When manufacturers give you mast and extension length for sails are they working on downhauling the sail pulley to pulley or leaving a gap between them, I've noticed on point 7 videos they are always leaving about 10cm space between pulley and Severne seem to pull it down pulley to pulley but there tack strap works much better if you leave a few cm gap.
I may have misunderstood your question. There are few factors to consider:
- actual mast length
- mast cap thickness
- mast extension true length
- sail cap design
- age of sail
All of these will affect sail tuning. This is why it's nice to be able to pair visual cues with measurements.
Manufacturers settings do vary, if they recommend 420, you can set 400+22 and leave 2cms adjustment, or 400+20 no gap or whatever combination works for you.
The downhaul measurement recommended is only a guide, and assumes you are using the sail manufacturer's mast and their extension. (Extension markings and pulley positions actually vary a lot between brands!)
You are allowed to vary the actual downhaul used, should you want to, and that's because we all weigh differently and therefore would not have the same ideal setting.
But, on topic, the recommended downhaul measurement would normally be pulley to pulley.
The setting of a tack strap is a whole other issue as it is used to affect foot edge tension and can be used to effectively add luff curve to the bottom of the sail - which in turn increases bottom batten rotation and, in turn, fullness at the sail foot.
The downhaul setting when using the tack strap should make no difference to the above - although that depends where the tack strap is attached to the sail.
It will be key - with any tack strap - that this attaches to the mast or your extension above the upper U/J bearing, and I suspect that some sails may need an extra gap between downhaul pulleys to allow that.
I don't have Point 7 sails, so maybe post a picture if you have an issue.
Above all, we set our sails so that they work well, and we go 'off road' with the recommendations where we want to achieve that better performance.
It's my understanding, that the luff measurement refers to the length of mast used, from tip of mast to bottom of sail pulleys. How you achieve that is up to you. As you say, it can be easier to leave a gap between the pulleys for the tack strap, otherwise it may have to go around the uni joint, which isn't ideal.
But as others have mentioned, the luff measurement should only be a guide. Use it first sail and see how it works. I did this the other day and had to let it off a couple of centimetres. Next time I'll try a stiffer mast and see if that makes any difference.
I find my ideal downhaul setting then adjust my extension until max downhaul is block to block. This works on my Chinook extensions and I like to keep the sail as low as possible on the mast. That way boom position in relation to the entire is repeatable and predictable each time and helps me sail overpowered (which is my preference).
Select to expand quoteBen1973 said..
I've noticed on point 7 videos they are always leaving about 10cm space between pulley
Why would they do that?
Maybe the guy is too tall and likes the boom above his head?
New slalom and windfoil boards have concave decks to get the sail lower on board for aerodynamic reasons.
I suspect this question has come from watching a P7 video where he says downhaul to all but 10cm to put the cams on. Not the final downhaul. Cant remember P7 video exactly. Some say add most downhaul, put the boom on, let a bit of downhaul off, put the cams on, add final downhaul. Each brand has a slightly different twist on how their sails rig up easiest.
Intrigued, I had a look at their videos. The no cam ACX rigging (they actually used a ACZ but didnt show putting the cams on), it was downhaul to the specs, so 1cm gap left or thereabouts.
For the 3 cammed sail ACK, he downhaul to around 12cm less than max to put the cams on, but on final downhaul did leave a 4cm gap. (Again the ACZ sail was used which has different specs to the ACK). No idea why he left 4cm gap, as it should be fully down to pulley block going off the specs for a 7.8m (other sizes have odd numbers on luff).
Clips are ACX final downhaul. Then ACK (ACZ) to put cams on followed by final downhaul.
I think the reason why he left 4cm gap after final downhaul was he was being lazy and didnt think people would take so much notice
He did say go off the specs & downhaul gauge marker on the panel at the top of the sail.
Select to expand quoteSea Lotus said..Ben1973 said..
I've noticed on point 7 videos they are always leaving about 10cm space between pulley
Why would they do that?
Maybe the guy is too tall and likes the boom above his head?
New slalom and windfoil boards have concave decks to get the sail lower on board for aerodynamic reasons.
That is one reason why some people would set their sails with a longer extension setting and more of a gap, as the sail then wont foul on the deck/straps. The reason for the concave deck is to get the mastbase lower and leverage lower down, not the whole sail. If they wanted to get the gap between sail and deck closer, they would just cut the foot of the sail differently.
The one time I used my sail on a slalom board with deep concaved deck and it fouled the straps and deck. I guess that is the reason, but he didnt explain that in the video. I guess it all depends upon your actual board and sail if you need to leave more of a gap or not.
Select to expand quotePhilUK said..
I think the reason why he left 4cm gap after final downhaul was he was being lazy and didnt think people would take so much notice
He did say go off the specs & downhaul gauge marker on the panel at the top of the sail.
I thought it might be a lazy thing as well.
with my overdrives it set correctly when pulley to puller give to take a bit but the tack strap doesn't work, it just folds the foot up to one side when you apply tension. If you draw a straight line along the foot and down the tach strap it goes around the uj which is not ideal, if you wrap around the groove in the extension where it's supposed to go it pulling the foot upwards almost.
I don't have point 7sails but they are on the wish list with avanti, looking for a more durable sail.
I pull my Overdrives down to about 10mm between pulleys using the recommended extension, that's when the luff pocket looks right.
Select to expand quoteBen1973 said..
with my overdrives it set correctly when pulley to puller give to take a bit but the tack strap doesn't work, it just folds the foot up to one side when you apply tension. If you draw a straight line along the foot and down the tach strap it goes around the uj which is not ideal, if you wrap around the groove in the extension where it's supposed to go it pulling the foot upwards almost.
I don't have point 7sails but they are on the wish list with avanti, looking for a more durable sail.
So we are talking about Severne Overdrives, and not Point 7 sails?
The tack strap should definitely NOT go over the U/J because that would mean the bearing above the UJ will not work and that means when sailing your deck plate will undo or else you will quickly wear out your U/J tendon because of extra twisting/torque load.
The rigging instructions for the Severne Overdrive show the tack strap over the base of the extension.
As you say, the line of tension should indeed form a straight line with the foot.
Are you using a Severne extension?
www.severnesails.com/wp-content/uploads/2019/07/Severne-Cam-Rigging-Guide-Overdrive.pdf
