Aftmast rigs???

Discussion in 'Sailboats' started by jdardozzi, May 28, 2002.

  1. michael pierzga
    Joined: Dec 2008
    Posts: 4,862
    Likes: 115, Points: 0, Legacy Rep: 1180
    Location: spain

    michael pierzga Senior Member

    Why don't multis handle anchors off the stem of each hull...then snub to centre line ? I can understand that weight forward in the hulls is not desirable but the versatility of two anchors, spread by the beam width, must be great. Breast anchoring, when you set the anchor, then go alongside is a very typical manoeuvre. The breast anchor keeps you off the seawall tidal range, clear of wave wash and is a very effective " bow thruster" when breaking off the dock with a beam wind.
     
  2. Paul B

    Paul B Previous Member

    This shows a basic lack of knowledge of racing rules.

    Most organized races are run with requirements for participants to conform to, such as the ORC Special Regulations for whatever Category the race is being run under.

    For a keelboat event like the Kings Cup the regs would require anchors, chain, and rode of the correct size/type/rating.

    Anyone not carrying the correct equipment is subject to disqualification, so pretty much every serious racer complies. In the old days the anchor size and location was noted on the rating certificate, as was the length and size of the chain.


    It is easier to bring along heavier tackle to be left as semi-permenant mooring during the day's racing rather than use the required equipment each night and have to pull it, clean it, and stow it every morning. Race boats do not have chain lockers, windlasses, or hoses to easily deal with tackle before each race.
     
  3. michael pierzga
    Joined: Dec 2008
    Posts: 4,862
    Likes: 115, Points: 0, Legacy Rep: 1180
    Location: spain

    michael pierzga Senior Member

    Gee Paul, I raced yachts for many years. We never carried 100 meters of chain, anchor winch, stem roller and correct ground tackle. Never..all gear was minimum required...aluminum anchors short length of chain and rope.
     
  4. Kojii
    Joined: Oct 2006
    Posts: 60
    Likes: 4, Points: 8, Legacy Rep: 45
    Location: Ensenada, BCN

    Kojii All is remodelling

    That's the nice thing about aftmast rigs. They never run aground due to dragging ground tackle because the aftmast keeps the owner from leaving the boat when he shouldn't do so.
     
  5. pbmaise
    Joined: Jul 2010
    Posts: 115
    Likes: 5, Points: 18, Legacy Rep: 80
    Location: Cebu the Philippines

    pbmaise Senior Member

    Aft-Mast Design

    Guys Please - Back on track
    In fact it might be good if a moderator moved all this nice chit chat about anchoring to a separate forum. We are here for aft-mast design consideration and I want to get some input.

    I am fortunate to be here in Miri Malayasia where several other sailors and fellow engineers have been going over the failure of my mast.

    Brian--You might be happy to learn your name was mentioned by Peter of Tigger. His cat is a Bermuda, however, word of what we are up to is spreading fast in the sailing community.

    My initial conclusion was side support. However, I now believe it was a matter of:

    C>>>>>O>>>>M>>>M>P<R<<S<S<<I<<<<O<<<<<N

    Lets review the events within 24 hours of the failure:

    Aboard the sailboat I had a mono-hull sailor who was very uncomfortable with the amount of play in my mast. He was used to masts that stood completely rigid and had very small movement. So it was largely at his instance that I began the following changes:

    1. I moved the sail from the 67 ft mark down to the 50 ft mark.
    2. This freed up the block at the 67 ft mark. Rather then leaving it empty I led a line from the bow over the block down to the base of the mast.

    Now I effectively had two lines to the bow I could tighten on a winch.

    This in turn directly resulted in my forward leading side stays to become slack.

    3. So I retightened my forward leading side stays. These were stays tied to two chain plates 17 ft in front of my mast on the two ama.

    Items 1-3 greatly increased forward pull on the mast which was off set by the back stays led over the back spar.

    4. To compound matters, for the first time I tightened the back spar tension lines using the power of a winch. That back spar and line was designed to prevent the mast from moving forward, which means it could add a tremendous pull backwards.

    All 4 changes added more compression. Yes the mast was stiffer, however, too stiff is what we collective concluded. As part of the argument Peter asked where the break was and did the rigging fail. The break was at about 29 ft and I inspected all rigging and found zero failures. Peter response was COMPRESSION.

    Live and learn.

