First of all everybody...Have fun at the 2013 Class Championship...will miss you...work intrudes.
So how much forestay sag do you run with in various conditions. Give me some inch numbers for flat water and waves. Does anybody take any loos gauge readings on their forestay.
We run about 12 to 15 (new loos) at the dock with no backstay. This depends on light air or heavy air shroud tensions.
At the dock...adding backstay (newer cascading system) tension NEVER eases forestay (see Spike Guide). At about half backstay or more we start getting forestay tensions increased to about 22 when full on. I imagine increasing mainsheet tension will affect sag in much the same way.
We have some new North Sails and they are cut differently than Boston and that is why this issue has come up.
We were heading upwind racing the other night in about 10 kts with main trimmed in and no backstay and our young bowman said the sag looked to be about a foot. 28/22 (new loos) on shrouds, old mast, very slight puckers in jib hoist, 50% draft, flat water.
Cheers / Doug
Forestay Sag
Moderators: sderby, Tim Bosma, Tom Elsen
Forestay Sag
Doug Frye
Re: Forestay Sag
I would like to learn more about this too. Our fancy new string genoa does not point well.
Actually, at 8 to 10 knots, our # 3 head sail points WAY higher than the string, and is faster as well.
Gotta be the forestay sag?
Or, somebody else suggested that the luff tension for the string sail should be low.
Comments ? Suggestions ?
Actually, at 8 to 10 knots, our # 3 head sail points WAY higher than the string, and is faster as well.
Gotta be the forestay sag?
Or, somebody else suggested that the luff tension for the string sail should be low.
Comments ? Suggestions ?
Re: Forestay Sag
Hey there guys,
I've been watching this post for a while and refrained from making a reply to give others a stab at it. After being labeled the "board know it all" by one member or words to that effect, I rarely post here anymore.
Forestay sag, twist, weather helm and such things are nebulous concepts at best for the simple reason that getting the optimum speed and angle for a given wind speed/water condition can and will vary greatly on two different boats of the same type except with different sails, different crew weights and such. Weather helm is the least nebulous of these, but on the 7.9 with it's radically counterbalanced rudder, how much of this one thinks they have and how much one REALLY has can be hugely different, but, this is the easiest one to get right if you just look at the tiller in relation to the centerline of the cockpit, and if you just keep the boat relatively flat it's academic!
Within fairly wide limits there is no right or wrong amount of headstay sag. That is to say, putting any number of inches, pounds or digits on a tuning gauge on it is fraught with peril, and the majority of sailors would just be guessing anyway! The only accurate way to see it (on the 7.9) is with a really tight Spinnaker halyard shackled right next to the headstay when sailing upwind, and even this will only tell you so much because the spi halyard will STILL be sagging some because of wind pressure as the apparent wind speed goes up. Then there's the measuring part of the equation; unless you have inches or centimeters marked on the center luff of the headsail, perpendicular to the luff for reference, you would only be guessing!
Instead of looking for numbers one should be listening to what the boat is trying to tell them. I call this learning the language of the boat. Many people say that they point better with the small jib than the Genoa. Some boats have narrower jib leads than Genoa leads, but the 7.9's are close to identical angles. The real culprit is (once again) .......... heel! When boats heel their leeway angle goes up. It doesn't matter where the bow is pointing or what the compass is saying, if the boat is heeling more to way more than the others of the same type in the same wind and water conditions, said boat simply will not seem to be "pointing" as well as the others.
The correct amount of headstay sag for a given headsail, apparent wind speed, water condition and mainsail trim would be that which allows the sail to take on it's designed shape, (entry, twist, draft location, etc.) along with allowing the boat to be sailed fast, relatively flat and high. Of course this is also effected by luff tension and lead and as emphasized, mainsail trim. Get any of these out of whack and I hope that you get my drift about putting a number on headstay sag!!!
Flat is fast and flatter is often faster, but remember that "flat" is a relative thing. This is not just the heel angle but also the sails. One only needs enough power to get the boat moving at optimum speed and angle for the things already mentioned. Most people reach 60-90% on trimming and hiking and then lay off, even though they don't think or realize this is happening. Light air is the antithesis to this up to a point, but even when crew weight is to leeward and the rig relatively loose along with a correspondingly large amount of headstay sag, you can often shift into another gear or two and increase the speed and angle by pulling on a little backstay and then re trimming to the new lesser headstay sag, greater mast bend, and more open leeches, etc. Often, you will find that some crew weight needs to be shifted to windward with these new settings because even though the true wind speed has not increased, the apparent wind speed has!
