A blog post from Rowing in Motion on how to manage the blade at the catch. The main insight here is how "rowing in" the blade actually slows the boat down:
If the hands move up too slow, we see the blade being “rowed in” to the water. The boat loses even more velocity as the rower starts pushing on the stretcher without generating a positive handle force to compensate for that.
I actually came across this blog post when researching backsplash, here called "V-splash" created:
... when the squared blade hits the water right before the maximum angle is reached (creating a backsplash) and is being moved into the water as fast as possible while beginning the stroke (creating a small frontsplash).
This post also contains a plain-English description of why faster catches make faster boats:
... earlier acceleration is better since it increases average boat velocity over the stroke. You can think about it this way: boat velocity changes during the stroke but at the end and beginning, it’s the same (since negative and positive boat acceleration add to zero and the boat maintains its average velocity). How do you increase this average velocity? When the boat is slowest at the catch you need to accelerate the boat as quickly as possible to be fast for as long as possible during the stroke cycle. That’s how you increase average velocity.
