Equilibrium rig,how its done at the bottom of the earth.

Footy Class General Discussion (Footy)
101

Hey Russell, it`s good to know you still have the passion and yes I am still doing it.:tophat:
Over 20 years and I think I am starting to get the hang of it.:jump4:

As for your spelling challenge, my recommendation is for you to visit the link I have provided below and download the free version of “Wordweb”[LEFT] for use with all your printed work. It is a most wonderful resource as not only does it check the spelling but it has a “thesaurus” function as well.
http://wordweb.info/

Alternatively if you type your contributions in word and then copy and paste them into the forum you can use the built in automatic spell check and grammar functions within “Microsoft word”.:disguise:
[/LEFT]

Finally if you Google “spellcheck” you will get the links to many programs often free that can be accessed as you type for automatic correction.:reyes:

102

I have been giving it some thought today. Appears simple enough to build and install. Will be keeping an eye on it and see how yours progresses.

103

Here are the photos that should accompany the earlier post.

1 the basic Choppa hull. The rudder is very small and the momrnt arm is short.

2The wire bsed rig. The bound section is too short and the wire is too thin, with the result that the whole thing

3 is far too floppy. This was when there was next to no wind.

Russell

104

Some more photos of my disastrous day out on Sunday last

1 the wooden rig, after stiffening the front end. Just about acceptable, but still too floppy

2 The wooden rig back home after the failure of the forward portion.

Russell

105

History man, love the Choppa! What an cool shape!

Where do you sail? In London?

106

Russell, I would encourage you to persevere with the wooden boom as I think with a different construction it will work well.
My photo shows a version I made using a balsa core with ply outer layers and I have another version using ceder venetian blind slats x 3.
I love the CHOPPA shape and show you a design called “Ode to Roger” a design by Bill Hagerup which continues the Stollery "Crazy Tube "theme.

107

Well, I was totally wrong about the last point: the boat ended up with unmanageable weather helm. My mistake was in visualizing the pivot as a “moment” (fixed) connection, which it obviously is not. Since it is a pinned (able to rotate) connection, the force vectors exerted a resultant lateral force further aft, resulting in increased helm. The downwind handling was improved, however.

So then I decided to “split the difference” by changing the bend in the Z wire only 1/2" aft from the original location & returning the pivot point to the original mast tube. This resulted in lee helm & difficulty coming about. The bottom line is that even small changes make a big difference in the balance of these boats.

So I returned to the original Z wire & it sails like a charm, I guess I got lucky the first time (thanks to Ian’s layout). However, it still needs more attention when running downwind, when the wind pipes up.

My next change will be to try an idea proposed by McGrimm some time back (post #55): angle the pivot tube slightly aft. This will result in the same CE/CLR relationship when pointing, but will shift the CE closer to hull C/L when running. I’m using only a 2 or 3 degree rake, but will hopefully result in calmer downwind control.

108

Bill K & all - About eight years ago I experimented with raking the pivot tube aft on one of my 36/600 swing rigs. In strong winds a 5 pound 13 ounce 36 with a 65 inch rig acts much like an overburdened Footy downwind. I was attempting to alleviate some of the downward pressure on the bow as the boat nosed down. I can’t say that the concept helped at all but I did note some interesting side effects.

The rig was set up to appear normal when sheeted in for a beat. As the sails where let out however the rake in the pivot tube slowly shifted the rake of the mast aft and to windward. Looking at the boat head-on while broad reaching, the hull would be heeled but the mast looked pretty much straight up and down. The CE of the sails moved closer to the centerline of the hull on both broad reaches and dead runs which is theoretically ideal because it would reduce the tendency to broach. Its why Laser sailors heel their boats to windward on the run. Also, the weight of the mast which is normally centered, would help to pivot the rig when the sheets were eased. Very helpful in light winds.

