does anybody know how to calculate the ce of a swing rig? Also, what amount of lead should there be from the CLR?
Thanks in advance
Kurt
CE is found the same was as a standard rig. Only difference is on a swing rig the sail split is 25/75 or 20/80 to make sure the CE is behind the mast.
As you can see the swing rig jib move backward.
This mean also that the full CE is mowing toward the stern
The amount of movement is of cousre depending on the size and form of the the sail plan.
By memory on a class M with about 7200cm² sail plan and 28% on the jib, the delta position of the mast step between the Classic and the Swing was is of about 5.5cm.
Thus the swing mast is moved toward the bow .
ClaudioD
Yes, the CE is behind the mast with a swing rig… otherwise the rig will not rotate properly… That is why the jib must be smaller than on a conventional rig…
On an RG65 I would think the rig should go about 1" forward (maybe 3cm?) of the position for a conventional rig with 40%/60% jib/main…
Bob
In my RG65 I use the swing rig (25/75), 1.5cm forward of the conventional rig and works very well.
You can se it in my avatar.
The mast does need to be forward of a conventional rig, but I found it wasn’t as much as I expected.
Claudios illustration is pretty good, a slight error, the jib does not sheet out as the main sheets out. The rig just turns so the ce will rotate about the mast in a circle.
okay, I think my jib may be too large. I used a sail plan that I found in the free rg65 website. I’ll measure each and see what I’ve got. The problem is that the boat will not point. It will just stall and move laterally. Any other problems I should check out? This is only my second swing rig, the other was on a footy, and I had a lot of trouble with that one too.
Thank you,
Kurt
If you remove the sheet the swing rig must “weathervane” and luff freely… If it tends to fill, even momentarily, with the sheet removed, the jib is too large… and the CE either too close to the mast or in front of it… The solution is a smaller jib and bigger main…
Bob
It does fill. I’ll try reducing the jib. Might take my “B” rig down to a “C” rig!
Hi Kurt,
The best jib to main ratio for your swing rig is 25/75 or 22/78. For someone new to swing rigs the 22/78 ratio helps the learning curve. The jib area in relation to the main can be increased as you get more familiar with sailing a swing rig.
One basic concept that most converts to swing rigs miss is that you are really sailing a soft wing sail, the slot between the jib and main somewhat comparable to the slot in a wing mast. Thats what Claudio missed in his diagram above.
I have written out detailed explanations of setting up and tuning swing rigs, mostly in the Footy threads and on the multihull thread. Search my posts for the swing rig related info and you will most likely find the answers you are looking for.
Niel,
I did not miss anyithink, the sketch above was only ment to answer to a question about the CE and the only purpose of the sketch was to show the jib CE swinging backward while all others sails CE move forward once changing direction from close hauled ! This is why the mast step shall move compared to a classic rig. That’s all !!
ClaudioD
Claudio & Kurt & all,
Claudio, your diagram considers only the CE of the jib. The swing rig acts more like a soft sail wing mast and the CE of the whole rig is what should be considered. Swing rigs have such small jibs so that the rig will weathercock rather than backwind when in irons or caught in wind shear. The majority of the rig’s sail area is aft of the mast (read pivot point of the rig) thus the CE of the sails considered together is aft of the mast as well. When comparing the upwind profiles of a conventional rig and a swing rig matching up their respective CEs will yield a mast position for the swing rig forward of that of the conventional rig. Just how farther forward is determined by the jib to main ratio of the swing rig. A smaller jib (easier to control for a beginner but more of a tendency to broach) will have a more forward mast location while a larger percentage of area in the jib will have a more rearward mast location (although more at risk for backwinding and stalling).
