[Hanoi5]

Let's say I play Gardener NT overcall, so the opponents open 1♠ my partner overcalls 1NT which could be Strong as in a NT opening or weak in any of the unbid suits. Opponents continue bidding (and I know they have the strength of the hand, so partner must be weak), am I obliged to tell them my partner has the weak hand? Do they get any reddress if they miss a slam if they say I knew my partner was weak? Is this convention too destructive to be played at Club duplicate level?

Let's say we have agreed to open in third position with almost any hand. We have this in our CC, and we alert it (do we need to). We have also agreed not to double for penalties when partner opens third hand (as it may be a funny opening). Do we need to add this to our convention card, alert it or anything? Is it legal?

[gordontd]

The answer to much of this depends on the jurisdiction under which you are playing.

[hrothgar]

Hanoi5, on 2016-March-14, 11:25, said:

Let's say I play Gardener NT overcall, so the opponents open 1♠ my partner overcalls 1NT which could be Strong as in a NT opening or weak in any of the unbid suits. Opponents continue bidding (and I know they have the strength of the hand, so partner must be weak), am I obliged to tell them my partner has the weak hand? Do they get any reddress if they miss a slam if they say I knew my partner was weak? Is this convention too destructive to be played at Club duplicate level?

If the information about the strength of the NT overcall is only observable based on the strength of your hand, then no.
If the information is systematic (partner's failure to double in subsequent bidding has meaning) then yes

[blackshoe]

Hanoi5, on 2016-March-14, 11:25, said:

Let's say I play Gardener NT overcall, so the opponents open 1♠ my partner overcalls 1NT which could be Strong as in a NT opening or weak in any of the unbid suits. Opponents continue bidding (and I know they have the strength of the hand, so partner must be weak), am I obliged to tell them my partner has the weak hand? Do they get any reddress if they miss a slam if they say I knew my partner was weak? Is this convention too destructive to be played at Club duplicate level?

Let's say we have agreed to open in third position with almost any hand. We have this in our CC, and we alert it (do we need to). We have also agreed not to double for penalties when partner opens third hand (as it may be a funny opening). Do we need to add this to our convention card, alert it or anything? Is it legal?

An awful lot of questions here. Gordon is right, but let's see...

1. Am I obliged to tell them my partner has the weak hand? In general no, but see Hrothgar's answer.
2. Do they get any reddress if they miss a slam if they say I knew my partner was weak? Same answer as above.
3. Is this convention too destructive to be played at Club duplicate level? IMO, no?
4. Do we need to alert this? Depends on your RA's regulations. I would expect yes.
5. Do we need to add this [the agreement not to double when partner opens third hand] to our convention card, alert it or anything? Add it to your convention card, probably yes. Alert it, probably yes. "Or anything?" I don't know what that means. In answer to all of these, it depends on your RA's regulations.
6. Is it legal? Depends on your RA's regulations. Gardner NT overcall is, I think, legal some places, illegal in others. I don't know about your "anything goes" opening treatment in third seat, though. I suspect that's too much for most jurisdictions.

Bottom line: find and read your RA's regulations.

[mycroft]

Basically, (which is what everyone else is saying too), if your RA allows Gardener/Comic NT Overcall at a particular event, then they believe the field is capable of handling it. That includes making inferences on when it's the strong and when it's the weak variant outside of "when advancer asks" or "when overcaller tells".

You have to Alert it and explain it correctly, of course; but if they've shown each other 30 high and haven't figured out it's the weak version, that's not your problem. If you know it's the weak version because *you're* the one with the strong NT, that's not your problem either. If, as Hrothgar noted, you know it's the weak variant because the strong variant would have doubled some later call, your opponents *are* entitled to that information.

[mgoetze]

gordontd, on 2016-March-14, 12:04, said:

The answer to much of this depends on the jurisdiction under which you are playing.

Must be his first post on the forums or something.

[szgyula]

Just one more angle: Opponents could have psyched. Thus, you can not be sure that your partner has the weak variant. Unlikely, but...

The bottom line is this: Opponents are entitled to know the SYSTEM you are playing. They are not entitled to know what is in your hand. Simple example: You have 25 HCP. Partner opens 2NT (20-22HCP balanced). When asked, you MUST tell this (20-22HCP balanced), even if you know for sure that it is not possible -- based on your own hand. And you must not give any hint that you know it is not the actual hand.

If there is some way to tell partner which version it is, than you must disclose this, alert it, etc. But again, this is the SYSTEM, not the actual hand that you disclose...