There are two primary parts to downwind sailing with spinnakers:
In the old days downwind sails were typically defined by weight...i.e. 0.5, 0.75, 1.5 etc. In the computer age (80’s onwards) Science overtook art and ‘Codes’ were given to sails based on their mold or ‘flying shapes’ which were optimized for different TWA and TWS. This is still evolving as we entered the supercomputer age of CFD and FSI analysis.
Pole height…
TWA and the Pole
Pole angle, height & projection
Tweaker / Downhaul
Tweaker down
Tweaker up
Roll the boat to windward for increased projection and optimise your downwind TWA. This is a common technique employed by race crews often referred to as ‘pressing’ or sailing on the ‘red line’. By adjusting the boat’s trim with crew weight on the weather side and grouped in the side stay area the windward heel can produce an effect which makes the helm neutral, projects the spinnaker and results in the boat sailing deeper at the same speed. Results vary with different boats – but is worth experimenting as the results can be dramatic!
Angles are everything! Be sure you know the TWA for your course so you can select the most suitable sail!
Trimming the Asymmetric
As luff length has a direct effect on how deep you can sail, you can alter this with your Luff tension (halyard, tack line) and your tweaker tension based on how much sheet you have eased out.
As you ease the sheet the leech will ‘fly’ more, so you may need to pull the tweaker on as the sheet gets eased to control the leech. This will result in you being able to sail deeper. If you ease the tack up, or the halyard down a little, this will allow the luff to project even more, adding to an increased TWA.
As the sail eases the leech twists
Tweaker down for deeper running as the sheet gets eased.
Ease the tack to induce luff projection = deeper angles.
Communication
As with trimming upwind the same ‘trim cycle’ must be applied to downwind.
The discussion is related to the balance of the boat, the desired angle to sail the boat...and this being synchronised between the helm, trimmers and crew.
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