Aftmast rigs???

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

  1. pbmaise
    Joined: Jul 2010
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    pbmaise Senior Member

    Well guys...2 ANSI 54-3 strain insulators shattered under load and sliced my Dyneema line.

    Next time, 54-4.

    it was working so well and to have a part rated at 22,000 lbs break is upsetting.
     
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  2. RHough
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    RHough Retro Dude

    Wow ...

    The most evolved sail plan came from classes where sail area was limited but rig design was not. Designers were free to have aft mast all jib sail plans or mast in the bow cat rigs. In every case I can find what evolved was a larger main, smaller jib fractional rig.

    These rigs evolved in two person boats. Sail area is easier to manage when set on spars. The spars take some of the load and the control sheets and halyards have smaller loads. Compare the size and power of a headsail winch to a conventional mainsheet winch. In a typical 30 foot masthead boat with near equal Genoa and Mainsail areas the Genoa requires a 40:1 winch to trim whilst the main can be trimmed with a 6:1 tackle.

    It was only after headsail area was rated separately from mainsail area that you saw rigs change. After the IOR rule came into use two things happened. *overlapping* head sail area was rated at 50% not 100% ... A 150% Genoa has 50% of its area overlapping the mast. That areas was "almost free". Masts moved aft so there was more "almost free" area upwind. A secondary result come from the way spinnakers are rated. Larger foretriangles allow much bigger spinnakers without penatly. There is no way that a equally rated boat could have more area with a large main.

    What happened was that the huge masthead rigs on heavy boats generated massive loads. The boats had to be heavy or the rigging loads would bend the boat itself. I've tuned more than one IOR vintage design and set maximum backstay/forestay tension at banana ... the point where more tension just bends the boat.

    Enter the return of the Fractional Sloop with a mast forward main larger than 100% foretriangle. Loads were lower. Fewer and smaller winches were required to handle the smaller headsails. The boats could be lighter and they were easier to sail. They did not require the huge headsail inventories the mastheast/big foretriangle boats did. Even with LESS sail area upwind they were faster. They were faster off the wind too even with LESS sail area.

    All the things that were bad about the large foretriangle IOR boats ... heavy structure to deal with huge loads ... larger more expensive hardware to and huge winches to handle large sails. Sheets on and deck hardware with thousands of pound of load in them. None of it safe, none of it easy to sail, and none of it the right choice for cruising.

    To top it all off a stayed sail has the wrong dynamic response to gusts. Once a boat is sailing at its design speed we call it powered up. More wind does not make the boat go much faster, it just heels a mono, or drives the lee bow down on a multi. This is where the sails need to be de-powered. This usually means making the sails flatter (reducing camber) to control heel and keep the boat on her lines. When a gust hits a stayed sail the load on the sail go up. Something has to give. The stay stretches - adding MORE camber and power just when you need LESS camber and power. This requires you to ease a sheet or make some other trim adjustment to keep the boat on her lines. A sail set on a flexible mast can be designed to have the correct response. A gust hits, the loads go up, the top of the mast bends and flattens the sail below the hounds and opens the leech above the hounds ... drive is maintained and the boat does not heel past her sailing lines. The crew does not need to put their latte down to trim to keep the fondue from spilling.

    The flexible mast fractional rig is a near perfect cruising rig for all the reasons it has proved to be the best racing rig. Most performance for least effort. What wins races works for cruisers too. Get their first ... have a choice of mooring balls. Get there first, be on the mooring for a day or two whilst the others are outside in no wind or fighting a gale you outran.

    For anyone to dismiss what racers to as bad for cruising shows little experience IMO. Racers tend to do things that are efficient and require as few crew to extract performance as possible. On an ocean race extra crew is extra food/water and weight. The same things that make for losing races make for long, slow miserable passages. The same things that win races make for swift, safe, pleasant passages.

    Trying to design out an easy to control low load per unit area sail like a fore and aft rig's main for a high load stayed sail is an interesting pastime. Has anyone ever made it work?
     
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  3. Spiv
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    Spiv Ancient Mariner

    But, the Genoa sheet is on a 1:1, while the mains are all on a on a block and tackle before they get to the winch....

    Absolutely right, nothing worse for a cruising boat.

    That's ok. However cruisers should set their sails for the gusts and let racers sit on the gunwale and dangle their feet....

    Please allow me to disagree here, there is NO comfort in racing and not a lot of safety either.
    Yes, speed is better, that is why we invented catamarans....
    Cats come in all shapes and forms, some are designed to sit in a marina and others to race, however, the latter are not as comfortable.

    Yes, I was in a fun race in Vava'u (Tonga) where about 30 cruisers participated and the winner was a S&S 64 KETCH rig, built in 1968.
    It took line honors in front of all the cats and big monos in the fleet, and they did not have feet dangling on the side either.


    I have a flexible mast and a fractional rig on my 48' cat; square top main etc. etc
    I hate that big main:
    • three men cannot hoist it, I must always use a winch.
    • At more than 120º it blankets the Genoa or the Code 0.
    • Taking reefs is always a task.
    • The boom is a pain, always in the way of something, especially the solar panels.
    I am stuck with this rig because this is the way they build them today because people watch races and they think that is what they want.

    If I had a choice, my rig would be as low as possible and with as many sails as possible, ALL ON FURLERS.
    But that's me....
     
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  4. RHough
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    RHough Retro Dude

    That was my point. A 4 or 6:1 tackle to a small winch allows a person to safely control a larger sail area. Sails set on spars are much better in this respect.

    Completely missing the point. For *any* comfortable angle of sail correct gust response equals less crew work required. Less crew work required equals more comfort.

