im looking at a new spinn what size range should i be looking for and is there a formula??? my boat is set up for one but did not come with one mast is 32' boat is 27' is 33'4" luff ok??? i think im in the right range *o
what size spinnaker :(
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Spinnaker formula
If you are racing, check to see if the size of your spinnaker is regulated by class rules. Chances are there are limitations on size. The general formula for determining spinnaker size is; Luff = your "I" dimension (deck to masthead for a masthead rigged boat) Foot = between 1.6x - 2x your "J" dimension (mast to base of headstay) If you want an asymmetrical spinnaker use this formula; Luff = "I" Foot = between 1.6x - 1.8x "J" Leech = 90% of Luff Check with Bacons Sails in Annapolis for used spinnakers Tom s/v Orion's Child
If you are racing, check to see if the size of your spinnaker is regulated by class rules. Chances are there are limitations on size. The general formula for determining spinnaker size is; Luff = your "I" dimension (deck to masthead for a masthead rigged boat) Foot = between 1.6x - 2x your "J" dimension (mast to base of headstay) If you want an asymmetrical spinnaker use this formula; Luff = "I" Foot = between 1.6x - 1.8x "J" Leech = 90% of Luff Check with Bacons Sails in Annapolis for used spinnakers Tom s/v Orion's Child
bad idea
I don't think it's a good idea to use the I dimension as the spinnaker luff. Measure it instead. Even on masthead rigs, different aspect ratios will lead to different results. One thing you need to think about is whether you want a full spinnaker (180% of J) or more of a shy kite. There's a lot to be said for building a #3 chute at about 165%, especially for cruising, especially if you plan on sailing shorthanded in a variety of wind conditions. You'll be a lot more likely to actually use the spinnaker if it's a more manageable sail. A case in point: we seatrialed a new North G3 last weekend. First words out of my wife's mouth were, "I love this sail." Now I'm telling her it's her valentines present.
I don't think it's a good idea to use the I dimension as the spinnaker luff. Measure it instead. Even on masthead rigs, different aspect ratios will lead to different results. One thing you need to think about is whether you want a full spinnaker (180% of J) or more of a shy kite. There's a lot to be said for building a #3 chute at about 165%, especially for cruising, especially if you plan on sailing shorthanded in a variety of wind conditions. You'll be a lot more likely to actually use the spinnaker if it's a more manageable sail. A case in point: we seatrialed a new North G3 last weekend. First words out of my wife's mouth were, "I love this sail." Now I'm telling her it's her valentines present.
Why???
John, Why is it a bad idea to use "I" as a luff dimension? What do you use? You said "measure it", measure what? Tom
John, Why is it a bad idea to use "I" as a luff dimension? What do you use? You said "measure it", measure what? Tom
Tom has it right
As Tom said the modern cruising boat sizes a spinnaker by the rule of thumb where the size of the luff = I. The foot should be between 1.6 x J and 2 x J And the I.O.R. rule allows the spinnaker luff to be a maximum of 95% of the square root of (I 2 + J 2). The sail width is no greater then 1.8 x J. All the best, Robert Gainer
As Tom said the modern cruising boat sizes a spinnaker by the rule of thumb where the size of the luff = I. The foot should be between 1.6 x J and 2 x J And the I.O.R. rule allows the spinnaker luff to be a maximum of 95% of the square root of (I 2 + J 2). The sail width is no greater then 1.8 x J. All the best, Robert Gainer
measuring
Run a fiberglass tape measure up the spinnaker halyard to the tack point for medium winds. (This point will usually be right about the height of the bow pulpit.) Then, if a sock will be used, subtract the distance of the head lanyard. On some masthead rigs this measurement will be very close to I, but on some it will not, especially on rigs with low-aspect dimmensions such as a cutter rig. On fraction rigs, of course, spinnaker luff will be further from I than on masthead rigs.
Run a fiberglass tape measure up the spinnaker halyard to the tack point for medium winds. (This point will usually be right about the height of the bow pulpit.) Then, if a sock will be used, subtract the distance of the head lanyard. On some masthead rigs this measurement will be very close to I, but on some it will not, especially on rigs with low-aspect dimmensions such as a cutter rig. On fraction rigs, of course, spinnaker luff will be further from I than on masthead rigs.
That’s a crude approximation of the IOR rule.
