Good on you Mauisails for showing how to accurately measure extension length so it can be compared with their recommended values. (see image below).
It seems clear that that a variety of mast extension measurements are possible, whether you measure to the lowest point of the lowest pulley, the lowest point of the highest pulley, the distance to the middle pulley centreline etc, etc, etc. Also, upon measuring up a NP vs Chinnook base, it was also clear that there could be up 3cm difference in extension length if both were downhauled to the max (ie pulley to pulley). That adds up to actual downhaul being potentially up to +/- 5cm different vs what you 'think' your are rigging in alignment with the sailmakers specs. Perhaps the source of SickemRex's belly problems on the 7.1?
So where should actual mast extension measurements be taken to for the popular brands? Anybody have an equivalent diagram/rule for NP or North?
I believe any guide should only be a rough guide , a real rough guide.
There are so many variables , age of sail , type of mast ( brand , curve , year , carbon content ), conditions , personal preference , it keeps on going.
A sail must be rigged by eye.
Its a big topic with many things to consider.
My tip ....dont go by the numbers on a sail.
Learn the visual cues , crease length between 2 and 3 batten , tightness of luff around mast at the boom , loosenes at the leech and so on.
Rider weight , wind and personal preference can vary so much so you have to experiment and each sail is different.
One cm of downhaul can make a big difference in power and how its delivered.
I suppose its about learning the vibe of sail tuning.
The race guys can faff around all day doing minor adjustments.
The only use for numbers on a sail is to set your extension to the right length, after that it's all judgement by eye.
Select to expand quoteeckas said..
So where should actual mast extension measurements be taken to for the popular brands? Anybody have an equivalent diagram/rule for NP or North?
Ive never seen one on either brands ,but north and ezzy has the VTS .with the dots
that s more accurate .visual...
but good on Maui for the diagram .I hope it was worth the ink.
The other issue is different extensions. Where that pic shows the lower line - at bottom of pulleys - is labelled zero, 2cm and 6cm on 3 of my extensions.
So some assume pulley to pulley contact which will never happen for most folks, therefore so many people would be missing 2cm - 5cm ish all the time.
In the worst case pulley to pulley contact - even if u achieve it thru good threading order and slippery rope - would still be 4cm ish short of spec.
Its dumb.
Pondering the dilemma of where on the sail to measure luff length in comparison with specs, I defer to the principles of maths and science.
If we assume that downhaul pulleys are only used to make rope function adequately, and in a perfect world they would be minimised to reduce weight, we have a calculus equation that as downhaul pulley diameter tends toward zero, the luff length of the sail tends towards being measured to the centreline axis of the downhaul pulleys. Thus I conclude that luff length should be measured to the centreline axis of the downhaul pulleys.
If we also note that in placing a tape measure between the mast base and the downhaul pulley, parallax error in reading the tape measure is minimised if the meausurement is made to the forward-most pulley's centreline axis, we have our solution! Luff length in a perfect world should be measured to the centreline axis of the forward-most pulley.
Yes I'm bored!!!!!
Nope, the original diagram you posted is the accepted industry standard now.
Measure to the bottom edge of the pulley block.
But don't rely too much on the printed measurements. measurements can be up to 4 or 5cm different with a different mast and individual sail tolerances! Look carefully at the sail, especially the depth and leech to make your final judgement. Test slightly different settings and go with what feels best.
Consensus seems to be that quoted figures area guide only, a good starting point.
There is no way a sail can be made mm perfect, it is stil comes down to experience when it comes to sail tuning.
Select to expand quoteImax1 said..
I believe any guide should only be a rough guide , a real rough guide.
There are so many variables , age of sail , type of mast ( brand , curve , year , carbon content ), conditions , personal preference , it keeps on going.
A sail must be rigged by eye.
Its a big topic with many things to consider.
My tip ....dont go by the numbers on a sail.
Learn the visual cues , crease length between 2 and 3 batten , tightness of luff around mast at the boom , loosenes at the leech and so on.
Rider weight , wind and personal preference can vary so much so you have to experiment and each sail is different.
One cm of downhaul can make a big difference in power and how its delivered.
I suppose its about learning the vibe of sail tuning.
The race guys can faff around all day doing minor adjustments.
Dear Imax 1,
I agree with you. I always rig my sail by my eye. My tuning time is 5 minutes. I never waste my time for tuning because if I do that I miss the wind. % 90 sail performance is enough for me.
Melih.
Guy Cribb has an easy and accurate way to ensure the downhaul setting is good. At different angles, the sun gives a false indication for those who look at the creases. He says that you look at the second batten, from the top, and how it aligns with the mast. More info about this technique is freely available on his website.
I think the master of rigging sails is Victor. bjorn dunkerbeck caddy.he once famously said you downhaul the sail until it dont go down anymore.
Select to expand quotegavnwend said..
I think the master of rigging sails is Victor. bjorn dunkerbeck caddy.he once famously said you downhaul the sail until it dont go down anymore.
That's just so wrong! 
I think that was a mischievous, flippant statement, maybe designed to mislead Bjorn's competitors. 
I sail on waves or in choppy water all the time. The biggest sail I used is 5.2 sq M. So my comments probably are not relevent to those bigger race sails.
I believe that on waves or choppy water, as soon as you hit a lump and lift off ever so slightly, all efficientcy is lost. Your sail would be flapping about, and you would be desperately trying to keep it under control. So how is the tiniest fine tuning is going to help ?
There is this guy who is fastitious about fine tuning his sail. He would spend half an hour, going back and forth all over the sail. Lifting here, tugging there, shaking it, flipping it. Yet he seems to end up downwind a lot of the times as he couldn't sail back upwind. And he resorts to walking back to where he started. His fine tuning is not helping, apparently.
