Aft Mast Main Sail type

Discussion in 'All Things Boats & Boating' started by Fanie, Nov 1, 2007.

  1. Fanie
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    Fanie Fanie

    I've read on the forum and some articles about the aft mast sailing method.

    Is this configuration a go or no-go ? Doesn't seem that this is a very popular configuration. There are various reasons I would prefer this, for one you can stop the yacht without turning into the wind, and there are less force on the mast. There is also no boom to smack you up your's if you don't look ;)

    It is also claimed to make more power on a shorter mast and is said to tend to lift the yacht instead of pushing it into the water.

    The sail gets wound up around the cable ? or rod ?, how is this done ? It is, according to the article quick to open or roll a sail up this way.
     
  2. tuks
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    tuks Junior Member

    Rig Info

    I dont know anything about the aft mast rig so I wont comment on that.

    You mentioned "The sail gets wound up around the cable ? or rod ?, how is this done ? This is called roller furling. An extruded aluminium section which contains a track for the sail is attached to the forestay(the wire). The sail is fed into the extrusion. A drum is attached at the base of the extrusion, which houses a line, which when pulled rotates the whole aluminium extrusion which winds the sail up around the forestay/extrusion. There is a swivel at the top.

    Harken is a company that makes rollerfurlers, there should be more information on their website. Harken Furlers. There are a few other manufacturers around that might be a bit cheaper. I dont know I dont own a furler.

    If it is possible to build a freestanding rig, that would be convenient for fishing because you do not have to pass the rod around the rigging while fighting a fish.

    For a new aluminium mast you might contact any number of rigging companies, If thats what you want to do I can refer you to some. If you want to design and build a new mast yourself to bypass that cost, Huletts alumnium has dies for a number of mast sections. I believe they only extrude 100kg batches but they do carry some stock. I think Huletts are the only extruder that has dies for mast sections. They did piss off alot of people a while ago by throwing out some dies that they did not use often. For rigging you probably want 1x19 SS wire. Alex Schon from Texwise Specialises in arcitectural rigging, he can sell you turnbuckles and he has a hydraulic swager.

    Hulamin

    There is some info to get you going on rigs, I will be interested to see if you can come up with some cost effective ideas.
     
  3. Fanie
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    Fanie Fanie

    It amazes me how everyone always tries to improve their performance using the same stuff someone else did before them. Doing the same thing over and over, yet expects different results.

    Since the aft mast is such a hot topic, are you sailing suckers too scared you'd out perform the competition ? Surely the lift the aft mast config with it's lift action alone should count for something. I can immagine a small sporty craft acting as a hydofoil would... without hydrofoils.

    Or is it about what someone else would say if you try something odd ?
     
  4. tuks
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    tuks Junior Member

    I have not heard about the aft mast rig before, it looks like it is trying to replace the bermuda rig mainsail with genoa type sails(Im not sure of correct terminology here). All the documents I have seen describe all the advantages of the genoa/jib type sails and the disadvantages of the mainsail, but they neglect to mention the disadvantages of these genoa type sails and the good points of the mainsail.

    The major difference between genoa and mainsail is how they set off the wind. When the sheet of the genoa is eased, the leech twists open, so the angle of attack at the top of the sail is too wide and at the bottom is too narrow, so only a small portion in the center of the sail is developing efficient lift. The other issue is that when you ease the sheet, the clew moves towards the tack, which makes the camber of the sail much too deep and it is inefficient. The boom on the mainsail allows the camber of the sail to be adjusted with the outhaul, the kicking strap is used to control twist and the mainsheet to control angle of attack. Similar controls are present on the Genoa, but the position that they sheet to is severely limited.

    Some racing boats carry specialised sails to use on reaches because genoas are so inefficient.

    I think that this rig will be good for upwind work but it will not be as efficient when reaching. Sailing upwind is unpleasant and slow and you want to avoid it as far as possible.

    Some other comments

    1)One of the biggest complaints, is turbulence from the mast, this is greatly reduced by rotating wing masts.

    2) The sail shape of a partially furled jib is very full and it suffers from turbulence along the luff caused by the partially furled sail. A mainsail with a reef in it still has a good shape.

    3) The mainsail is a highly tuneable sail, far more so than a jib/genoa. The equipment necessary for this flexibility, the boom, vang traveller, cunningham are described as clumsy and excessive hardware. But remember that to get similar adjustment in a genoa type sail you will need some combination of adjustable jib fairleads, barber haulers, jib cunningham and roller furling. You will still not have the adjustability of the bermuda rig mainsail and most of the clumsy and excessive hardware.

    4) Modern Carbon Fiber masts have flexible tips which bend off during a gust which depowers the mainsail and allows greater sail area to be carried. This is not possible with this rig.

    My conclusion, this rig is good for upwind work, but if you are looking at developing a new sailplan you would get better returns if you looked at rigid wings, rotating wing masts, camber induced sails, or double luff sails.
     
