I read with interest the guest expert forum reguarding converting a bolt rope main to loose footed main. I was encouraged by his suggestion that this was possible to try with out having the sail converted first. He said to try it out and if it was a positive experience, to take the sail to a sailmaker and have the conversion done. I think that I would like a loose footed sail as everyone seems to like the improved outhaul control. I decided to give it a try as soon as it warmed up a little. Then I started to worry. Does anyone know what effect the change in the geometry of the forces on the boom would have? My boat is a 1975 Hunter 25 with mid boom sheeting. Thank you very much.
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Your test may not tell you what you need to see.
Your test of a loose foot wont really give you what you want to know. The foot shape is what this is really about. The sailmaker has to reshape the bottom of the sail to conform to a boom bolt rope. That adjustment in the lower panel of the sail makes it straight and flat to follow the boom. On a loosefooted main the tack and clew are on line but the foot in between is free to assume the foil shape of the rest of the sail. It makes it alot easier to look ant the draft and see what effect changes in tension on the sail does. The downside if there is one or two... you have to depend on the tack and clew to take all the load. but that really happens anyway, and ah i cant think of why you would not do it. I love mine.
Your test of a loose foot wont really give you what you want to know. The foot shape is what this is really about. The sailmaker has to reshape the bottom of the sail to conform to a boom bolt rope. That adjustment in the lower panel of the sail makes it straight and flat to follow the boom. On a loosefooted main the tack and clew are on line but the foot in between is free to assume the foil shape of the rest of the sail. It makes it alot easier to look ant the draft and see what effect changes in tension on the sail does. The downside if there is one or two... you have to depend on the tack and clew to take all the load. but that really happens anyway, and ah i cant think of why you would not do it. I love mine.
Pops, I think that you are just interested to see the mechanics of the loose foot rather than how your current sails shape will change. You cannot elimanate the shelf foot without removing it, so naturally the shape will not be as good until you do. However, with reguard to "what effect the change in the geometry of the forces on the boom would have?"....there really is no change in the forces on the boom. Your question is thoughtful but the answer is 'no' there is no change. A number of years ago, I wanted to upgrade the mechanical advantage on my main traveler from the stock 3:1 to 5:1. This meant stacking sheeves on the car (2 instead of 1). I called Schaefer(the car manufacturer) to purchase 2 extra sheeves. They put me through to the "tech" dept. The tech told me that this could not be done because of the "increased loading on the car". I explained that the load on the car was to remain unchanged, but that the MA was going to be higher. His responce was 'No you can't do it' and would not sell me the sheeves (legal issues). I was angry because the tech didn't know what he was talking about. I went to WM and bought 2 Schaefer cheeck blocks and cut out the sheeves. I mounted them on the car and needless to say, I've had a 5:1 traveler for years.
Disagree
A year and a half ago I bought new sails, including a loose-footed main. The difference in performance was dramatic, and my boat began to run up front in the fall racing series. I enjoyed the ease of trimming and reading the new sails, especially the main. This spring, when setting up the boat (not a Hunter) for launching, I foolishly rigged my 4 to 1 tackle to the mid-boom mainsheet bail (I use the boom as a gin-pole for raising the mast) instead of to the end of the boom. I figured it wouldn't make that much difference. It did. We could see the boom flex and arc a little when we got the mast vertical and near a position where we could attach the backstay. Even then I didn't think much of it as spars are supposed to bend a little, aren't they? The next day, while leading our class in the first race of the series, in 15 to 25 kt winds, the boom broke when we gybed the boat with very little slack in the mainsheet and the genoa reefed about 20%. It broke right at the bail bolt holes, and the metal was clearly distorted in that area. I'm sure that bending it the night before was a major contributor to the failure. But my main point is that ALL the force acting through the back part of the main is passed through the clew attachment in a loose-footed sail. In a bolt rope sail, at least some of that force has to be distributed to the boom through the foot of the sail. My "mid" boom sheet actually attaches about 2' forward of the end of the boom, but the sail still had that 2' of leverage to bend and eventually break the boom. On larger boats the forces would of course be magnified. So if you have end-boom sheeting, no sweat, the forces are in opposition. But if you have mid-boom sheeting, make sure the boom is sound and consider multiple points of attachment rather than just one bail.