Also...... Yes, I did say backstay! Too many sailors make the mistake of never touching the backstay until "X" wind speed is reached or the rail is in the water. Remember, the boat is talking to you and telling you everything you need to know, you only need to learn it's language and then be willing to listen! Don't let theories and conjecture stop you from experimenting.
Lots of sailmakers and good sailors say that the sheets are your gear shift, but to me this is totally wrong when it comes to keelboats with stiff masts and backstay adjusters. The BACKSTAY is your gearshift and your sheets are the throttles. Just as in a car or anything else with a transmission, pushing the throttle to the floor will only get you going so fast, to go faster you must first shift to a higher gear.
I hope that I haven't confused you or gotten too far "in the weeds" here! My point is that talking about headstay sag and headstay sag only (in a vacuum) is fruitless because if all the other variables. The "right amount" is a constantly changing target as is everything else in sailing, and I rarely think about headstay sag when sailing, only how the boat feels and what it needs to stay fast, flat and high. IMHO, concentrating on one aspect of the big picture without considering the MANY others involved in sailing will only cause consternation and frustration!
I've been watching this post for a while and refrained from making a reply to give others a stab at it. After being labeled the "board know it all" by one member or words to that effect, I rarely post here anymore.
Forestay sag, twist, weather helm and such things are nebulous concepts at best for the simple reason that getting the optimum speed and angle for a given wind speed/water condition can and will vary greatly on two different boats of the same type except with different sails, different crew weights and such. Weather helm is the least nebulous of these, but on the 7.9 with it's radically counterbalanced rudder, how much of this one thinks they have and how much one REALLY has can be hugely different, but, this is the easiest one to get right if you just look at the tiller in relation to the centerline of the cockpit, and if you just keep the boat relatively flat it's academic!
Within fairly wide limits there is no right or wrong amount of headstay sag. That is to say, putting any number of inches, pounds or digits on a tuning gauge on it is fraught with peril, and the majority of sailors would just be guessing anyway! The only accurate way to see it (on the 7.9) is with a really tight Spinnaker halyard shackled right next to the headstay when sailing upwind, and even this will only tell you so much because the spi halyard will STILL be sagging some because of wind pressure as the apparent wind speed goes up. Then there's the measuring part of the equation; unless you have inches or centimeters marked on the center luff of the headsail, perpendicular to the luff for reference, you would only be guessing!
Instead of looking for numbers one should be listening to what the boat is trying to tell them. I call this learning the language of the boat. Many people say that they point better with the small jib than the Genoa. Some boats have narrower jib leads than Genoa leads, but the 7.9's are close to identical angles. The real culprit is (once again) .......... heel! When boats heel their leeway angle goes up. It doesn't matter where the bow is pointing or what the compass is saying, if the boat is heeling more to way more than the others of the same type in the same wind and water conditions, said boat simply will not seem to be "pointing" as well as the others.
The correct amount of headstay sag for a given headsail, apparent wind speed, water condition and mainsail trim would be that which allows the sail to take on it's designed shape, (entry, twist, draft location, etc.) along with allowing the boat to be sailed fast, relatively flat and high. Of course this is also effected by luff tension and lead and as emphasized, mainsail trim. Get any of these out of whack and I hope that you get my drift about putting a number on headstay sag!!!
Flat is fast and flatter is often faster, but remember that "flat" is a relative thing. This is not just the heel angle but also the sails. One only needs enough power to get the boat moving at optimum speed and angle for the things already mentioned. Most people reach 60-90% on trimming and hiking and then lay off, even though they don't think or realize this is happening. Light air is the antithesis to this up to a point, but even when crew weight is to leeward and the rig relatively loose along with a correspondingly large amount of headstay sag, you can often shift into another gear or two and increase the speed and angle by pulling on a little backstay and then re trimming to the new lesser headstay sag, greater mast bend, and more open leeches, etc. Often, you will find that some crew weight needs to be shifted to windward with these new settings because even though the true wind speed has not increased, the apparent wind speed has!
