RM tested on the water the two keel solutions and the results were accordingly what had been previewed by Marc Lombard with the help of CFD studies.
We are comparing not only two different keels but two boats with different drafts, 1.65m for the twin keels and 1.90m for the mono keel. The results, has I have already said are amazingly good, considering the difference in draft. I don't now if with 1,65 draft a mono keel would have and equal performance to the twin keel and it would be very interesting to have that data, but we have not.
Twin keels offers other advantages as contributing to a slightly better comfort and sea motion as well as giving the big advantage of being able to beach the boat for cleaning the antifouling or repairs. All this at a very slightly cost in overall speed.
I have talked about some few tenth's of a knot, here you have the full story (the wind speeds are misaligned: the first one goes with the first boat speed)
These are the previewed results by Marc Lombard for the RM 1060 that real testing on the water showed to be accurate.
We can see that, as it was expected, the worst results are with very weak winds where drag assumes more importance and with smaller angles of heel. Close to the wind at 36º TW with 12K, with probably one keel vertical the difference is of only 4%. That means that on that situation, while the Deep draft mono keel boat is doing 6.76 the shallow version with twin keel is doing 6.5.
On most conditions and points of sails the difference is 1% to 2%. That, considering 2% and 7K will represent a difference of 0.14K. The difference is much smaller than between a boat with a fixed propeller and a folding one.
That explains why RM recommends the twin keel version and why almost all the French buy the twin keel versions. In France the concept is well understood, it is on the boats made to export that they sell more boats with mono keels. It seems that abroad they are more suspicious about their advantages