What is the Clew Outhaul and how to use it

12 February 2019

The clew outhaul connects to the clew of the mainsail. The outhaul runs through the length of the boom and the boom is controlled by the mainsheet and the vang / kicker.

The outhaul, when pulled tight, pulls the foot tight across the length of the boom and in doing so it helps to flatten the sail, especially the foot, thus increasing cord length and reducing draft.

We use the outhaul in conjunction with the vang, main halyard tension, sheet and traveller position to change the shape of the mainsail to best trim it for specific AWA (Apparent Wind Angles) and AWS (Apparent Wind Speed). 

When trimming on a beam reach or upwind, we are trying to improve boat speed. We do this by accelerating using maximum lift (using a deeper draft and less sheet) and then by ‘changing up gears’ to get faster still. As we do this we are usually reducing draft and sheeting on.  We check sail trim by examining the sail ‘telltales.

Putting on more outhaul means grinding on more outhaul tension.  We would usually do this in calmer water where we are in a higher gear looking for better speed and less drag.  We might also do this, in combination with sheeting on the main hard and dropping it down the traveller, if we wanted to flatten and de-power the mainsail and we didn’t want to reef.

Easing off the outhaul creates a deeper belly (or draft) which increases lift (but also drag). We can then move that draft forward or aft by using halyard tension.  We would generally ease the outhaul when bearing away and sailing ‘off the wind’. 

Some instructors might refer to the outhaul as reef zero.  It is useful to think like this as the reefing lines run parallel with the outhaul and when they are used they effectively replace the outhaul. 

Two golden ‘Outhaul Rules’;

  1. When adjusting the outhaul always make sure to depower the mainsail so as to not overstress the outhaul and inboom mechanism.
  2. Remember to ease off the outhaul when you have flaked the sail at the end of the day. This will prevent the foot becoming stretched and extend the sail’s useful working life.


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