A skeg is a fixed fin projecting down from the hull immediately ahead of the rudder. On a skeg-hung rudder the rudder is hinged along the trailing edge of the skeg, which supports it, protects it and adds directional stability. Beginners can think of it simply as a rudder support. Experienced sailors know the distinction between a full skeg, which runs the whole depth of the rudder, and a partial skeg, which supports only the upper part and leaves a balanced area of rudder blade below it, and they know the trade-off a skeg represents: protection and tracking on one side, helm weight, drag and agility on the other. The word is also used for the small fixed fin on the stern of a dinghy, canoe or kayak that helps it hold a straight course.
Types of Rudder Support
- Keel-hung rudder: on a traditional full-keel boat the rudder hangs on the aft edge of the keel itself. Maximum protection, heaviest helm.
- Full skeg: a fin running the full depth of the rudder, with the rudder hinged along its trailing edge on several bearings. Strong, well protected, no balance area ahead of the rudder stock.
- Partial skeg: a shorter fin that carries the upper bearings, with the lower portion of the rudder extending below and often forward of the stock, giving a partly balanced rudder.
- Spade rudder: no skeg at all; the rudder hangs on its stock, cantilevered from the hull, with part of the blade ahead of the stock to balance it. Lightest helm, most efficient, most exposed.
What a Skeg Does
The skeg does three jobs. It carries rudder bearings along its trailing edge, spreading the loads on the rudder over a long hinge line rather than a single stock, which makes the installation very strong. It shields the leading edge of the rudder from lobster-pot lines, floating debris and a grounding, and on a boat that dries out or is hauled on a slip it takes the weight instead of the rudder. And as a fixed vertical surface well aft, it resists yaw, so the boat holds her course with less input from the helm, which matters greatly to a self-steering system or a tired watch-keeper offshore.
The costs follow directly. A fixed fin ahead of the rudder means the rudder cannot be balanced by putting blade area forward of the stock, so the helm is heavier and the boat is slower to answer. And the same directional stiffness that makes the boat easy to steer on a long passage makes her reluctant in a tight marina or a tacking duel.
Skeg, Helm Balance and the Sail Plan
A skeg-hung rudder is less balanced than a spade, so it magnifies whatever helm loads the sail plan produces. Weather helm that a spade-ruddered boat would shrug off becomes real work on the tiller of a skeg boat. This is one reason sailmakers pay close attention to the mainsail on such boats: a flat, well-controlled leech, a mainsail that does not hook when the backstay is eased, and a headsail sized to keep the centre of effort forward all lighten the helm. Reefing the main a little earlier than the wind strictly demands is often the fastest and most comfortable way to sail a heavy-helmed skeg boat upwind, and a mainsail with a flattening reef or a deep first reef makes that easy.
Cruising and Racing Perspectives
Ocean cruisers have long favoured skeg-hung rudders for their strength and for the way they protect the one appendage a boat cannot sail without. Many bluewater designs still specify a partial skeg for exactly this reason. Racing boats almost universally use spade rudders, sometimes twin spades on wide-sterned hulls, because the balance, low drag and instant response are worth more than protection when there is a crew on deck and a lift-out at the end of the season.
When the boat is hauled out, wobble the rudder to check for play in the bearings, look for cracks where the skeg meets the hull, especially after a grounding, and make sure the gap between skeg and rudder is even along its length.
Frequently Asked Questions about Skegs
Is a skeg-hung rudder safer than a spade rudder?
It is better protected and less likely to be lost after a collision or grounding. A well-engineered spade rudder is perfectly seaworthy, but a skeg puts the strength where the risk is.
Why does a boat with a skeg have heavier steering?
The skeg prevents the rudder from carrying any blade area ahead of the stock, so the water pressure on the blade is not balanced across the pivot. Every degree of helm has to be held by the helmsman or autopilot.
The skeg is a designer’s answer to a question every offshore sailor asks: what happens if I hit something? It buys strength and tracking at the price of a heavier helm and a little speed, and sailing a skeg boat well means keeping the sail plan balanced so that heavier helm stays light in the hand. See also rudder, weather helm, keel and balance.