Hand-tight, reactive, compound standing rigging

Discussion in 'Sailboats' started by pbmaise, Nov 18, 2013.

  1. pbmaise
    Joined: Jul 2010
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    Location: Cebu the Philippines

    pbmaise Senior Member

    Now that manufacturers are beginning to build aft-mast rigs, I thought it best to break out one of the finer points of this topic into a separate thread.

    How best to support a mast placed in the back of the boat is something I have worked on for a long time. My mast has just stood against super typhoon Yolanda and the estimated 100 mph plus winds we had here in the Philippines. The eye of the storm hit within 30 miles of my sailboat.

    Let me start with some definitions.

    Hand-tight standing rigging = Lines run from chainplates to mast to hold it upright. The lines are under low tension. No turnbuckles or winches create a high tension on the lines.

    Reactive standing rigging = Rigging that, when under load, has no weather or lee side. In the rig I designed 4 chain plates support the mast from the rear and all 4 are connected by just one line. Weather and lee side are always under the same tension. They are the same line.

    Compound standing rigging = Rigging wherein a single line makes multiple trips between the mast and chainplates. The lower backstay line for my new design makes 6 trips between the mast and chainplates. Load is spread to all 4 plates all the time.

    My efforts were part of a quest to come up with ways to reduce mast compression. I learned that my sailboat lacked the ideal place to a new chainplate and came up with a way to merge two chainplates mid-air to obtain a better angle of support.

    The presentations below describe how I came up with my solution.

    In this thread, I am seeking input from others who may have attempted something like this.
     

    Attached Files:

  2. michael pierzga
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    michael pierzga Senior Member

    My head is spinning...........

    And your method rigging tension reduces the shroud angle and increases compression.
    And whatever sails fly forward on stays will create...COMPRESSION CITY ....on your mast


    The rest of it I just couldnt understand.

    For safety install a couple diesel engines and keep the tank topped up
     
  3. pbmaise
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    pbmaise Senior Member

    No sails fly on any forward stays. There is no forestay. It is really quite amazing now to walk around my boat. There is nothing, nada, zip, from the bow to 37 feet behind the bow. It is all just one giant open space for my lifting sail to self-tack without touching a single line.

    At the 37 foot mark, there are two forward leading sidestays that prevent the mast from falling backwards. The only load pushing the mast backwards is the wind. Mind you a 100 plus mile an hour wind lately attempted to push the mast way backwards.

    Regarding the shroud angle...that is where I used a little three dimensional thinking to join two lines in midair. It is a bit more complicated then that since there are multiple midair connections behind the mast now. The net result is the pulling angle of the backstay is nearly 45 degrees. All connections are to glass smooth surfaces. I'm done with thimbles. They cut into my Dyneema lines like razor blades. I now use strain insulators.

    Regarding mast compression, this is a traditional lifting sail. I found I have to let the sail out far even when upwinding. There is really very little compression here. The halyard, (terminated correctly on the deck with a deck winch), just lifts the sail. The sail is also lifted with a compound lift as I now see in the Lagoon 620.

    Therefore I venture to say I have a fraction of the compression seen on a Bermuda rig. And that was the whole point. My first mast failed under compression in part because I was told again and again that sail shape and high tension on sail was important. That proved not true.

    I definitely know I have way less compression then the original Bermuda rig as it had 3 mast mounted winches and did not compound lift any of the sails.

    Thanks for advise on the iron horse. This is a cruising sailboat. If I do need to call upon my 150 hp engine, I carry enough fuel for 1000 miles if I keep speed down to about 6.5 knots. This is just above idle speed.
     
  4. DCockey
    Joined: Oct 2009
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    DCockey Senior Member

    Have you done vector analysis of your rig?
     
  5. pbmaise
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    pbmaise Senior Member

    Yes, I spent many many hours doing an analysis. The analysis helped me confirm angles, line lengths, and load calculations. It is owing to this analysis and my design case that I went out and purchased big forged galvanized shackles.

    I came up with several designs on paper. I then tested.

    I made a 1/3 scale model and placed a digital scale at the bottom. Concerns over previous mast compression led me to search for the least possible compression.

    The results when testing the original Bermuda rig were surprising. I didn't know till I did the tests that mast compression will initially stay the same, or drop as sail load is applied.