Select to expand quoteJupiter said..
I sail on waves or in choppy water all the time. The biggest sail I used is 5.2 sq M. So my comments probably are not relevent to those bigger race sails.
I believe that on waves or choppy water, as soon as you hit a lump and lift off ever so slightly, all efficientcy is lost. Your sail would be flapping about, and you would be desperately trying to keep it under control. So how is the tiniest fine tuning is going to help ?
There is this guy who is fastitious about fine tuning his sail. He would spend half an hour, going back and forth all over the sail. Lifting here, tugging there, shaking it, flipping it. Yet he seems to end up downwind a lot of the times as he couldn't sail back upwind. And he resorts to walking back to where he started. His fine tuning is not helping, apparently.
I don't think half an hour tuning is necessary but you do want to have an idea on what your doing rather than going off specs.
The Ezzy system seems to be the most foolproof of all. When each sail is made it is rigged with a load cell on the recommended length Ezzy mast, and the bottom edge of the mast is marked on the tack of the sail. This reduces pretty much all of the variables that can be considered in getting correct downhaul. Sure, you have to use one of their masts and there are a few other factors involved, but it is hard to get much closer than this.
Great idea! 
But that is not going to work when the bottom of the mast is hidden under the luff pocket as in most Cambered sails. 
Select to expand quotesailquik said..
Great idea!
But that is not going to work when the bottom of the mast is hidden under the luff pocket as in most Cambered sails.
I read once on seabreeze that the difference with guys who use cammed sails is they will always find something to whinge about 
(I do own one by the way).
Clarence
The beauty about race sails is you can set it (tuned) to the conditions on that day.
Select to expand quotesailquik said..
Great idea!
But that is not going to work when the bottom of the mast is hidden under the luff pocket as in most Cambered sails.
The sail in the video had a mast pad but it could be pulled back so you could line up the mark .. Can't you do that with most cambered sails? 
I used to own one of those North "Power XT" mast extensions, or whatever they're called. The ones with the lever.
So, so good when I was still learning. I could play around with the downhaul settings effortlessly. No need to leave the water. You can even adjust the downhaul while sailing. Click-click; that easy.
Select to expand quoteevlPanda said..
I used to own one of those North "Power XT" mast extensions, or whatever they're called. The ones with the lever.
So, so good when I was still learning. I could play around with the downhaul settings effortlessly. No need to leave the water. You can even adjust the downhaul while sailing. Click-click; that easy.
Yeah I'm stuck with whatever I first rig as I don't have the strength to add or let it off while on the water. Usually play safe and just go out with max down haul as it doesn't take much for me to get overpowered..
The you are in for a treat with that new KA Koncept Sue. I am just a frail little old man, and I've not even looked like having to use my downhaul winches since 2014 on Koncepts, or this year my 7.1m KA Race. Use Formula line and get a good downhaul handle like the Unifiber one and then carry it in your vest when sailing. Easy!
I am a true skeptic when it comes to sails. Perhaps that is because I have been sailing for too long.
I remember the way to rig up a sail is
(1). Put suffcient downhaul to set the mast sleeve,
(2). Outhaul until the clew touches the boom-end. That is meant to bent the mast a bit more so that it is easier to apply the downhaul.
(3). Apply downhaul so that the sail is nice and tight.
(4). Let out the out-haul so that a nice curve/belly is formed for power.
And that is all there is to it. Now, there is the wind strength indicators at the top to check. Wrinkles to inspect, and a whole range of things to worry about.
And the verdict ? I still have a trailerful of sails of 10 years and older vintage, and an old board. I constantly sail past folks with supposedly well-tuned sails. So where have I done wrong ?
Select to expand quoteJupiter said..
I am a true skeptic when it comes to sails. Perhaps that is because I have been sailing for too long.
I remember the way to rig up a sail is
(1). Put suffcient downhaul to set the mast sleeve,
(2). Outhaul until the clew touches the boom-end. That is meant to bent the mast a bit more so that it is easier to apply the downhaul.
(3). Apply downhaul so that the sail is nice and tight.
(4). Let out the out-haul so that a nice curve/belly is formed for power.
And that is all there is to it. Now, there is the wind strength indicators at the top to check. Wrinkles to inspect, and a whole range of things to worry about.
And the verdict ? I still have a trailerful of sails of 10 years and older vintage, and an old board. I constantly sail past folks with supposedly well-tuned sails. So where have I done wrong ?
You know it makes a difference when you downhaul another 2 cm and you add another 2 knts to your top speed. All sail brands are different, mine there is about 5 cm downhaul to play with. Just trial and error really 
Select to expand quotesboardcrazy said..sailquik said..
Great idea!
But that is not going to work when the bottom of the mast is hidden under the luff pocket as in most Cambered sails.
The sail in the video had a mast pad but it could be pulled back so you could line up the mark .. Can't you do that with most cambered sails?
Not if the extension is more than about 10cm.
Downhaul amount according to windspeed, and your choice of sail size.
If you choose too big a sail for the wind, use max or slightly more than max downhaul.
If you choose too small a sail for the wind, use less downhaul and less outhaul.
You won't know until you've done a few runs, and conditions change while you're out sailing.
Select to expand quoteevlPanda said..
I used to own one of those North "Power XT" mast extensions, or whatever they're called. The ones with the lever.
So, so good when I was still learning. I could play around with the downhaul settings effortlessly. No need to leave the water. You can even adjust the downhaul while sailing. Click-click; that easy.
Where can you buy the power xt?
