Mid-boom sheeting
Al, the technological progress from ships of the 1700s to yachts of the 1970s is like the progress from food storage systems in the 1700s to those of the 1970s. I don't know anyone who wants to go back to that (speaking as an 18th-C scholar here!); and I don't know any of us who confuse our intelligently-designed late-20th-C boats for sailing ships built by eye by men with a 3rd-grade education. So I won't say any more about that.
Jim, however well your mid-boom sheeting works, the loads I have described are still in play. Simplistically stated (not in pure theory) there are three points to pull down on a boom-- the downhaul, the sheet and the vang. (In theory there are infinite points. You could have a vang every 2 inches if you wanted.) All help determine sail shape, performance and handling characteristics. I too have Wallace Ross's book; and his point applies to the vang when boom-end sheeting is used as well. I have seen race boats from the 1970s (when Ross's book was written) rigged with a permanent secondary mainsheet track for the vang to keep it vertical as it rolled along the deck or cabin top between tacks. This is how crucial a proper vang is in a normal (boom-end) sheeting application. The vang is intended to enhance sail shape, not to hold up the boom (for convenience) as with so many modern 'performance cruisers'.
And you do admit that convenience is part of your preference; and that's fine. But let's not cloud user-convenience issues by misinterpreting theory, which is what I came to talk about.
I have seen new Beneteaus with the sheet line less than 50% back (about where Al said he would move his to) and then they have a rigid vang forward of that. The vang in such a case would be entirely unnecessary. The two bails are less than 2 feet apart. This is what the average new-boat buyer will fall for; and it's mainly for marketing, not engineering, purposes. Please-- let's not deny who really 'designs' yachts these days.
I have to conclude two things from such a setup, especially when owners sing its praises:
One, the traveler system must be like a bridge girder in strength, attachment points, tackle and purchase and so on. I mean it's necessarily overbuilt, when if it were moved aft it could be less massive, less heavy and less strong. Almost always such systems are mounted at two heavily-reinforced points rather high up on the superstructure rather than taking advantage of the consistency of many smaller fasteners upon the deck, all in tensile and much less in shear than those of the traveler bridge have to be. Anyone in aerospace tech knows that many smaller, lighter fasteners are better than few large indispensible ones. This is also the fault with Hunter's single-point shroud attachments on the smaller (and not so small) models.
Two, the boom must be phenomenally strong and stiff, perhaps like those Selden extrusions with multiple longitudinal webs inside, to keep the tail end of the main from falling off. If you want to bend the boom for sail shape, you want to bend the clew and leech to windward, not let it fall off to leeward. What else stops it from doing that with mid-boom sheeting? Of course many of these modern boats have loose-footed roller-furling mains, which really only makes the point I am making more important. With a loose-footed main the only sensible set-up would be to have boom-end sheeting (where the clew is sheeted to the boom) and no vang at all-- what would be the point of one if the sail itself isn't attached there? So if there is mid-boom sheeting on a loose-footed main, imagine how strong the boom has to be to combat the mechanical tendency to just pull the middle of the boom down (and let the clew and leech sag off). And hence we have hydraulic and electric mainsheet systems on cruising boats now.
I'm not saying such boats are engineered badly, given what they are. I'm saying they are necessarily engineered the way they are because of one or two technically poor decisions (on the part of marketing, no doubt) that require the level of sophistication they have. At a certain point we've all got to agree that sometimes the simplest thing is the dearest, strongest and most inherently reliable; and that's all I meant to say about bridge-deck-mounted travelers being as close to the end of the boom as possible.
Al, the technological progress from ships of the 1700s to yachts of the 1970s is like the progress from food storage systems in the 1700s to those of the 1970s. I don't know anyone who wants to go back to that (speaking as an 18th-C scholar here!); and I don't know any of us who confuse our intelligently-designed late-20th-C boats for sailing ships built by eye by men with a 3rd-grade education. So I won't say any more about that.
Jim, however well your mid-boom sheeting works, the loads I have described are still in play. Simplistically stated (not in pure theory) there are three points to pull down on a boom-- the downhaul, the sheet and the vang. (In theory there are infinite points. You could have a vang every 2 inches if you wanted.) All help determine sail shape, performance and handling characteristics. I too have Wallace Ross's book; and his point applies to the vang when boom-end sheeting is used as well. I have seen race boats from the 1970s (when Ross's book was written) rigged with a permanent secondary mainsheet track for the vang to keep it vertical as it rolled along the deck or cabin top between tacks. This is how crucial a proper vang is in a normal (boom-end) sheeting application. The vang is intended to enhance sail shape, not to hold up the boom (for convenience) as with so many modern 'performance cruisers'.
And you do admit that convenience is part of your preference; and that's fine. But let's not cloud user-convenience issues by misinterpreting theory, which is what I came to talk about.
I have seen new Beneteaus with the sheet line less than 50% back (about where Al said he would move his to) and then they have a rigid vang forward of that. The vang in such a case would be entirely unnecessary. The two bails are less than 2 feet apart. This is what the average new-boat buyer will fall for; and it's mainly for marketing, not engineering, purposes. Please-- let's not deny who really 'designs' yachts these days.
I have to conclude two things from such a setup, especially when owners sing its praises:
One, the traveler system must be like a bridge girder in strength, attachment points, tackle and purchase and so on. I mean it's necessarily overbuilt, when if it were moved aft it could be less massive, less heavy and less strong. Almost always such systems are mounted at two heavily-reinforced points rather high up on the superstructure rather than taking advantage of the consistency of many smaller fasteners upon the deck, all in tensile and much less in shear than those of the traveler bridge have to be. Anyone in aerospace tech knows that many smaller, lighter fasteners are better than few large indispensible ones. This is also the fault with Hunter's single-point shroud attachments on the smaller (and not so small) models.
Two, the boom must be phenomenally strong and stiff, perhaps like those Selden extrusions with multiple longitudinal webs inside, to keep the tail end of the main from falling off. If you want to bend the boom for sail shape, you want to bend the clew and leech to windward, not let it fall off to leeward. What else stops it from doing that with mid-boom sheeting? Of course many of these modern boats have loose-footed roller-furling mains, which really only makes the point I am making more important. With a loose-footed main the only sensible set-up would be to have boom-end sheeting (where the clew is sheeted to the boom) and no vang at all-- what would be the point of one if the sail itself isn't attached there? So if there is mid-boom sheeting on a loose-footed main, imagine how strong the boom has to be to combat the mechanical tendency to just pull the middle of the boom down (and let the clew and leech sag off). And hence we have hydraulic and electric mainsheet systems on cruising boats now.
I'm not saying such boats are engineered badly, given what they are. I'm saying they are necessarily engineered the way they are because of one or two technically poor decisions (on the part of marketing, no doubt) that require the level of sophistication they have. At a certain point we've all got to agree that sometimes the simplest thing is the dearest, strongest and most inherently reliable; and that's all I meant to say about bridge-deck-mounted travelers being as close to the end of the boom as possible.
