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Sail luff lengths

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Created by mr love 22 days ago, 15 Mar 2020
mr love
VIC, 1915 posts
15 Mar 2020 2:59PM
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Ever wondered why the luff dimensions on your sail just don't work? Take a look at this picture. 3 different RDM mast extensions with the pulleys close to aligned . The line I drew on with the marker is the center of the hole they label as 10cm. Mmm, which ones are correct?


decrepit
WA, 9851 posts
15 Mar 2020 1:18PM
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I'm guessing the middle one to the top of the pulleys?
Top one is maybe 10cm from min adjustment, not from pulleys.
Bottom one is 10cm from bottom of pulleys, The difference between 2nd and 3rd is about pulley diameter.
A bit like a lot of windsurfing stuff, ever manufacturer makes up their own standard. A bit like a certain fin company that measure their weed fin lengths down the blade instead of their draft.
Then there's that whole equivalent volume thing when boards first went wide.
Don't start me on tuttle bases!

Te Hau
390 posts
15 Mar 2020 4:39PM
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Barry Spanier has a sensible method. From the bottom of the mast to the bottom of the pulley is the Downhaul distance, ie 12 and if it's a 430 mast the luff is 430 + 12 = 442

choco
SA, 3525 posts
15 Mar 2020 7:11PM
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Orange Whip
QLD, 727 posts
15 Mar 2020 8:25PM
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choco said..




The bottom dotted line would not necessarily be in line with the bottom of the sail on the mast tube, would it? I've always assumed the bottom of the luff length is to the bottom of the sail not to the bottom of the pulleys. Is that not correct?

Orange Whip
QLD, 727 posts
15 Mar 2020 8:25PM
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Select to expand quote
choco said..




The bottom dotted line would not necessarily be in line with the bottom of the sail on the mast tube, would it? I've always assumed the bottom of the luff length is to the bottom of the sail not to the bottom of the pulleys. Is that not correct?

Ben1973
325 posts
15 Mar 2020 8:56PM
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My Overdrives using Severnes recommended settings, mast and extension seem to rig best with about 4cm between pulleys not pulley or pulley like I assumed to start with.

decrepit
WA, 9851 posts
15 Mar 2020 9:29PM
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Orange Whip said..
>>>>> Is that not correct?



When every body does something different, assuming there is a universal, "correct", is going to lead to trouble.

But I agree, pulleys touching means 0 extra downhaul, makes more sense, and is easier to measure.

gorgesailor
283 posts
17 Mar 2020 3:11AM
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mr love said..
Ever wondered why the luff dimensions on your sail just don't work? Take a look at this picture. 3 different RDM mast extensions with the pulleys close to aligned . The line I drew on with the marker is the center of the hole they label as 10cm. Mmm, which ones are correct?




You shouldn't measure to the center of the hole. It should be from the top of the collar - where the mast rests, to the lowest point where the sail pulleys can reasonably be pulled - usually about 1cm above the downhaul block.

choco
SA, 3525 posts
17 Mar 2020 6:05AM
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Orange Whip said..

choco said..




The bottom dotted line would not necessarily be in line with the bottom of the sail on the mast tube, would it? I've always assumed the bottom of the luff length is to the bottom of the sail not to the bottom of the pulleys. Is that not correct?


Use a tape measure to check in saying that are masts the correct length as well?

Imax1
QLD, 2514 posts
17 Mar 2020 6:55AM
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That's why I only rig to visual cues , never numbers.

mr love
VIC, 1915 posts
17 Mar 2020 10:24AM
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gorgesailor said..

mr love said..
Ever wondered why the luff dimensions on your sail just don't work? Take a look at this picture. 3 different RDM mast extensions with the pulleys close to aligned . The line I drew on with the marker is the center of the hole they label as 10cm. Mmm, which ones are correct?





You shouldn't measure to the center of the hole. It should be from the top of the collar - where the mast rests, to the lowest point where the sail pulleys can reasonably be pulled - usually about 1cm above the downhaul block.


Irrelevent to the point I am making. All these pullers are roughly alligned give or take 5mm yet the difference in the printed graphics is huge..40mm. If I rigged to the sail specs on the chinnok using the numbers on the base it would be 40mm different to the other base using their printed numbers.

decrepit
WA, 9851 posts
17 Mar 2020 8:08AM
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mr love said..
>>>>If I rigged to the sail specs on the chinnok using the numbers on the base it would be 40mm different to the other base using their printed numbers.

