As I understand it, on a masthead rig, the only function of a backstay adjuster is to increase tension on the forestay when sailing on the wind or when the wind picks up, both situations in which the forestay wants to sag off to leeward. Why, then, have an essentially infinitely adjustment on the backstay? Why not just have two positions: normal, for broad reaching and running; and tight, for beating and close reaching? Since any setting is basically a judgement call anyway, this would take out some of the guesswork and perhaps keep from overtensioning the rig, too. What are your thoughts?
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Bob: Actually the main function of the back stay adjuster on a masthead or fractional rig sailboat is to take the fullness (draft depth) out of the main. The secondary problem you run into is the effect bending the mast has on the head stay. On a masthead rig, you can't really bend the mast as you can with say a J boat etc. You end up just tilting the mast backwards. For example, on my C30, I'd have better luck bending a telephone pole than I would to bend my mast so there is not a lot of effect on the headstay. To illustrate what the bending is suppose to look like - bend your middle finger and notice how the knucle goes back. In a true bending situation, that effect would pull the fullness out of the center of the main.
Don, I still don't understand
how tensioning the backstay on a masthead rig, especially one with a fairly rigid mast, will change the shape of the mainsail much at all, and your response indicates that it doesn't. On my boat the upper and lower shrouds are in the same plane as the mast, so there is little resistance to the mast's "rocking" back as the backstay is tightened up. I understand how the mast is bent in a fractional rig, but my question is still about using backstay tension to "rock" the mast back and thus put more tension and less sag in the forestay. Why not have just two positions: normal and tight?
how tensioning the backstay on a masthead rig, especially one with a fairly rigid mast, will change the shape of the mainsail much at all, and your response indicates that it doesn't. On my boat the upper and lower shrouds are in the same plane as the mast, so there is little resistance to the mast's "rocking" back as the backstay is tightened up. I understand how the mast is bent in a fractional rig, but my question is still about using backstay tension to "rock" the mast back and thus put more tension and less sag in the forestay. Why not have just two positions: normal and tight?
Why not have just two positions: normal and tight?
Because there are various wind speeds between 10 and 30 knots. You can crank it in as the wind builds, since it rarely only blows soft and hard.
Because there are various wind speeds between 10 and 30 knots. You can crank it in as the wind builds, since it rarely only blows soft and hard.
Stu, what are the criteria
for how much to tension it as the wind increases? For example, assume sailing on a close reach in 8kts of wind - how tight should the adjuster be and as the wind gets up, what adjustments should be made, in what increments?
for how much to tension it as the wind increases? For example, assume sailing on a close reach in 8kts of wind - how tight should the adjuster be and as the wind gets up, what adjustments should be made, in what increments?
Backstay Adjustments
Bob The concept is to reduce the headstay sag. With a split backstay controlled with a vang the easiest approach would be to sight the forestay from the leeward side of the cockpit when sailing closehauled, and starting with your 8 knots, increase tension on the forestay to reduce the sag as the wind builds. No way to eliminate it completely, so don't pull too hard
Going downwind, the tension should be released.
Bob The concept is to reduce the headstay sag. With a split backstay controlled with a vang the easiest approach would be to sight the forestay from the leeward side of the cockpit when sailing closehauled, and starting with your 8 knots, increase tension on the forestay to reduce the sag as the wind builds. No way to eliminate it completely, so don't pull too hard
Going downwind, the tension should be released.Backstay tension reasons
This topic and the replies are helpful in some ways, but are generating some confusion as well, in my opinion. First, a backstay tensioner is used to adjust the ... backstay tension. For most rigs, this has the inevitable result of bending the mast and taking the sag out of the headstay. The latter is because, in theory, the backstay and headstay tensions are always equal, and when tension is increased, the sag is lessened. The headstay will sag more that the back, due both to gravity, sagging down, and to wind loads, to leeward. This is because the headsail is attached to it. A backstay adjuster is not used to adjust the rake (referred to incorrectly as "rocking" in a previous reply) of the mast. The rake is established when the rig is set up, using a combination of adjustments including the wedges at the partners for keel-stepped masts, and the initial, static fore and backtay tensions, and the lowers as well. A pre-bend aft is usually put in at this time as well. For a rig with single lowers and a deck-stepped mast, and no baby stay (inner forestay), it may be near impossible to get any bend in the mast using a backstay adjuster. Why bend? Fortunately, bending the mast results in the jib and main taking new shapes, in concert, which are more appropriate to higher winds and on-the-wind sailing. The main is cut with a curved luff such that with a straight mast it is more full, i.e., more camber; and when the mast is bent aft, the main flattens. Flat is better for higher winds, and higer pointing. Similarly a headsail, the luff of which is sagging off to leeward, is more full and more appropriate to off-wind sailing and lighter winds; when the headstay is tightened taking out the sag, the sail flattens, which is more advantageous for higher winds and on-wind sailing. One should aim to adjust the rig so the headstay sag and mast bend are in proper proportion for the sails. A continuously variable backstay adjuster is preferable to one with only two posiitons, since you will want ot adjust or trim differently for different winds and points of sail. Incidentally, to Don, and I think we discussed this here a year or so ago, the mast on my C36 TR is quite "bendy," in my opinion. Laid out on saw horses, I can lift one end a couple feet without the ceter coming off the saw horse. That's the sideways bend, though. Fore and aft I'm sure its a bit stiffer, but still bendable. Since its down now, perhaps I can make a measurement of some kind before its stepped this season.
