When it comes to headsail trim, there doesn't seem to me much discussion about headstay sag. I know that an adjustable backstay can be used to induce/reduce sag but how do you determine the maximum sag. I read somewhere that a 30 foot masthead rigged sloop should set the headstay tension at 500 pounds. I've also heard mentioned that you should try to match headsail luff curve with headstay sag but in what conditions does this apply? I know that maximum headstay sag would be used in the lower wind strength range of the sail that's in use. Any suggestions on setting the initial sag/tension of the headstay? Assuming you are looking to power up for light wind or to get through heavy chop going upwind, how much sag is too much?
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Ted,
You don't indicate what boat you have; so here's a couple things maybe specific to some Hunters (I have a Mast head double spreader B&R rig on an '86 Hunter 28.5 set up for racing).
Max headstay sag at maybe 6" gives a fuller head sail luff , and maybe more power off the wind and going down wind. Two to three inches of sag is about right for my mylar 155% Genoa in normal conditions.
Tightening a backstay adjuster on a mast head B&R rig will tighten the headstay, then induce mast bend and flatten the entry for higher pointing, but at some point it can then be too hard to stay in the 'groove'.
I do use our backstay adjuster to flatten the main and had the sailmaker measure the sail for the max and min mast bend to do that effectively.
You don't indicate what boat you have; so here's a couple things maybe specific to some Hunters (I have a Mast head double spreader B&R rig on an '86 Hunter 28.5 set up for racing).
Max headstay sag at maybe 6" gives a fuller head sail luff , and maybe more power off the wind and going down wind. Two to three inches of sag is about right for my mylar 155% Genoa in normal conditions.
Tightening a backstay adjuster on a mast head B&R rig will tighten the headstay, then induce mast bend and flatten the entry for higher pointing, but at some point it can then be too hard to stay in the 'groove'.
I do use our backstay adjuster to flatten the main and had the sailmaker measure the sail for the max and min mast bend to do that effectively.
S Sauer,
You mentioned that you set up your boat with a maximum of 6" of headstay sag. At what apparent wind speed are you setting up for? Six inches of sag at 15 knots of apparent wind would require very different tension setting than if the apparent wind was 5 knots. Sea state also comes into play here. You can have a flatter luff entry if there isn't much wave action but what kind of setup works for higher winds and waves? I would suspect you would want more headstay sag to power up the headsail and make upwind steering easier but wouldn't you begin to be overpowered in the higher wind conditions? I guess it would than be time to change to a smaller headsail. All thoughts appreciated. Thanks.
You mentioned that you set up your boat with a maximum of 6" of headstay sag. At what apparent wind speed are you setting up for? Six inches of sag at 15 knots of apparent wind would require very different tension setting than if the apparent wind was 5 knots. Sea state also comes into play here. You can have a flatter luff entry if there isn't much wave action but what kind of setup works for higher winds and waves? I would suspect you would want more headstay sag to power up the headsail and make upwind steering easier but wouldn't you begin to be overpowered in the higher wind conditions? I guess it would than be time to change to a smaller headsail. All thoughts appreciated. Thanks.
Ted,
Our deep draft 28.5 has a 155%, a 135% and the OEM 110 % Jib on a Tough Luff headfoil and a split backstay adjuster with an 8:1 purchase. The double spreader rig is somewhat 'bendy' as it has the same mast section as a J-29. I wouldn't have more than 2-3 inches of sag going to windward, typically that's where the headsail luff curve seems to be cut for pointing ability, regardles of wind speed. Of the wind in light to medium air I'd release the backstay adjuster and move the Genoa leads to outboard snatch blocks (we run non-spinnaker). Above 18 knots I like the #2 up; and above about 23-25 I throw in a reef or start thinking about the 110. Again, I feel I'm more interested in the backstay adjuster as a means of flattening the main and helps to ballance the rig with each of the headsails, but what boat and rig are you asking about?
Our deep draft 28.5 has a 155%, a 135% and the OEM 110 % Jib on a Tough Luff headfoil and a split backstay adjuster with an 8:1 purchase. The double spreader rig is somewhat 'bendy' as it has the same mast section as a J-29. I wouldn't have more than 2-3 inches of sag going to windward, typically that's where the headsail luff curve seems to be cut for pointing ability, regardles of wind speed. Of the wind in light to medium air I'd release the backstay adjuster and move the Genoa leads to outboard snatch blocks (we run non-spinnaker). Above 18 knots I like the #2 up; and above about 23-25 I throw in a reef or start thinking about the 110. Again, I feel I'm more interested in the backstay adjuster as a means of flattening the main and helps to ballance the rig with each of the headsails, but what boat and rig are you asking about?
