How power and split relate on RP3
Comparing power and split values on the RP3.
At RP3 the flywheel has been the constant between all our machines for decades. While rowing we continuously measure the angular velocity of the flywheel during both the drive and recovery phases. During the recover, while the flywheel is slowing down, we can calculate the amount of drag the flywheel experiences originating from all external sources such as air resistance, but also from, for example, wear of the bearings. Combining this with known physical constants we can deduct how much effort is required to overcome this drag.
To calculate the speed at which the "boat" is traveling (i.e. the split time) we can directly deduct this from the speed at which the flywheel is spinning. There is little difference in speeding up a flywheel through air or a boat through water as they're both accelerating objects through fluids. Meaning we can use a linear correlation between the flywheel speed and the boat speed. Combining the speed of the flywheel with the drag coefficient as well as some constants describing the type of boat and weight of the rowers we can very precisely approach the speed of the boat.
Power is a different story, the amount of power required to speed up the flywheel increases as the flywheel is spinning faster. Again, similar to a boat in the water, gaining the first few meters per second is relatively easy, but gaining a couple of meters per second while at the highest level is very hard. This is why we use a non-linear correlation between the flywheel speed and the power scales with a power of three compared to the angular velocity.
Want to compare with other rowers such as Concept2? Make sure to select "Split Power" instead of "Power" as a data field. This will show you the power based on the split time as per the Pace-to-Watts Calculator.
Improved power calculations
We've made some changes to the "power" field.
The "Power" field now reflects the physics of the RP3 rowing machine and its flywheel, and is the most precise power value to measure your performance. If you want your power values to be calculated based on the 500m split, choose the "Split Power" field instead. This field will calculate the power based on the 500m split using the 2.80/speed³ calculation.
Note! To compare values between the 2.13.5 and 3+ versions of the RP3 Rowing app you need to know if you were using the "RP3 Split" as split setting on 2.13.5 (90kg rower with a 4x boat type). If you were using the "RP3 Split" you should compare the power with the new "Split Power" field. If you were using custom weight and boat types you can compare your past results with the new "Power" field.