In real world conditions I have seen very few conventionally rigged r/c sailboats that have their sails work together on points of sail other than directly upwind. Part of it has to do with the axis of rotation of the jib (on a diagonal) and that of the mast/gooseneck (more or less vertical). Coordinating how the two sails pay out seems to be a simple matter of creating the same distances from the pivot point to the tie-down for both sails. If that were the perfect solution then folks wouldn’t need jib trimmers or other get-ups to try to adjust the jib’s relationship to the main on an offwind reach. I think that for the most part these attempts at fine tuning the rig are more a placebo than an aid, once the boat is out there it is very hard to see what is going on and the only objective verification is if the boat seems to be going faster. Conventional rigs are better suited to sit on boats where you are right there to do the fine tuning in person.
Swing rigs are so effective because they carry the same upwind settings on all points of sail. Swing rigs are set up to generate lift on all points of sail except dead downwind (a swing rig should only really sail dead downwind in very light wind where they present all the sail area to the wind). The CE of the rig actually moves very little.
Now a lot of folks object to swing rigs on many grounds. They don’t look like big boats so they wreck the fantasy of sailing a “real” yacht. Some guys can’t get the concepts down and can’t understand the information the rig conveys to them. Some never get the feel for tuning them. Some complain that they dive a lot, although I’ve found that they dive at the same time as conventionally rigged boats do its just the inexperienced skipper doesn’t know what to do when it happens. Learning to sail a swing rig well may take some time so stick with it Kurt. But it is my belief that if you want to win races swing rigs are the way to go.
Look, what it boils down to is setting up your boat so that it works well with a minimum of weight above the waterline. In a new design I will usually start with a mast trunk so that I can move my swing rig around and adjust its rake until I find the right spot for it. There are so many variables involved in tuning a swing rig that anyone can only give you starting points. Building in a lot of flexibility for positioning the rig will help to get the right set determined more quickly. Once you’ve found the sweet spot you can rebuild the structure over the winter to a more limited set of location options.
Niel,
Actually big boats start using balestron to !
Now you should present a table of all rigs used on M class with all the percentages of jib surfaces either for classic or balestron setting.
This will help people to l understand better !
ClaudioD
Niel -
from a support viewpoint, having a diagram - or better, a photo - of your preliminary setup would be very helpful. I am struggling with some sort of insert to use in a hull on which to mount/test swing rigs. Being able to shift the rig forward or aft, and also adjust the rake BEFORE a final location is determined and deck added would prove to be immeasurably helpful. Any chance you can post your trial mast support? Right now I am using a muti-tube affair that sits on bottom of hull and is held in place by some horizontal bracing. The entire deck is covered in plastic packaging tape - mainly to keep the water out. I can use a small pen-knife to cut hole to insert mast. If wrong, another small piece of tape covers it and I try a different location. My newest version will use a small squeeze clamp (like big clothes pin) to manage location of tubes relative to fore/aft of hull.
Isn’t there some science to setting up a swing rig? IE, calculating the overall center of effort, and where that should be in terms of CLR, and, if you like, pivot point? I’ve read over the skeenes book on rig setup, and I found that it doesn’t amount to a hill of beans for swing rigs.
A swing rig is no different for figuring CE to CLR. If you know the distance for a standard rig, then the swing rig will have the same distance.
The difference is that the swing rig has to have a sail split that puts the CE behind the mast. The mast is positioned more forward due to the sail split difference not a change in CE to CLR. Usually on a conventional rig I run a 40/60 split and with a swing rig it is 25/75.
On a swing rig, the CE will essentially move in a circle about the mast since the sail plan only rotates and the sails do not move in relation to each other. So as you sheet out the CE will move forward, but only up to even with the mast since most people dont let the sail more that 90 deg out.
Swing rigs are really not that mysterious, although they are a bit different to sail. Personally I like a conventional rig better, but use a swing rig since it is much easier to change rigs.
well, that makes sense. I’ll have to measure the sail area of the two sails and determine the ratio, and the ce.
Thanks all, updates as soon as I am able!
I just cut the jib down, the current ratio is 37/63. Think this will work better?
before it was 46/54.
