Topic : Stepped Out Jib Head

I notice on the new Pinnel and Bax jib, the leach does not run directly into the head and actually joins the head at a step out (for want of a better term), there is a good picture of Tom sailing at Thorpe Bay which shows the 'step out' extremely well.

I could be wrong, but I was led to believe this is outside of the rules for MR jibs, would nayone like to make comment. Sail Makers, Measurement Man?

Posted: 02/10/2007 15:14:49
The jib does measure at the requirement for the 50 mm. jib head measurement does not have to be perpendiclar to the luff of the jib but to the nearest possible point. Therefore they do measure as we had this discussion with graham Williamson as our one was exactly the same cut.
Sure Graham will clarify later.
Bye for now.

Posted: 02/10/2007 15:44:00
By: Barnsie
If the measurement is not perpendicular to luff, where is it taken from...?

Posted: 02/10/2007 16:10:50
Alverbank have been cutting my jibs and mains like this for three years now, all within the rules, nice to see a trend catching on. 
Are you going for the wing lets next??

Posted: 02/10/2007 16:19:16
By: DaveF
but doesn't the stepping out stop the jib being "nominally triangular" and also from being "supported by the luff only"

The jib in the photo would appear to be a four sided shape and supported by the head reinforcement as well as the luff?

Posted: 02/10/2007 16:35:26
By: curious
I heard when new ISAF measurement rules come into effect in near future they may not be allowed anymore. GGGGG or other sail measurers can confirm further.

Posted: 02/10/2007 16:37:07
By: Captain Ross
Once new ISAF rules are adopted they will have to measure the top of the luff from where the natural extended lines of the leach and luff cross. Hence as the designs currently stand they would measure over size,..I think. Ofcourse if your sail is measured before this new rule change is enforced it will continue to be legal, so there is an argument to be had for buying in bulk if you think the current design is fast.

Posted: 02/10/2007 17:06:15
By: Alex
The measurement is taken from a point 50mm down the luff from the headpoint 'to the nearest point on the leech'.  ie, at whatever angle is appropriate.

The head is not supported by anything other than the luff wire and legal reinforcement, ie no battens or abnormal stiffening.

The sail is still nominally triangular - the tweak is minimal.

When we fully adopt the ISAF measurment code, the leech and luff will have to be extended to establish the forward headpoint for the purposes of calculating the area, and therefore to accommodate the 'distorted leech' a considerable reduction in actual surface of sail will result.

Interestingly, most of the sails with this configuration that I have measured have come out at 2.6x sqm against the permitted 2.8 sqm, so one hasn't got terribly excited about it...


Posted: 02/10/2007 17:10:25
By: Measurement Man
However G, isn't there much more unmeasured area given that the leach is extended further aft than in the 'normal' configuration?

P.S. I haven't read the whole rule, and need my training expedited!

Posted: 02/10/2007 18:37:15
By: deepy
I presume this is the photo in question. Not overly clear, but visible.

Posted: 02/10/2007 20:36:00
By: Mags
The idea of the fat head is to increase the overlap of the jib and Main as far up the slot as possible, hence increacing the the overall wing effect of the sail.
This is the section from the were the 'slot' (top of the jib still overlapping the main down to the boom) is the height of the wing and from the forstay to the leach of the main being the width of the wing effect.
This means that in a normal 'Triangle' jib the top 200-300mm of non overlap is useless and has reduced the overall height of the wing.
Have a look at the gap in the linked photo 3660, 3555

Posted: 02/10/2007 23:35:52
By: Davef
Would someone be kind enough to post the relevant measurement rule, I do not have a copy at work.  I would be interested to make my own interpretation.

Posted: 03/10/2007 12:18:58
Its a pdf so i can't cut and paste.
but follow the link, rule 12D

Posted: 03/10/2007 12:54:47
By: daveF
I think it is questionable, exactly where the leech of the sail begins.  To me the head of the sail has been constructed to support the leech, technically not a headboard, but perhaps not leech either...?

Posted: 03/10/2007 15:03:22
And as previously posted a 4 sided shape i.e. not a triangle by any description....

Posted: 03/10/2007 15:45:38
When I was doing O level geometry I think such a four sided figure was called an irregular quadrilateral irrespective of how long or short any of the sides happened to be.  Four sided figures have internal angles adding up to 360 degrees unlike triangles which have internal angles adding up to 180 degrees.  Maybe, 30 years on, things have changed and we shall soon be back to the square rigged vessels of old.  I'm off home to sew an extra flap onto the top of my (triangular) sail. Not that Gannet will ever win anything!!

Posted: 03/10/2007 16:31:12
By: Garry R
This is not a new thing, Dickie Dee had an late 80's/early 90s alverbank jib with a rounded head. Quick in the light or heavy stuff but too twisty for general use

I think that in specific circumstances the rounder head would be better than the stepped heads we are seeing today. There may be a question of legality, but Dickie's got past Tony Donaldson!

Posted: 03/10/2007 17:58:49
By: Chris M
Or it never happened.  That said with GGGGGGGGGG opining as above it appears to be quite legal!