    Last edited: Nov 3, 2007
  5. Fanie
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    Fanie Fanie

    Good grief Tuks, why don't you just use plain English ? I'll have to figure out what it is you're saying. Blimey when left is not left any more eh ! Why all the weird terms ?

    I'll comment back after I've translated. Thanks for going to the troubles.
     
  6. Fanie
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    Fanie Fanie

    Ok, I think I get it.

    Now assume a simple single main sail configuration on a cat, you have one sail. The one uses the standard bermuda ? (the one with the boom) compared to the aft wast jib. If you assume the roller furling of the latter is fixed to boat centre then what you explained could be true - the angle of attack at the top of the sail is too wide and at the bottom is too narrow. Same size sails.

    Now assume one makes a floating roller furling that can be moved either to the port hull, or to the starboard hull. How would this turn out ?

    Another question, if the roller furling is moved more foreward, or more upward, would this improve the angle of attacks ?
     
  7. tuks
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    tuks Junior Member

    Simplified version

    When sailing upwind, the Genoa(foresail) on a sloop rig is very efficient. When you reach you must let the sails out This causes the shape of the genoa to change. The genoa will become very deep and it will twist - see figures. This occurs because the genoa sheet must run through a pulley on the deck. The mainsail is different because the sail is pulled to the end of the boom which can be outside of the boat.

    Twist in the mainsail is adjustable because there is a rope underneath the boom called the Kicker or Vang which pulls the boom down so you can controll the twist in the mainsail. There is some adjustment of the position of the genoa sheet pulley on the deck, but it is much more limited.
    [​IMG]
    [​IMG]

    Ok I see you figured it out already
     
  8. Fanie
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    Fanie Fanie

    Looking at your bottom picture of the jib, the wind from the same angle on my picture, would it work the same as in your picture 1 ?

    If you beat or reach, won't you be able to keep the sails flat in my pic by adjusting the roller furling to port or starboard ?
     

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  9. tuks
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    tuks Junior Member

    Moving the roller furler becomes complicated because that is part of the forestay which is required to hold the mast up.

    The mast aft rig does seem like it will be easy to handle, just expect performance on a reach will be a bit worse than the standard Bemuda rig, but it might be worth is fro ease of handling. I was just trying to illustrate that it is not the perfect rig design, like everything, it is a compromise.

    For you I think the ideal rig would be an unstayed mast, with one sail attached to the mast and boom. You dont have any rigging to hold the mast up that gets in the way when fishing. Also if you want to stop the boat, you let go of the mainsheet(attached to the boom), the sail will swing around and will flap harmlessly like a flag(if you have rigging you cant do this). Your cabin seems high and the boom will be well above everyones head. You can use an boom furling system for the mainsail.

    The engineering on a free standing mast is complicated and you may need to using carbon fiber to build it - very expensive, so I suspect that you will end up with the proven bermuda sloop rig because it is easy to handle and effecient.

    www.sponbergyachtdesign.com/Masts.htm
    http://www.wyliecat.com/
     
  10. Fanie
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    Fanie Fanie

    Ok, this will only work on the cat, which is already faster than your monohull :D I'm thinking of using a single sail on my Boxy Fisher with an aft mast config, basic as showed in my pic. Now if the roller furling is made adjustable as showed, won't it work better ?

    Also, there should be a relationship between the position of the roler furling and the loose end, carrying through blocks may well ease up the wrestling with a big sail.

    Also, won't the cat tend to lean less over toward the starboard side like this, as well as have a more foreward pull from the sail, as well as an upward pull ?
     
  11. tuks
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    tuks Junior Member

    I think that your rig will work fine, keep in mind that I am a have only ever raced boats, not at any super competative level, but small issues with sail trim that bugs me most cruisers will never notice. I think ease of handling, should be your priority rather than max performance.

    I think moving the furler is a bad idea, I need to think about this a bit, but I think it will just make the boat sail sideways through the water when sailing close to the wind, it may help on a reach though. I think you will find that it is going to be difficult to engineer for little benefit. Remember there is quite a bit of tension in the rig and it will load the hulls unevenly and will twist the structure.

    Search for a "self tacking jib", this is a curved track, in a radius around the furler that the loose end of the sail(the clew) attaches to, it might give you some ideas.

    http://www.harken.com/rigtips/selftack.php

    Another idea I always thought would be good for cruising is to put two sails on one furler so that you can sail the "wing on wing" when sailing downwind. Im not sure how it would work. Check it out.

    http://alado.com/manual.htm
     
  12. Fanie
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    Fanie Fanie

    I'm looking for a very basic sail setup, easy to handle and one that can stop the boat as when you're fishing, but it mustn't be pathetic either. The mast must also be light enough to be put up or taken down by two people, but a hand whinch could also be used for assisting with that.

    I'm currently reading the rotating mast pages, very interesting.
     

  13. Fanie
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    Fanie Fanie

    I was thinking, if the aft mast setup is used, using a double sail (two sails rolled up together) one should have double the sailing area if you sail downwind by letting each sail out on different sides of the rolling furler and hold the loose ends on oposite sides of the cat.
     
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