The downsides of my experiments where enough for me to discontinue trials of this concept (which I thought, while preparing the raked rigs, would be a major breakthrough). First, in the metro New York area our winds can change in velocity radically, particularly during the summer. A heat can start in dead calm and blow up rather quickly and return to drifting conditions. With the raked rig sheeted out in a lull, gravity would reverse the camber of the sails. This would put me at a disadvantage because a puff of wind might not be enough to “pop” the sail and establish flow. Other boats accelerated away when I was still waiting on my sails. When the winds piped up again I found that dead downwind there was no real difference to the fore and aft trim of the hull, there was no noticeable reduction in pressure on the forward part of the hull. There was a more pronounced tendency oscillate side to side on the run, and when the mast would swing too far to windward it would initiate a deathroll. Believe me, broaching is preferable (Laser sailors being on their boats have more control by shifting their weight than a remotely controlled boat has). As the sails were let out on progressively more open reaches the weather helm would increase because the CE, while moving closer to the centerline of the hull, would also be moving aft with the most pronounced shift at the top of the sail (in the strongest part of the wind). One of the first problems I encountered though was purely mechanical. I found that I hadn’t anticipated how far the forward spar would tilt down when the sail was all the way out. On my first day testing my contraption the forward end of the swing rig boom jammed on the side of the deck and popped my rig up out of its tube. My rig toppled over into the water. “Genius at work”. After that mishap I angled the forward part of the spar upward to clear the deck when it swung out. Not at all attractive. I continued to tinker with the rig for the next several months but some of the negative effects could not be engineered away or adjusted to through with experience.

I abandoned this idea because there were control problems that seemed incurable. I used an eight degree rake angle, and perhaps that was too much, or perhaps I didn’t go far enough. I don’t want to discourage experimentation if one of you wants to pick up where I left off. And perhaps on a Footy the forces will be less extreme and the boat’s behavior will be more tame. I can’t say for sure but I thought it important that I share my experiences with raked pivots so you inventive types know what to look out for. I would also caution against using more that 30% of the sail area ahead of the pivot point on balanced rigs (like the eualibrium rig). Go larger and the weathercocking effect of the balanced rig is compromised, increasing the risk of backwind stall if the sails reverse themselves in a heading shift.

109

Greetings gents.

I am completely new to forums so I hope this works out. I am equally as new to RC. sailing, having started building my first boat, a razor, in the last week of March, & sadly missing the internet race by not having a measurement box prepared by the end of April, my last opportunity to record some times. Be that as it may, I am now confident of providing some real future competition for our New Zealand winner.

Speaking of which, Brett, I want to ad to the record my personal thanks for sharing with the community the phenomenon that is the “Dunedin rig”. Absolutely brilliant, well done mate. I had only had my boat on the water once or twice with a standard jib & main, when I saw your first posting. I literally threw one together @ the lake side & haven’t had the std. rig on since.

I have done a few trials myself & hope my tupence will be of some benefit. Previously, there has been quite some discussion about boom bend. Personally, I don’t think that there is any significant advantage to it. My belief is that the brilliance of this design is in the twisting of the horizontal leg of the Z & the stiffer the boom & mast are the better, after all, they are what maintain the “all important” shape & efficiency of your sail. Experimenting with the amount of out-haul & matching the centre of effort to your hull is more important. I have found that adjusting the rake of the mast directly affects how high you can point, or in other words, how close to wind you are able to sail.

I hope to include a photo that illustrates the method I use to attach my boom to the Z. Simply, being the operative word, the boom is bound onto the wire with an elastic band, using closer wraps towards the bends in the wire & fewer in the middle. The idea being to attach the boom without diminishing or affecting the twisting aspect of the Z. It also means there is no waiting time for glue to dry, different boom materials can be tried @ the waters edge & running repairs carried out. I used spring steel wire, 16 S.W.G – 1.6MM, should be readily available @ your local hobby shop. I hope this is helpful.

Sorry guys. My photo file size is too big to upload. Will see if I can reduce or take another.

110

Hi Gary,
I would be interested in your thoughts on the “mast rake”
Some of my proto rigs just used electrical tape to hold the boom in place,quite sucessfull as well.
Don’t underestimate the bending boom component of the rig,without it the sail maintains the same shape as the gusts hit the rig,the rig merely leans over with the “torsion” action of the Z wire.
The bending boom opens up the leech spilling air from the top of the sail,The rig is not as effective without the bendy boom in my opinion.

I note that a few building rigs have tried to shift the pivot further aft,quite a natrual thing to try and do.This doesn’t seem to work as well as you would think and The position and sizes of my rig did not come into being with out many experiments.The only sloop rigged yachts that would have the CE directly over the centreline of the hull would have to have a mainsail and jib of equal area,this is not common and most yachts will need some steering input downwind to track straight.My design is no different.All design is a compromise and this rig still has some shortcomings.

111

Hi Brett

Electrical tape sounds good. I imagine anything that is not ridged, holds the boom, & easy to apply.

I meant to mention last post that bamboo bar-b-q kebab skewers make good booms.

I hear what you say about opening the leech. I guess we need to find the happy medium as the boom stiffness on this rig also serves as the kicker in close haul mode.