S Sauer
The boat is a C&C 29. It's a masthead rig with single spreaders, single lowers a split backstay and babystay. I also race the boat and have a 155%, 145%, 125%, 100%, headsails. My backstay and babystay adjuster are very powerful and I have no problem bending the mast or tensioning the headstay. The boat points very high and I place well in winds under 10 knot true. The conditions which need some tweeking are in winds over 15 knots true with waves and chop. The combination that I haven't tried yet is switching down to a smaller headsail and putting more sag in the headstay to power up this smaller sail. I know that pointing will suffer but I think that the additional power will help me get through the chop. Any thoughts?
The boat is a C&C 29. It's a masthead rig with single spreaders, single lowers a split backstay and babystay. I also race the boat and have a 155%, 145%, 125%, 100%, headsails. My backstay and babystay adjuster are very powerful and I have no problem bending the mast or tensioning the headstay. The boat points very high and I place well in winds under 10 knot true. The conditions which need some tweeking are in winds over 15 knots true with waves and chop. The combination that I haven't tried yet is switching down to a smaller headsail and putting more sag in the headstay to power up this smaller sail. I know that pointing will suffer but I think that the additional power will help me get through the chop. Any thoughts?
Ted -
There is no 'short answer' yet only ONE correct set up tension for a forestay ... depending on the wind strength, depending on the accuracy of the jib winch handle, etc. etc. etc. .... It all has to do with how the head sail is designed and what 'cut' there is at the luff !!!!!
Allow me to bore you with the details. Setting proper headstay sag is probably THE most important adjustment when racing or precision sailing. Without such adjustment you can trim and shape until the cows come home but you'll only be guessing about the optimization of the sail shape and its trim if the headstay isnt properly sagged (or not). This is a loooooong explanation, so please be patient:
When a sailmaker designs a headsail thats either attached to a foil or is attached by hanks, the sailmaker ‘assumes’ that the rigging is at normal tension (usually about 12-15% of the breaking strength of the wire). Unless specified otherwise a ‘cruising’ sail will be designed for ~15kts. of wind and the sailmaker will expect that headstay to ‘stretch’ a wee little bit when the sail is wind-loaded at the design windstrength. When beating, the stay will also begin to ‘sag’ off to the lee-side of the boat ... usually quite predictably. This expected sag (aft and to the lee side) is ‘compensated for’ by the sailmaker cutting a smooth curved amount of sail material from the luff section of the sail - called “luff hollow”. If the hollow isn’t cut to this shape and when the headstay does sag all that material at the midsection of the luff would be ‘pushed’ towards the center of the sail and the designed point of maximum draft would move aft (increasing weather helm) and the amount of draft would get much deeper causing the boat to heel more ... sometimes causing even more apparent weather helm. Also, since the center of effort of the sail is now moved/sagged off to leeward ... its like someone moved that headstay several feet to leeward or radically somehow changed the sail’s angle of attack: the boat ... heels over, slows down, can’t point, and starts to ‘skid’ off to leeward ..... and all because the headstay sag no longer *matches* the luff hollow that the sailmaker designed into the sail !!!! Its all action and reaction. If the forestay sag exactly matches the 'luff hollow' thats cut into the front section of the sail ... thats PERFECT.
How to induce headstay sag (and make pointing ‘worse’): loosen the backstay; apply too much winch tension to a sheet (all that applied load to the jibsheet eventually ‘distributes’ to the *headstay* which increases the sag); sail in wind well beyond what was the target design wind-loading for the sail.
How to know when the luff hollow shape is matching the normal sag in the headstay:
1. Ask the sailmaker how much luff hollow was cut into the sail, and where on the luff up from the tack is that maximum amount. When on a hard beat and with a Mark 1 eyeball near the tack, look up along the luff and simply estimate that the ‘sag’ you see is approximating that value that the sailmaker gave. If too much sag, tighten the backstay or release some sheet tension; if too little sag, loosen the backstay or increase sheet tension.
If this is too approximate, there is a more precise way ... .
2. Take the jib/genoa and lay it FLAT on FLAT **clean** ground or floor and make an ‘accordian fold’ about 2 ft. back from the luff - the accordian fold looks like a flattened Letter "S" with the leech trailing out from the 'fold'. The accordian fold will allow the ‘curved’ 3D shape of the luff of the sail to lay FLAT on the ground. Work out ALL wrinkles from the luff section - you want the luff to be absolutely FLAT. Then take a string and pull tight along the curved luff shape .... what is ‘missing’ between that tight string and the FLAT sail luff is the ‘luff hollow’ that the sailmaker cut from the luff edge of the sail. Measure and record or REMEMBER that ‘hollow’ shape if you want that sail to take the ‘shape’ as was designed.
