Had several attempts at getting more downhaul on my 6.7 (2010) Severne O/drive today before getting on the water knowing I would be powered to the max at 23-28 knots. Didn't look right and came in to downhaul some more after hour and half sailing but decided against going out again as the wind was building and need some fuel in the tank for tomorrow.
Before derigging I had a go at downhauling some more and gained 3cm without much trouble, sail looked a lot more like it should.
My thoughts are that the mast pocket, left salty from previous use and stored for quite a while shrinks and wont stretch within reason to get desired downhaul (gave mast pocket a good rinse when I got home, and if at that location next time I rig I will give it a pre-rigging soak under the shower before rigging)

AM I right or dreaming?

( used to have the same opinion a few years back with the Gaastra GTX's )

Luff pocket and rope friction are reduced when wet.
I had some sails that were almost all cross cut shaped, so there was no extra shape in the luff curve. This meant that the mast was very tight against the pocket before full downhaul could be achieved. Even though there wasn't a lot of mast bend getting full downhaul took a lot of effort.
I used to pre wet the luff pocket before rigging, it made things much easier.

i think Decrepit has got it. A lot of the work (Force times distance ) of down hauling goes into friction. If the system was frictionless the tension in the rope would be the same regardless of whether you were putting on more downhaul or letting it off slowly. It seems to me that once you've got that cleat undone the tension while letting off downhaul is noticeably less.

It always puzzled me that the old NP RS slaloms took a lot to downhaul but the mast didn't seem unusually curved? I thought maybe the bend was biased and unnoticed in the stiffer lower section? Maybe the luff material just stuck to masts? I used to use a silicon spray on the mast to make down hauling a bit easier, but water is probably a better idea.

Sometimes I wet my downhaul line to make it a bit easier to downhaul the sail when rigging. It works very well.

How cold was it?

It is more than likely the webbing that is often folded over to protect the stitching on the vertical seam in the luff sock that has shrunk.

Select to expand quote

Sputnik11 said..
How cold was it?

20 ish degrees, according to willy weather temp graph, forecast was 23.

I think your onto it..I leave a few sails at my mates place in WA and only use them ones a year .in his hot shed ...the ones I don't wash are as stiff as a board ..maybe use some fabric softness ..on the sail cloth pocket ?

I normally allow my sail to dry before de-rigging it, beer time, so when I release the down haul, the mast pocket can't shrink because it's already dry.
But when I re-rig it, it's hard to down haul because of some friction in the pocket, but mostly with the down haul line and base extension being dry.
Like mentioned before, I pour some water on the down haul line only, as well as the base, easy rigging is the result. Even salt water will work if you only have a little drinking water, or beer even.

At least you weren't asking about mast shrinkage.

Formuline (dyneema) rope.