Skegs do tend to be rather long and of limited fore aft thickness hence of rather spindly and weak as to impact strength but they do add a second vertical strengthen compared to non-skeg mounted rudder so there is a sharing of loading across the two structures.
Recommend reading the comments of Kraken Yachts regarding skeg mounted rudders:
"In the old days, the rudder on a typical blue water
cruiser was hung on the back of a long keel
. Indeed the occasional retro-design still has this feature.
Then in the ‘60s leading yacht designers such as Sparkman & Stephens moved to fin keels and hung the rudder on a skeg. This became the norm for cruiser-racers until – in pursuit of ever more speed – skegs began to disappear and most rudders became ‘stand-alone’ spades.
However the vast majority of blue water
cruisers hung onto their skegs. Sailors and designers valued the extra support, strength and protection that a skeg undoubtedly provides. And as ever-more unidentified floating objects (UFOs) now litter the oceans, this protection is even more important.
So why have almost all large modern production cruisers abandoned their skegs?
And why – even more surprisingly – is this habit spreading to serious blue water cruisers? Why are so many unsupported spade rudders now hanging under blue water cruising sterns?
The answer – predictably - lies in the cost.
It is far cheaper to suspend a spade rudder under a flat surface than it is to incorporate a tough skeg into a hull and attach the rudder to it.
Kraken Yachts Ltd always prefers the ‘safety first’ approach. So the Kraken 50 ft sailing yacht, 58 and 66 models all have robust skegs. This process may cost more – but what price
can you put on safety
If you study the increasing number of mid-ocean rudder losses in events
such as the ARC
(occasionally leading to the abandoning and/or sinking of the yacht) you will find that unsupported spade rudders are leading culprits. Indeed, it was reported that one couple who lost
their yacht were ‘now looking for a boat with a longer keel and a skeg-hung rudder.’ The same applies to the growing trend towards twin rudders. Unless these have strong skegs to absorb or deflect the impact of UFOs, they are just as vulnerable.
Kevin Dibley and Kraken Yachts have opted for a ‘belt and braces’ approach. Dibley explains; “The bottom of the K50’s rudder is attached to the skeg by way of a bronze
heel plate. Although both the robust Kraken rudderstock and the full depth
skeg are self-supporting, the skeg will absorb a large part of the energy of hitting a UFO. All of this force would otherwise be on the rudder blade’s leading edge and stock.”
Kraken chairman Dick Beaumont has cruised well over 250,000 nautical miles so he understands the importance of safety
at sea. Kraken Yachts’ robust skeg-hung rudder design and construction are further proof of his determination to supply safety as standard."
One might also find of interest Kraken's Zero Keel structural configuration. Zero as in NO BOLTS holding the keel with its lead ballast.