I think weight has a bigger impact than you might think. Unlike cycling as rowing is in water. Water will generate a significant amount of drag which constantly effects the boat and the heavier your boat is the more drag you will generate. Secondly unlike cycling rowing does not have constant power application, each stroke will have approx 1s of power application and 1s of recovery as the rower takes the next stroke. This means that while oars out of the water the boat is relying on momentum, so minimising drag is key to reducing the boat slowing in the period. Additionally more force will be required to accelerate the boat at the start of each stroke with more weight. Finally a rowers weight will significantly move within the boat on each stroke against the direction of travel of the boat. This will cause the boat to slow with more weight.

Some coaches will weight adjust everyone’s times off the water for their crew selection because of these factors.

On the rowing data, rowing has a light weight class that’s 72.5kg for men which explained the bulge in the middle. The minimum coxes weight is 55kg which explains the small bulge at the bottom as there is only one boat class that has coxes at the olympics.

The heavier you are the more power you need to produce to offset the extra weight (and therefore drag) you bring to the boat, where weight v height/power output can be accounted for. As Coaches evaluate weight v power for athlete selection, there is a wider distribution of weights for the heavier athletes.