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  #61  
Old 09-04-2013
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Re: How Far Do You Heel...?

Overhangs are useful for reserve buoyancy and good looks over rated as speed additives.
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  #62  
Old 09-04-2013
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Re: How Far Do You Heel...?

I use bow overhang for two reasons:
To get the headstay where I want it to balance the rig.
To get the anchor roller away from the stem so I am not banging the stem when I raise the anchor.

In the stern I like some overhang to insure a clean wake at low speeds.

When I did the MS CAPAZ the client wanted 9 knots under power. It was a 49' boat. I was a bit nervous about the 9 knots so I called my old mentor Bill Garden. He told me to eliminate all overhangs. I did and I got my 9 knots easily.

I would not call it an elegant look but it is handsome to my eye and very functional with good visibility from the inside pilot station. And, as a bonus the boat sails very well. The client didn't like it when I referred to the boat in my review as a "sailing tugboat".
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Last edited by bobperry; 09-04-2013 at 10:28 AM.
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  #63  
Old 09-04-2013
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Re: How Far Do You Heel...?

Quote:
Originally Posted by bobperry View Post
Machine:
That's the traditional theory anyway. But the next time you are heeled over look over the bow and the stern and see just how much of your boat is immersed. If it's not in the water it's not doing anything to extend the sailing length. This effect or imagined effect is over rated. I don't care that it has been standard theory for years. Overhangs are the result of old rating rules and are marginally effective at best.
I am well aware.. otherwise race boats would not use Plumb Bows and reverse transoms
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  #64  
Old 09-04-2013
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Re: How Far Do You Heel...?

When your boat is already completely inefficient in every way, it allows you a certain freedom to heel as much or as little as you'd like as your mood and the wind dictate.

T37Chef, bobperry and harmonic like this.
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  #65  
Old 09-04-2013
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Re: How Far Do You Heel...?

How far do we heel???

Well, we heel until we get there.

Regards,
Brad
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  #66  
Old 09-05-2013
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Re: How Far Do You Heel...?

Quote:
Originally Posted by ScottUK View Post
Would this not induce more weather helm Jeff?
Scott, I apologize in advance that there is a huge amount of verbiage here, and also that I wrote this for another purpose, but it does explain my thinking.

If I were to give an uncharacteristically (for me) terse explanation of what happens when you increase backstay tension on a modern fractional rig, I would say that increasing backstay tension decreases weather helm and heeling, by flattening the sails, reducing the angle of attack of the upper sail, and as counter intuitive as this sounds, moving the center of effort forward. If you want the short answer, that’s it and so stop reading here.
V
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V
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Still here? Good, because, that summary of the ‘whys’ does not explain how any of that happens. But to explain how tightening the backstay on a modern fractional rig decreases weather helm and heeling, flattens the sails, reduces the angle of attack of the upper sail, and moves the center of effort forward takes a lot of verbiage, because frankly there are a lot of pieces and parts in motion, and it’s the interaction of those parts that tells the whole story. By necessity, explaining how a modern fractional rig functions has enough “Gizmo A pulls on Gadget B which bends Object C’s” to make Rube Goldberg proud. But a modern fractional rig is anything but a Rube Goldberg device. It is a highly evolved and sophisticated system which works with surgical precision and a Rolex like synchronization of nearly all of its moving parts working in unison to depower the boat with the singular application of more backstay tension.

So starting at the backstay, no matter what mechanism is used to increase backstay tension, there is a shorting of the dimension between the transom and the masthead. This pulls the masthead aft and downward. In fact, depending on the rig proportions, the force downward will typically be 3-4 times the force pulling straight aft.

And those combined forces move the masthead towards the stern and towards the deck.
And that shortens the dimension from the masthead to the end of the boom.
And that loosens the tension on leech of the mainsail.
And that allows the aft end of sail to twist to leeward.
And that reduces the angle of attack of the mainsail.
And that reduces the side forces on the aft edge of the sail,
And that alone reduces heeling and weather helm.

But that’s only the beginning.
What keeps the mast from being pulled over the stern or crumpling to the deck are the forestay and shrouds. The forestay acts as a fulcrum bending the mast in much the same way that your hand on the grip of a bow (i.e. bow and arrow) allows the tension of a drawn bowstring to bend the bow further.

