Nomad revisited
Both John D. and I have built Bolger proa style rigs and both of us failed miserably. However - that doesn’t mean it cannot be done! One of the big problems we had was we attempted to put too much roach into the sail, making it closer to the theoretically ideal ellipse, however that caused all sorts of problems. I appears that your sail is a true triangle, which should help a lot, and the junk control lines will help, too.
MTP said: I wouldn’t worry too much about the momentary “broadside” condition, for a couple of reasons. Firstly, the sail is not at all “under full power” during the shunt, but is in fact quite depowered as the flow of air across it has stalled out so the aerodynamic effects are negligible and the only forces at play are strictly of the laundry-hanging-on-the-line sort…
I agree. There are so many great advantages to a bi-directional rig for a proa that some risk of failure is worth it, IMHO. I’m glad to see you are not making the same mistakes I did, so who knows, this may be the “lightbulb” that finally works.
John Dalziel (owner of the Yahoo proa_file group) built one of the Bolger proa rigs more than ten years ago and the shunting scared him enough to give up on it. You might want to contact him to retell the story.
I’ve read everything I could lay my hands on that John wrote about his experiences with the Bolger rig, most of the pertinent stuff still resides on the archives of this forum (I think). His experience and sharing of same was instrumental in the path I’ve taken.
1) John’s absolutely right about the two tack lines and the inevitability of things going out of control, the concept is probably in the Murphy Hall of Fame or at least on a short list. I’ve gone to a single sliding tack line and separated the sheet function(s).
2) His experience and writing about the lift line moving back in some circumstances led me to stay with more purely triangular planforms rather than the theoretically perfect elliptical.
3) At least for me the curved batten mainsail was a mixed bag, when it was good it was very very good, when it was bad it was very very bad. My biggest problem was in ghosting conditions, at times the blasted boat would be nailed in place while boats I’d blasted by in a little breeze would merrily slowly drift past me. A big part of the problem was my lack of experience sailing but I think there’s some fundamental difficulties with the approach.
But there is some fundamental goodness in a boomed staysail I had some luck with the approach in various wind conditions even though my early iterations were shall we say ....... crude. The big drawback to this kind of rig for me is the horrendous loads involved, no biggy if you’re into that sort of thing, but the idea seems to be out of place in my “easy does it” kind of mindset.
I haven’t made and tried a bidirectional cambered junk yet but it’s heavy on my mind, partially due to following your experience 😉 I think it has real potential for what I have in mind, easily handled, forgiving, low rig stress; about the only downside I see at the moment is that sure is a lot of line(s).
I’m dusting off the earlier Bionic Broomstick concept and will build a fairly quick and dirty iteration in a couple of months after some scheduling clears up.
Thanks for the input,
Skip
Tack location. I do not understand your idea of moving the tack downhaul. Surely there is a ‘tack’ downhaul’ at both ends that swaps on shunting?
Thinking through the junk rig part. Do you not have a problem with reefing geometry as the lower battens, in effect move backwards when lowered? Then on shunting, they have to move backwards to the other end!
The panels would have to distort, ie are not stacked vertically. This preclude adding extra short battens between the main battens, which will be very advantageous to support the leading edge.
I assume the battens are curved. Do not go for too much. Cruising junks advise around 4% off shore, perhaps 6% inshore. Being an easily driven hull, a slimmer profile is probably best. The Bolger example appears to have pretty fat sails, which would be a handfull. I would also only connect the sail at each end, the batten being to the lee. Then the sail can feather into the wind.
The main problem for a crusier will be being caught aback. The sail would rest against the mast and be held by the tack downhaul, so would not feather. How much of a problem this would be is probably the downfall of an otherwise very tempting idea. So look forward to your success with trials (& tribulations).
Mark
PS there are some good Youtube vidoes of a similar junk proa, goes very well. It is only seen in light winds, so how this would work on a larger boat, in a big sea is another matter.
Tack location. I do not understand your idea of moving the tack downhaul. Surely there is a ‘tack’ downhaul’ at both ends that swaps on shunting?
Should have done this some time ago…..the diagram shows schematically the idea of a sliding tack. The problem with having two tack downhauls as John D wrote about and I experienced is that sooner or later it will get away from you and it is not something you want to repeat .......ever.
I hope the diagram is reasonably readable, a few other comments about the setup.
1) Not shown in diagram is option to have the tack line continuous on the hull side of things with a rope clutch so that the shuttle location on the boom can be adjusted while on one tack or the other to allow for balanced downwind sailing.
2) There’s going to be some chafe in the crossed tack lines and we’ll just have to see how it works out.
3) The tack should be able to be positioned over a reasonable range on each tack by stopping the shunt line before shuttle gets to the end of slide on the boom.
cheers,
Skip
Now I get your drift.
I see the problem with this is that to get a tight luff, the tack line will need quite a lot of tension. This will require some expensive sliders if it is going to slide freely.
Also, how does this work with the junk sail reefing?
My thoughts are that it would be best to connect to a slider on the mast. See sketch, (hopefully attached). Each batten has this arrangement and the line each side is continuous up the battens. The joint between mast sleeve and batten sleeve would have to allow movement, (in fact could be a parrell and beads to the batten.)