Posted: 03/10/2007 20:52:33
By: Protest!
Not sure I agree.  If the step out is considered part of the leech then it would appear to be a four sided shape and if it is not part of the leech it would not measure...

Posted: 04/10/2007 10:53:00
But the rule states, extention of the leach to the join point, the fact we cut the leach early, doesn't break the rules.

Posted: 04/10/2007 12:40:45
By: DaveF
Legal or not it's clearly stretching the rules to gain an advantage ie. extra sail area in slot - one of the most important areas !
So it needs clarification! I know of several other sailmakers who were very unhappy when they first appeared.
I would guess than "nominally triangular" was to allow some leeway in manufacturing. This is not the case here and has been shaped like that to gain a perceived advantage. Very dodgy in my humble opinion.

Posted: 04/10/2007 13:43:47
By: Judge
Development classes testing the boundarys of the rules, always good to see.

If this development is consistantly legal under the ISAF measurement code, could it filter through to the more 'restricted' classes with small overlaps on the jib (firebucket maybe), or is it purely a pecularity of the merlin measurement system?

Posted: 18/10/2007 09:51:06
By: Devils advocate
At the moment sails are measured as 2d items, so there is no rulling on the 3rd dimention.

Posted: 18/10/2007 12:37:54
By: davef
Why dont you move the tack aft if you want to increase the overlap!

Posted: 18/10/2007 17:43:47
By: Old fart
but moving the tack back alters the rake angle and raises the clue opening the leach and not increasing the overlap at the top of the slot.

Posted: 18/10/2007 19:48:59
By: Davef
Just moving the tack back would tighten the leech! 
Anyway surely that why you have adjustable jib leads to cope with variations.

Posted: 18/10/2007 20:38:08
By: -
Depends on how hard you pull

Posted: 19/10/2007 08:27:16
By: davef
The MR is not a one design, you can alter the shape of your jib, raise or lower the clew etc. I'm not sure its all about the overlap!

Posted: 19/10/2007 08:38:02
By: Old fart
What overlap?  There is no overlap - just look at the pic of Tom at Thorpe Bay on the home page - there is barely overlap at the clew, let alone the head.

There is a slot, of course, which is critical and truly sensitive to rake, tack position, luff tension, clew height, fairlead position and sheet tension. It is hard enough to get all these variables right, isn't that enough to be going on with?!


Posted: 19/10/2007 10:35:57
By: Measurement Man
Here, here!

Posted: 19/10/2007 11:30:40
By: Richard (3233)
I seriously doubt that it's anything but an advantage to have extra (however little)  unmeasured sail in the slot area...else why go to the trouble of doing it, its clearly not the easiest way to make the head. 
Of course GGGG is right and there are many other variables but that argument could be used for many other measurments!

Posted: 22/10/2007 11:23:14
By: Judge
I think we should apply the rules as they are written... As previously commented and demonstrated (the internal angles of a triangle combine to make 180 degrees), this is clearly a four sided shape.

Posted: 22/10/2007 11:29:01
There is already a rule in section 12 limiting the width of the foresail at 50mm down the luff from the head to 50mm so there is very little to be gained out of exploiting the potential for extra sail are here.

Posted: 22/10/2007 12:34:20
By: Andrew M
in that case the mainsail is 5 sided shape??

and what about the radius at the bottom of the jib and main, and if these are ignored, then the top of the jib could have a curve on it with no orientation point for a 4 sided object.

Posted: 22/10/2007 12:34:51
By: davef
Headboard dear boy, headboard....

Posted: 23/10/2007 15:37:12
You can stick as much curve on the edges of the foresail as you can make to set, both now and always.  Without battens in fact the fastest foresails have a hollow in the leech not extra area as having something flapping around in the slot is about 50 times worse than having less area.  The luff will also be slightly hollow or there is no allowance for sag of the luff wire, so the only place for the extra area is where we have it, along the foot.

Posted: 23/10/2007 21:56:46
By: Andrew M
no, top battern!! nolonger triangular, inner angles add up to 180 ????

and Andrew my top leach doesn't flap, and what good is all the extra sail at the bottom of the jib when its curled up on the deck?

Posted: 23/10/2007 22:36:08
By: Davef

the extra area on the deck creates a great end plate effect when the sail is sheeted hard.

off the wind the sheet is eased and the sail starts to move from the deck. the more area at the bottom the more slowly it leaves the deck enhancing the end plate effect.

finally the sail is eased enough for it to be free of the deck and you have a bigger sail than if you had not added the free area.

the area is low down, not as useful as up high, but still useful.

fat had jibs are fast as the sail starts working sooner. seem legal to me too.

Posted: 25/10/2007 20:19:32
By: jib sheeter
I know this i was just being facetious, the deck plays a very, very important part in the air flow through the slot, by stopping the air flow off the bottom of the Jib and channeling it throught the slot.