John, That’s a crude approximation of the IOR rule. Do you think this is this mainstream thinking today for cruising boat spinnaker design? All the best, Robert Gainer
John, That’s a crude approximation of the IOR rule. Do you think this is this mainstream thinking today for cruising boat spinnaker design? All the best, Robert Gainer
here's what i got
i= 33.75' j = 11.25' its a santana set for a spinnand the one i'm looking at is 33'4" luff 20'foot that puts it where i need to be i recon
i= 33.75' j = 11.25' its a santana set for a spinnand the one i'm looking at is 33'4" luff 20'foot that puts it where i need to be i recon
Check withy Sailnet.com
Suggest you visit Sailnet.com, their sail loft. They are set up for you to enter you boat make and size and the site then gives you the spinnakers size,price,colors,etc. Takes about 2 minutes to do.
Suggest you visit Sailnet.com, their sail loft. They are set up for you to enter you boat make and size and the site then gives you the spinnakers size,price,colors,etc. Takes about 2 minutes to do.
Suggestions ....
By all means do the 'actual' measurement yourself or if the loft is local let the sailmaker do the measurement. Actual measurements are ultimately better than 'catalogue' dimensions. Also have the sailmaker make the correct 'deduct' dimensions of the luff if you will be using a spinnaker sock .... as if you 'fill' the luff dimensions for the sail ... and then add a sock, the total luff length (sail luff + sock shackels, etc.) may be too long and you will/may prevent good 'closer to the wind' performance. Also as John Farnsworth posted consider a Spinn with 160-165% LP dimension for your 'first' spinnaker, as the slightly shorter LP will make the sail much easier to fly/handle. Consider to have the sail designed/cut as an 'all purpose' / 'cruising cut' for ease of setting/handling/trim ... as this will result in a 'cut' that doesnt require constant trimming to keep it stable ... a spinnaker with built-in "forgiveness". Spinnakers are made from rip-stop NYLON which is subject to rapid UV degradation. For long term 'life' considerations, avoid white or 'light' colors ... as UV tends to destroy these 'light colors' the fastest. Choose 'dark' colors for 'life'; but, if you 'must' choose (for aesthetics) the lighter colors consider at least to have the reinforcing 'corner patches' made of 'dark' material as the 'corners' are where all the stress in the fabric occurs/and concentrates. hope this helps
By all means do the 'actual' measurement yourself or if the loft is local let the sailmaker do the measurement. Actual measurements are ultimately better than 'catalogue' dimensions. Also have the sailmaker make the correct 'deduct' dimensions of the luff if you will be using a spinnaker sock .... as if you 'fill' the luff dimensions for the sail ... and then add a sock, the total luff length (sail luff + sock shackels, etc.) may be too long and you will/may prevent good 'closer to the wind' performance. Also as John Farnsworth posted consider a Spinn with 160-165% LP dimension for your 'first' spinnaker, as the slightly shorter LP will make the sail much easier to fly/handle. Consider to have the sail designed/cut as an 'all purpose' / 'cruising cut' for ease of setting/handling/trim ... as this will result in a 'cut' that doesnt require constant trimming to keep it stable ... a spinnaker with built-in "forgiveness". Spinnakers are made from rip-stop NYLON which is subject to rapid UV degradation. For long term 'life' considerations, avoid white or 'light' colors ... as UV tends to destroy these 'light colors' the fastest. Choose 'dark' colors for 'life'; but, if you 'must' choose (for aesthetics) the lighter colors consider at least to have the reinforcing 'corner patches' made of 'dark' material as the 'corners' are where all the stress in the fabric occurs/and concentrates. hope this helps
RichH
“Also as John Farnsworth posted consider a Spinn with 160-165% LP dimension” Can you explain this? Thanks, Robert Gainer
“Also as John Farnsworth posted consider a Spinn with 160-165% LP dimension” Can you explain this? Thanks, Robert Gainer
advantages of a shy kite
(I'm speaking of Akites here, incidentally, although much of this would also apply to symmetricals.) A smaller kite is built to 165% rather than 180%, just as a smaller gennoa will be built to 130% rather than 150%. Indeed, North has begun to number its gennakers and assymetricals 1, 2, 3, in a similar way to how racing headsails have traditionally been numbered. I just bought a North G3 for my boat, which is basically a #3 gennaker. The advantage in heavy wind should be obvious: reduced sail area. The flip side, however, and this is where you need to bend your mind a bit, is that a smaller chute often outperforms a larger chute in light air because the big chute is too heavy to support its own weight and fly itself up into the good air beyond the main's wind shadow. Gary Jobson tries to explain this every four years during the Americas Cup telecasts, why they fly smaller chutes in light air, and still hasn't done a good job of it. Bottom line is that a spinnaker isn't supposed to hang from the halyard the way a jib hangs; it's supposed to fly, kite-like, generating lift with its shoulders. A smaller kite is more likely going to be able to lift itself out of the bad air behind the mainsail. I don't agree with the sentiment, often expressed on this board, that spinnaker dimensions are not as critical as jib dimensions. An ill-fit chute tends to wallow because it doesn't bow into the correct shape. I want my luff to be cut within an inch of perfect shape for my boat PRECISELY because I'm a cruiser. I often set the chute for hours at a time, and it would fatigue the crew to have to tinker with the sail constantly the way a racer will. Unless your chute is cut perfectly to the boat's dimensions, you have no chance of having a "set it and forget it" chute. Bottom line is that I want to be able to read and/or grade papers once the kite is flying. At which point I return to my original advice in this thread. Don't guess--measure. And don't allow yourself to think that a used kite or a cheap production kite will serve your needs the way a new custom kite will. There has been tremendous design improvement in Akite shape in the last five years because sailmakers have finally figured out that they don't act like symmetricals, and therefore shouldn't be built like symmetricals. Prior to 2007, the last kite I had built was in 1998. The difference in performance is spectacular.
