Main Sail Rigging: Center Boom Sheeting or Traveler System

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Main Sail Rigging: Center Boom Sheeting or Traveler System

Postby nickc » Fri Jan 06, 2023 5:12 pm

I am continuing on my ‘78 DSII project. My boat is missing the main sheet block that attaches to the centerboard so using the rigging I currently have in order to save money isn’t an option as I am going to have to buy new rigging either way. What are the advantages and disadvantages of the center boom set up combated to the traveler set up? For some background: This is my first ever sailboat, I will likely be sailing it single hand, or with one other person, almost exclusively. I have no interest in racing. I would like to use it on local lakes for day trips and possibly some camping, gunkholing, style over night trips. As I am a total newbie to sailing I have no idea which route to go in order to best meet my goals. Any advice and opinions are greatly appreciated.
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Re: Main Sail Rigging: Center Boom Sheeting or Traveler Syst

Postby reedd » Sun Jan 22, 2023 9:01 am

I have the exact same question, but no answer. I’m not new to sailing but the physics elude me — beyond the basic Bernoulli principle and fast v slower air flow over sails providing lift or forward thrust. But I did find this article
https://www.practical-sailor.com/blog/end-boom-vs-mid-boom-sheeting

It might be of help. If anyone else has thoughts, please chime in!
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Re: Main Sail Rigging: Center Boom Sheeting or Traveler Syst

Postby GreenLake » Sun Jan 22, 2023 8:18 pm

First, I love "Practical Sailor". It's a great publication, even if many topics only apply to larger boats. For main sail rigging, the effect of the different options on the cockpit is somewhat different. Whether you use center boom or end-boom sheeting, the main sheet swivel is always in the same location. Some people use a traveler in the middle of the cockpit with center boom sheeting. This configuration will definitely make the cockpit a more crowded space, contrary to big boats with center boom sheeting that have a traveler on the coach roof, in other words, forward of the cockpit itself.

About the physics: of primary importance is the direction the main sheet pulls, measured as the angle from the vertical. The smaller the angle, the more the pull is downward. For a vang, the pull is down (and forward, but let's ignore that aspect for now). A vang only affects leech tension, not the (horizontal) angle the boom has. That is controlled by the sheet. However, sheets aren't horizontal, so they also affect the leech tension (and with it, the twist of the sail). Different rigging options will have different effective angles and therefore a different distribution between downward and inward pull.

A center boom arrangement is easy to analyze because everything happens along a single line between boom fitting and mainsheet swivel. It's easy to see the angle of pull, which gets shallower as the main sheet is let out. As you ease the sheet, not only does the boom swing to leeward, the change in angle means that less of the pull contributes to leech tension. That's in addition to the pull being reduced overall as you ease the sheet. Therefore, you are adding twist as you ease your sheet.

If you also have a vang, you can use it to maintain a lower twist. That's beneficial because it allows you to keep your main flat as you ease it, so the sail doesn't power up as it might with the leech being more slack.

How is end-boom sheeting different? There are several configurations, but let's pick one that is easy to take apart: the fixed triangle. A traveler rope forms a triangle with the apex connected to the sheet and the two other corners at the corners of the transom. (Sometimes the traveler is run through blocks at these corners, but its position is fixed by some other means, so that the distance between the apex and one of the corners is always a fixed length).

In this setup, the angle of sheet pull will be initially towards the apex, and both sides of the triangle are under tension. The apex sits higher than the main sheet swivel, so as you let out the boom, the angle of sheet in the rear becomes more horizontal more quickly than for the part that continues forward and then goes to the main sheet swivel. This affects the relative influence of sheet tension on leech tension vs. sheeting angle. You find that you affect sheeting angle more than leech tension (the pull is more horizontal).

As you let the boom out further, the imaginary line from end of boom to transom corner will dip below the highest point on the fixed triangle: the windward side will go slack and the apex will drop to be in line. From that moment on, the traveler acts as if you had sheeted directly to the transom corner. Your angle is still more horizontal as you are not pulling towards the center of the boat, but to its windward side.

The effect of the traveler is that you can have more twist at the same sheeting angle. If you combine it with a vang, the range over which you can change the ratio of leech tension vs sheeting angle now goes from more twist, with vang off to less twist, with vang on. If you used center boom sheeting you would be limited in how much twist you can achieve with the sail sheeted in.

A typical setup for end-boom sheeting doubles up the part at the end of the boom; because it's also twice as far out from the gooseneck, that part contributes four times as much as the remaining part that is led to the center and from there to the mainsheet swivel. For all practical purposes, you can ignore the contribution of that part, even if it's pull is always at a slightly different angles from that at the end of the boom.

Finally, the discussion assumed that the boom is perfectly rigid. No boom ever is. The article mentioned that pulling at the center of the boom can break it, if it isn't strong enough, and it can certainly bend it a bit. Bending the boom, like bending the mast, will pull at the edge of the sail, with a tendency to flatten it. However, mainsails are either loose footed, that is only connected at tack and clew, or they have a foot shelf sown in, a reserve of fabric, which will therefore absorb any effect due to bending the boom before it can affect the shape of the sail. Well, technically, bending the boom makes it shorter, and thus could add a bit of belly in the sail, but I'm convinced that effect is on a small enough scale to be noticed.