A year and a half ago I bought new sails, including a loose-footed main. The difference in performance was dramatic, and my boat began to run up front in the fall racing series. I enjoyed the ease of trimming and reading the new sails, especially the main. This spring, when setting up the boat (not a Hunter) for launching, I foolishly rigged my 4 to 1 tackle to the mid-boom mainsheet bail (I use the boom as a gin-pole for raising the mast) instead of to the end of the boom. I figured it wouldn't make that much difference. It did. We could see the boom flex and arc a little when we got the mast vertical and near a position where we could attach the backstay. Even then I didn't think much of it as spars are supposed to bend a little, aren't they? The next day, while leading our class in the first race of the series, in 15 to 25 kt winds, the boom broke when we gybed the boat with very little slack in the mainsheet and the genoa reefed about 20%. It broke right at the bail bolt holes, and the metal was clearly distorted in that area. I'm sure that bending it the night before was a major contributor to the failure. But my main point is that ALL the force acting through the back part of the main is passed through the clew attachment in a loose-footed sail. In a bolt rope sail, at least some of that force has to be distributed to the boom through the foot of the sail. My "mid" boom sheet actually attaches about 2' forward of the end of the boom, but the sail still had that 2' of leverage to bend and eventually break the boom. On larger boats the forces would of course be magnified. So if you have end-boom sheeting, no sweat, the forces are in opposition. But if you have mid-boom sheeting, make sure the boom is sound and consider multiple points of attachment rather than just one bail.
Bob, I'm sorry but.....
..but you've got this one all wrong. On a main with a shelf foot, there is no load on the foot bolt rope in the vertical axis. As the outhaul is applied, the bolt rope is pulled tighter on the horizontal, removing the shelf but still no vertical component. The exact same thing applies to a loose footed main. The big benefit is there is no shelf to restrick movement of the draft of the lower part of the sail. With respect to your boom, sounds to me like the boom was getting ready to fail. With a 4:1 tackle, if you were able to exert even 150lbs of force to raise the mast, the boom was seeing 600lbs at the bail. Certainly not enough to damage a normal healthy bail. I have a 10:1 midboom sheet and can easily put 200lbs on it. Thats 2000lbs of force at the bail when it's blowing ten buckets of snot. It puts a serious catinary in the boom and thats well within the limits of the boom.
..but you've got this one all wrong. On a main with a shelf foot, there is no load on the foot bolt rope in the vertical axis. As the outhaul is applied, the bolt rope is pulled tighter on the horizontal, removing the shelf but still no vertical component. The exact same thing applies to a loose footed main. The big benefit is there is no shelf to restrick movement of the draft of the lower part of the sail. With respect to your boom, sounds to me like the boom was getting ready to fail. With a 4:1 tackle, if you were able to exert even 150lbs of force to raise the mast, the boom was seeing 600lbs at the bail. Certainly not enough to damage a normal healthy bail. I have a 10:1 midboom sheet and can easily put 200lbs on it. Thats 2000lbs of force at the bail when it's blowing ten buckets of snot. It puts a serious catinary in the boom and thats well within the limits of the boom.
meanwhile, back at the main (ahem) question...
...we must look at potential disadvantages of a loose-footed main. The primary one, especially in light air, is that the laminar flow over the sail is less focused, because the shelf on a conventional main's foot serves to direct any downward flow aft. In my estimation, however, this is a small price to pay in terms of the sail-shaping advantages a loose-footed main provides. Bottom line: the more wind you tend to encounter, the more advantageous it is to keep the main's foot loose. (A secondary, extremely minor consideration, for those who sail without lazyjacks, et cetera, is that a loose-footed main doesn't allow you to "sea furl" the sail during a douse.)
...we must look at potential disadvantages of a loose-footed main. The primary one, especially in light air, is that the laminar flow over the sail is less focused, because the shelf on a conventional main's foot serves to direct any downward flow aft. In my estimation, however, this is a small price to pay in terms of the sail-shaping advantages a loose-footed main provides. Bottom line: the more wind you tend to encounter, the more advantageous it is to keep the main's foot loose. (A secondary, extremely minor consideration, for those who sail without lazyjacks, et cetera, is that a loose-footed main doesn't allow you to "sea furl" the sail during a douse.)