If you have seen my boat (3542)this year you will might have noticed, the vortex wings that have been on the top of the jib and main, and flow smothers up both sails. And in the early part of the season a wing on the boom (wich needs re thinking for next season).
They have helped, in the speed, power and exceleration of the boat. measured against known quantities.
And before you maon about rules, they were looked at buy a measurer, and as commented on before in this topic there is no rules for the 3rd dimension on sails, at present!.
and the fat head jib and main allowed for this anti vortex tips to be applied.
I will send Mags a few pictures for you to look at.

Posted: 25/10/2007 23:27:06
By: Davef
See vortex1 and 2 photos here:

Posted: 29/10/2007 10:10:34
By: Mags
Vortex2 also shows Daves mainsheet that a sheepshank in the middle there?!?!

Posted: 29/10/2007 10:11:50
By: Mags
Look like battens in the jib to me.

Posted: 29/10/2007 10:22:29
By: -
Thanks Mags

for Unknown
Their not batterns, as there made from sailcloth, and no extra support to the leach.

Posted: 29/10/2007 11:59:06
By: davef
great stuff - love it!

Posted: 29/10/2007 15:09:32
By: interesting thread
Do you think then that a shelf footed (bolt rope and track.) main rather than loose footed one might be better? With an inverted triangular boom (Like a smaller version the J class Park Avenues booms.)As long as it fits the overall dimension rules. It would certainly give you the fence effect you seem to seek.

Posted: 02/11/2007 10:11:22
By: Ancient Geek
With the outhaul tight, doesn't a loose-footed mainsail bunch up against the boom anyway?

Triangular boom sounds more painful if you get hit...

Posted: 02/11/2007 11:13:37
By: Mags
I agree that fences are desirable, and I think Dave is doing a good job at pushing the boundaries.  Don't you want the fence at the top of the mainsail though, and only really in conditions where you're not trying to induce too much twist?  I reckon that having decks, crews, booms, spinnaker poles etc probably applies enough of a fence effect lower down.  Presumably the wind shear forces are such that there is an upward by the time it gets to the boat, in flat water &c &c, component in it, meaning fences along the batten pocket might be quite good, no?

Posted: 02/11/2007 12:37:38
By: deepy
There are no rules on the dimensions of the boom (only the black sail band,) but I agree with mags that a triangle would be a danger to the crew.

Mags,The loose foot main does curle up, but its not uniform or wide enough to do the job required, same with the bulk rope foot.
I'm in the process of revising, my first version the i took off at the Rutland training

Dave F

Posted: 02/11/2007 12:39:31
By: davef
There must be some support to the leech, not the same as a batten but stiffer than if there was nothing there.

Posted: 02/11/2007 13:57:36
By: Blogger
Nothing more than a seam would do and there are no rules to how many seams there can be!, the only rule that I can see that applies is the folding of the sail, and it does fold.
The central jib one has been removed and the other 2 are in the stiffening area.

Posted: 02/11/2007 15:18:12
By: davef
Aren't we getting off subject... what about the original question? Let's take a straw poll; legal, not legal, unconvinced either way

Posted: 02/11/2007 16:00:08
I'd guess that because it is inelegent were it proved to be efficatious it would be banned.
Do they need to be in exavt alignment to the air flow or not.
This morning in humid conditions I watched the swirls from the winglets on my SAS Flight (An MD11 I think.) seem a lot of turbulence but the designers know what they are doing - I hope!

Posted: 02/11/2007 17:00:18
By: Ancient Geek
The boom has to pass through the 13cm circle though doesn't it?

Posted: 02/11/2007 17:08:21
By: Chris M
What if the boom had flexible protrusions that would pass through a 13cm circle when squashed?!

Posted: 02/11/2007 21:01:20
By: Mags
Mags, thats what I remember although it was 5" in my day, but a glance at the rules as published on this site seems under "Spars" to refer only to masts and I could see no other reference to booms (Except spinnaker booms.) except black bands on the main booms.

Posted: 02/11/2007 22:46:40
By: Ancient Geek
Thats the rule None, apart from the black band, and the mast 5" rule means that thoes masts with moulded attached spreaders, fail.

Posted: 04/11/2007 19:17:46
By: DaveF
So you mayt have a 2 foot or more deep boom - masive extra projected area in carbon it wouldn't weigh much, but  it would be just like sailing a Finn! Crash helmets and then those could be made heavy...........!

Posted: 05/11/2007 09:09:54
By: Ancient Geek
There are those who will recall 'New Potato' which when brand new sported a very large section  boom which was prebent to exploit the free area below the foot / clew line. Sadly the pre-bent boom decided to carry on bending and by the end of its first championship race the boom was almost touching the thwart and Messrs Morrison and Gunson were 'limboing' under it to tack! But perhaps made of carbon........

Posted: 05/11/2007 15:48:39
By: Peter Scott
Presumably the bit about permentaly bent masts and booms had been annuled? Incidentaly the reason bendy booms didn't work was they actualy added flow by shortening the distance between the clew and tack as the boom bent.

Posted: 05/11/2007 20:41:47
By: Ancient Geek


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