Also...... Yes, I did say backstay! Too many sailors make the mistake of never touching the backstay until "X" wind speed is reached or the rail is in the water. Remember, the boat is talking to you and telling you everything you need to know, you only need to learn it's language and then be willing to listen! Don't let theories and conjecture stop you from experimenting.Lots of sailmakers and good sailors say that the sheets are your gear shift, but to me this is totally wrong when it comes to keelboats with stiff masts and backstay adjusters. The BACKSTAY is your gearshift and your sheets are the throttles. Just as in a car or anything else with a transmission, pushing the throttle to the floor will only get you going so fast, to go faster you must first shift to a higher gear.
I hope that I haven't confused you or gotten too far "in the weeds" here! My point is that talking about headstay sag and headstay sag only (in a vacuum) is fruitless because if all the other variables. The "right amount" is a constantly changing target as is everything else in sailing, and I rarely think about headstay sag when sailing, only how the boat feels and what it needs to stay fast, flat and high. IMHO, concentrating on one aspect of the big picture without considering the MANY others involved in sailing will only cause consternation and frustration!
Last edited by dave on Mon Oct 28, 2013 6:41 pm, edited 1 time in total.
Re: Forestay Sag
Dave, thanks for the advice !! I'm ruminating on it - munch, munch !!
Actually, I think it could be argued that both you and I don't post too much, but that others post too little.
Come on people, there are 120 views here, but only two of us posting.
If you lurkers out there also help out you'll make your 7.9's more valuable by making the fleet more successful, not to mention making this site more welcoming to newkies.
Seriously, prospective 7.9 buyers look at that sort of thing . .
Actually, I think it could be argued that both you and I don't post too much, but that others post too little.
Come on people, there are 120 views here, but only two of us posting.
If you lurkers out there also help out you'll make your 7.9's more valuable by making the fleet more successful, not to mention making this site more welcoming to newkies.
Seriously, prospective 7.9 buyers look at that sort of thing . .
Re: Forestay Sag
Thanks for the thanks AJ! 
Be careful about overthinking things like how much headstay sag, mast bend, etc. Let the boat tell you what it needs. IMHO, the biggest mistake that most sailors make is setting their boat up to a tuning guide (or at least THINK) they have, set the leads, halyards, outhaul to whatever "looks right", and that's about it whether they are going well or poorly. Being willing to do thing that go against what many say will bring big dividends. Things like sailing with a loser rig than most, aggressively using the backstay more and more often and such can and will open up a whole new level of speed and angle, but not if they are never tried!
Be careful about overthinking things like how much headstay sag, mast bend, etc. Let the boat tell you what it needs. IMHO, the biggest mistake that most sailors make is setting their boat up to a tuning guide (or at least THINK) they have, set the leads, halyards, outhaul to whatever "looks right", and that's about it whether they are going well or poorly. Being willing to do thing that go against what many say will bring big dividends. Things like sailing with a loser rig than most, aggressively using the backstay more and more often and such can and will open up a whole new level of speed and angle, but not if they are never tried!
Re: Forestay Sag
I got a good chuckle out of the "I'm ruminating on it!! Munch, munch!!" 
From now on I will probably think of this when I see a deer, cow, etc!!!
From now on I will probably think of this when I see a deer, cow, etc!!!
-
normbue
Re: Forestay Sag
Regarding boat and sail handling. I've read a lot in these forums about the importance of mast rake in light air. does the same hold true in heavy gusty wind? Or is this something you have to experiment with to find a balance.
Re: Forestay Sag
please note that I have edited this a few times to hopefully be more clear and concise.
On the 7.9 you set the headstay at the class legal pin to pin measurement and go.
The gusty and shifty stuff is my absolute favorite to race in because it puts a premium on gear shifting and tactics. If you are one of those folks who don't play the backstay much, remember what I said earlier: the backstay is your gear shift. If one is always sailing in the same gear, that's bad enough. After all, would you drive your car in one gear? Problem is that when a puff comes through the headstay will sag relative to where it was before, making the headsail fuller, no matter how tight your rig is. Add to this the fact that your sails will stretch some and become fuller even if they are $$$$ high tech fibers and laminates and you now are in a LOWER gear than before (more lift and drag: HEEL) instead of being in the higher gear (less lift and less drag) that's needed for the increased apparent wind.
