In everyday speech, people say "I'll try and do it" and so on, when they mean '"I'll try to do it". Taken literally, 'try and do it' means that the speaker will do it and so 'try' is unnecessary. If they do it, they must have tried and succeeded.
Is 'and do' incorrect? Or is this some correct grammatical construction which has a name? And does the use of 'and' bring some nuanced meaning which 'to' does not?
they never say "I tried and did it" in the past, only "I tried to do it".
None the less, as you say, it's everyday speech - wrong but probably too common do do anything about. The English language isn't always logical. (Shouldn't "laughable" be "laughatable"?")
In theory, "laughable" ought to refer to someone or something which can laugh. However, -able tagged onto a verb often carries the meaning of the passive rather than the active. e.g.
a winnable race is one which can BE WON
an unsavable shot is one which cannot BE SAVED
So, laughable means something which can BE LAUGHED (at).
Yes,indeed boxtops, there is a nuance. To me, "I'll try to do it" means literally that, and no more. "I'll try and do it" puts the emphasis on the trying, the suggestion being that some effort will be made but without any firm conviction that ' it' will, in fact, be done.
the OED's earliest citation for unsinkability (1860something) equates it with armour-plating, suggesting it means unable to be sunk. Armour-plating won't stop you sinking.
In the 1926 edition of his Modern English Usage, H W Fowler wrote, "Try and is an idiom that should not be discountenanced, but used when it comes natural."
If he could consider the phrase "an idiom" and "natural" 86 years ago, I can see no great need for us to question it today. (I just love 'discountenanced'!)