Loosefoot main and vang

[ebb]

Tony's reefhook query brings to mind a raft of unsettled questions I had about the loosefooted main and rigid vang. It is obvious that A/C racers and cruisers both benefit from a loosefoot main. The vang is used to control the boom, holding it down and letting it rise, and useful for flattening the sail. Boom out on a broadreach the vang controls rolling, preventing a broach. It does this by hauling the boom down. Vang is used as a jibe preventer but can this be done with the Garhauer used on the Bay Ariels?

I do not understand how a loosefooted main and the rigid vang can work together? Especially with the original boom and fittings.

Does seem that the slug rigged main provides support for the boom in the way it apparently distributes forces evenly along the foot. If you haul the vang down on the boom with the sail attached along the foot you will get results in sail shape. But is this true of the loosefooted rig? Won't the boom bend? What influence is there on the central areas of the sail?

The triangle formed by the rigid vang must consetrate loads on the gooseneck and the boom that were never originally engineered. The main use for the rigid vang, as this inexperienced sailor sees it, is as an expensive topping lift/boom holder.

I'm looking at a loosefoot cruising version of the main for 338: no roach, no battens, very deep reef points, hand sewn rings in the corners. But I'm very concerned about what gear is used to haul the clew out, and control it, since that also is only way to control sail shape. Seems to me it would have to be some strong eight-part set up [on a track] on top of the boom or under the boom?

Is 338's original boom really going to be able to take the stress of a loosefoot main? Does the Garhauer vang bend the boom. What is the best upgrade for the gooseneck and the boomend rigging.

Triton Tim ended up with the modern rig AND it cost him a new boom.

There is that lovely photo of MAIKA'I in the Summer Sailing post of Sept '01 clearing showing her l.f. foot main driving her at 90 kph!!

[Tony G]

Ebb,

You have caught some of the concerns I've had all along. In the past it has been suggested that the gooose neck should be the weak link in the system. We designed/copied/dreamt-up a much stronger goose neck here and I can't wait to use it.

I've thought many times that a footed main without a shelf would indeed help distribute all that tension over the length of the boom. But then what happens when you reef the main and all of the load is carried on the reef clew and cringle? The sail ties in the middle of the main should be loose enough that they don't distort the main or carry any presure. So, in a sense, we're back to a loose footed, smaller main. A smaller main with probably just as much presure on it because the damned wind is blowing so hard we had to reef. I will grant you, the clew is farther forward in a reefed main so the upward leverage on the fulcrum, the vang bail, is reduced. How much? I don't know. Maybe enough, maybe not. After all these boats did come with a boom vang. Just not one so shiney.

Another factor in the buckling boom paranoia is all of the holes drilled into the sides of my boom. Surely they must have some sort of compounding effect on the remaining strength of the metal. How much? I don't know. Maybe enough, maybe not. I'm pretty confident though that if the boom snaps it will be the result of something stupid I did while sailing. I've resigned to the fact that I may have to buy or build a new boom one day. I'm okay with that just as long as nobody gets hurt when the original one goes.

As for outhaul equipment. I've thought about track and cars, slugs and slides any thing I see that moves like that I consider an option. But the sailmaker I'm working with said a strop. That's right, I said strop. At first I thought he said strap but his accent made it come out sounding 'oppy'. But I guess it actually is a strop! One with a heavy duty velcro-type attachment. It's strong enough for the America's Cup boats and it's strong enough for me. And it's low-tech which I really appreciate. I asked about UV resistance and wear and it's apparently not as big a problem as I worried about. Just replace the strap(ex that) strop. It will, however, need a pretty decent purchase to move the outhaul under load. Or else one could ease the sheet to tighten the out haul. I'm hoping to send the reefing lines on one side and the out haul blocks and lines down the other. That part we'll have to wait and see. (wait and see if somebody else figures it out before me!)

I think we'll still be using the same sheet end casting for the boom. However, the neck end of the casting will be modified. You know I'll post pictures of the goose neck when it comes back from the shop. As for now I'll just leave you with this one...

[ebb]

Hey Tony.
Hope that an opinionated and experienced sailor drops in here for a chat!