    I am pretty certain I know what is going on.
    A. The lee side stay on a typical Bermuda rig is under high tension. Most of this tension translates into mast compression.

    B. When the wind forces pull on the mast, they don't pull at the same angle. The wind's pulling angle is less acute. This means the wind is adding less compression then it is removing by pulling the mast horizontally. Once the lee stay is slack, compression forces as measured at the base of the mast go up the greater the wind load.


    The presentations summarize the testing, and eventually I will publish results and graphs.

    Philip Maise
     
  6. pbmaise
    Joined: Jul 2010
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    pbmaise Senior Member

    Being sold the wrong bill of goods

    In my presentation I claim owners of big multihulls are being told they can simply just reef. Further, that isn't feasible for cruising multihulls with limited crews, fast squalls, and sailing at night.

    Here is the quote I found. It refers to a Bermuda rig on a multihull.

    In the real world cruising sailors can't always reef in time. Many owners have realized this and big crusing multihulls tend to sail reefed. This in turn hurts their ability to go to wind.
     
  7. sharpii2
    Joined: May 2004
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    sharpii2 Senior Member

    PB

    I enjoyed reading your presentation and I partially agree with you on your criticism of the Bermudan rig, especially the way it is used on so called high performance boats.

    IMHO, a fat head main has no place on a cruising sailboat, mostly for the reasons you mentioned in your presentation. This is because they are high aspect ratio and need battens to stand properly. Also, the battens need to be flexible, so the sail can get it's famous, efficient airfoil, fore and aft shape.

    But this particular application of the Bermuda rig does not condemn the whole tribe.

    It is possible to design one with very low rigging loads. Simply making the sail more triangular in profile, then making it lower aspect ratio (AR) goes a long way in this direction. On a wide boat, such as a multi, it is possible to eliminate the boom as well. The jib on it, as the one on your boat, does not need to be bar tight. I once sail a boat with a fractional Bermuda rig (3/4) which had a dismaying amount of slack in the rigging. It still sailed reasonably well upwind. So reasonably that it was able to sail up a channel that was only three boat lengths wide, dead upwind.
    Lots of tacks, of course. Maybe more so than if the rig had been tight. But she did manage.

    With a lower AR, the Center of Area (CA) is also lower, which makes it far less scary on a capsizeable multi. A good example of such is a Wharram polycat day sailor I once saw making its way across a small lake in a stiff breeze. An older gentleman was sailing her, along with his grand daughter. No hiking on this boat. Both sat comfortably on the wing deck as the water sluiced by at maybe 10 to 13 knots. The mast wasn't much longer than the boat, and the boom was almost as long as the mast.
    It had a very small jib in front.

    Granted, a Hobie Cat, roughly its size, would probably eat it for lunch, on a race course, but nobody was racing that day.

    According to a Wikipedia I read, the Bermuda rig evolved from the Lateen rig. The long, singing yard was replaced with a stiffer one that was stepped like a mast (it in fact was one at this point). This mast raked aft considerably, and there was usually more than just one.

    So, you can see there was quite a long voyage from what the Bermudan rig once was to what it is today, in its more recent incarnations.

    As for your rig, I feel you deserve a lot of credit thinking this through on your own, and coming up with something far more suitable for your purposes.

    My main concern is the long, continuous "blue line". If this line ever parts, there goes your rig. It looks to me like a deadly fail point with no back up. What makes it more worrisome is that it has to go through at least six turning blocks (or insulators), all of which put heavy localized stresses on it.

    I imagine and hope you went ridiculously heavy, with this line and its blocks, to all but guarantee it will never fail. If I were designing it, I'd go with four separate back stays with the 7x49 sized to hold the mast up, to the point of capsize, if only the inner ones held.

    This would more than double your safety factor, without having to add all that much more weight. With a jib only rig, there would be no slack on any of three stays, as the sag in the fore stay, or just the luff of the jib, would pull the top of the mast forward, no matter which direction the wind was coming from (except, maybe, dead ahead).

    With the sail attached to the mast, as with a Bermuda rig, There would be times in which one stay would go slack. Especially if it were sailed the way mine was, with the jib taken in first, in rising winds.

