Self steering

Self steering is almost essential for single handed sailors and is the means whereby a yacht's steering can be delegated to a mechanical or electronic device while the sailor sleeps or attends to other tasks on the yacht.

Self steering gear can be broadly categorised into two groups:

Electronic
Electronic self steering gear uses an electronic compass (flux-gate compass) or interface with GPS system to provide the input control signal to an electrical or hydraulic servo which acts directly on the yacht's steering gear.

Advantages of this system include:

• The yacht will steer a true desired course regardless of wind / currents
• The steering servo can be high powered and able to steer large yachts
• They are (relatively) simple and cheap to purchase
• They are simple to install and having no underwater parts are not prone to damage

Disadvantages of this system include:

• They are entirely dependent on electrical power.
• Unless very sophisticated, they may not make reference to wind shifts which can result in incorrect sail trim or other dangerous rig loadings
• Being an electronic device in a harsh environment, water ingress to electronics may result in damage
• They are almost impossible to repair at sea

Vane type
Vane self steering relies on a wind vane and pendulum to provide the input to either a small steering servo tab on the main rudder, or a seperate self-steering rudder.

Advantages of this system include:

• They are entirely mechanical and do not rely on electrical power (useful on a yacht with a limited electrical system)
• They use wind power and direction to provide steering input and will thus keep the yacht at the desired angle to the wind
• The harder the wind blows, the better they work.
• They are inherently reliable
• They can usually be repaired with simple hand tools
• They are quiet in operation

Disadvantages of this system include:

• Initial purchase costs can be high (they are often custom made)
• They have underwater parts which could be prone to damage
• Wind shifts may result in the yacht steering away from the desired course (although perfectly safely)

Footnote
I have used both and favour wind vane type self steering as it fits better with my sailing ethos (work with the wind rather than against it and use no electronics or engine).