Regarding mast rake, I’m not sure there is anything I could teach you. What I have learned is that there is a fine line between what works & what doesn’t. Starting with the top of the mast above the pivot, the best position seems to be somewhere forward of that. As I leaned the mast forward, the boat pointed higher, but there came a point where it would sit head to wind & I couldn’t get it to turn it into the wind (close hauled) with out excessive helm. (I nearly didn’t get it back that time). A bit of a catch 22 as it was the slight weather helm I was trying to cure in the first place. From here I think the way forward is balancing the best rake angle, for optimum point, & adjusting the shape of the sail plan, moving the centre of effort, to reduce the weather helm. Depending on the shape of your existing sail plan, bending the wire at the top of the pivot, tipping the whole rig forward could achieve both. If you believe you have the best rake, then trim the leach of your sail to move the CE forward, too much & you will need a new sail. Obviously this applies to trim when sailing to wind. Down wind trim will hopefully be good once the CE is taken care of. The problem I have with my razor is nose diving. As you have noted, moving the pivot aft is the natural reaction. More experimentation required. Unfortunately, all hulls perform differently so what remedies one may not work with another.

I’m not sure if this is of any help to you but may benefit others. Please let me know if you think I am on the right track.

You mentioned shortcomings, but I don’t think you should beat yourself up. The perfect rig design doesn’t exist, but I will be happy with near enough. I think what you have produced is pretty much there.

112

Brett,
After my attempts to play around with the layout, I’ve come to totally agree with the above & appreciate the design you have evolved. As others have said, the rig has to be closely matched with the hull’s characteristics & you have done a great job.

Neil,
Good points about pivot rake issues. Actually I discovered that some of my downwind control issues were because I had a slight forward rake in the mast tube which made matters worse. So the rake I’ve introduced will be pretty minimal, but still enough to cause a 1" shift in CE towards hull C/L when running downwind (compared to what it had been previously.)

Gary,
I also look forward to hearing more about mast rake trials. I’m a bit surprised that raking it forward caused increased weather helm, I would have expected the opposite.

Getting ready for the trip to Sheboygan. Hopefully I won’t be totally embarassed by Graham, Angus & others. Looking forward to a fun day of racing, as up until now there has been no basis of comparison.

113

Bill, Gary & all - Bill, with my swing rigs on both M class and 36/600’s I angle the mast pivot forward about 3 degrees as standard practice. The reason for this is two-fold.
First, my masts are curved under compression from a stay running from the masthead crane to the aft part of the main boom. This compression can be adjusted to alter the camber of the sail, full for light winds or flattened out when the wind picks up. The curve of the mast shifts the Ce of the main sail aft in comparison to a sail on a straight mast. Angling the pivot forward (for rigs 75 to 85 inches tall) allows the pivot point to be father aft in relation to the Ce of the whole rig than if the mast (at the deck) were perpendicular to the waterline. The effect of this forward angled pivot is when the boat is becalmed with the rig cracked out from close hauled the mast weight (being forward of the pivot axis) helps to pull the sails out. Because the rig is canted slightly forward the weight of the sails insure that the camber is filled out and ready to react to the next puff.
Second, on broad reaches and runs having the rig angled forward enhances acceleration and to a certain degree mitigates diving (on 36’s its most noticeable). The forward angle encourages flow over the sails earlier because the wind is deflected more easily over the top of the leaches. With most conventionally rigged boats downwind sailing involves trapping the wind in your sails. The swing rig is essentially a uni-rig with two sails. Single sailed dingys rarely sail dead down wind. Reaching is the fastest point of sail for a swing rig as it is for a windsurfer. I often sail with my swing rig trimmed beyond 90 degrees to the centerline, particularly if I’m trying to preserve starboard tack advantage as I approach a mark. The curved mast is is under compression, which makes it stronger fore and aft. Therefore I use a lighter carbon mast than I would with a straight mast. The mast is more springy side to side though which deflects some of the energy from the type of gust that would send a boat diving, giving me a second more to react.
The rig under discussion here has a similar spring effect which maybe why reports indicate that the boats are more easily handled downwind, and why angling the pivot forward gave Bill control problems. Since the rig deflects under load, and Footies accelerate really well anyway, angling the pivot axis forward might not help achieve the positive effects mentioned above.

Gary, it sounds to me like the pivot point is in the wrong position. You shouldn’t get weather helm by altering the rake angle of the mast forward in relation to the boom. My guess is that the pivot point (and hence the whole rig) has to be moved forward. If you located your mast pivot position using the location provided for the mast position of a conventional jib/main type rig then you probably need to recalculate your equilibrium rig’s pivot point. The Razor design has a tendency to round up in gusts anyway. That is probably due to its sharp bow and hard chine (and easy to build) construction method. Every boat has its quirks, thats something everyone has to adjust to with their particular hull. But finding the “sweet spot” of rig location may require more holes in your deck.

