Sail luff lengths

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!

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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?

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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.

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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?

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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.

The Ezzy one is correct. Ooops, it isn't in the photo.

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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:

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choco said..

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

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.

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)

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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.

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.

Do you LOOK at the sail during all that?

Look, memorize, try to repeat that same look.