sparingly, and the redouble as a weapon for hands that are already locked.

When to double

The bidder has won a contest of bids and finished higher than their hand supports. A bid pushed to 22 after a 20 from your partner is a classic double.
You hold the Jack and the 9 of what is likely the bidder's suit, or a marriage in it.
The score means a single point will not save you anyway. At −5, doubling a hand you expect the bidder to fail may be your only way back.

When to redouble

You hold a sure trump suit: the Jack, the 9 and some length.
Your partner bid strongly before you took over.
The defenders doubled before seeing the trump. That often means they are bluffing on a weak hand.

Reading a double

A double tells you where the strength sits: with the defender who spoke. Lead through that player, not into them, and expect the Jack of trumps to be on their side of the table.

Double and redouble in 29 Royale

Both are part of every match unless you turn them off. The bots were tuned for them. They fight for the contract against a team at +4 or +5, double a caller who reaches +5, and weigh the score before they redouble. Expect a challenge whenever you overbid. 29 Royale is free on Google Play. See how long your bids survive a table that doubles.