The naval architect quoted here talked about fat headed mains - probably any cruising cat main built today , elliptical or square top would qualify.
Looking into what the naval architect is saying is interesting. Our boats usually, unless they are accelerating, have the rig forces equally and oppositely opposed by the hull forces. If this didn't happen we would fly away with the wind like a balloon.
Heavy catamarans with minikeels have an underwater configuration that is high drag. They cannot operate at high lift to drag ratios. There is a lot of tip losses, skin friction and the
keel may not be the ideal NACA-like section. For a 3 metre long (chord) minikeel a 0009 NACA section (which is about as thin as most designers go) would be 270mm wide. I have never seen a
keel this wide so the designers go to thinner, probably too thin to be efficient, keel sections.
This means that the underwater
parts of a minkeel cat are in high drag mode. The sections cannot be then asked to operate at low angles of attack. The lift to drag co-efficient will be low.
The rig will produce forces that get exactly opposed by the hull and appendages. If we put on a rig that is very efficient and can operate at very narrow angles of attack you may think that you could point very high into the wind, like an Etchell or Laser. The problem is that rest of the
boat has very high drag - the
cabin,
davits, high freeboard, lots of weight, immersed transoms etc. This means that the drag of the entire boat has been only marginally reduced but the lift of the rig (think power) has been reduced to get a rig that can sail at lower angles of attack.
Now because the underwater sections are inefficient you cannot sail high into the wind, even with efficient sails, without the underwater sections getting into a high drag configuration. You have to bear away and "get the boat going" or it just stops. A good cat
designer will understand that the boat will be in "get going mode" most of the time and design a rig that suits. Not a tiny jib/large main rig that is seen in AC cats but one that has a larger
jib. One that has a planform that is efficient at a high power (high lift) or low lift/drag configuration. This is what the naval architect was probably talking about.
If I design a 40ft
racing cat with no accommodations the rig planform, sail shape and said design would be very different from a 4-5 times heavier minikeel cruiser. The
racing cat will be operating at low angles of attack and at a high lift/drag co-efficient both above and below
water. It will rarely be in "get going" mode but instead be in "pointing"mode. The cruiser will be operating at a totally different performance zone and its rig should be designed as such.
Of course minimising aerodynamic drag will be helpful for the minikeel cat, so efficient sails, maybe with an elliptical planform to reduce induced drag will help. But the rig should have a larger jib than the
racer and the sails cut with deeper
draft for higher lift (and more drag).
Whether a square top is best for cats is problematic as we don't have a definition of a square top and it is rather expensive to do the testing. In
Australia we have a development class called the NS14 that has no restrictions on the rig other than sail area - it is 100 square foot and you could have it all in the main if you wanted. The attached
photo shows the start of last years nationals titles. Close observation will show that there is a range of head designs - no predominance of square tops over combination square /elliptical. These boats operate at much high lift/drag ratios that most cruising cats and so rig drag reduction would have large effects in performance and if large square tops were faster then everyone would have one. I haven't used the example of A class or other cats as they operate at very different performance areas than our boats.
The rig design of the
Seawind 1160 is probably something similar to what the naval architect was talking about with small jibs/ large mains. In this
photo the ratio of jib size is smaller in the
Seawind than the NS14, even though the NS 14 operates at higher lift to drag ratios which favour small jibs. Of course a small jib is nice to tack and our boats have to do a broad range of jobs whereas a
racer like the NS14 has to do only one thing - win races.
So the naval architect is pretty much in line with
current thinking. Still is is always nice to reduce drag any way you can.
cheers
Phil