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. |
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. |
If the measurement is not perpendicular to luff, where is it taken from...? |
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. |
but doesn't the stepping out stop the jib being "nominally triangular" and also from being "supported by the luff only" |
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. |
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. |
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. |
However G, isn't there much more unmeasured area given that the leach is extended further aft than in the 'normal' configuration? |
I presume this is the photo in question. Not overly clear, but visible. http://www.merlinrocket.co.uk/gallery/view_photo.asp?folder=gallery/open_meetings/thorpe_bay/2007&file=thorpe2007_stewart.jpg |
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. http://www.merlinrocket.co.uk/gallery/view_photo.asp?folder=gallery/salcombe_week/2006&file=start.jpg |
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. |
Its a pdf so i can't cut and paste. http://www.rya.org.uk/NR/rdonlyres/18AA0447-9BD0-45AC-905D-2C2008CE08D9/0/ClassRulesMerlin.pdf |
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...? |
And as previously posted a 4 sided shape i.e. not a triangle by any description.... |
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!! |
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 |
Or it never happened. That said with GGGGGGGGGG opining as above it appears to be quite legal! |
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... |
But the rule states, extention of the leach to the join point, the fact we cut the leach early, doesn't break the rules. |
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 ! |
Development classes testing the boundarys of the rules, always good to see. |
At the moment sails are measured as 2d items, so there is no rulling on the 3rd dimention. |
Why dont you move the tack aft if you want to increase the overlap! |
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. |
Just moving the tack back would tighten the leech! |
Depends on how hard you pull |
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! |
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. |
Here, here! |
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. |
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. |
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. |
in that case the mainsail is 5 sided shape?? |
Headboard dear boy, headboard.... |
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. |
ITK |
davef |
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. |
See vortex1 and 2 photos here: http://www.merlinrocket.co.uk/gallery/default.asp?folder=gallery/salcombe_week/2007 |
Vortex2 also shows Daves mainsheet arrangement....is that a sheepshank in the middle there?!?! |
Look like battens in the jib to me. |
Thanks Mags |
great stuff - love it! |
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. |
With the outhaul tight, doesn't a loose-footed mainsail bunch up against the boom anyway? |
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? |
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. |
Dave, |
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. |
Aren't we getting off subject... what about the original question? Let's take a straw poll; legal, not legal, unconvinced either way |
I'd guess that because it is inelegent were it proved to be efficatious it would be banned. |
The boom has to pass through the 13cm circle though doesn't it? |
What if the boom had flexible protrusions that would pass through a 13cm circle when squashed?! |
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. |
Thats the rule None, apart from the black band, and the mast 5" rule means that thoes masts with moulded attached spreaders, fail. |
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...........! |
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........ |
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. |