You can’t tell a butterflyer to hold water at speed, you have to...

If butterflyers can’t hold water at speed, they won’t swim fast.
If we want them to learn this skill, we have to show them how.
First, we’re going to use the parachute to encourage swimmers to create more propulsion.
Second, we’re going to ask them to go far AND fast against the parachute.
And each round, we’re going to change their hand position during the first two repetitions to force them to use the whole arm to create propulsion.
It’s a whole lot more effective at creating change that matters as compared to just telling them what to do.