This topic and the replies are helpful in some ways, but are generating some confusion as well, in my opinion. First, a backstay tensioner is used to adjust the ... backstay tension. For most rigs, this has the inevitable result of bending the mast and taking the sag out of the headstay. The latter is because, in theory, the backstay and headstay tensions are always equal, and when tension is increased, the sag is lessened. The headstay will sag more that the back, due both to gravity, sagging down, and to wind loads, to leeward. This is because the headsail is attached to it. A backstay adjuster is not used to adjust the rake (referred to incorrectly as "rocking" in a previous reply) of the mast. The rake is established when the rig is set up, using a combination of adjustments including the wedges at the partners for keel-stepped masts, and the initial, static fore and backtay tensions, and the lowers as well. A pre-bend aft is usually put in at this time as well. For a rig with single lowers and a deck-stepped mast, and no baby stay (inner forestay), it may be near impossible to get any bend in the mast using a backstay adjuster. Why bend? Fortunately, bending the mast results in the jib and main taking new shapes, in concert, which are more appropriate to higher winds and on-the-wind sailing. The main is cut with a curved luff such that with a straight mast it is more full, i.e., more camber; and when the mast is bent aft, the main flattens. Flat is better for higher winds, and higer pointing. Similarly a headsail, the luff of which is sagging off to leeward, is more full and more appropriate to off-wind sailing and lighter winds; when the headstay is tightened taking out the sag, the sail flattens, which is more advantageous for higher winds and on-wind sailing. One should aim to adjust the rig so the headstay sag and mast bend are in proper proportion for the sails. A continuously variable backstay adjuster is preferable to one with only two posiitons, since you will want ot adjust or trim differently for different winds and points of sail. Incidentally, to Don, and I think we discussed this here a year or so ago, the mast on my C36 TR is quite "bendy," in my opinion. Laid out on saw horses, I can lift one end a couple feet without the ceter coming off the saw horse. That's the sideways bend, though. Fore and aft I'm sure its a bit stiffer, but still bendable. Since its down now, perhaps I can make a measurement of some kind before its stepped this season.
Bob:Before I give you the mast bend settings, let me say I have a solution to your problem and it involves ALL your sail trim controls for your main and jib. Take a look at my Sail Trim Chart, which is sold on this site. It gives you the settings for all your trim controls for all wind speeds and points of sail. There are 7 trim controls for the main plus some other items that all have to work together to obtain 100% efficiency. It is like an 8 cylinder engine - you can't just adjust 1 cylinder and expect it to run smoothly. You are only adjusting 4 items and they are draft depth, draft position, twist and angle of attack. Mast bend only adjusts draft depth in the main and jib. The other mainsail control for draft depth is the outhaul. Anyway, here are your settings: windward 1 to 2 knots = straight 2 to 5 knots = minimal tension 5 to 15 knots = moderate tension 15 to 18 knots = heavy tension Reaching Light wind = straight Medium wind = medium tension Heavy wind = maximum tension Running Light wind = straight Medium wind = straight Heavy wind = minimum You also might want to take a look at my book, The Sail Trim Users Guide, which is also sold on this site. As outlined above, I told you WHAT to do, which is what my chart does, and my book tells you WHY you are making a particular sail trim adjustment. Mast bend only changes the shape of the middle and upper portions of the mainsail. The outhaul changes the shape in the bottom 2/3. The mainsail looks triangular but it isn't. It has an exaggerated leech (roach) and curved Luff (luff curve). Masts are bent for luff curve. What you are trying to do is bend the mast so the bend matches the luff curve and making the sail flatter, because when sailing upwind you want to remove fullness and move the draft position aft. Draft aft = more power. When you do this, twist comes into play and must be dealt with also. In chop or when sailing downwind the mast should be straight or even bent forward, which would create and even fuller sail. I hope I have not confused you or anyone. I try to keep my explanations as simple and non technical as possible because when I was learning this stuff the high tech answers confused me. As always, I suggest everyone try the settings I suggest and see if they work for you.
