[Liversidge]

LHO opened a weak 2♠. Partner bid 3♦ and RHO raised opener to 3♠.
I had 11 HCP, five good clubs, five good hearts one spade and two diamonds. Was I unwise to double for takeout, seeing as how we have not come across this situation nor discussed it? (Partner passed thinking it was for penalties. Opps made 3♠ doubled.)

[helene_t]

The "expert" treatment is that this double is take-out (more precisely: responsive). A responsive double is the following:
(opening)-simple_overcall_or_double-(raise)-double

You may indicate on your convention card to what level responsive doubles apply. Probably it should be at least 4♦ although it is a reasonable view that this double is never pure penalty regardless of the level (maybe a double of 7♠ should be penalty, though).

But of course it is a matter of agreement whether you play responsive doubles or not.

Note that responsive doubles do not apply if partner has made a conventional two-suited overcall or a jump overcall. And maybe not if he has made a natural notrump overcall.

Your shape is good for a responsive double. It may be a bit scary to double with a singleton in opps' suit and no aces, but you can't be blamed for not always being given the perfect hand.

[The_Badger]

Liversidge, on 2017-September-07, 17:36, said:

LHO opened a weak 2♠. Partner bid 3♦ and RHO raised opener to 3♠.
I had 11 HCP, five good clubs, five good hearts one spade and two diamonds. Was I unwise to double for takeout, seeing as how we have not come across this situation nor discussed it? (Partner passed thinking it was for penalties. Opps made 3♠ doubled.)

This is the one situation - an opening weak two raised pre-emptively to three (raising to three is not a game try amongst the vast majority of players, but a barrage action) that you need the double as responsive as Helene says. What you did was right, but partner didn't understand it.

Technically, a responsive double is in the auction 2♠ - X - 3♠ - X* asking partner to choose a suit but it also applies if partner has bid a suit as in your auction.

A different way of looking at responsive and takeout doubles is all doubles on the first round of bidding up to 4♦ are takeout because the worse thing you can do is double the opponents in a part-score into game as happened here. Easy to remember.

[Liversidge]

The_Badger, on 2017-September-08, 00:26, said:

Technically, a responsive double is in the auction 2♠ - X - 3♠ - X* asking partner to choose a suit but it also applies if partner has bid a suit as in your auction.

Thanks both. I checked my references afterwards, but could only find examples of responsive doubles like the one you have given, and none that dealt with my specific case.

BBO is a fantastic resource!!