    Being comfortable does not mean sailing slowly or having a rig that is not capable of good performance. The reason many cruisers have fuel cans lashed to the deck is because they can't or won't learn how to sail well.

    No, you are blessed with a rig that allows you to make statements like "Yes, speed is better, that is why we invented catamarans...."

    Then you would have a slow catamaran. ;)
     
  5. DennisRB
    Joined: Sep 2004
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    DennisRB Senior Member

    No main sheet winch has been needed at all on some boats of that size which have sailed.

    My 43' cat with huge main can almost be trimmed by hand without the winch. The much smaller jib? Forget it. The winches are huge and I already had to re-bed a turning block to the deck for the sheet and increase the size of the backing plate due to overloading*

    * = me thrashing stuff. :p
     
  6. DennisRB
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    DennisRB Senior Member

    I have been there also. Was the race just off the shore near Neiafu? I saw a few fun races there. The way to win in that area shrouded by cliffs would be mainly tactical IMO.
     
  7. Spiv
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    Spiv Ancient Mariner

    It started in Neiafu and ended in one of the Eastern anchorages, 16NM all up.
     
  8. brian eiland
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    brian eiland Senior Member

    Some boats can accelerate to alleviate these extra loads imposed at the head of the sail,....at least multi's,....isn't this purpose of the sail forces...to drive the vessel ever faster.

    And of course if the conditions are extremely gusty, then a little reefing would be called for, and the modern sail materials and roller furling gear should be capable partners here.
     
  9. RHough
    Joined: Nov 2005
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    RHough Retro Dude

    The rig can be designed to store the energy without heeling the boat off her lines. The rig then pumps the energy back into the boat in the next lull.

    Until the hull(s) speed limit is reached, yes you want the boat to accelerate. At some point displacement monos ans multis stop accelerating in gusts and heel more or bury a bow. That is why I pointed out the "fully powered up" condition where a stayed sail rig has the wrong response.

    Modern sail material and in boom roller furling works very well. It keeps the main under control much better than an eased sheet and flogging headsail. Slab reefing is quicker and easier than trying to roller reef a head sail. A well built main has an efficient (low drag) shape when reefed. Very few roller head sails perform well when reefed. Even fewer boats have the gear to properly roller reef a headsail. Roller furling (all in or all out) is common. A proper roller reef is not. A reefed sail should also be flatter. A search for roller reefed head sails will show the variety of solutions attempted to get decent roller reefed shape. A reefed roller head sail has the same aerodynamics as a sail set on a spar. This negates the no mast, clean luff argument for all the sails on furlers. The larger the head sail is the more likely you will need to change down to a smaller one in breeze. It is much more efficient to have a small jib and reef the main.

    This thread was started in 2002 ... 12 years ago. Read the first few posts from tspeer ... nothing has changed:

     
  10. CT249
    Joined: May 2003
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    CT249 Senior Member

    Ummm, if you're going upwind or close reaching and you accelerate to a gust, your acceleration actually increases the apparent wind, rather than alleviating it.

    Secondly, if you get extra forestay sag as the wind increases you're not going to 'drive the vessel ever faster'; you're going to end up with an overly deep sail with an overly tight leach. To drive the vessel ever faster you need a forestay that doesn't get excessively loose in gusts.

    Ever sailed with someone like an AC winning sailmaker/sailor/head of design, and found them inducing extra forestay sag as the breeze picks up? Nope - there's a very good reason that almost all OD classes increase forestay tension in strong winds.

    Secondly, if you reef down in extremely gusty conditions then you are going to be either underpowered or overpowered, or more probably one and then the other. In contrast, with a modern fractional rig you can depower with a tweak of traveller, backstay and perhaps barber hauler. Easing all of these together is less work than rolling in a few reefs.
     
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  11. gggGuest
    Joined: Feb 2005
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    gggGuest ...

    Not quite true, I submit. I reckon we've learned a fair bit more about the amazing things sailors can convince themselves of if they start with enough misconceptions and misunderstandings, and we've learned a bit more about how emotional commitment to an idea can override local evaluation. Sadly the people who've learned least are those who most needed to, and its a shame to see such time and trouble so misdirected.
    Sill, I suppose if the value in recreational sailing is in the journey, not the destination, then there's not much harm in some folks going off on a journey in an odd direction, chasing schools of red herring...
     
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  12. markstrimaran
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    markstrimaran Senior Member

    aft mast with a forward or a stern spar.

    Yes I am still at it. Been very busy waiting for the ice too melt sewing up custom trampoline and a soft top. On my 1/2 scale. I mean 1/8 scale. 14' trimaran.
    The stern mounted spar is some thing I pondered. After looking at crawler cranes. Is this out in left field or what. Any one see a stern " bow spirit". A 20 pound 2" x 4" 14 Guage tube about 8' long. At a 45 degree angle off the transom. Maybe something lighter and springy. Kind of a shock absorber. Sorry I should not of said that.
     

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  13. brian eiland
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    brian eiland Senior Member

    Sorry to think that you are such an expert of original thinking and commitments. I might suggest you look back at this posting, #100

    http://www.boatdesign.net/forums/sailboats/aftmast-rigs-623-7.html#post198608

     

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  14. brian eiland
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    brian eiland Senior Member

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  15. brian eiland
    Joined: Jun 2002
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    brian eiland Senior Member

    And I guess this fellow's bi-pod rig is just no gain in efficiency either....its just not a Burmuda rig I guess.
    And certainly a bi-pod rig is just going to have to much aero drag to be any good :rolleyes:
     
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