And so in that manner the backstay pulling aft increases the bend the mast, while at the same time pulling the head of the forestay aft as well, increasing the tension on the forestay.
And the bend in the mast and the increased forestay tension forces the attachment point of the forestay slightly downward and back toward the stern.
And that moves the head of the jib closer to clew of the jib,
And that loosens the tension on leech of the jib.
And that allows the aft edge of jib leech to twist to leeward.
And that reduces the angle of attack of the jib.
And that reduces the side forces on the aft edge of the sail,
And that also helps reduce heeling and weather helm.

But that is not all;
As the mast bends, and as we said above, the upper part of the mast above the forestay bends towards the transom. But below the forestay that increased bend actually moves the mast and attached sail towards the bow.
And since there is more mast bending towards the bow than towards the stern, the geometric center of the mainsail is actually moving forward in the boat.
And that increases the proportional center of the forces toward the forward edge of the sail,
And that also helps reduce weather helm.

But that still is not all;
Because, the increased tension on the forestay straightens the forestay and the luff of the jib.
And in doing so the geometric center of the jib is also moving forward in the boat.
And that increases the proportional center of the forces on the forward edge of the sail,
And that also helps reduce weather helm.

But that is not all either;
Because as the mast bends, the masthead moves aft and the upper leech of the sail also moves slightly aft, but at the same time the curvature at the mast moves the leading edge of the mainsail forward towards the bow.
And as the distance between the leech and the luff gets physically longer, the curvature of the sail gets stretched flatter.
And that results in a depowering (flattening) of the sail so that the mainsail now generates less side force relative to its drive.
And that depowering also helps reduce heeling and weather helm.

And we are still not done;
As mentioned above, the increased tension on the head of forestay straightens the curvature of the forestay and so the middle of the forestay moves towards the bow increasing the distance between the leech and luff of the jib as well. In much the same way as the mainsail description above, as the distance between the leech and the luff gets physically longer, the curvature of the jib gets stretched flatter.

And that results in a depowering (flattening) of the jib so that the jib now generates less side force relative to its drive.
And that depowering also helps reduce heeling and weather helm.

And all that combined reduction in heeling, also reduces weather helm.

And that all happens all at once when you tighten the backstay on a fractional rig.

When new sailors hear or read this explanation, they sometimes think. “That sounds way too complex for me to be able to use effectively.” But here is the really great news about this, virtually all fractional rigs come with an instrument that tells them rather precisely how much backstay to apply. Its called ‘the helm’.

All you need to do to tell how much backstay to apply is to watch and/or feel the helm. As you apply backstay you will feel the force lessen on the helm, and you will be able to visually watch the helm move back towards being neutral, and when you get to the spot where the helm is where it feels or looks about right, you have enough backstay tension. If the boat starts feeling sluggish, you probably have too much tension. Using the backstay adjustment on a modern fractional rig is just that simple.

Jeff





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Last edited by Jeff_H; 09-06-2013 at 08:51 AM.
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  #67  
Old 09-06-2013
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Re: How Far Do You Heel...?

Nice. Can you write it again now for a masthead rig?
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  #68  
Old 09-06-2013
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Re: How Far Do You Heel...?

Cheers Jeff.

So from what I gather the mainsail is flattened at the leading edge in the area of the mast bend and then the leech would not have as much tension thus adding more twist and spilling more wind. It has been what I thought but have heard conflicting information.

I understand moving the top of the forestay aft and down would also decrease the tension on the leech of the headsail and so induce twist. Not sure about flattening the headsail though. If the foreatay tension is tight and is moved aft through increased backstay tension wouldn't this just decrease the angle of the straight line of the forestay and not reall effect the luff. But I guess it would all depend on the initial forestay tension.
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Old 09-06-2013
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Re: How Far Do You Heel...?

Quote:
Originally Posted by chucklesR View Post
Since now I'm sailing a monohull I find that past 20 degrees makes my non-gimballed cup holders less efficient if holding a full rum and coke.

Therefore, from a performance and efficiency point of view I tend to keep my heel below 20 degrees by trimming the sails with the iron genny.
That is how I sail...drinks spillin' is not an efficient heel angle
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  #70  
Old 09-06-2013
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Re: How Far Do You Heel...?

Quote:
Originally Posted by PaulinVictoria View Post
Nice. Can you write it again now for a masthead rig?
(You really asked for this? Same apologies as above.)

While tensioning the backstay on a fractional rig puts a lot of parts in synchronized motion, inherently, far less happens automatically in a masthead rig. But it’s also harder to talk in absolutes with masthead rigs because much of what happens is dependent on the specifics of the rig components and its proportions.