On the chinook, if you subtract the difference between pulleys and first hole,does that bring it back into line with the others?

MikeyS
VIC, 1460 posts
17 Mar 2020 12:28PM
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The Ezzy one is correct. Ooops, it isn't in the photo.

Basher
182 posts
17 Mar 2020 7:57PM
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We'e known this for some time - and I've certainly written about it before.

The key for most people is to either use the same brand extension from the sail manufacturer and use their mast too, or else to try different rigging settings,

Half a centimetre of downhaul can make all the difference to a sail and you soon get to know how yours should look when rigged on the beach. The ultimate test is how it feels on the water.

For those who need definite answers when rigging sails - and for those who get obsessed with measurements - it's worth noting that different weight sailors apply different loads to any given sail size. So that means that different weight sailors will often use different downhaul settings for the same sail.

The measurements printed on the sail should only ever be seen as a starting point. Occasionally they are very wrong.

gorgesailor
283 posts
18 Mar 2020 3:20AM
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decrepit said..

mr love said..
>>>>If I rigged to the sail specs on the chinnok using the numbers on the base it would be 40mm different to the other base using their printed numbers.


On the chinook, if you subtract the difference between pulleys and first hole,does that bring it back into line with the others?


Should be like this:






mr love
VIC, 1915 posts
18 Mar 2020 6:27AM
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Yes and on one of these extensions that hole is marked as 2cm which is my point.

NotWal
QLD, 7309 posts
18 Mar 2020 12:50PM
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choco said..




That doesn't make sense. That's mast extension not downhaul.
Gorgesailor is correct IMO.

PhilUK
30 posts
18 Mar 2020 3:00PM
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Its why Ezzy sails have a tape measure on the tack strap and a gauge on the sail to line up level with the bottom of the mast.

Basher
182 posts
18 Mar 2020 10:37PM
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This is a problem of 'standardisation' and to understand it you have to remember how our equipment has changed over time.

In the old days, you'd typically own just one length mast and instead of a mast extension you'd have an adjustable head on the sail - allowing different size sails to fit the same mast.
At the base of the mast was a simpler mast foot 'plug' which had no height adjustment. If I remember correctly, the typical wave mast was 450cms long and the mast foot added a further 8-10cms to that.

So a mast extension was/is like the mast plug but had/has a tube insert for the mast which allows the mast to be raised further from the board deck. The question then started as to where you take a measurement from.

Some brands had it so the mast extension fully inserted determined their 'zero extension' setting. When you add the extension collar to take the mast 2cms away from the zero setting, that's marked as 2cms extension. Raise the ring 4cms further and that's the 6cms setting, and so on.

The problem then comes that the extension pulleys sit below the base of the mast on the mast foot 'plug' section. We now know that those pulleys might be positioned very differently on different extensions, at different distances from the base of our mast. No mast extension has a true zero setting.

So the proper way to standardise a modern mast extension is, as has been already said in earlier posts here, is to measure the distance from the base of the mast to the point where the sail tack pulleys and extension pulleys meet (i.e. where you can't downhaul further without setting the extension higher.)
Some modern extensions a marked that way. Others measure from the base of the mast to the centre of the extension pulley sheaves.

In the original photo shown at the top of this thread, the top two extensions have got markings based on the original system. So their 10cms marking is 10cms above the extension's minimum setting, ignoring the amount of mast plug which lies below.
In the photo, the blue extension is the one I'd describe as most correct - and it's a Chinook, I think. . But I'll bet the markings on that do not exactly match my Severne extensions.

bigdaz
NSW, 250 posts
19 Mar 2020 7:44AM
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PhilUK said..
Its why Ezzy sails have a tape measure on the tack strap and a gauge on the sail to line up level with the bottom of the mast.


That's another thing I love about my Ezzy sails!!! It takes all of the guess work out and is absolutely fool proof - perfect rigging every time no matter what brand extension you use. It's the best system I've ever used.


choco
SA, 3525 posts
19 Mar 2020 9:11AM
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Wow so many different solutions, so at a guess there maybe some sailors out there not rigging their sails right, min/max marks maybe the best solution(that's if they have been placed in the right spot from the factory)

sailquik
VIC, 4949 posts
19 Mar 2020 9:10PM
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IMHO, this is the ONLY method that make sense!

The 'Luff Length' is exactly that. The only question is at what point it is measured. And I was under the impression that this IS the industry standard for the measurement.

And yes, you WILL need a ruler or tape measure the first time you rig and you cant rely on most of the extension markings. But after the first time, you should know, especially if you have marked your extension with a permanent marker like I do.








