Foam luff
- Thread starter Quoddy
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It allows you to partially reef your jib without completely destroying the luff and sail sail shape. It is built into the luff of the jib by the sail maker. I'm sure most sail maker's websites will discuss the details.
The leading edge of the luff of jibs/genoas are not a 'straight line' between the head and tack of the sail. The luff leading edge is purposely cut 'curved' to compensate for the stretch/sag of the wire that occurs when the sail is fully wind loaded and the headstay is 'stretched'. With this 'hollow' shape in the leading edge of the luff when you 'roll' a sail on a furler, the top and bottom sections will roll 'first' on the foil then followed by the middle of the sail -causing a lot of 'bagginess' in the middle sections of the sail. So, when you roll the sail the area near the head and tack of the sail are tightly rolled on the foil but the center section 'lags' thus leaving 'excess' material 'unrolled', thus the sail becomes very 'full' or 'baggy' in the center when rolled. Sails arent flat, they are somewhat '3D-spherical' in there shape.
The foam used is approximately 1/8" thick and is sewn down on the sail's luff in a tall triangular pattern ... one point of the triangle is near the head, one point near the tack, and the most important point is located about 15-20% "up" on the luff length and about 12 to 18" back from the front edge of the luff. This 'tall thin triangular' shape of foam makes the fabric 'thicker' in the mid sections of the luff, so that when the sail is rolled the center portions of sail (now 'thicker') roll up 'just as fast' as the head/tack so the 'bagginess' (that would occur without the foam) is lessened.
Without a foam luff you cant 'reef' a jib/genoa due to the 'bagginess' that develops when roller furling - so its either all the way out or completely furled. With a foam luff you can 'reef' - typically reducing the sail area by 30% at best, Beyond 30% sail area reduction the unrolled portions of the sail will again gain a lot of bagginess/fullness in the mid panels/sections.
Modern computer sail design/cutting programs can alter the leading edge shape of the luff so that foam luffs are not absolutely necessary and still affect up to 30% sail area reduction without distortion of the shape of the sail. Sometimes in very large sails a sailmaker will apply a very 'special geometric shape' (a somewhat s-shaped curve) to the luff leading edge AND apply a foam luff.
For more than 30% SA reduction one can apply a 'second' foam luff which is installed near the "30% reduced/rolled shape" ... and get down to 50+% SA reduction and still have good shape - very rarely done and usually only seen for 'passagemaking' or boats that sail the open ocean.
;-)
The foam used is approximately 1/8" thick and is sewn down on the sail's luff in a tall triangular pattern ... one point of the triangle is near the head, one point near the tack, and the most important point is located about 15-20% "up" on the luff length and about 12 to 18" back from the front edge of the luff. This 'tall thin triangular' shape of foam makes the fabric 'thicker' in the mid sections of the luff, so that when the sail is rolled the center portions of sail (now 'thicker') roll up 'just as fast' as the head/tack so the 'bagginess' (that would occur without the foam) is lessened.
Without a foam luff you cant 'reef' a jib/genoa due to the 'bagginess' that develops when roller furling - so its either all the way out or completely furled. With a foam luff you can 'reef' - typically reducing the sail area by 30% at best, Beyond 30% sail area reduction the unrolled portions of the sail will again gain a lot of bagginess/fullness in the mid panels/sections.
Modern computer sail design/cutting programs can alter the leading edge shape of the luff so that foam luffs are not absolutely necessary and still affect up to 30% sail area reduction without distortion of the shape of the sail. Sometimes in very large sails a sailmaker will apply a very 'special geometric shape' (a somewhat s-shaped curve) to the luff leading edge AND apply a foam luff.
For more than 30% SA reduction one can apply a 'second' foam luff which is installed near the "30% reduced/rolled shape" ... and get down to 50+% SA reduction and still have good shape - very rarely done and usually only seen for 'passagemaking' or boats that sail the open ocean.
;-)
Question for Bill
Seriously, I was under the impression that the foam luff in jibs were a thing of the past replaced by computer technology in sail cutting. Will someone please correct me if i'm wrong
Seriously, I was under the impression that the foam luff in jibs were a thing of the past replaced by computer technology in sail cutting. Will someone please correct me if i'm wrong
Re: Question for Bill
Quoddy's question seems to imply a retro fit to an existing sail. I have a 10 year old CD 135 that had some restitching done and a foam luff added. Since it came with my boat I can't tell you how it was before, but the reefed shape is beautiful compared to prior attempts at reefing the jib on my Lancer 25. However, the Hood Seafurl on my current boat has a head swivel, which the CDI furler on my Lancer 25 did not. That also has an impact on reefing, from what I understand, providing some improvement in shape itself.
Quoddy's question seems to imply a retro fit to an existing sail. I have a 10 year old CD 135 that had some restitching done and a foam luff added. Since it came with my boat I can't tell you how it was before, but the reefed shape is beautiful compared to prior attempts at reefing the jib on my Lancer 25. However, the Hood Seafurl on my current boat has a head swivel, which the CDI furler on my Lancer 25 did not. That also has an impact on reefing, from what I understand, providing some improvement in shape itself.
Re: Question for Bill
Given the relative newness of Quoddy's boat, I suggest a call to Hunter to see if such design considerations (those which would remove the need for a foam luff) were included in the sail provided stock with the boat. However, perhaps the best answer lies in whether or not Quoddy is having any performance issues when reefing?
