Their overall concept is to help stabilize the blades at the catch quicker. Basically, they prevent the oar from going to deep during the first part of the drive, which makes it possible to “anchor” the blade at an earlier stage of the stroke. The result is a quicker connection at the catch and therfore a higher overall boat speed.
One set of Randallfoils includes one foil for the left and one foil for the right oar.
The same Randallfoils fit on sculling oars and sweep oars, and fit all
For testing, the foils can be fitted temporarily with double sided adhesive, for permanent mounting Ian Randall (the Inventor) recommends epoxy glue.