my thought process was something like "our teammates won't probably
find this game. so if 4
♥ makes it's all the same if I double it or not. If it fails, our point expectancy only rises - declarer was going to look for the points at me anyway." Of course this thought process is a little flawed, but this was the basis.
On the other table 5
♦ fell twice (Dad made the practical direct leap to 4
♥ in the first round against a limited (4+) 1
♦), so it was always going to be a good score anyway.
Thinking about it again I think adjusting this one to +50 seems only fair (or not to bother at all. At the moment I didn't like being accused, but I have to concede that they're more right than wrong.
Anyhow, I just wanted to thank you all for being kind enough to reply. This is really a one-of-a-kind forum about a one-of-a-kind game!
... and I can prove it with my usual, flawless logic.
George Carlin