Back in the late 80's Randy Smyth (one of the top cat sailors in the world at the time) said something very profound and unbelievably simple: "When you have more lift than you can use, the only way to go faster is to decrease drag".
Before I go any further, don't let the "cat sailor" thing throw you off the scent! Sailing is sailing. All boats have idiosyncrasies and cats aren't limited by hull speed, but the same principles apply. Randy's words ring true in every boat that I've ever sailed. The main difference is the speed potential between gears and the ultimate speed potential, and again, even on a heavy displacement hull like the 7.9 you never know what the boat can do upwind if you aren't willing to continually be pulling on things (especially the backstay and the vang) and see what happens.
In case anyone missed it, you decrease lift and more importantly drag by doing what it takes to make the sails flatter and lessen the angle of attack, also known as the traveler! Of course you have to keep track of luff tension if things are getting out of hand, but remember that draft forward shapes lead to a wider steering groove and quicker acceleration while draft aft (both relative to the normal positions) usually lead to higher angles and ultimate speed made good to windward, if you can drive to it! That last bit can be a problem if one isn't a really good driver with a really dedicated crew that HIKES HARD!!! Having the possibility of higher angles with great speed will do you no good if the boat is out of the groove half the time, or worse!!! The first choice is usually better in relatively choppy/wavy conditions for the wind strength and/or skippers and crews with little experience in such conditions, while the latter is usually better in flatter water relative the the wind and/or more experienced driver and crew. Again, the point is to experiment and not get pigeonholed into doing nothing because the rig is "tuned to the wind range in the guide"!
On the 7.9 you set the headstay at the class legal pin to pin measurement and go.
The gusty and shifty stuff is my absolute favorite to race in because it puts a premium on gear shifting and tactics. If you are one of those folks who don't play the backstay much, remember what I said earlier: the backstay is your gear shift. If one is always sailing in the same gear, that's bad enough. After all, would you drive your car in one gear? Problem is that when a puff comes through the headstay will sag relative to where it was before, making the headsail fuller, no matter how tight your rig is. Add to this the fact that your sails will stretch some and become fuller even if they are $$$$ high tech fibers and laminates and you now are in a LOWER gear than before (more lift and drag: HEEL) instead of being in the higher gear (less lift and less drag) that's needed for the increased apparent wind.
Back in the late 80's Randy Smyth (one of the top cat sailors in the world at the time) said something very profound and unbelievably simple: "When you have more lift than you can use, the only way to go faster is to decrease drag".
Before I go any further, don't let the "cat sailor" thing throw you off the scent! Sailing is sailing. All boats have idiosyncrasies and cats aren't limited by hull speed, but the same principles apply. Randy's words ring true in every boat that I've ever sailed. The main difference is the speed potential between gears and the ultimate speed potential, and again, even on a heavy displacement hull like the 7.9 you never know what the boat can do upwind if you aren't willing to continually be pulling on things (especially the backstay and the vang) and see what happens.
In case anyone missed it, you decrease lift and more importantly drag by doing what it takes to make the sails flatter and lessen the angle of attack, also known as the traveler! Of course you have to keep track of luff tension if things are getting out of hand, but remember that draft forward shapes lead to a wider steering groove and quicker acceleration while draft aft (both relative to the normal positions) usually lead to higher angles and ultimate speed made good to windward, if you can drive to it! That last bit can be a problem if one isn't a really good driver with a really dedicated crew that HIKES HARD!!! Having the possibility of higher angles with great speed will do you no good if the boat is out of the groove half the time, or worse!!!
The first choice is usually better in relatively choppy/wavy conditions for the wind strength and/or skippers and crews with little experience in such conditions, while the latter is usually better in flatter water relative the the wind and/or more experienced driver and crew. Again, the point is to experiment and not get pigeonholed into doing nothing because the rig is "tuned to the wind range in the guide"! Re: Forestay Sag
No problem.
Thanks for the thanks!
Thanks for the thanks!