As a very broad generality, masthead rigs come in two flavors; inflexible masts, and bendy masts, and at the extremes of both, masthead rigs behave very differently. I would guess that inflexible masts make up the vast majority of masthead rigs which are out there. They were the original version of the masthead rig, and they have come back in vogue due to in-mast furling, which requires a stiff straight spar to function properly.

The short answer to your question would be.... on a boat with an inflexible mast when the backstay is tightened, the forestay attachment point moves aft and easing the leech and tensioning the stay thereby reducing sag in the stay and so depowers the jib. On a boat with a flexible spar, when used in concert with a babystay, there is also some bending of the mast and depowering of the mainsail. But compared to a fractional rig, the reduction in weather helm and heeling is less apparent on a masthead rig.

Again, to explain why this is so will require a very long explanation. If you are interested in that long explanation and having been forewarned, here is the detailed answer.

The masthead rig began life simply as a way of beating a racing rule. Prior to that rule, yachts and working water craft were predominantly fractionally rigged. When the early masthead rig boats began to show up, they were designed with inflexible spars.

Strictly from a structural engineering standpoint, there are good reasons why a masthead rig wants to have an inflexible spar, while a fractional rig with the same sail area potentially is better suited for a flexible spar. Starting with the basics, a stayed sailboat rig inherently behaves like a truss, meaning that the majority of the loads experienced by its components are axial (either compression or tension).

But a sailboat rig is not a pure truss, because the side force of the mainsail puts the mast in bending and in torsion. In the case of a fractional rig, the extension of the mast beyond the forestay further dramatically increases the bending forces on the mast section. Pure trusses do not have bending forces on their components.

I would like to stop for a moment and do a quick discussion on structural terminology to make sure we are all on the same page. (I apologize for this divergence if you already understand structural terminology.) I will be using the term ‘compression’, and ‘buckling’ with the assumption that this term is understood by everyone in the same manner as it is used in structural design. But for those who are not familiar with structural design, the easiest way to visualize compression is to think of the loads pushing on each end of a structural component straight towards the other end. In buildings the most common compressive members are columns and bearing walls.

On boats the mast and spreaders are predominantly acting in compression. The boom is also loaded in compression from the outhaul and vang trying to push the boom through the mast, but a typical boom also experiences a lot of bending force.

In a strict sense, a failure strictly due to compression is crushing of the material such that the material separates. You can perhaps visualize this type of failure if you think of a drinking glass sitting upright on a counter and then weight is slowly added on the top of glass. At some point the weight will exceed the capacity of the glass and it will shatter (usually explosively) sending shards in different directions.

But structures under compression can also fail due to buckling. If you visualize pushing down on the end of a thin dowel. At first the dowel might hold the vertical load, but at some point the dowel will bow out to one side and the amount of load it can withstand will decrease. That bowing of the dowel is called buckling.

Aluminum masts almost never fail due to simple compressive failure. Most aluminum mast failures are some mix of a buckling and a bending failure, with the crushing of the walls of the spar extrusion being a major contributing factor in the event of a complete collapse. Composite spar failures can be pure compressive with a greater frequency than aluminum spar failures, but like aluminum are more likely to be a buckling or bending failure.

Which brings us back to rigs; speaking in broad general terms, while individual components may experience higher loads than they do on a beat, collectively, almost any rig experiences its largest loads when going upwind. By and large, on a stayed rig with jibs, the single largest force is the compressive forces on the mast when going upwind. And while the total amount of the compressive force comes from resisting a collection of stay and shroud loadings, The single largest compressive loading comes from the vertical force component that is generated by the forestay and vertical component generated by the backstay in resisting the horizontal pull of the forestay.

The amount of this compressive loading is proportionate to the size of the jib (if the wind force is in lbs/sq. ft., a greater area generates more side force), the shape of the headsail (a fuller sail generates more force that an flatter cut sail), the stability of the boat (if it takes more force to heel the boat, the side force of wind is absorbed by the sail rather than by heeling over), the drag of the boat (if it takes more force to move the boat, the side force of wind is absorbed by the sail rather than by accelerating), forestay sag (it requires more forestay tension to reduce sag, and with greater tension there is greater compressive loads resisted by the mast), and to a lesser extent, and the length and stretchiness of the forestay (the longer or more stretchy the forestay the greater the stretch, and the greater the stretch the greater the sag, so for an equal acceptable amount of sag, these would require a greater tension).

As a broad generality, for any given sail area, a masthead rig will generally have larger jibs and longer forestays than a fractional rig. And because of that, a masthead rig will generally have higher forestay tension and the vertical component of that higher forestay tension will induce significantly higher compressive loads into the mast.