114

Niel,
Thank you very much for sharing your swing rig experiences in this thread.
It is very much appreciated by me and I am sure the others.
Seems to me that there is a a definite relationship between these 2 rig types.

My rig is really just a simplified swing rig for use on smaller yachts.

115

Thanks for the comment Bill. Made me doubt myself, so went back to the water & guess what, You were right. Sorry for the duff gen guys.

The incident sitting head to wind, I remember now, was with a high aspect ratio sail I tried where the mast was 700 mm long, foot 270mm, pivot 100 aft of the mast. (The hull carried this sail amazingly well, in light airs of course). The top of the mast was behind the pivot point, which put the C of E too far back & the boat weather-cocked, stalled, & wouldn’t steer into wind. Tipped it forward, problem solved.

The rig I used to retest was mast 500mm long, boom 300, pivot 100 aft of mast with a sail very similar in shape to Ian H-B’s Tane. I did as I suggested previously bending the wire @ the top of the pivot, reducing mast rake angle & moving the C of E forward.

Initially the boat pointed higher & weather helm was reduced but never completely went away. The point, to which I incorrectly referred to previously, happened quite suddenly, the result being the best & virtually only point of sail was a broad reach. It was impossible to turn through the wind as on a normal tack & even needed considerable motion to accomplish the turn down wind where control was poor. I only did this manoeuvre once before tipping the rig back to a better position.

To further try to reduce the weather helm to the hands off stage that others have achieved I began to trim the leech of the sail gradually. After three trims I ended up with a triangular sail, no reduction in weather helm, & diminished performance, I presume due to reduced sail area & loss of efficient sail shape.

I aborted any further experimentation that morning as I was now quite wet from the rain & had very little sail left to play with.

I hope this has gone part way to restoring any credibility I may have once had. Keep at it men.

I look forward to hearing how things went at Sheboygan?

116

Thanks for the advice Neil. I had already resigned myself to the fact that there will be a few more holes in the deck.

117

Hi has anyone used 2 booms-a stiff one attached to the wire with a flexible one (1mm CF) attached above it with sliding adjusters such as cable ties which could be moved along to adjust its stiffness according to the wind strength?? Brian

118

nearly 7000 hits to this thread
amazing.

119

Brett
Interesting that you bring that up. I was just about to post a couple short videos showing the flexing of unarigs using the same sail rig & a floor fan, but with different wire thicknesses. The 1st video is using 2mm “music wire” from the hobby store, the 2nd is 1.6mm (1/16"). This is not intended to be rigorously scientific, but gives a very clear visual comparison with the different wires. The floor fan created a rather turbulent air flow, but you can really see the working flex:
http://www.youtube.com/watch?v=3rexyNQ8DTM

http://www.youtube.com/watch?v=tbdnUSWmdF0

Brian,
Good idea, have you tried it yet? It would make a big difference where you decide to connect your sheeting line to the boom.

Bill

120

I did a little experimenting of my own this weekend. I wanted to see if a really tall rig would work in light winds. I also wanted to beat a friend’s very well executed Razor with a standard Bermuda rig. In the past I could catch him downwind but got killed upwind.

My first McRig followed Brett’s suggested size. This one is a bit taller.

Initial specs
Luff 710mm
Boom/foot 310mm
Pivot 100mm from luff

It worked ok in very light winds but developed a crease whenever the wind picked up a bit. It pointed but not as well as my competition. After a little experimenting I decided the top of the mast was too far back and the clew pulled too much. I bent the wire to bring the mast directly over the pivot. Now the sail needed reshaping, break out the scissors and trim the foot to a better shape.

Now the luff is only 680mm. Much better, no crease and pointing at least as well as the Razor. The winds had picked up a bit by now (we sailed bigger boats for a while too) and the tall McRig still performs great. I can beat the other guy upwind and down. It handles 8mph reasonably well, the bow digs in some but not too bad. It’s great at finding wind when the other boat is becalmed.

I thought this experiment would have me trimming the sail down to the 550mm range but it surprised me. 8mph is probably the max for this size but now I have a light air rig. The next improvement will be better mylar. I need to find 2 mil. This wrapping paper is just too thin, maybe 0.3-0.5 mil (Angus thinks I stripped a NASA probe). The boom could be a bit stiffer too.