I found this table on a french paper , it may help more then 1000 words !
ClaudioD
Hi Kurt,
I’m afraid that 37/63 will not make much of an improvement. Consider that the swing rig is like your balanced rudder, too large an area forward of the rudder shaft and the rudder will start to oscillate at higher speeds and if you turn it the forward area may stick there due to water pressure and stall.
That is not exactly what happens with a swing rig but just an illustration of balance that may be more familiar. Kurt, have you actually built your boat and have tried to sail with your swing rig?
So, on to mast trunks. I used to sell kits for swing rig components and my mast trunk system some twenty years ago. These were sized for the M class and worked well on the 36/600 as well. The concept is scaleable for the RG but the tollerances will be close.
The mast trunk kit was comprised of a kevlar extrusion (kind of a rectangular tube that flared at the top), a rectangular carbon tube with a series of holes on the top and a thin stainless strip glued to the bottom, two carbon tracks with smaller holes with the same center-to-center spacing as those on the rectangular tubes, a Delrin slide plate with a hole for the mast and a series of holes along either side that lined up with the holes in the tracks but were at a different spacing, and a stainless wire staple that locked the slide plate to the tracks by inserting it in any holes that aligned between the slide plate and the tracks.
Okay, if you followed all that then maybe an image is starting to come together. I have worked in architectural model making for many years and I’ve been using machine tools for both work and personal projects (like model yachts). In the old days we used vernier calipers to measure decimal inches. They had two jaws, one that slid and one that was stationary, and a series of carefully spaced marks on the sliding part and decimal inch marks on the shaft’s track. This would give accurate measurements to the thousands of an inch of the space between the jaws. My mast trunk design uses the same concept for fine adjustment of mast position and rake angle.
The way it all goes together; The mast trunk is basically a sleeve just a bit wider than the diameter of the mast. My original trunk for the M class was about 3" long and .700" wide, by the depth of the hull (I sold the trunk extrusion extra long). An RG will need a smaller trunk. At the base of the trunk is the carbon extrusion which lays on its side. It fits snugly into the bottom of the trunk sleeve. Down the center of the top of the CF extrusion are a series of holes just slightly larger than the diameter of the pivot pin at the base of the mast. These holes form the rough locations for the mast. Down the center of the bottom of the CF extrusion is a stainless steel strip that acts as the bearing surface for the mast pin to rotate on.
At the top of the trunk extrusion (where it meets the deck) there is a short flare out on the forward/aft axis of each side to accomodate the side tracks that engage the slide plate. The holes in the tracks are at the same center-to-center spacing as those in the CF extrusion at the base of the trunk sleeve, but a different diameter to allow the staple to pass through. The Delrin slide plate has a hole in the center for the mast and a series of holes along each side sized to allow the staple to pass through but at a different center-to center spacing than those holes in the tracks. The holes in the slide plate must match up with holes in the tracks, this is the most ticklish part for a home builder to get right. I had several complicated molds to create the tracks and the slide plates I had cut on my company’s laser. I was in production then but the first few were done on a drill press jig to work out the bugs.
With different spacings of the holes in the slide plate and the tracks it can slide in there are a lot of places where sets of holes line up. By choosing which set of holes to put the staple you can control rake angle of the mast. With several holes in the CF extrusion at the base of the trunk there are several choices of where to locate the mast to start.
On my larger boats I would use a forward rake of about 3 degrees. I used masts that were bent under tension so the forward rake would bring the top of the mast in line with the base of the mast. The forward rake also encouraged the rig to go out on its own rather than center. This helped in the ghosting conditions to accelerate because the rig was already part way out and ready to react to the slightest puff. Gravity is an amazing thing.
I will try to get some photos of my vernier mast trunk together over the weekend. That may help you guys to get a better understanding of the concept of adjustable trunks. Although it sounds complicated to construct its function is very simple to grasp and very flexible in placement options.