In terms of rigging a DS, you'll get a lot out of adding a powerful vang: in addition to the effects described, it also pushes the boom forward, helping to put a bend into the main. This bend, in turn, helps flatten the sail by pulling on the luff along the length of the main up to the spreaders. (Look for a discussion on pre-bend in this forum). It thus adds twofold to keeping a flat main, and that makes it a powerful instrument in sailing at the upper end of the wind range or in gusts, where without it, you'd be forced to reef earlier or feel less in control. (Both valuable even for cruisers).

End-boom sheeting extends the range across which you can control the relative contribution to twist and sheeting angle; at the cost of a small chance that the sheet tangles at the end of the boat (motors, cleats). Something that is generally kept under control by remembering to sheet in at the start of a gybe.

Mounting a traveler car on a track in the middle of the boat allows you likewise to change the angle of pull (by position of the car), but it is really inconvenient in the middle of the cockpit, and using a vang (with the technique called "vang sheeting") makes it somewhat redundant.
~ green ~ lake ~ ~
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Re: Main Sail Rigging: Center Boom Sheeting or Traveler Syst

Postby nickc » Sun Jan 22, 2023 10:39 pm

I appreciate the reply Greenlake, but you used so much terminology you lost me. I have no experience sailing. The mid book setup looks simpler so I think I will just go with that for now.
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Re: Main Sail Rigging: Center Boom Sheeting or Traveler Syst

Postby GreenLake » Mon Jan 23, 2023 1:17 am

Nick,

sorry if some of that went over your head. It's not intentional, but I like reasoning about the physics of sailing. When you are more experienced, you may at some point come back and re-read it with a different level of understanding. (When I started out, I did that with a lot of written resources. They all yielded to repeated efforts where a head-on attack just left my head hurt.)

In the meantime, since your boat doesn't have anything you can simply replicate, center boom sheeting is not a bad option. Do consider getting a vang though, soon after you've started sailing in earnest. (Following the idea of not adding too much rigging 'on spec', but only after you know what it will do for you).

By the way, switching between the two styles of rigging the mainsheet is not that big a deal, so don't fret getting this "perfect".
~ green ~ lake ~ ~
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Re: Main Sail Rigging: Center Boom Sheeting or Traveler Syst

Postby nickc » Mon Jan 23, 2023 2:23 am

I know it wasn’t intentional! I very much appreciate any and all replies because I can always come back and reread them! But yes a lot of the sailing terms and jargon go right over my head haha. I do fret about getting things perfect so I appreciate that, it puts me at ease. I have seen the bangs on D&R. I haven’t gotten to the point where I quite understand what it does. I know it puts downward force on the boom, but I haven’t gotten to the point why I understand how that is helpful yet haha. They are a little pricey for my very strained college budget, so the plan is to look into that next winter after I get some sailing in. I’m trying to get her in the water this spring/summer while spending as little as I can to get the job done right. College robs me blind haha! Your expertise is always appreciated!
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Re: Main Sail Rigging: Center Boom Sheeting or Traveler Syst

Postby tomodda » Mon Jan 23, 2023 5:29 pm

Nick:

Good to see you educating yourself about sailing and going step-by-step. It's the best way to learn! A lot of reading and re-reading and trying things out on the water, it's a life-long journey.

I want to throw out a visualization, to see if it helps you understand sails....

Think of a modern jet airliner's wing - it's long and pretty much rigid and the wind going over the wing (due to jet speeds!) creates lift, and that's how jetplanes fly. As you fly along, you need to modify the lift, as you speed up or slow down and/or change your angle relative to the horizon (up and down, or turn). You do all this with various flaps and fences which you deploy or retract - ailerons, lift flaps, speed brakes, etc. But the wing itself doesn't change shape or it's angle in relation to the body, it's rigid.

Now think of an eagle soaring in the breeze, a living glider. He also gets his lift from air going over his wing, in his case the wind comes from his speed falling forward. He modifies his lift by changing both the angle and the very shape of his wing. He twists his entire wing like a human articulating his arm, and moves his feathers around like fingers on a hand. Similarly, think of a goose or a duck coming in to land on a lake, opening up their wings, tilting them around, and they spread out each feather, to almost scoop they air as the touch down on the water. They changed both the angle and the shape of their wing for their landing, an angle and shape that are completely different from when they are gliding along.

Our sailboats are much like the birds in the air, we change the angle and shape of our sails like they change the angle and shape of their wings. However, we don't have muscle and bone inside of our wings, so we can't do what they do. We have a large piece of cloth that we hold open with sticks (mast and boom). We change the angles by moving the boom around, but we change the shape by putting varying tensions on the edges of the sailcloth. For the most part, we vary the tension on the sail's edges by pulling on the corners, just like pulling on the corners of a bedsheet. It may sound complicated, but just remember that the our sails have only 3 edges and 3 corners. The more you pull on a corner, the flatter the edge of the sail becomes. And on your mainsail, you can simply pull down on the entire boom, so now you're pulling the bottom edge and two corners, with all sorts of fun results. You'll quickly get the hang of it, just remember that it's all about changing the shape of the sail.

