We will certainly have a code 0 + an asymmetric spinnaker, for more range and better speed. You know, dinghy sailors...
But I still think the code D can be a good compromise if one does not want to carry (and/or invest in) both sails. I also enjoy sail changes as a part of sailing fun, but I’m sure many other cruisers find it cumbersome and will be glad to trade some performance for more versatility.
And when it comes down to costs, a code 0 + a furler and a spinnaker + a snuffer or a high-tech furler will of course be much more expensive than a single code D + furler.
Concerning genoa’s versus non overlapping jibs, it will probably very much depend on the basic design of the rig and thus the sailplan.
Both headsails are less efficient on a fractional rig, especially upwind, because they take lesser profit from the upwash of the main. Mast top rigs now seem old fashioned, but in this concept the small, tall main (short boom, high aspect ratio) gives little power but creates upwash along the full lufflength of the genoa, which provides most of the power. This is one of the many reasons why IOR designs perform well upwind.
This configuration has been given up in modern designs, racers following rules when the IOR rating disappeared. And for cruisers because reducing sail meant frequently changing the headsail.
Then came the fractioned rigs, allowing to tune the mast rake -and trim the shape of the main- much more efficiently. And roller reefing systems, which do not work well with big genoa’s.
Mainsails are now much larger, generating more power and much better to trim to very different shapes. Subsequently foresails become smaller, less powerful but also better manageable when tacking and easier to reef with a roller.
I think Paulo’s example of the Bavaria 36, a very successful design, might illustrate the latest stages of this evolution.
Already a fractioned rig but still with a genoa (36 m2) significantly larger than the main (30 m2). Shrouds are built inwards to allow a correct sheeting angle of the genoa upwind.
In the sailplan of the latest version of the 36 the mast has moved forward, with a longer boom, bigger main (42 m2) with a lower aspect ratio and smaller jib (27 m2).
Shrouds are now fitted on the toerail which prohibits headsails overlapping more than 5 to 10 %.
The total sail area has grown a little from 66 to 69 m2. The displacement much more so the sailplan by itself cannot explain differences in performances, but it seems Paulo’s 36 must be quite faster than the latest version because of an much better S/D ratio.
But the issue in this discussion is that the main has grown from 45% to 61% of the total upwind sail area. The headsail shrinked from 55% to 39%.
The mainsail is now privileged for power, the question is whether this will impair performance upwind, even against a heavy sea. My personal feeling is that this would not be the case with a fractioned rig, because it pays less to favor the headsail for power.
Downwind is a very different matter. A big main will very soon screen off a smaller jib, which becomes mostly useless when sailing lower than a beam reach.
For some time an genoa behind a smaller main will perform better, certainly if a sufficiently long track rail is fitted to control the sheeting angle. But at some point the genoa will need a pole, which can also be used with a code D.
Dead downwind, nothing beats a symmetric spinnaker. But I think this is way off David’s LIM concept.
In conclusion, don’t you think a modern design with the shrouds on the toerail, a forward placed fractioned rig, a big main for power and a small headsail for handling, a code D for fun and a staysail (+ a deep third reef in the main) for security can work very well for cruising in most conditions?