This is further compounded by the fact that greater backstay tension is required to resist the greater forward thrust of the greater forestay tension. And the vertical component of that greater backstay tension also results in significantly greater compressive forces on the mast.

But beyond that, the portion of the fractional rig mast that extends above the forestay, acts as a lever, reducing the amount of horizontal force that the backstay needs to impart in order to achieve the same horizontal force on the forestay. And that reduction in horizontal force, also results in a significant further reduction in the compressive forces on the mast.

In that regard given the high compressive loads on a masthead rig, an inflexible spar makes sense since it is less likely to buckle. But unfortunately without being able to bend the mast, tightening the backstay can only minimally impact heeling and weather helm.

Going through this a step at a time, when the backstay is tightened on a mast head rig, the top of the mast moves aft, and that moves geometric center of the mainsail aft as well. That increases weather helm. This is partially offset by moving the head of the mast slightly aft which slightly shortens the distance between the aft end of the boom and the head of the sail, which slightly opens the leech, which slightly depowers the mainsail.

At the same time, as the masthead moves aft, its attachment point moves aft, which slightly shortens the distance between the jibsheet lead and the head of the sail, which slightly opens the leech, which slightly depowers the jib. It also tensions the forestay, which takes some of the sag out of the stay. As the stay straightens it moves forward, and the length between the leech and the forestay increases, flattening and depowering the sail further. That reduces weather helm and heeling some.

The good news about the fact that tightening the backstay on a masthead rig with an inflexible spar mostly affects the jib, is that the jib is typically substantially larger than mainsail, so if you are going to impact only one sail, its good that it’s the bigger of the two. The bad news is that most of the impact is closer to the lateral center of resistance (than on a fractional rig), and so has less leverage to change weather helm.

As the racing rules began to evolve, masthead rig mainsails became proportionately larger. And as mainsails became larger, designers began to attempt to get the kind of sail shape control that comes naturally on a fractional rig. And from that came masthead rigs with bendy spars. Because masthead rigs lack the natural bending fulcrum that the forestay provides on a fractional rig, the earliest bendy masthead rigs were bent simply by increasing the backstay tension until a controlled buckling occurred in the mast. Quickly, checkstays were added to control the amount of the buckling.

For those who are not familiar with rigging terms, checkstays are different than running backstays. Running backstays are a backstay, which attaches to the mast at the hounds (where a jibstay is attached to the mast) and are mostly found opposing jibstays on cutters and forestays fractional rigged boats. They are called running backstays because their attachment point below the head of the mast, means that the leeward one needs to be eased, and the windward one needs to be tightened on each tack or jibe. This easing and tightening every tack and jibe is done in a variety of manners.

Checkstays attach to the mast between the forestay or jibstay and the deck. While they may look like a running backstay their role is strictly to control the amount of bend in the mast, and not to oppose the forward force of a jibstay. But like a running backstay because of the rig geometry and their position below the masthead, they too need the leeward one eased, and the windward one needs tightened on each tack or jibe.

And while checkstays allowed bending via a controlled buckling of a flexible spar masthead rig in the forward direction, it did not prevent the spar from ‘inverting’ due to spin pole reaching forces or pumping, and buckling aft. That quickly resulted in adding babystays. And as soon as baby stays showed up on the scene, crews and designers figured out how to tension them so that they acted as a fulcrum to induce bending in the mast with lower compressive forces in much the forestay does this on a fractional rig.

The shortcomings of babystays are that they make tacking and jibing more difficult, and they do not address the inherent inefficiencies of a masthead rig. But when used in concert with the backstay tensioner, they allow similar depowering characteristics to adjusting the backstay on a fractional rig, but of course with more complexity and multiple items to properly adjust in sync with each other.

While not exactly a part of this question, as a broad generality, for the reasons described above, for a given sail area, a masthead rig puts significantly greater strain on a hull and its rig. This of course can be offset by proper engineering, but that engineering typically results in needing a heavier mast, shrouds and stays, and additional hull structure, which tends to make masthead rig boats heavier than a fractionally rigged boat with similar safety margins.

Its not unusual to hear a novice say that some particular manufacturer's masthead rigger is much better rigged than some other manufacturer's fractional rigger since the frac has lighter shrouds, and spars and smaller winches, when in fact, the Frac may have larger safety margins and better sized hardware, and with a lighter and more easily adaptable rig, the Frac may also have more stability, or need less ballast to obtain a similar stability.

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Last edited by Jeff_H; 09-06-2013 at 06:40 PM.
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