The operation is quite simple. The slider is normally about 1/3 back from the luff, so the sail can act normally and feather. Going into a shunt, pull on the rear lines. The battens move forward until the sail flips. Tighten in the sheets. Pronto and no real time side on to the wind.
Disadvantages, the boards will have to be used to adjust the hull centre of pressure.
Look forward to comments.
Mark
Mark,
That’s slick, I’ll have to think on it a while but your idea may well be the best bidirectional rig yet.
So many ideas so little time 😉
Skip
There’s going to be some chafe in the crossed tack lines.
Not necessarily. Use a double-sheave block on one side, say on the hull. The lines cross each other inside the double block, without chafe.
I have described the stacking issue that Mark mentioned in my thread on new proa rigs. There are two aspects to it. One is that you may not be able to get the batten to where it needs to be. I think the angle between battens and turning axis of your sail is not so large that you have to worry. I’d need to see exact drawings of the planform to be sure.
The second issue is sheets getting caught in the protruding lower battens of already reefed panels. That is primarily an issue with single sheets that have to get to the other side of the sail. It should be less of an issue for a proa, where the sheet always stays on the same side of the sail.
Regards
Robert Biegler
There’s going to be some chafe in the crossed tack lines.
Not necessarily. Use a double-sheave block on one side, say on the hull. The lines cross each other inside the double block, without chafe.
Thanks, hadn’t considered that since I’m usually working in a quick and dirty lash it together mode.
Bionic Broomstick will now have a fixed double block on hull shuttle.
Skip
Bionic Broomstick will now have a fixed double block on hull shuttle.
Skip
It will try to twist. Choose one without swivel, or else give one side a double line and use a triple block on the hull, and a single and a double on the boom.
As you have drawn the lines, the slider on the boom and on the hull will move at the same rate, meaning that the boom will not move from end to end. You want the slider on the hull move more than its counterpart on the boom. I think you can do that by leading the lines on the boom through blocks at each end and back to the slider. Then the boom should move relative to the slider only half as much as the sliders move relative to the hull. Then the boom is pulled towards the current bow.
Regards
Robert Biegler
I decided I was being a bit too high-tech. Junk(ies) like being basic.
It is basically a standard junk arangement, but with a parrell with beads holding the battens close to the mast, allowing free sliding. The luff parrells are repeated a the ‘rear’ of the sail. (The luff parrells normally serve a cople of battens.)
Not shown is a tack downhaul at each end of the lower batten. In operation the luff parrells would be slackened, the tack down haul pulled in, which would swing the to the new end. The luff parrels then adjusted to remove creases.
Whether this is better than a convention junk swung through the wind is debatable. It should be quicker and would suit a smaller craft. I think the security of a normally feathering sail would be preferable off shore.
I realise it is a junk sail that is gybed. It could even be tried out on a dinghy (I have a Topper)
Mark
Robert,
You’re right, the boom will not move in relation to the hull but that is what I’m looking for in this iteration. Long term your approach may work best but I’m fixated on a central sail.
Mark,
The sliding parrels on the battens are going to interfere with attaching sail to battens without another layer of complexity. The drawing reminds me of an idea I doodled with for a while that had my typical canted mast freestanding from the sail and a zigzag of lines from the 1/4 points of battens to blocks on the mast on collars that would slide up and down for reefing and stowing sail. Had some interesting possibilities but by the time you got to 3 or 4 battens the amount of line from close hauled to running was staggering.
cheers,
Skip
The battens are straight. The sail connected at each end, with sufficient looseness to give the desired camber.
Not that many more lines to a ‘standard’ junk. There is the additional sheets and the luff parrels. Some other ‘standard’ junk lines will not be required. (‘standard’ being the current practice, with a good level of adjustment).
Mark
Thanks to everyone that’s made comments. As a result of feedback plus some conversation with John Wright I’ve decided to go ahead first with the Bionic Broomstick.
Skip
How do you plan on getting the rudder pods to rotate smoothly? Upper and lower bearings? Something has to keep it from going up and down and something has to keep it on. What were you thinking of?
I’m REALLY intrigued with this direction. But I’m not sure its as simple as the newick/brown rudder. Of course, that depends on the details…
Best,
Chris
Rudder pods (good description, thanks) rotate just as a tapered cone on Nomad and a straight cylindrical segment on the Bionic Broomstick. Basic premise is large area keeps loading low. A tab at the top of the hull should keep pods in place and from floating up. Pods are kept in place on the hull by a line that goes thru a tunnel in the hull, held in place by elastic cords (bungies) that give some give when hitting stuff.
Simple’s a slippery word. The concept seems fairly simple to me but so far there’s a dozen pieces in each pod on the Bionic Broomstick that I’ve started. The cylindrical surface is a piece of 3” thinwall PVC pipe with a graphite/epoxy/fiberglass “socket” molded against it that will be glued into the hull ends. At the moment it seems pretty smooth and slick, very little friction. Will have to wait and see how it all works when put together.
The major difference between this and the newick/brown rudder is the ability to use the rudder partially or wholly retracted, a virtual necessity where I want to go. Having the ability to pop-up a bit is a bonus. Downside is the fragility of the ends of the boat. Time will tell.
cheers,
Skip