Always equated strop with something you hang on to - as in subway car strop. Envision strop with block off end of boom (rather than a bail or the pair of tangs on 338's boom held on by a loose bolt stuck in the end casting) leading to travelor?

The outhaul tackle on top or bottom of boom would have to, IMHO, be infinitely ajustable and easy to use while sailing. Would have to be mounted to a track or something - with ballbearing cars like the sheet travelor? Maybe the strop the tailor was talking about goes over or around the outhaul on top of the boom to take some of the strain off the outhaul? You know, like a super velcro muff?

This multipart outhaul (or whatever outhaul for the loose foot) must pull the boom into the mast considerably. Flattening the sail with the outhaul while sailing must measured in 100s of pounds. Shouldn't the mast at the boom-end have a sort of saddle-plate? Distributing the point force over a wider area on the mast?

I don't like the 'weakest link' being the gooseneck fitting either!

It is, however. the 'quietest' point for an accident to occur. Wouldn't I prefer a kindof universal joint at the gooseneck?

Gooseneck is a misnomer now, isn't it, as there is no downhaul anymore. Right? Howabout a ball-in-socket joint for the boom to mast fitting? The loads would be fair at almost any boom angle.

But I really hope someone will enlighten us about the forces on the A/C loosefoot boom. And what are the highest recomendations for the end fittings and mast connection? 338's boom is not a very impressive piece of aluminum.

[Tony G]

Ebb,

I'm not sure if I'm reading you right or not. The strop is a means of attaching the clew to the boom so it can't fly upwards. The outhaul can then be used to move the clew in or out to help flatten or bag the main belly. Of course this means the aft foot or so of the boom can't have a bunch of accessories on it. I don't envision the clew having to travel forward more than that.

Maybe that's the question. How far do the active sailors out there move their clew, fore and aft, to tweak their mainsails? And then who's busted a boom.

Even though the line would be lead back to the cockpit via the mast, wouldn't the pressure difference be between the tack and clew, independant of the mast? We're really 'stretching' the foot of the main between those two points. That said, I've put a fairly generous mating surface on the 'mast end' of the new goose neck. More so to keep it from pulling out rather than being pushed in and crushing anything.

[ebb]

G'day Tony,
Just you and me so far.
I am confused about the outhaul. The outhaul influences the shape of the sail. The outhaul is under more tension in heavy air and upwind. The ajustment to change the shape will be small (inches) - tweeking and untweeking. Maybe in a nonracing mode little will be required.

OK then, what is the mechanism used at the boomend? Seems to me all the forces are tugging at the end of the boom - loosefooted clew and the sheet. I'm inclined to think that the loads should be spread out here. How is this done and what is the best way.

I guess I'm not sure what the forces are at the gooseneck. Pulling at the sheet with a belly full of wind would put a strain on that fitting, no? In the unlikely event that the boom gets into an unnatural angle with the mast, I'm just asking if there is an optimum fitting that won't be as vulnerable as one 338 has.

When I look at the boom and imagine this as a strut in the loosfooted main setup, I can't see what influence the vang can have without bending the extruded boom. It is rather meager sectioned. If you curve the boom by hauling it down with the vang, areen't you increasing the chord in the sail? Buckling the boom is definitely something to consider here!!

I'm concerned about what is the strongest and most elegant way to upgrade what I have, if possible. I'm convinced loose foot IS the way to go.


[I get into esoterica I know, but as long as we're on the subject of the main: I'm going with a tilted up boom of the same original length so I can get some headroom in the cockpit aft of the dodger. Not going to change the goosneck position.

Also, regarding a straight leech on a cruising sail, I may be far off base.
Raising the outboard end of the sail will decrease the area. I have just read and been influenced by Steve Dashew's comparison of a triangular sail with a roached sail. He points out that "the effective aspect ratio of the roached sail will be much hgher..." and "the roached main has a much better tip shape and less tip loss which is a major contributor to induced drag." Roaching 338's will add area back. Ohoh, there's that pesky backstay!

