Hi Peter - happy new year.
I use the double hall more through force of habit than anything else. I find that my line hand just starts hauling when casting

I do not do it perfectly by any means however, but am getting better with practice.
It does not take that long to learn; any good instructor will teach you and books like Casting with Lefty Kreh are also good.
The double haul is useful for getting extra line speed to overcome wind and when chucking bigger flies too, not just for more distance. Just remember to put about half the force into the cast with your rod hand than you think you might need (with a trout rod), and when hauling, reduce the power applied in your cast via the rod hand accordingly or you'll have tailing loops aplenty. Also try not to drift your rod hand forward after the back cast before the forward cast proper - I do it and it doesn't help

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Oh and it's not the holy grail - far from it - that's catching lots of fish! If you can do that without double hauling then why bother?! I just wanted to be able to do it. Good luck and there are plenty on here far more knowledgeable than me to help.