I don't want to suggest that all boat designers are the same, or that John Cherubini (Sr.) didn't test a bunch of prototypes in all conditions before going with this chosen skeg design, but... I recently read a nice blog by boat designer Robert Perry about a famous and successful commissioned design of his. The owner contacted him to tell him that he needed advice because the rudder skeg had broken off. Perry's first question was "How did it steer without the skeg?" and the owner said "Better!" So they left it off and went with a pure spade rudder!
Reasonably, for a balanced rudder, you have two options: the skeg and the balanced blade (spade). In both the general idea is to provide 18% of the total area as that before the rudder post. On a spade rudder, this portion actually goes the wrong way, which can add to steering problems especially if the boat is heeled hard over (it will try to lift or bury the stern) and especially if the rudder is angled backwards, such as on my friend's older Pearson and others (upper end of rudder post being forward of the lower end). Olin Stephens criticizes the angled-post spade rudder setup intelligently (as he does with everything else) in
All This And Sailing Too.
The spade rudder is also vulnerable to damage and, when damaged, falling off the boat due to its being hung only by the rudder stock, which has to do too many contradictory jobs: to stay straight, to hold the weight of the rudder, to withstand torsional loads, and to keep out water. Its best advantages are a quickness in steering, preferred by small-keelboat racers (making the boat more like an unballasted dinghy) and simplicity of construction (by cheap-boat builders). That said, the Star, perhaps the most wonderful small keelboat ever, has a skeg-hung rudder (sort of).
I would prefer my H25 to have a skeg; but the boat was co-designed by Bob Seidelmann who was, indeed, one of those small-keelboat racers (the Star in fact).
For all sorts of reasons, the better setup is the skeg-hung rudder. It steers more reliably at high angles of heel, is stronger, and is vastly easier to handle when reversing under power! It is somewhat more expensive to build; but, once installed, is easier to maintain and even to repair. In my view it's even more streamlined and thus faster; and it virtually eliminates the likelihood of collecting lobster-pot strings, to which the spade rudder is just about designed to be vulnerable. In my opinion the spade rudder is not meant for serious ocean voyaging; and few serious ocean voyagers will disagree.
I submit that Mr Perry's suggestion that the boat with the skeg-hung rudder, steered better without the skeg, is only of anecdotal value. Technically the boat should be
harder to steer, especially at speed or even at very low speed (fluky conditions). I don't mean that it's harder to turn the helm. I mean that, without either the skeg or the balanced leading edge, the rudder can stall, creating drag but no steering effect. Being raised by my dad who used to teach, 'Steer with authority', I expect the boat to go round when I put over the tiller and I don't see a skegless, unbalanced rudder helping me do that.
But I allow that much of the evidence for and against may be ultimately anecdotal after all.