For easy bombproof ‘precision’, take that taught string and move it a few inches across the luff and so that its parallel to the ‘first’ string position but now laying over sail material. Then get some 3/8" or 1/4" wide adhesive backed ‘draft stripe’ material and apply ’straight as an arrow’ just behind the leading edge of the FLAT sail luff on the ground. When sailing and having ‘pointing problems with increased weather helm’ ... just take a walk forward and ‘see’ (with your mark I eyeball looking perpendicularly from the boats centerline). if that vertical stripe along the luff is dead-straight (headstay sag now *exactly* matching the ‘luff hollow in the sail’) the sail will be exactly at the shape that the sailmaker cut, the position of max. draft will be correct, etc. If that 'line' or hollow is not exact, then, do any adjustment necessary (backstay tension, jibsheet tension, running backstay, etc.) to keep that stripe ‘straight’ .... and your boat will now ‘point like a banshee’, with less heel, and wont be skidding off to leeward (and with the helmsman erroneously blaming ‘weather-helm’, etc.). Its very easy to overload a jibsheet on a large genoa ... and totally destroy the critical forward leading edge shape of the luff.
Want to race, quickly move to the side of a squall, point higher, or get to your far destination faster? ... **match** the headstay sag to the “luff hollow”.
So the only answer to the question of how much forestay sag? ... just enough backstay (or running back stay) tension so that the sag of the forestay ***exactly*** MATCHES the shape of the luff hollow that was cut into the sail. Anything less or more will not result in optimum shape of the headsail. Once the sag is matching the 'luff hollow' exactly ... THEN you can shape and trim the rig to perfection .... If the sag doesnt match the hollow ... then you will NEVER reach optimum trim.
hope this helps.
(If someone can advise how to upload pics *directly*, I can post such graphics that will more easily explain)
There is no 'short answer' yet only ONE correct set up tension for a forestay ... depending on the wind strength, depending on the accuracy of the jib winch handle, etc. etc. etc. .... It all has to do with how the head sail is designed and what 'cut' there is at the luff !!!!!
Allow me to bore you with the details. Setting proper headstay sag is probably THE most important adjustment when racing or precision sailing. Without such adjustment you can trim and shape until the cows come home but you'll only be guessing about the optimization of the sail shape and its trim if the headstay isnt properly sagged (or not). This is a loooooong explanation, so please be patient:
When a sailmaker designs a headsail thats either attached to a foil or is attached by hanks, the sailmaker ‘assumes’ that the rigging is at normal tension (usually about 12-15% of the breaking strength of the wire). Unless specified otherwise a ‘cruising’ sail will be designed for ~15kts. of wind and the sailmaker will expect that headstay to ‘stretch’ a wee little bit when the sail is wind-loaded at the design windstrength. When beating, the stay will also begin to ‘sag’ off to the lee-side of the boat ... usually quite predictably. This expected sag (aft and to the lee side) is ‘compensated for’ by the sailmaker cutting a smooth curved amount of sail material from the luff section of the sail - called “luff hollow”. If the hollow isn’t cut to this shape and when the headstay does sag all that material at the midsection of the luff would be ‘pushed’ towards the center of the sail and the designed point of maximum draft would move aft (increasing weather helm) and the amount of draft would get much deeper causing the boat to heel more ... sometimes causing even more apparent weather helm. Also, since the center of effort of the sail is now moved/sagged off to leeward ... its like someone moved that headstay several feet to leeward or radically somehow changed the sail’s angle of attack: the boat ... heels over, slows down, can’t point, and starts to ‘skid’ off to leeward ..... and all because the headstay sag no longer *matches* the luff hollow that the sailmaker designed into the sail !!!! Its all action and reaction. If the forestay sag exactly matches the 'luff hollow' thats cut into the front section of the sail ... thats PERFECT.
How to induce headstay sag (and make pointing ‘worse’): loosen the backstay; apply too much winch tension to a sheet (all that applied load to the jibsheet eventually ‘distributes’ to the *headstay* which increases the sag); sail in wind well beyond what was the target design wind-loading for the sail.
How to know when the luff hollow shape is matching the normal sag in the headstay:
1. Ask the sailmaker how much luff hollow was cut into the sail, and where on the luff up from the tack is that maximum amount. When on a hard beat and with a Mark 1 eyeball near the tack, look up along the luff and simply estimate that the ‘sag’ you see is approximating that value that the sailmaker gave. If too much sag, tighten the backstay or release some sheet tension; if too little sag, loosen the backstay or increase sheet tension.
