The Waverley has eight float paddlewheels which are actually rimless (and wooden) in the old North British fashion.
The floats feather using a feathering mechanism which means the angle of the floats to the rim or shaft change depending on its position during rotation.
Non feathering blades would be fixed and set at 90 degrees to the rim and point directly at the shaft.
The feather works so that as the float comes over the top and then comes down to the water the blade angle sharpens so that the blade enters the water at a sharper angle. As the float passes through the bottom (six o'clock) position the mechanism has angled the blade so that it is at 90 degrees to the shaft then as it passes backwards before leaving the water it angles less so that, effectively, the float pushes the water backwards a bit. It the blades did not feather at this point they would be lifting the water up into the paddlebox rather than pushing.
Feathering much more effective than fixed.
To do this each paddle float swivels on the rim and has bracket extending from the float that has swivelling arm attached and all these arms point towards the centre shaft and a central star assembly. However, this star is displaced from the main shaft so that its pivot location is, usually, in front of and above the main shaft and it is this displacement that causes each float to change its angle as wheel makes one revolution.
However, all eight floats cannot have articulation linkages or the mechanism wouldn't work so one float's linkage is fixed and that is the king float and all the other floats take their positioning from it.
It is the king float that, for reasons not quite known, causes the bam, and the others the bump as they hit the water.
Various Clyde paddlers had differing setups of kings giving differ patters but Waverley has hers identical on either side.
Varying speeds alter the loudness, as does paddle box to water level height and float dip. For example the old Jeanie Deans had eight blade rimless floats, quite high paddle boxes and a shallow dip so, it is written, when she was at speed she sounded like a speedboat or machine gun.
Waverley sits lower.
Folk forget that, if pushed, the Waverley can hit 18knots. Last year on our club run coming up river, she was really motoring on a bit.
https://www.youtube.com/watch?v=fccfEtklovkYou can see in Kim's video of his model paddle wheels that one of the feathering arms is larger than the others. That controls the king float.