    The problem with your dynamic mast support rig (I dare not call it "standing rig", even though it serves the same function) are the long, continuous lengths of cable. The stretch of a line is a factor of its elasticity multiplied by its length. The longer a line of a given strength is, the more it's going to stretch under a given load.

    This is not necessarily bad thing. More stretch equals greater resilience.
    Such resilience may explain why your mast was left still standing after the typhoon. Shock loads are far greater than relatively static ones.

    With a sudden gust, everything stretches and sags, just to return to its original dimensions after the event ends.

    My only worry would be if you were caught, fighting for your life, off a lee shore in a gale wind. If the jib luff sags too much, you may lose all windward lift and fetch up on a reef. But much of that depends on the three dimensional shape of the jib. The flatter it's cut the less likely this is to happen. It could also be cut with concave curve it its luff to allow it to stand better with less luff tension.

    Only time and experience will tell.

    I've been studying these strange creatures, known as sailboats, long enough to expect surprises.
     
    Last edited: Nov 19, 2013
  8. pbmaise
    Joined: Jul 2010
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    pbmaise Senior Member

    Wow sharpii2!

    Thank you thank you. I have invested many many hours trying to make these presentations understandable. You are helping me get ideas to improve the presentation so it is more clear.

    Let me respond to some of your points and questions:

    You wrote:
    My only worry would be if you were caught, fighting for your life, off a lee shore in a gale wind. If the jib luff sags too much, you may lose all windward lift and fetch up on a reef. But much of that depends on the three dimensional shape of the jib. The flatter it's cut the less likely this is to happen. It could also be cut with concave curve it its luff to allow it to stand better with less luff tension.

    Well for starters I hope I am never in this situation. As you can see with the super typhoon that came into the Philippines I had enough word to get into a marina and lock it down with 15 lines to shore. As a rule I never sail within 5 miles of a lee shore in case my crew are not paying attention to the GPS. If I am fighting for my life the first thing to do would be to start the 150 HP engine and power out with the big propeller. I consulted two surveyors in Thailand and both agreed the propeller the original owner had installed was too small for the engine. I found it rather cheap in Thailand to make the propeller bigger at a specialty prop shop. The new problem with the engine is speed. The slowest I can go is about 4.5 knots. Further I get some neutral spin. Bringing in my rig into the small local marina here I had the engine off and 6 lines to shore. I brought it in foot by foot. It took almost all day. If I had trouble with control while under power or sail, then tossing in one of the three Jordans might help. Then again I might use one of my 2 paraanchors. The next attempt would be to snag an anchor. There are three in case one is lost this way. Finally, there is what I call the final Hail Mary option. That is to just toss a huge loop of line out hoping it would catch on something.

    Secondly, is a jib that is 100% flat flat enough for you? My sail is a lifting sail with a very low tension on the halyard.

    Here is what the lifting sail looks like when it self-tacks. It is being supported in this video by the first mast I snapped in the South China Sea.
    http://www.youtube.com/watch?v=4JSH1s6aGEQ

    You wrote:
    "My main concern is the long, continuous "blue line". If this line ever parts, there goes your rig. It looks to me like a deadly fail point with no back up. What makes it more worrisome is that it has to go through at least six turning blocks (or insulators), all of which put heavy localized stresses on it."


    There is nothing like having a 82 foot mast come crashing down around you to make you change your mind. I was determined when designing the first rigging on the 82 foot mast to make everything as redundant as possible and get tension on my foresail as tight as possible. All of that meant compression so engineers I consulted post mortem were not surprised a mere 50 knot blow under sail brought that mast down. Among the big mistakes I made was tightening the lines I had in place a redundant backup.

    In this new low tension and hand tight mindset, I am comfortable taking off the redundant lines. When I first erected the mast, I had redundant lines up, however, this time they were left slack. I have a much happier 62 foot mast that doesn't bend around like the 82 foot mast.

    That big line making a trip up and down is brand new Dyneema and cost me almost $5,000. It was sized for the previous 82 foot mast. Breaking strength is over 15,000 lbs. Insulator breaking strength is 20,000 lbs.

    However, I am compounding this line spreading the load out greatly. Essentially there are 6 lines coming down from the mast to the chainplates that are all rated over 15,000 lbs. All lines are equal tension and no line has more load. There is another Dyneema line I am calling the upper backstay line for now. That line is rated at 20,000 lbs.