If this is too approximate, there is a more precise way ... .
2. Take the jib/genoa and lay it FLAT on FLAT **clean** ground or floor and make an ‘accordian fold’ about 2 ft. back from the luff - the accordian fold looks like a flattened Letter "S" with the leech trailing out from the 'fold'. The accordian fold will allow the ‘curved’ 3D shape of the luff of the sail to lay FLAT on the ground. Work out ALL wrinkles from the luff section - you want the luff to be absolutely FLAT. Then take a string and pull tight along the curved luff shape .... what is ‘missing’ between that tight string and the FLAT sail luff is the ‘luff hollow’ that the sailmaker cut from the luff edge of the sail. Measure and record or REMEMBER that ‘hollow’ shape if you want that sail to take the ‘shape’ as was designed.
For easy bombproof ‘precision’, take that taught string and move it a few inches across the luff and so that its parallel to the ‘first’ string position but now laying over sail material. Then get some 3/8" or 1/4" wide adhesive backed ‘draft stripe’ material and apply ’straight as an arrow’ just behind the leading edge of the FLAT sail luff on the ground. When sailing and having ‘pointing problems with increased weather helm’ ... just take a walk forward and ‘see’ (with your mark I eyeball looking perpendicularly from the boats centerline). if that vertical stripe along the luff is dead-straight (headstay sag now *exactly* matching the ‘luff hollow in the sail’) the sail will be exactly at the shape that the sailmaker cut, the position of max. draft will be correct, etc. If that 'line' or hollow is not exact, then, do any adjustment necessary (backstay tension, jibsheet tension, running backstay, etc.) to keep that stripe ‘straight’ .... and your boat will now ‘point like a banshee’, with less heel, and wont be skidding off to leeward (and with the helmsman erroneously blaming ‘weather-helm’, etc.). Its very easy to overload a jibsheet on a large genoa ... and totally destroy the critical forward leading edge shape of the luff.
Want to race, quickly move to the side of a squall, point higher, or get to your far destination faster? ... **match** the headstay sag to the “luff hollow”.
So the only answer to the question of how much forestay sag? ... just enough backstay (or running back stay) tension so that the sag of the forestay ***exactly*** MATCHES the shape of the luff hollow that was cut into the sail. Anything less or more will not result in optimum shape of the headsail. Once the sag is matching the 'luff hollow' exactly ... THEN you can shape and trim the rig to perfection .... If the sag doesnt match the hollow ... then you will NEVER reach optimum trim.
hope this helps.
(If someone can advise how to upload pics *directly*, I can post such graphics that will more easily explain)
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Ted -
For 'chop' dont forget the 'coriolis effect'. Due to this effect starboard tack will require different trim and shape than the port tack. The coriolis effect will usually (in the northern hemisphere) cause the starboard tack to be favored and with the port tack having the chop/waves coming slightly more straight-onto-the-bow. Therefore the port tack usually require a wee bit more of 'powered-up' sail shape and trim (but a little less twist due to the increased pitching). Racing a 'game of inches' so any inches you can save from such info ... will bring you further towards the front of the fleet. So, unlike most who 'set-up' on starboard and blindly think that the set-up for port tack is the exact same, know that the two tacks require different trim and sail shape optimization.
If you have it, follow the VMG function of your GPS (and speedo - if on the boat's centerline) when beating to be able to discern the best trim/shape - for each tack!!!!!
Keep records of your settings, wind/wave conditions, etc. and/or analyse your GPS track after every race and practice session.
The C&C 29 is a very nice boat to race and have 'fun'.
For 'chop' dont forget the 'coriolis effect'. Due to this effect starboard tack will require different trim and shape than the port tack. The coriolis effect will usually (in the northern hemisphere) cause the starboard tack to be favored and with the port tack having the chop/waves coming slightly more straight-onto-the-bow. Therefore the port tack usually require a wee bit more of 'powered-up' sail shape and trim (but a little less twist due to the increased pitching). Racing a 'game of inches' so any inches you can save from such info ... will bring you further towards the front of the fleet. So, unlike most who 'set-up' on starboard and blindly think that the set-up for port tack is the exact same, know that the two tacks require different trim and sail shape optimization.
If you have it, follow the VMG function of your GPS (and speedo - if on the boat's centerline) when beating to be able to discern the best trim/shape - for each tack!!!!!
Keep records of your settings, wind/wave conditions, etc. and/or analyse your GPS track after every race and practice session.
The C&C 29 is a very nice boat to race and have 'fun'.
