The Advantages of a Skeg
We believe that a modern cruiser should have a fully protected rudder and prop aperture and we protect ours with a full skeg. Unlike the rudder on a full keel, our rudder and skeg do not extend to the full depth of the keel; this will hopefully mean that if (or when) you run aground it will be just the keel that makes contact leaving the rudder with a safe margin of water under it. This is perhaps most important when aground in soft mud or sand because it allows you to wiggle the boat free far more effectively if the rudder is still able to maneuver. And because our drive line is virtually parallel with the water flow our exceptional high thrust efficiencies work to float the boat off the bottom by forcing large amounts of water between the bottom and the hull – literally lifting the boat free.
There are other advantages to a skeg as well…
- The full skeg allows the prop to be in a protected aperture. The skeg not only helps to deflect debris from the prop when underway, it also often prevents snagging lobster pots and other underwater obstacles. The prop shaft also has reduced exposure with most of its’ length being inside the boat.
- The skeg also increases the strength of the rudder by allowing a bearing to be placed at the very bottom of the shaft which drastically reduces shaft loading.
- Like a full keel, the skeg acts like the tail feathers on an arrow or the vertical stabilizer on an aircraft, improving the direction stability of the boat as it tracks through heavy sea states.
But like most things in yacht design there are a few compromises and in the case of a trailing rudder it often means not being able to utilize a balanced rudder blade. With a spade rudder design a designer can have up to 10% of the surface area in front of the shaft. As the rudder turns, the area in front of the shaft sticks out into the water flow and helps lighten the load on the trailing surface. You may notice the leading edge of our rudder has an usual shape; this is designed to allow for some balance above and below the prop (you can not have a balanced blade directly behind a prop as this will cause the rudder to capsize (stay in a turn) and be held there by the pressure of the prop wash). This design works very well resulting in a light, but sensitive, feel on the helm.