(I'm speaking of Akites here, incidentally, although much of this would also apply to symmetricals.) A smaller kite is built to 165% rather than 180%, just as a smaller gennoa will be built to 130% rather than 150%. Indeed, North has begun to number its gennakers and assymetricals 1, 2, 3, in a similar way to how racing headsails have traditionally been numbered. I just bought a North G3 for my boat, which is basically a #3 gennaker. The advantage in heavy wind should be obvious: reduced sail area. The flip side, however, and this is where you need to bend your mind a bit, is that a smaller chute often outperforms a larger chute in light air because the big chute is too heavy to support its own weight and fly itself up into the good air beyond the main's wind shadow. Gary Jobson tries to explain this every four years during the Americas Cup telecasts, why they fly smaller chutes in light air, and still hasn't done a good job of it. Bottom line is that a spinnaker isn't supposed to hang from the halyard the way a jib hangs; it's supposed to fly, kite-like, generating lift with its shoulders. A smaller kite is more likely going to be able to lift itself out of the bad air behind the mainsail. I don't agree with the sentiment, often expressed on this board, that spinnaker dimensions are not as critical as jib dimensions. An ill-fit chute tends to wallow because it doesn't bow into the correct shape. I want my luff to be cut within an inch of perfect shape for my boat PRECISELY because I'm a cruiser. I often set the chute for hours at a time, and it would fatigue the crew to have to tinker with the sail constantly the way a racer will. Unless your chute is cut perfectly to the boat's dimensions, you have no chance of having a "set it and forget it" chute. Bottom line is that I want to be able to read and/or grade papers once the kite is flying. At which point I return to my original advice in this thread. Don't guess--measure. And don't allow yourself to think that a used kite or a cheap production kite will serve your needs the way a new custom kite will. There has been tremendous design improvement in Akite shape in the last five years because sailmakers have finally figured out that they don't act like symmetricals, and therefore shouldn't be built like symmetricals. Prior to 2007, the last kite I had built was in 1998. The difference in performance is spectacular.
LP defined
LP (Length Perpendicular) is the distance from the forestay to the clew, and that line (dimension) is perpendicular (90 degrees) to the forestay. A sail whose LP is 165% would be 65% larger than an LP that stopped at the mast (which would be a 100% sail). % values of of sail area (100%, 120%, 170% etc. are a percentage of LP ...... and not the "J" dimension. Sail area = 1/2 (LP X luff length) So, why not just use the J dimension? ... the J dimension doesnt take into consideration how 'high' the clew is above the deck or tack location of the sail. The critical dimensions of a spinnaker: Luff, LP, mid girth, foot. Once you have (or decide) all these dimensions, all others are calculated (or derived).
LP (Length Perpendicular) is the distance from the forestay to the clew, and that line (dimension) is perpendicular (90 degrees) to the forestay. A sail whose LP is 165% would be 65% larger than an LP that stopped at the mast (which would be a 100% sail). % values of of sail area (100%, 120%, 170% etc. are a percentage of LP ...... and not the "J" dimension. Sail area = 1/2 (LP X luff length) So, why not just use the J dimension? ... the J dimension doesnt take into consideration how 'high' the clew is above the deck or tack location of the sail. The critical dimensions of a spinnaker: Luff, LP, mid girth, foot. Once you have (or decide) all these dimensions, all others are calculated (or derived).
