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That's an interesting comment and just doesn't appear to be correct, as best I can tell: the lift/drag ratio of a well designed foil is much greater than the hull. Not only that, adding length w/o adding SA is just adding drag.
Adding length without adding SA is certainly not just adding drag. Ask any one of the major dinghy or skiff designers and they will say that adding length (without increasing SA) allows major speed improvements. That's why top dinghy designers say things like this;
"Length is not quite everything. Say ninety-nine percent”.
Length is "very (important); especially upwind and in waves - maybe not much when being blown down wind like a leaf behind a large asymmetric. Wavemaking still comes into it even for faster classes”.
“We’ve done out a whole bunch of research where we’ve worked out what is the ideal length for a two man boat, and it’s around 17’6”( ). The ideal length for a three man boat is around 21’ ( ). And as time and technology progresses, that length will get longer not shorter. Things get lighter and stiffer, and as you’re able to build things at a lighter weight without greater mass, then the ideal length will get longer not shorter.”
If you take the same boat and give it extra length, you basically;
1) increase hull speed, therefore allowing the boat to move to the speed where it can start planing more easily. This avoid the issue of boats like Cherubs where it is said ""The Cherubs are at a disadvantage sailing against other boats in light winds at hull speed, since they are so short" or 14s where it is said "“The biggest limitation to the speed of a 14 upwind stems from the fact that it is a short boat with a sailing displacement to length ratio similar to that of performance keelboat”
2) fine up the entry, which is of considerable importance when going upwind at speed;
3) reduce the rocker;
4) dramatically reduce the DLR; as Paul Bieker says "the concept of the hull changes drastically with displacement/length ratio";
5) make for a boat that handles waves much better
Ask the guys who design 14s, 12s, Moths and Cherubs and they will routinely say that the fact that one of the major restrictions of such boats is that they are very short. The Int 14 actually has a higher DLR than a 420 or 470; a 12 Foot Skiff or R Class has a DLR is similar to that of a Snipe or Mumm 30.
These are the reasons that people like a former world I-14 champ said that it would be easier and cheaper to increase the speed of I-14s by giving them longer hulls without foils, rather than adding foils. Of course, they recognised the issues, but their point was the question of class development was more complex than simply saying faster boats = better boats.
Of course, short boats have their own very special appeal - for example, they are light and very quick downwind in a breeze. In no way am I criticising them.
The point is that adding length may be a more economical and lower-maintenance way to increase speed and handling than adding foils. There are more definitions of efficiency than the simple one of speed to length ratio. Ratios like speed to cost, speed to maintenance and speed to complexity are arguably at least as important.
