Unfortunately, watt meters in boats is still a bit of a reach. The only real consumer product is www.smartoar.com
but it is still a bit involved and expensive. If/when it becomes more common and cheaper, I think it could be quite a revolution for rowing, ie, if everyone could get detailed force curves over the complete duration of the stroke. We'll see though. The population of rowers is small and that makes it hard to drive prices down with volume.