RichH,
Thanks for the explanation. It's just the information I was looking for. I wanted to have a logical starting point, something that I could actually quantify. I have VMG info on my boat and do set port and starboard tack sail trim settings slightly different from each other. Sorry that I can't tell you how to post photos/drawings but I hope someone else can jump in here and give some insight. A picture would certainly make things easier to understand although I have a good handle on what you just described.
Let's assume for a moment that a headstay was properly tensioned and sag matched the sailmakers designed luff hollow. If you reduced headstay sag, wouldn't pointing improve at the expense of less power? This condition could exist at the upper range of the wind speed for which the sail was designed. VMG may or may not be maximized but if tactically you needed to outpoint a competitor or make a mark, this may be a headsail trim option.
I'm amazed at how little information sailmakers provide regarding headstay sag. Most of it is based on a visual reference comparing the draft in the upper and mid sections of the headsail. Your explanation really helped me understand what was happening and how to recognize proper/improper sag and make the necessary adjustments to achieve proper headstay trim. Thank you for taking the time to post this detailed explanation on such an important aspect of sail trim.
Thanks for the explanation. It's just the information I was looking for. I wanted to have a logical starting point, something that I could actually quantify. I have VMG info on my boat and do set port and starboard tack sail trim settings slightly different from each other. Sorry that I can't tell you how to post photos/drawings but I hope someone else can jump in here and give some insight. A picture would certainly make things easier to understand although I have a good handle on what you just described.
Let's assume for a moment that a headstay was properly tensioned and sag matched the sailmakers designed luff hollow. If you reduced headstay sag, wouldn't pointing improve at the expense of less power? This condition could exist at the upper range of the wind speed for which the sail was designed. VMG may or may not be maximized but if tactically you needed to outpoint a competitor or make a mark, this may be a headsail trim option.
I'm amazed at how little information sailmakers provide regarding headstay sag. Most of it is based on a visual reference comparing the draft in the upper and mid sections of the headsail. Your explanation really helped me understand what was happening and how to recognize proper/improper sag and make the necessary adjustments to achieve proper headstay trim. Thank you for taking the time to post this detailed explanation on such an important aspect of sail trim.
Generally changing the headstay sag amount from the design optimum will tend to slow the boat, unless one is overpowered. I think a better way to accomplish what you desire is to increase the genoa halyard tension to get the position of maximum draft more forward .... then retension the backstay to regain the matching of the luff hollow. Simply retensioning as a means to decrease luff sag will tend to make the leech ‘hook to weather’ (slows the boat); conversely, an increase of the luff tension will tend to ‘trip’ or open the leech (more flatter speed shape). You need to adjust both backstay AND luff/halyard tension.
Especially if you have ‘roller reefing’, beware that overtensioning the halyard may cause the furler to jam – probably the chief reason that you hardly see roller furling on maxed-out racing boats.
The above is more applicable to a jib/genoa that is specifically ‘cut’ for racing – a sail that has a relatively FLAT entry, one that has to be ‘steered’ with great precision. In contrast, a ‘cruising cut’ jib will have a ‘rounded’ entry or luff section, one that will have a ‘wide steering range’ of 10-15 degrees (or more) – a ‘forgiving’ or easy to steer sail .... and that rounded luff entry may more easily promote a separation stall on the leeward side if you increase that ‘curve’ by excessive backstay (sag) or halyard tension. Separation stalls are more common in the ‘lighter’ wind ranges when the wind has less relative energy ‘to make the turn around the luff’ – watch the leeward steering row of telltales to observe the beginnings of a separation stall.
There are many many other strategies and tactics to make a boat 'go' while on a beat ... and perhaps you should repost this on the 'general' forum for a full discussion by many contributors.
Especially if you have ‘roller reefing’, beware that overtensioning the halyard may cause the furler to jam – probably the chief reason that you hardly see roller furling on maxed-out racing boats.
The above is more applicable to a jib/genoa that is specifically ‘cut’ for racing – a sail that has a relatively FLAT entry, one that has to be ‘steered’ with great precision. In contrast, a ‘cruising cut’ jib will have a ‘rounded’ entry or luff section, one that will have a ‘wide steering range’ of 10-15 degrees (or more) – a ‘forgiving’ or easy to steer sail .... and that rounded luff entry may more easily promote a separation stall on the leeward side if you increase that ‘curve’ by excessive backstay (sag) or halyard tension. Separation stalls are more common in the ‘lighter’ wind ranges when the wind has less relative energy ‘to make the turn around the luff’ – watch the leeward steering row of telltales to observe the beginnings of a separation stall.
There are many many other strategies and tactics to make a boat 'go' while on a beat ... and perhaps you should repost this on the 'general' forum for a full discussion by many contributors.
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