John Visser: Good to hear from you again. I'm glad your still visiting the forum because your knowledge adds to the infomation. I was thinking about the bend ability of the C36 mast and maybe your results are because your mast, plus being a tall rig, is so much longer than my C30. I agree about the confusion that result from some of the comments. Every time I answer a question I think that I wish space would permit a more complete expalnation. My book is what I believe contains everything the beginner to intermediate needs to know about sail trim for the main and jib in about 65 pages, so the subject is not nuclear research. I knew I had it all when the material I was researching started repeating itself. The problem with discussing sail trim is it has to be discussed in the big picture and not in little pieces. In other words, you can't discuss mast bend without discussing the outhaul and then the outhaul leads to something else. Folks want it all in 5 minutes and that is not possable. I tell seminar participants to just be patient with my presentation because when I finish it will all become a clear. I've got to stop writting or I'll confuse myself!!!
Thanks for the input, Don and John, especially
the chart values - that's really what I was looking for (and I am going to buy the book and the chart). You guys kept talking about mast bend, and on my boat that's pretty much a non-issue. I understand how controlling the mast bend works to shape the mainsail on a fractional or babystay rig. But that isn't pertinent to the original question, which was: on a masthead rig, where mast bend is not an issue, and backstay tension is used to take the sag out of the forestay (by "rocking" the mast back to where it was, not bending it), why are more than two settings necessary? Stu hit it with his reference to differing wind strengths, and Don's chart was even more specific - in fact, it would allow me to mark my adjuster for 5 positions. That's what I needed to know. Thanks guys
the chart values - that's really what I was looking for (and I am going to buy the book and the chart). You guys kept talking about mast bend, and on my boat that's pretty much a non-issue. I understand how controlling the mast bend works to shape the mainsail on a fractional or babystay rig. But that isn't pertinent to the original question, which was: on a masthead rig, where mast bend is not an issue, and backstay tension is used to take the sag out of the forestay (by "rocking" the mast back to where it was, not bending it), why are more than two settings necessary? Stu hit it with his reference to differing wind strengths, and Don's chart was even more specific - in fact, it would allow me to mark my adjuster for 5 positions. That's what I needed to know. Thanks guys
Bob: I was in your boat in that people I questioned about sail trim would tell me to adjust this or that control but they never could tell me which way or how much or for what wind conditions. Actually, that is how my Chart was developed - it was for me as I thought I was the idiot of the sailing world and the only one who did not know how to trim his sails. Once you get my Sail Trim Chart, you'll be able to mark ALL your sail trim controls such as the outhaul, main and jib halyards, boom vang and the most important sail trim control of all, which is the jib fairlead. As a marker on some controls I use a piece of black tape (halyard at full hoist) or a mark on the boom (outhaul) but you can use anything. All boats are different but my Chart will get you in the ball park for your boat and then you can tweak the setting for your personal taste. The most important aspect of my Book is that you will know exactly WHY you are making a particular sail trim adjustment and when and what adjustemnt is needed. I've been on race boats where the skipper tells me to "adjust the outhaul" for example. He doesn't say ease or trim or how much. In many cases I wonder why he is requesting this change and why we are not dealing with the other portion of the sail but I do it anyway because he is the skipper. Once you finish with my stuff you know exactly why your making a sail trim change and will know more about sail trim than 75% of the sailors worldwide. That's my guarantee.
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