Had a bad day on the water yesterday and just couldn't understand why the sail(s) had no power, twitchy and spinning out all the time, and this in 15-25knts. After a bit of reading when I got home I now realise I didn't have enough downhaul...doh 
Moved to a north 430 rdm mast at the beginning of the season and this was probably only second time in 6 mths I'd rigged the 5.4 and 6.0 x-types on the this mast, what I thought looked right compared to the settings on the sail obviously wasn't (luff 463+-1).
Rigged the 6.0 in the garden this morning and experimented;
found if I increased the mast base by one more setting from 34 to 36 it made all the difference in a better looking loose leach and getting that scallop right in the second panel, etc, etc. whereas the sdm was perfect on the 34 setting.
Hope this bit of advise helps someone and stops then from ruining what should have been a great day.
Select to expand quotestanly said..
Had a bad day on the water yesterday and just couldn't understand why the sail(s) had no power, twitchy and spinning out all the time, and this in 15-25knts. After a bit of reading when I got home I now realise I didn't have enough downhaul...doh .
Did you mean you had too much downhaul?
Twitchy sail and no power are a result of too much tension.
Or too much outhaul.Check your "ratio" between outhaul and downhaul. You'll find that if you're increase the tension at the outhaul too much, you'll have to increase the downhaul tension most of the time.
Select to expand quoteRob11 said..
stanly said..
Had a bad day on the water yesterday and just couldn't understand why the sail(s) had no power, twitchy and spinning out all the time, and this in 15-25knts. After a bit of reading when I got home I now realise I didn't have enough downhaul...doh .
Did you mean you had too much downhaul?
Twitchy sail and no power are a result of too much tension.
Pretty sure it was not enough downhaul, there was heaps of back hand pressure, just couldn't get going or lock it in and would just spin out if I did get it going. Once I rigged it with the mast ext. at 36 setting, the head and leach became loose as it did on the sdm at 34 and there is the clearly defined scallop on the second panel to the vts marks. Amazing just about 1cm more and the scallop appears and moves towards the mast with the minimal of more tension. At max of the 34 mast ext. setting there is a wrinkle in the vts panel but that is a different shape to the scallop and doesn't line up with the vts marks.
See how it goes next weekend.
Problem is with the way they label the extensions. Have a look and you will see the numbers may start at 4 or 6cm where the bottom plastic bit meets the tube.
They vary..... and the numbers on the sail only work if you get pulley to pulley contact which none of us do really.
I add 4cm if on my Chinook extension, and 2cm on my Severne extension. Unless I am using the Severne extension with a severne sail and the pulleys on the sail match the base (most sails are 90deg "out") - on the Severne sail I can pull it right down.
Thus I feel that writing numbers on the sail and the extension to make it easier, really hasn't. Many people downhaul with the extension set to the numbers printed on the sail, but the pulleys on the sail are still 2-5cm short of the zero mark on the extension. They are thus under- downhauled to blazes.
To make it easier for those who don't rig by sight, I reckon the best system is North with the sticker on the sail showing where the looseness should extend in from the leech.
Alternatively, dunno why they just don't ALL rotate the pulley block on the sail to line up with the extension (like Severne) or rotate the the pulley/cleat block on the extension like NP do. Lets get a standard.......? easiest is surely for sail manufacturers to mount the pulley block on the sail so it lines up.
Last summer, I was rigging up for a 25-30 knot seabreeze. As always happens, the rigging area is a catchup session with people you haven't seen for a long time. They is always lots of talking and I'm a very poor multi-tasker 
. Anyway, rigged up my Hotsails 4.0 Superfreak and 69L waveboard, but the top of the mast didn't go into the top of the sail properly, and I unknowingly rigged it with 20cm less download while deep in the throws of gasbaggin/bull s***tin to the guy next to me also rigging up. I headed out on my 1st run, planing and in the straps and noticed the sail felt really odd. Looked up and around it and my 1st thought was a malfunction (ie: busted mast etc). Did I gybe, and headed back to shore. When I got back to the rigging area, I was relieved to discover my error !. I fixed my mistake and enjoyed the rest of the session. The incorrect rigging wasn't bad to sail, although it was very hard to point it up wind 
I use RDMs in all my twin-cam free-race sails and they require 2cm more downhaul than when I previously used SDM masts. I figured it was because RDMs are thicker and therefore stiffer?? Whatever the reason, RDM always require more DH than SDMs in my experience.
Did similar thing a couple of summers back down at kingscliff. Over half a metre of mast poking out the top, boom heading down towards my knees. No hope of pointing. End result: long walk of shame. And i didn't have excuse of gasbagging, just wasn't paying attention when I set up. On the topic of down haul I think manufacturer numbers are a basic guide but you have to rely on how it looks and feels. Make notes if you are the organised type.
I've measured my masts and extensions and was amazed at how much deviation there was from the listed dimension. Similiar deviations (although hard to measure) also occur with sails.
When rigging a sail for the first time, I use the recommended settings, taking into account the above deviations. I then check the sail for twist, draft and rotation and then make minor adjustments to the downhaul to suit. I make note of extension positions for each mast sail combination and adjust over time to taking into account performance on the water and the sail stretching with use.
Select to expand quoteN1GEL said..
I use RDMs in all my twin-cam free-race sails and they require 2cm more downhaul than when I previously used SDM masts. I figured it was because RDMs are thicker and therefore stiffer?? Whatever the reason, RDM always require more DH than SDMs in my experience.
I'm no expert, but i would imagine that more curve is required in a RDM to get the leading edge of the mast to follow the same curve as an SDM's leading edge would follow (due to the diameter difference) and perhaps take up the additional luff pocket area that's not wrapping around the larger diameter 
.