Disadvantages of loose-footed main (re: John F)
John F's point about the inability to boom-furl a loose-footed main in a blow is significant. I too have a traveler on my first-generation H25 (not end-boom sheeting) and have also questioned the efficiency of a loose-footed set-up. I recently suggested to a sailmaker that I might just take the boom off and tack the main to the spinnaker turning blocks to see what it does, and the sailmaker said to just leave it out of the boom groove, use the outhaul, and test it that way. The fact is that it is practically impossible to tension a boom-footed sail so tightly as to remove ALL effect of its being supported by the boom. Every book on sailing I have read says that the common tendency to shorten sail on a ketch or yawl to just jib and mizzen is a mistake. The jib pulling from one point on the masthead places tremendous bending and compression moments on the spar, especially in a blow, whereas dropping the mizzen and jib and shortening to moderately-reefed main alone is easier to control, provides calmer sea motion, and relieves those masthead stresses. And that is with a boltrope mainsail on vertical spar supported at least eight different places with shrouds and end stays. Consider also the Cherubini 48 staysail schooner, as originally designed with NO Bergstrom rig, nor a standing backstay, using only running backstays and the mainsheet, drawing against the enormous hoist of the mainsail boltrope, to support the entire rig of two headsails and a fisherman's top-- no differently than all the famous schooners of John Alden. If the boom boltrope is unimportant to strength, is there no reason to not fly the H dimension loose too, like a staysail behind the mast? But there IS. A much smaller boom, unsupported but for sheet, outhaul, and gooseneck (especially with mid-boom sheeting, not pulling opposite the outhaul), is placed in a recipe for breakage under extreme conditions. So the sailor concerned about this will probably shorten to his roller-furling headsail alone, and we are back to the first point-load problem again. I have seen people break booms on moderate days by jibing with the preventer still set. I do NOT want to be in a situation in which my boom is asked to bear all those point loads without having any other option. The mainsail was long ago designed with a boom not because sail designers and boat designers did not have any better idea. It would have been just as simple to fly a loose-footed main in the 1700s as now. The boom-footed main was intended to provide flattening and support along the base of the sail. In the face of the benefits of a loose-footed main, the boom-based main has to be seen as a compromise for safety and strength. That's the price we pay for being careful. Neglecting to consider what has been proven by empirical and mathematical data is tantamount to shoddy seamanship. Do without the boom if you like; but don't claim you have not compromised strength or safety. JC 2 cherubiniyachts@aol.com
John F's point about the inability to boom-furl a loose-footed main in a blow is significant. I too have a traveler on my first-generation H25 (not end-boom sheeting) and have also questioned the efficiency of a loose-footed set-up. I recently suggested to a sailmaker that I might just take the boom off and tack the main to the spinnaker turning blocks to see what it does, and the sailmaker said to just leave it out of the boom groove, use the outhaul, and test it that way. The fact is that it is practically impossible to tension a boom-footed sail so tightly as to remove ALL effect of its being supported by the boom. Every book on sailing I have read says that the common tendency to shorten sail on a ketch or yawl to just jib and mizzen is a mistake. The jib pulling from one point on the masthead places tremendous bending and compression moments on the spar, especially in a blow, whereas dropping the mizzen and jib and shortening to moderately-reefed main alone is easier to control, provides calmer sea motion, and relieves those masthead stresses. And that is with a boltrope mainsail on vertical spar supported at least eight different places with shrouds and end stays. Consider also the Cherubini 48 staysail schooner, as originally designed with NO Bergstrom rig, nor a standing backstay, using only running backstays and the mainsheet, drawing against the enormous hoist of the mainsail boltrope, to support the entire rig of two headsails and a fisherman's top-- no differently than all the famous schooners of John Alden. If the boom boltrope is unimportant to strength, is there no reason to not fly the H dimension loose too, like a staysail behind the mast? But there IS. A much smaller boom, unsupported but for sheet, outhaul, and gooseneck (especially with mid-boom sheeting, not pulling opposite the outhaul), is placed in a recipe for breakage under extreme conditions. So the sailor concerned about this will probably shorten to his roller-furling headsail alone, and we are back to the first point-load problem again. I have seen people break booms on moderate days by jibing with the preventer still set. I do NOT want to be in a situation in which my boom is asked to bear all those point loads without having any other option. The mainsail was long ago designed with a boom not because sail designers and boat designers did not have any better idea. It would have been just as simple to fly a loose-footed main in the 1700s as now. The boom-footed main was intended to provide flattening and support along the base of the sail. In the face of the benefits of a loose-footed main, the boom-based main has to be seen as a compromise for safety and strength. That's the price we pay for being careful. Neglecting to consider what has been proven by empirical and mathematical data is tantamount to shoddy seamanship. Do without the boom if you like; but don't claim you have not compromised strength or safety. JC 2 cherubiniyachts@aol.com
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