Sailboat Rudders 

The primary purpose of sailboat rudders is of course to give the helmsman the ability to steer the boat, but a well-designed one will also provide hydrodynamic lift to windward, in the same manner as does the keel.

Racing sailboat hull in cradle ashoreThese twin high-aspect ratio rudders on an all-out race boat are clearly optimised for their hydrodynamic performance.

Placing sailboat rudders into distinct categories is fairly straight forward - they're either:

  • Outboard or inboard rudders, which can be
  • Unbalanced, balanced or semi-balanced, and be
  • Keel-hung, skeg-hung, transom-hung or spade rudders.

Take a stroll around any fair-sized boatyard during the lay-up season and you'll see examples of most of them...

Inboard & Outboard Sailboat Rudders

If the rudderstock passes through the underside of a boat's hull, it's an inboard rudder. Conversely, if it doesn't, it's an outboard rudder.

Most outboard rudders are turned by a tiller as there's no rudderstock to which a wheel-steering quadrant can be mounted.

The two rudders shown below are quite different examples of outboard rudders.

An Outboard Rudder on a heavy displacement, long-keeled, canoe-sterned sailboat.Fig 1 - An Outboard Rudder on a heavy displacement, long-keeled double-ender.
An outboard rudder hung on the transom of a light-displacement sailboat.Fig 2 - An outboard rudder hung on the transom of a light-displacement sailboat.

Fig 1 shows an example of a keel-hung outboard rudder that is seldom seen on today's cruising boats.

Outboard rudders like the one in Fig 2 can be easily removed for service or repair with the vessel afloat. You might struggle with trying to do that with the 'barn door' of a rudder in Fig 1 though!

Examples of inboard rudders can be seen in Figs 3, 4, 5, 6, 7 & 9.

Unbalanced Rudders

This unbalanced rudder is supported by a full-length skeg.

It is unbalanced because the entirety of the rudder is aft of its axis, the axis being on the centreline of the rudderstock.

When turned, the full force of the water flowing past the skeg acts on one side of the rudder - a fact that will be very much apparent to the helmsman, particularly on a tiller-steered boat.

An unbalanced sailboat rudder.Fig 3 - An unbalanced sailboat rudder.

Balanced Rudders

The rudder shown here is said to be balanced because part of it is forward of its axis.

As the rudder is turned, the force exerted by the water flow acting on the forward part partially counteracts the force applied to the area of the rudder that is aft of the axis.

This reduces the load on the tiller and makes life easier for the helmsman.

A Balanced Rudder on a sailboat.Fig 4 - A Balanced Sailboat Rudder.

Semi-Balanced Rudders

The rudder shown here is supported by a half-length skeg.

The upper part of the rudder (aft of the skeg) is unbalanced.

However, the section of the rudder below the skeg is balanced by the part of the rudder projecting forward of its axis.

The helm loads will be lessened as a result. 

Hence this type of rudder is said to be semi-balanced.

Semi-Balanced Sailboat RudderFig 5 - A Semi-Balanced Sailboat Rudder

Keel-Hung Rudders

Keel-hung rudders are often seen on heavy-displacement, long-keel boats of yesteryear.

This one's on a Nicholson 32 from the 1960's.

Whilst the propellor is well protected, the propwash from it acts on only a small area of the rudder which, combined with the massive displacement and full-length keel, makes close-quarters manoeuvring under power something of a hit-and-miss affair.

A Keel-Hull Sailboat RudderFig 6 - A Keel-Hung Sailboat Rudder

Skeg-Hung Rudders

The skeg is a structure built into the hull of a sailboat solely for the purpose of supporting the rudder.

Full length skegs provide a high degree of rudder security but can be generate high helm loads, requiring a long cockpit-sweeping tiller or wheel steering.

Half-skegs can solve this problem as they allow for a semi-balanced rudder.

A Skeg-Hung Sailboat RudderFig 7 - A Skeg-Hung Sailboat Rudder

Transom-Hung Rudders

Transom-hung rudders are attached to the boat by hinging mechanisms known as Pintles and Gudgeons.

Pintles always incorporate a pin, whereas Gudgeons always have a hole for a pin.  Usually, Pintles are attached to the rudder and Gudgeons are attached to the transom - but not always.

The example shown here (on a Sadler 25) is something of a hybrid, incorporating a full length skeg to provide additional security.

A transom-hung rudder with additional support provided by a full-length skeg.Fig 9 - A Skeg-Hung sailboat Rudder

Spade Rudders

From a hydrodynamic point of view, the Spade Rudder is most efficient and is becoming the norm on modern sailboats.

The smaller the gap between the rudder and the hull, the greater the end-plate effect provided by the hull.

But being a cantilever with no support along its leading edge, unless it's properly designed and engineered, robustness may be an issue.

A Spade RudderFig 9 - A Spade Rudder

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