difference between halyard tension and cunningham tension -
With a bolt-roped sail, halyard tension
primarily controls the stretch-out of the bolt rope which allows for precise positioning of the sail's point of maximum draft
in a fore/aft relationship. So therefore, halyard tension (beyond getting the sail up and raised) allows the luff to be stretched to its designed length AND correctly position the 'point of where maximum draft' occurs. This is because the bolt-rope is 'bound' to the bolt-rope sleeve/sail at both the head and
tack of the sail.
Pull halyard tension ... the luff stretches in luff dimension, the tack stays in place, .... and the clew 'rises'.
'Perfect' halyard tension results when sufficient 'designed' stretch-out occurs .... so that the sail's designed 'tack angle' is met. The tack angle is usually derived from the boat designers requirements - typically most tack angles are in the range to 87°-89° for boats with 'straight up' / non-raked masts, less with purposely designed raked masts.
Rx: halyard tension controls - 'weather helm'.
's primary function is to aid shaping the (bolt-roped sail's) luff entry shape
. The cunningham (cringle) is located well above the binding of the bolt-rope to the sail near the tack. This allows luff material to 'slide' somewhat along the bolt rope near the bottom and mid panels. Tensioning the cunningham will cause the luff to become 'more rounded' (for better aerodynamic effect in the higher wind ranges where the airflow 'can' stay 'attached' to the lee side at the luff for better energy transfer from the wind to the sail). The majority
of the developed 'suction peak' (Bernoulli) occurs along and quite near the 'luff entry'!!!
When tensioned by a cunningham, the luff shape starts to become 'more rounded' and to a lesser extent the mid section of the sail becomes more 'flattened'. When over tensioned, the sail will develop a crease (girt) just behind or at the luff.
Rx- the cunningham is more of a 'speed control' due to its better sail 'flattening' of the mid section AND luff 'rounding' ability because the functional
binding to the bolt rope is ONLY from the sail twine binding at the head of the sail.
Sliding goose necks
Were an outgrowth from when wire halyards were popular when racing. The sail was raised, the wire was attached to the mast via a ball swaged on the wire and the swaged ball was inserted into a 'hook' or 'jaw cleat'. This allowed the sail to be raised 'precisely' to correct (racing legal) position of the 'black band' at the top of the mast - 'precisely'. Then, to obtain correct
bolt rope tension the sliding gooseneck was pulled down and then locked into position according to 'helm pressure' when beating for each days wind strength and sea-state.
IF the sail's luff dimension with the halyard 'locked' in place exceeded
the lower 'black band' then the cunningham was ALSO used to 'help' additionally tension the luff ... by stretching out the sail material along the luff; but, NOT the bolt rope
, so that the sail's 'as raised' dimension was at or less than
the (racing legal) dimensional space between BOTH black bands.
Racing 'cuts' vs. cruising 'cuts'.
The above discussion applies only/principally to dacron sails made with 'pre-loaded' (shortened) bolt-ropes. With plain vanilla woven dacron 'cruising' sails
, since about the year ~2000, bolt rope preload has essentially been abandoned - and the shape you buy is the shape you get. You just raise such a sail and ignore any 'precision or high performance' shaping possibilities ----- but you still 'can' over
stretch the bolt-rope to aid in lessening and control of 'weather helm'; but the sail will not develop its 'as designed' shape due to the now 'overstretched' luff bolt rope.
Racing dacron sails are usually 'cut' with 'preloaded
' (shortened by 1" for each 10-11FT. of luff length) bolt ropes, and FLAT luff entry shapes ... a flat entry requires a very precise helmsman, as the range of the angle of attack is VERY narrow. The flatter entry shape also benefits from a cunningham, as increased c-ham tension increases luff entry 'roundness' - a much better shape
for very FAST boats in HIGH winds, AND the 'more rounded' luff shape is 'more forgiving' vs. the range of attack angle at the higher wind ranges.
FWIW - here's a detailed article I did quite a few years ago on how to properly raise
a woven dacron sail WITH
PRELOADED BOLTROPE ... Plus, how to analyze the ever changing shape/dimensions and what to do about it, .... without breaking your savings account:
hope this helps.