    I'm a strong advocate of keeping the forward leading side stays. These stays enable me to completely remove the combination forestay/halyard. However, as you can see in the above analysis they are interactive. Tightening the forward leading side stays loosens the forestay which in turn leads you to tighten that even more. Then you have to go back and tighten again. Each time adding compression.

    I have already hinted about my line of thought to correct this situation. When I mentioned it to a sailor here from Spain he was so excited. He saw masts like these when he was a kid.

    In the vast collective years of experience among you guys...have you ever seen a mast with a curve?
     
  6. brian eiland
    Joined: Jun 2002
    Posts: 4,955
    Likes: 181, Points: 73, Legacy Rep: 1903
    Location: St Augustine Fl, Thailand

    brian eiland Senior Member

    Absolutely, used loose diamond wires all the time to allow mast bend (big bend) on Prindle 19's, Tornados, Hobie 18's when in combination with rotation. Here is one reference:
    http://www.hobiecat.com/forums/viewtopic.php?f=34&t=4344

    You could find many more such references to bending the mast into curves to control sailshape for various wind conditions. So yeah, lots of 'curved mast'

    The problem I am have in trying to evaluate your rig is I have NO definitive dwgs of what your rig looks like, and where each rigging piece is located. You talk about this 'new rig' of yours without proper definition. And I think you have deviated so far from my aftmast design that there are no comparisions to be made, other than the fact that you've placed the mast at the aft end of the vessel, and have some sort of long slopping forestay (I think?). Give us some dwgs that we can relate to if you wish for someone to comment on it with any intelligence.
     
  7. Kojii
    Joined: Oct 2006
    Posts: 60
    Likes: 4, Points: 8, Legacy Rep: 45
    Location: Ensenada, BCN

    Kojii All is remodelling

    I don't know much about rig design. I'm a geographer by training.
    The following is based on my experience and conjecture, which I am fully aware of - so please everyone, let's skip the pissing contests and talk about ideas. The curved mast idea is interesting. Ours is a wishbone mast - two curves - forming a catenary or quasi-catenary arch with a pole on the top of the catenary to reduce windage/weight aloft. It is already bent so it is not being pulled and twisted at points along the span to keep it straight - contrary to all the dynamic forces on it which are effecting to bend it. The arches spread the tension/compression along the entire arch, or nearly so, rather than focus it on points of eventual failure (29 ft up). If it has built in modulus sufficient to sustain the vagaries of wind and wave action and is built expertly enough you should see it moving within the limits of the material/construction and that is actually a sign of it's ability to absorb and/or distribute stress. Like the overstressed and therefore rigid sail that blows out in the storm, the rigid mast breaks at weak points. One logical approach therefore is to reduce the number of stress points to zero (impossible) or increase the number of stress points infinitely and in so doing reduce the "weakness" value of each point along the arch below the critical threshold.
    Spendy, hand laid, time-consuming project. Ours is carbon/kevlar co-fab triaxial with a glass wrapper for protection using Cargill Hi-performance resin. It is 20 years old this year and so far...no outward signs of failure/overstress, and we have been tough on it. I have said this all before in this forum, but like Brian I figure someone might be willing to step out of the box for a minute. Hope this is fruitful for you.
     
    1 person likes this.
  8. pbmaise
    Joined: Jul 2010
    Posts: 115
    Likes: 5, Points: 18, Legacy Rep: 80
    Location: Cebu the Philippines

    pbmaise Senior Member

    Curved Aftmasts Estabrook and Wear Bridge

    Aloha Brian and Kojii
    Thank you for your replies. Essentially I am engineering a solution by eliminating items from the previous design which led to over compression. My thoughts are a curved mast that is curved in line with hull and not the beam. I've done a lot of web searching and sure enough found others that have had thoughts along my line. The photo below of Wear Bridge shows a curved structure that first leans backwards before curving around to lean forward. This type of configuration would eliminate the backspar. Digging digging I found a very interesting design by David Estabrook. Photo attached.

    He even has a patent on it.
    http://www.freepatentsonline.com/6662738.html

    Notice it is an aftmast design and as of yet we have not mentioned his name anywhere in this forum. Has anyone seen a working rig of his?

    One thing I like about this curved mast idea is the possibility of adjusting the CE ratio. I envision a track at the top of the mast which I can move to change the horizontal location of the halyard attachment point. Moving the CE ratio forward on my boat is important for downwind performance.