    I have yet to mention post typhoon analysis on my rig. I returned from that elementary school on the hilltop overlooking the marina and inspected the lines. I had to take up about 1 inch of slack. The only line I had to adjust was the port forward leading sidestay. This sidestay and the port side saw the greatest initial wind speed. Later in the typhoon winds shifted around and keep from behind the boat. I saw no stretching of this line.

    One thing I want to point out is that anyone with a big multihull like mine should seriously and I mean seriously consider what type of wind load a 100 mph wind makes. Holding my front end and port side where the highest winds were expected were 4 dyneema lines, 2 huge polyesters, and 4 chains connected to cement posts. Further, I had antichaffing gear on all lines. If you find yourself in this situation don't forget that the ball the rotating mast sits on is your strongest tie point. People came back to the marina after the storm and were asking why the marina staff went around loosening lines. They didn't realize the workers did nothing and all their lines had stretched.

    To prevent as much stretch as possible on my lines I had 7 bags of cement midway on the lines. The wind had to first pick up 7 bags of cement before the line became tight. Other sailors couldn't believe the extent to which I protected the boat. Oh..I mentioned all glass was protected and everything triple tied down?

    Regarding your concern about localized loading on the line. I was really really pleased to have found strain insulators. In this new rig not a single Dyneema line contacts metal of any sort. I learned this lesson form the first mast. The strain insulators are glass smooth surfaces with a wide turning radius. Some of you may not have the time to read the full presentation so let me at least post a picture of a strain insulator so you know what I am talking about. They are made and used by the millions to support utility poles. Unfortunately all I can find locally are brown ones and to get the white ones requires a huge minimum order.

    .....
    You wrote:
    IMHO, a fat head main has no place on a cruising sailboat.

    I agree with your mindset about a smaller rig and making it with lower aspect ratio for cruising sailors. Perhaps if vendors had suggested this in Thailand I would have gone this route. I hope to see more people agree with you as fewer cruising sailors will have the negative experiences the former owners of my boat had.
     

    Attached Files:

  9. tspeer
    Joined: Feb 2002
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    tspeer Senior Member

    I believe what you have created is known as a self-equalizing equal-tension system. These are widely used in rock climbing for belay anchors.

    See:
    http://www.caves.org/section/vertical/nh/51/Multi-point pre-equal anchors.pdf
    http://www.rescuedynamics.ca/articles/pdfs/EarnestAnchors3.pdf
    Rescue Systems 1 Chapter 11

    There are ways of rigging this kind of system so the load is shifted to the remaining chainplates if there is a failure of one of them. It would be possible to have redundant tensioning lines, too, so there are no single point failures in the backstays.

    Basically, all of the heeling moment from the rig is being taken by your forward shrouds. Because the backstays have equal tension on both sides, they are equivalent to a single backstay on the centerline. The rig is statically determinate, which is why it does not benefit from preload.
     

  10. pbmaise
    Joined: Jul 2010
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    Location: Cebu the Philippines

    pbmaise Senior Member

    Aloha Tom,
    Thank you for the terms. I don't want to reinvent terms and will update my presentations to term my rig as a self-equalizing equal-tension system.

    I appreciate your technical term statically determinate and explanation why there is no benefit from preloading. Of all the things that raise eyebrows about how I designed my rig, it is the low load on rigging lines that concerns other sailors. They are used to strumming rigging lines like piano wires and they universally say I must tighten my lines far more. However, I think I really have really been there and done that with the first mast I over compressed.

    It has really taken me a lot of resolve to pick the ball up again and rethink my previous fiasco.

    There is one correction to your post that may further raise eyebrows.

    The only function of the forward leading stays is to prevent the mast from being pushed backwards when the sail is not up. With the sail up, the mast is being pulled forward, and both forward leading side stays are unloaded.

    I made the attached drawing to try and show how heeling load is taken up primarily by the lines connecting the spar in the foot of my sail.

    QUESTION: I doubt I have been the only one to ever think along these lines. Any other designs of self-equalizing equal-tension rigging?

    Philip Maise

    p.s. I updated Presentation 1
     

    Attached Files:

    Last edited: Nov 26, 2013
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