Hope this helped,

Tom
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Re: Main Sail Rigging: Center Boom Sheeting or Traveler Syst

Postby tomodda » Mon Jan 23, 2023 5:29 pm

Nick:

Good to see you educating yourself about sailing and going step-by-step. It's the best way to learn! A lot of reading and re-reading and trying things out on the water, it's a life-long journey.

I want to throw out a visualization, to see if it helps you understand sails....

Think of a modern jet airliner's wing - it's long and pretty much rigid and the wind going over the wing (due to jet speeds!) creates lift, and that's how jetplanes fly. As you fly along, you need to modify the lift, as you speed up or slow down and/or change your angle relative to the horizon (up and down, or turn). You do all this with various flaps and fences which you deploy or retract - ailerons, lift flaps, speed brakes, etc. But the wing itself doesn't change shape or it's angle in relation to the body, it's rigid.

Now think of an eagle soaring in the breeze, a living glider. He also gets his lift from air going over his wing, in his case the wind comes from his speed falling forward. He modifies his lift by changing both the angle and the very shape of his wing. He twists his entire wing like a human articulating his arm, and moves his feathers around like fingers on a hand. Similarly, think of a goose or a duck coming in to land on a lake, opening up their wings, tilting them around, and they spread out each feather, to almost scoop they air as the touch down on the water. They changed both the angle and the shape of their wing for their landing, an angle and shape that are completely different from when they are gliding along.

Our sailboats are much like the birds in the air, we change the angle and shape of our sails like they change the angle and shape of their wings. However, we don't have muscle and bone inside of our wings, so we can't do what they do. We have a large piece of cloth that we hold open with sticks (mast and boom). We change the angles by moving the boom around, but we change the shape by putting varying tensions on the edges of the sailcloth. For the most part, we vary the tension on the sail's edges by pulling on the corners, just like pulling on the corners of a bedsheet. It may sound complicated, but just remember that the our sails have only 3 edges and 3 corners. The more you pull on a corner, the flatter the edge of the sail becomes. And on your mainsail, you can simply pull down on the entire boom, so now you're pulling the bottom edge and two corners, with all sorts of fun results. You'll quickly get the hang of it, just remember that it's all about changing the shape of the sail.

Hope this helped,

Tom
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Re: Main Sail Rigging: Center Boom Sheeting or Traveler Syst

Postby nickc » Mon Jan 23, 2023 5:49 pm

Very helpful! I am a very visual learner. I have yet to find a book about sailing with good visual aids, if anyone has any suggestions please let me know. I appreciate everyone’s assistance! I hope to have my fiberglass, resin, and fairing compound in next week. Hopefully within in the next month I can complete the repairs on the stress cracks on the hull. Soon after that I will take the buffer to the hill to remove the oxidation while I already have the boat upside down. Next will come the transom repair and repairing a crack in the cuddy roof. After that I need to give the running rigging a good go through and hopefully I will be lake bound!
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Re: Main Sail Rigging: Center Boom Sheeting or Traveler Syst

Postby GreenLake » Mon Jan 23, 2023 10:36 pm

Thanks for being so understanding and giving yourself permission to grow into a better sailor over time.

FYI on vangs. While D&R is absolutely the go to source for DS-specific parts, sometimes you need to look elsewhere. The factory-standard 3:1 vang is near useless, so when the time comes look up how you can put together your own anywhere from 12:1 (minimum) to 20:1. (You'll find relevant discussions here on the forum).
~ green ~ lake ~ ~
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Re: Main Sail Rigging: Center Boom Sheeting or Traveler Syst

Postby nickc » Mon Jan 23, 2023 10:50 pm

I appreciate it! I’ll keep that in mind with the vang.

My goals for the boat presently are to get it operation on as lean of a budget as possible. For my goals it’s not imperative that I get it all right from the start. I just want to learn and enjoy it. I enjoy tinkering with things so if I decide later that the way I rigged it initially isn’t what I want anymore I will enjoy researching and working on it down the road too. I just want to make sure I get all of the hill work done the right way so it doesn’t cause issues later, but that’s a post for another thread and another time.
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Re: Main Sail Rigging: Center Boom Sheeting or Traveler Syst

Postby GreenLake » Tue Jan 24, 2023 12:49 am

Right. That sounds pretty reasonable. I wish you lots of luck and may you fix all your problems "just in time".

By which I mean: "when your increased sailing skills and inclination to take risks or try something harder are pushing the limit on the state of your refit at that moment."
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Re: Main Sail Rigging: Center Boom Sheeting or Traveler Syst

Postby Hesedguy » Wed Feb 01, 2023 6:54 pm

Nick, The book I (and my wife) started with is "Sailing: The Basics: The Book That Has Launched Thousands" pretty cheap and it does cover all the basics well. Lot's of diagrams for visual learners, but not childish either.
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