Given the relative newness of Quoddy's boat, I suggest a call to Hunter to see if such design considerations (those which would remove the need for a foam luff) were included in the sail provided stock with the boat. However, perhaps the best answer lies in whether or not Quoddy is having any performance issues when reefing?
You are 'mostly' right. Yes, computer aided sail design 'can' lessen the use of foam luffs by the somewhat complex shape of the leading edge (entry) shape of a luff; but, this also assumes that the tension in the forestay is absolutely correct to match the calculated curves (complex luff hollow geometry) in the front edge of the sail ... something that almost all cruisers and a lot of racers simply dont do. In most cases the computer cut quasi-curve will be 'sufficient' for a so-so roll/reef ... but not always and especially true for 'big' rigs with very long luff dimensions that are difficult to predict the forestay 'sag' accurately. In these circumstances a smaller foam luff is usually needed to compensate for what the complex computer cutting cannot do nor predict.
The 'downside' of foam luffs is that is causes a large cylindrical excess shape at the rolled luff of the sail .... with lots of adverse turbulence and drag at THE most important aerodynamic portion of the sail ... the 'entry' to the luff.
You are 'mostly' right. Yes, computer aided sail design 'can' lessen the use of foam luffs by the somewhat complex shape of the leading edge (entry) shape of a luff; but, this also assumes that the tension in the forestay is absolutely correct to match the calculated curves (complex luff hollow geometry) in the front edge of the sail ... something that almost all cruisers and a lot of racers simply dont do. In most cases the computer cut quasi-curve will be 'sufficient' for a so-so roll/reef ... but not always and especially true for 'big' rigs with very long luff dimensions that are difficult to predict the forestay 'sag' accurately. In these circumstances a smaller foam luff is usually needed to compensate for what the complex computer cutting cannot do nor predict.
The 'downside' of foam luffs is that it causes a large cylindrical excess shape at the rolled luff of the sail .... with lots of adverse turbulence and drag at THE most important aerodynamic portion of the sail ... the 'entry' to the luff.
I've got two headsails for my H28.5. One is a 150 with a foam luff, the other a 120 without a foam luff. I've found that when the wind rises to the point where I have roll up some headsail, it seems to make little difference in "luff entry" and performance whether or not I have a foam luff. If I were to buy a new headsail, I would not order this option.
foam luffs continued
Ive got a CDI furler with a 125 and a working jib no foam. I dont do much roller reefing. Im not happy with the boats performance with a partially rolled jib, on my boat anyway. I prefer
to slab reef my main It dosent take much more time than rolling. If necessary I take the main down my masthead rig performs ok under jib alone.
Ive got a CDI furler with a 125 and a working jib no foam. I dont do much roller reefing. Im not happy with the boats performance with a partially rolled jib, on my boat anyway. I prefer
to slab reef my main It dosent take much more time than rolling. If necessary I take the main down my masthead rig performs ok under jib alone.
If you partially furl the 120 you will notice that the center of the luff is baggy. The foam luff is designed to give you a better shape under sail. Which translates to better upwind performance. I have a North genoa that has various lengths of line sewn into a long pocket. Same concept
CDI, I do believe, is a furling, but not reefing system, so a foam luff is not so important. But, when you reef a sail, foam is a good thing for better sail shape. North Sails actually uses a rope luff and not foam anymore. (a few lengths of rope sewed into the sail luff like foam is. If you buy a new sail the sail maker will design it for furling/reefing specifications, but the foam or rope luff helps more. If you modify an older genoa to fit a furler, then foam, I think, becomes more important.
Most one design racing boats that are fitted with furlers do not have foam or rope luffs, because they don't reef their sails. If they race phrf, then they might, or will just have various sizes of sails to suit the wind velocity.
Most one design racing boats that are fitted with furlers do not have foam or rope luffs, because they don't reef their sails. If they race phrf, then they might, or will just have various sizes of sails to suit the wind velocity.
Luff stuff
Thanks for the detailed answers to my question. They have given me a start on my investigation of its usefulness.
Thanks for the detailed answers to my question. They have given me a start on my investigation of its usefulness.
My impression is that a good furler/reefer such as a Harken MKIV is independently swiveled at the head and the tack, making a foam luff unnecessary. I would much prefer to invest my money in a premium furler and avoid the performance sapping foam luff.
Go with the foam luff
As stated by Cayennita above - the foam luff actually improves performance (mostly when partially furled).
I actually struggled with the idea of a foam luff when purchasing my new headsail 3 seasons ago and I must say I am very impressed with the sail shape (not just because it is new) when partially furled. I wouldn't hesitate on getting it or recommending it to anyone.
In reguard to the rope luff - this seems like a good idea on doing the same thing but I believe the disavantages are that they get wet and heavy, as well as molding in the right conditions.
As stated by Cayennita above - the foam luff actually improves performance (mostly when partially furled).
I actually struggled with the idea of a foam luff when purchasing my new headsail 3 seasons ago and I must say I am very impressed with the sail shape (not just because it is new) when partially furled. I wouldn't hesitate on getting it or recommending it to anyone.
In reguard to the rope luff - this seems like a good idea on doing the same thing but I believe the disavantages are that they get wet and heavy, as well as molding in the right conditions.
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