getting confused a bit
RichH, You might be getting confused a bit. Everything starts with the J dimension. The LP for whatever overlap you want is the percentage times J. A 150% Genoa is 150% times J and that number is the LP. The LP of a headsail does not enter into spinnaker design at all and it just confuses people to try and describe a spinnaker that way. Spinnakers do not have an LP dimension. The LP by the way also has nothing to do with the height of the clew. A high cut reacher with an LP of 150% has the same LP that a 150% deck sweeper has. John Farnsworth, I have no idea what you are trying to say. There is a lot of room for discussion about spinnaker size so how critical can it be? Any thing close works just fine unless you are sailing a 12 meter and I don’t thing anybody looking for advice today is racing a 12. The foot can range from 1.6 J all the way to 2 J and still be considered standard. To sum it up, the standard rules are, Spinnaker luff = I. The foot should be between 1.6 x J and 2 x J If you want to discuss the I.O.R. rule then the luff is a maximum of 95% of the square root of (I 2 + J 2). The sail width is no greater then 1.8 x J. Notice that both rules have nothing to do with LP. All the best, Robert Gainer
RichH, You might be getting confused a bit. Everything starts with the J dimension. The LP for whatever overlap you want is the percentage times J. A 150% Genoa is 150% times J and that number is the LP. The LP of a headsail does not enter into spinnaker design at all and it just confuses people to try and describe a spinnaker that way. Spinnakers do not have an LP dimension. The LP by the way also has nothing to do with the height of the clew. A high cut reacher with an LP of 150% has the same LP that a 150% deck sweeper has. John Farnsworth, I have no idea what you are trying to say. There is a lot of room for discussion about spinnaker size so how critical can it be? Any thing close works just fine unless you are sailing a 12 meter and I don’t thing anybody looking for advice today is racing a 12. The foot can range from 1.6 J all the way to 2 J and still be considered standard. To sum it up, the standard rules are, Spinnaker luff = I. The foot should be between 1.6 x J and 2 x J If you want to discuss the I.O.R. rule then the luff is a maximum of 95% of the square root of (I 2 + J 2). The sail width is no greater then 1.8 x J. Notice that both rules have nothing to do with LP. All the best, Robert Gainer
Sorry to confuse you ...
What I listed is 'standard practice' for sailmakers. Been making (my) sails for 35 years, and those are the dimensions used. Fpr a spinnaker the LP is defined as the length perpendicuar between the head ---- tack construction line ... and the clew is at the terminal end of that line. All J defines is the "horizonta/level' distance from the tack/stem to the mast. In NO WAY is a sail calculated by J, ... only as a geometric relationship of the LP and height of the clew vs. tack position. Just consider a yankee cut, or any sail (including spinnaker !!) that has an 'elevated' clew. Even a deck sweeper % is defined by the LP.
What I listed is 'standard practice' for sailmakers. Been making (my) sails for 35 years, and those are the dimensions used. Fpr a spinnaker the LP is defined as the length perpendicuar between the head ---- tack construction line ... and the clew is at the terminal end of that line. All J defines is the "horizonta/level' distance from the tack/stem to the mast. In NO WAY is a sail calculated by J, ... only as a geometric relationship of the LP and height of the clew vs. tack position. Just consider a yankee cut, or any sail (including spinnaker !!) that has an 'elevated' clew. Even a deck sweeper % is defined by the LP.
It's not me thats confused
RichH, You haven’t confused me, just yourself. What you listed is standard practice for you and not for sailmakers in general. If you Google it you will find lots of pages describing how it works. The first page I came up with is, www.baconsails.com/saildimension.html and you might want to start reading there. If your system works for you I think that’s great but don’t confuse people by using the wrong terms and methods. I am not in the office so I can’t quote any books tonight but I think we have 8 or 9 on sail design and construction. If you have trouble finding a good reference let me know and I can look in our library for you. Of course nothing says I have it right. Can you point me to anything as a reference that describes it your way? All the best, Robert Gainer
RichH, You haven’t confused me, just yourself. What you listed is standard practice for you and not for sailmakers in general. If you Google it you will find lots of pages describing how it works. The first page I came up with is, www.baconsails.com/saildimension.html and you might want to start reading there. If your system works for you I think that’s great but don’t confuse people by using the wrong terms and methods. I am not in the office so I can’t quote any books tonight but I think we have 8 or 9 on sail design and construction. If you have trouble finding a good reference let me know and I can look in our library for you. Of course nothing says I have it right. Can you point me to anything as a reference that describes it your way? All the best, Robert Gainer
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