    Phil
     

    Attached Files:

    1 person likes this.
  9. brian eiland
    Joined: Jun 2002
    Posts: 4,955
    Likes: 181, Points: 73, Legacy Rep: 1903
    Location: St Augustine Fl, Thailand

    brian eiland Senior Member

  10. brian eiland
    Joined: Jun 2002
    Posts: 4,955
    Likes: 181, Points: 73, Legacy Rep: 1903
    Location: St Augustine Fl, Thailand

    brian eiland Senior Member

    Attached Files:

  11. Kojii
    Joined: Oct 2006
    Posts: 60
    Likes: 4, Points: 8, Legacy Rep: 45
    Location: Ensenada, BCN

    Kojii All is remodelling

    Materials had to be invented to make Montgomery & Bolger's vision come to fruition in the aft mast designs of the last few decades. What materials are available to make an aft mast that hangs out over the deck and does not flex from the weight of the wind in the sails? Boeing just built a new airliner with carbon spars in the wings. We watched it's shakedown flights over the Straits. Considerable flex in those wing spars. If it did not flex it would snap or have to be so heavy as to lose it's raison d'etre - economy. Incorporate flex into your design. The one recurrent (and spot on) criticism of the aftmast rig is the increased tension needed in the forestay due to the angle (not the length) of the stays. Our rig has a flexible spar on top of the arch. We can crank back on the big back stays to bend the spar to get the proper forestay tension because the materials allow such bending. This is more similar to a longbow (the sail would be the arrow). Racers have this bend successfully of course many decades. Bending the mast forward seems to be predisposing it to sag forward and poor performance. Without proper tension the rig sails poorly. With proper tension it snaps to attention and scoots. Brian worked out the tensions in a previous postings I am sure you have read. I was impressed by the marginality of increased tension required and that has been my observation. Small increments of increased tension have large refunds in performance. With the curved stick it does not all go into compression. With a longer foot and shorter stick you can accomplish a lot in light air without wasting a lot of sailcloth aloft. Experimentum periculosum.
     
  12. brian eiland
    Joined: Jun 2002
    Posts: 4,955
    Likes: 181, Points: 73, Legacy Rep: 1903
    Location: St Augustine Fl, Thailand

    brian eiland Senior Member

    Lifting of Bow on new AC45 Catamarans

    Just happened across this very recent reference to a 'lifting' situation.

    SW: How does she perform downwind, is it a matter of sheeting in and hanging on?

    Murry Jones: It was actually easier with the gennaker up than with the wing alone, because we had more lift in the bow. We are pushing the bow down a little when we are wingsail alone. Not that it is dangerously at all. But when the gennaker was up, it was really comfortable. It feels very good in that respect.


    http://www.sail-world.com/USA/index.cfm?SEID=2&Nid=79491&SRCID=0&ntid=118&tickeruid=0&tickerCID=0
     
  13. brian eiland
    Joined: Jun 2002
    Posts: 4,955
    Likes: 181, Points: 73, Legacy Rep: 1903
    Location: St Augustine Fl, Thailand

    brian eiland Senior Member

    SODEBO Trimaran

    Sodebo almost pitchpoles at start of singlehanded race. Thank goodness she didn't have her full mainsail up.

    I particularly like this photo of her with her rig set well back on the boat, and sailing under a three sail combination.

    ...more photos and a video of the wild ride here:
    http://www.sail-world.com/index.cfm?Nid=79811&refre=y&ntid=118&rid=4
     

    Attached Files:

  14. brian eiland
    Joined: Jun 2002
    Posts: 4,955
    Likes: 181, Points: 73, Legacy Rep: 1903
    Location: St Augustine Fl, Thailand

    brian eiland Senior Member

    Frame Structure Suggestion for Stiletto 23 Experiment

    I thought I had posted this rough sketch of a suggestion for a temp frame structure for this fellow's Stiletto 23 experiment...but apparently I had not...so here it is.

    I had another fellow asking about such an experiment using a Hobie 16...NOT a good candidate for such an mast aft experiment....even worst than Stiletto 23.
     

    Attached Files:


  15. Pericles
    Joined: Sep 2006
    Posts: 2,006
    Likes: 133, Points: 63, Legacy Rep: 1307
    Location: Heights of High Wycombe, not far from River Thames

    Pericles Senior Member

Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.