Basher
182 posts
19 Mar 2020 6:44PM
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sailquik said..
IMHO, this is the ONLY method that make sense!

The 'Luff Length' is exactly that. The only question is at what point it is measured. And I was under the impression that this IS the industry standard for the measurement.

And yes, you WILL need a ruler or tape measure the first time you rig and you cant rely on most of the extension markings. But after the first time, you should know, especially if you have marked your extension with a permanent marker like I do.









That's a bit curious, isn't it?
'Downhaul length" ? What is that?
That drawing shows how Maui Sails measure their recommended extension length but that won't be helpful when using other brands.
To me, maximum downhaul for and extension setting is where you go block to block.

Measuring luff lengths of sails also varies, because you might start at the head but at the tack the sail can extend below the tack cringle or pulley.

So my advice for this minefield remains the same as ever:
1) Ideally, use the sailmakers recommended components, because that's the only way you can hope the sailmaker's recommenced settings will make any sense.
2) Expect to set your sail to a different downhaul setting than the recommended one.
3) Ditch the tape measure (which can be a distraction) and learn instead to set your rig by eye on the beach, and learn to feel on the water when it's working well or not.
4) For any rig, different weight sailors will probably need a different downhaul setting.
5) If you are still a beginner or improver, practice rigging your sail on windless days, so that downhauling becomes easier - as that skill stops you being frightened of making simple adjustments.

sailquik
VIC, 4949 posts
19 Mar 2020 10:22PM
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I would say Downhaul length and Luff Length are the same thing.

It's not just a Maui sails thing. Every sail brand I have rigged in the last 10 years or so seems to have used this method of specifying luff length. But perhaps my experience with other brands is a bit limited?

I should have added that one must include the mast length in you specifications for DH Length/Luff Length but I guess I thought that was obvious.

So if the specified luff length is eg: 442cm and you are using a 430 mast, the luff length will be the mast length plus 12cm to the bottom of the tack pulley. And yes, you will want to make your extension a couple of cm longer than that, probably set at (an actual) 15cm from the top of the collar to the top of the base pulleys. Is that too hard to figure out?

I have been known to rig my sails, 'block to block', but that is not the normal thing. We usually have 1-3cm of gap (on slalom/Race/Speed sails) to allow for fine adjustment. Of course, the ideal luff length (amount of downhaul) will vary slightly with different conditions, sailors and even masts, but the specifications should be a very good guide for a starting point, and some manufacturers do even specify a range from Max to Min.

Basher
182 posts
19 Mar 2020 9:07PM
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I guess we're in intellectual armchair sailing mode now, but if I was being picky then I'd say that luff length is fixed - whereas 'downhaul length' is variable, within a limited range.

On the Maui sails diagram, above, they show 'downhaul length' as being the extension setting.
But I guess they mean mast length + extension length = downhaul setting.


Most of us actually know how to set our sails. We get the specified mast and then set the extension to achieve the recommenced luff length setting, as printed on the sail. If the sail looks wrong when we downhaul the sail then we adjust the extension setting.

sboardcrazy
NSW, 6919 posts
20 Mar 2020 11:57AM
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choco said..




That one is hard to use if the sails luff covers everything..
I ended up measuring from the bottom of the pulleys to a point on the black plastic base. Say it was 30mm. I then marked 30mm on a piece of wood that I hold against the setup and match the downhaul to that.

LeeD
1238 posts
20 Mar 2020 9:58AM
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Do you LOOK at the sail during all that?

sboardcrazy
NSW, 6919 posts
20 Mar 2020 4:24PM
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LeeD said..
Do you LOOK at the sail during all that?


Yes. I've got the sail working well the first time and then take measurements as the guide for future sessions.. obviously checking everything still works ok each time. I was having trouble with sail rotation but they work A1 with this system.

LeeD
1238 posts
20 Mar 2020 11:36PM
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Look, memorize, try to repeat that same look.

sailquik
VIC, 4949 posts
23 Mar 2020 7:58PM
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LeeD said..
Look, memorize, try to repeat that same look.



AND, take heed of the recommended measurements!!!!

Unfortunately, it has been my experience that a lot of less experienced sailors dont know what their sails should look like for best set. And even quite experienced sailors if the model or brand is new to them. (not all sails look the same when set optimally)

It's just a no brainer really.

For experts like LeeD, just go with your gut feeling and preconceived biases.



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"Sail luff lengths" started by mr love