I know we are not talking about sail shape especially from the cruiser's view.
It is interesting tho that cruisers now have huge roached sails because of high aspect ratio mains, sometimes requiring full battens up top and shorter ones controlling the leach. Dashew says the real driver on a cruise rigged boat is the mainsail, rather than the genoa or geneker. Have to talk with Hogin about this. I didn't want ANY pockets because, as I read, most repairs to the sail are in these places.]

[commanderpete]

Most people never adjust the outhaul. Trying to adjust the outhaul while underway from the end of the boom is awkward, to say the least.

I suppose with a loose footed main it becomes important.

Here's what Tim Lackey did:

http://www.triton381.com/sailing/equ...ghardware2.htm

I never really thought about breaking the boom itself. Weren't these extrusions used as masts on smaller Pearsons?

Anything can happen, of course.

[John]

I am a part time.....make that a sometime, racer so I look for correction on this from the experienced ones. My view of the the traveler and mainsheet are that main angle (to the wind) is controlled not with the sheet but with the traveler, when you are sailing to windward. Sail tension/flatness are set with the mainsheet. Except in light winds where you want some fullness in the main, or in really hard winds where you want to flatten the main beyond what you can do with a cunningham or the downhaul I have, you want almost no vang tension or lift. Only after the sheeting angle puts the boom outside of the traveler, do things change. At that point, sheeting angle is set with the main sheet, and sail set/tension is set with the vang.

I have a standard main, so the following is conjecture. The only real loss with a loose footed main is the ability to add tension under high wind conditions when sailing off the wind. This makes your outhaul and downhaul/controls all the more important. In light winds, you still can support the weight of the boom to keep fullness in the sail, and I believe that the use of traveler, sheet, and vang remain the same. Also if you try to flatten a loose footed main with the vang, as has been stated, it really puts a lot of force on the gooseneck and the boom itself. So that's my story

Happy Thanksgiving to all.

[Theis]

I'll add my two cents for whatever it they are worth. When I had my loose footed main built, I was told by the sailmaker - Quantum Sails in Texas - that the benefit of a loose footed sail is that it spills wind at the foot, and the foot keeps its wing shape at the foot. A loose footed sail therefore is faster. The non-loose footed sails were developed because of racing rules, I was told, which required that the foot be attached to the boom throughout its length. Those rules have now been changed. - That is why everyone today is going loose-footed (allegedly 95% according to the sailmaker).

In the non-loosefooted sails (which I used to have), the sails could not have a wing shape at the boom but had to be "tucked in" to conform with the straight line of the boom. In other words, the wing shape had to be terminated above the foot in favor of a straight line. That meant the shape of the sail was lost approaching the foot. Pulling the foot tight with a vang in such a case would wreck the sail shape further up the sail, in addition to bending the boom. The outhaul and downhaul/cunningham and the sheet/traveler are the only running rigging adjustments to the foot and luff.

The vang/preventer should not used for sail shape, other than in a down wind run to keep the boom/outhaul from lifting when the sheet/traveler can be of no help, and decreasing the effective sail area. And to help prevent a flying jibe.

[ebb]

MORE
M O R E
M O R E !

[Theis]

As for me, I only offered two cents worth as I mentioned. The next bit of wisdom, or lack thereof, goes up exponentially. I can afford a two cent investment, but I don't have $500 cash investment (the next increment for an additional pearl of wisdom) on the table at this moment.

Hope you had a good Thanksgiving dreaming of the blue waters, the warm days, and the fresh winds.

[John]

Ok...I don't know if this is worth $500 but here goes.


The shape issue has been solved with out being loose (if you will excuse the expression)...Here is an example on something just slightly larger than our beloved A/C's.

http://www.offshorespars.com/websitenews_aug04.pdf

The Park Ave Boom terminates the foil fairly well. There have also been sails built with a zipper foot, allowing the draft to be carried way down towards in the sail. There are also terminated foil sections on keels with these keel plates/wings. So that solution has also been examined.

If you have draft stripes or ribbons on your main, then you use either the sheet on the wind or the vang off the wind to adjust sail twist just to the point when the flow almost stalls. Generally this will align your top batten with the boom. I don't see how you have this control off the wind with a loose footed main. But I have no experience with a loose footed main.