Chris 249 said..
The info around seems to indicate that there is no inherent structural advantage in a skeg over a spade. Large ships have spade rudders, not skeg-hung ones. If you can built a spade rudder that will steer a destroyer, aircraft carrier or supertanker and not get knocked off then you can build a spade rudder that will steer a yacht and not get knocked off. Ship designers don't use spade rudders because they are idiots who like losing rudders.
One of Australia's DDG's hit two whales off San Diego last year at speed. I believe they hit the stabilisers as the ships staff would have known if the whales were wrapped around the rudders. The stabilisers are like a spade rudder pointing out each side, to control roll at speed to allow more precise targeting and response.
They would have been a significant impacts, not seen a DDG but similar frigate stabilisers have a rudder stock of above 300mm diameter in a marinised high tensile steel (not stainless). They also have massive support ribbing around them and thicker hull plating in this area.
But the truely impressive part of the story is the twin gas turbines. The ship caught the whales, then the gas turbines spooled up under load and no one was the wiser. I think the Officer of the Watch just thought the whales had dropped off.
