"split" mainsheet question

Discussion in 'Multihulls' started by aussiebushman, Aug 13, 2015.

  1. aussiebushman
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    aussiebushman Innovator

    Found this old thread at http://www.boatdesign.net/forums/sailboats/mainsheet-systems-41110.html but it did not really address my question:

    On the new inshore catamaran I'm building, cockpit space is tight and the stern needs to accommodate the mainsheet as well as the tiller and the outboard tiller, Headroom under the boom is very limited.

    The main is quite small - approx 8m luff and only 17.5 square metres so other than lacking the convenience of a single place to adjust the sheet and the ability to move the traveller along the track,a "split" sheeting arrangement will be preferable to a track system - see picture

    Does anyone have experience of this sort of system and suggest any reason not to adopt it?
     

    Attached Files:

  2. redreuben
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    redreuben redreuben

    Aah, now, you need to talk to oldsailor7 about the Buccaneer 24 mainsheet. Its in one of the Bucc threads.
     
  3. philSweet
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    philSweet Senior Member

    They are perfectly good, but are are most often found on heavy cruisers that don't require constant sail adjustment. The knock against them would be that they don't isolate the control functions. Meaning, you now have to adjust two lines every time you want to adjust either the "sheet" angle, or the sail twist. This also requires more energy since the two are now linked. For small, light, twitchy boats, a rope traveller and single sheet work better IMO. I would also mention the cost and weight penalty. A pair of 4 part sheets and their tackle will cost a lot more than a 2:1 rope traveller and single 5 or 6 part sheet. There are some cute tricks you can do with them such as set the boat up for short tacking up a channel. Handy if you also have a self-tending jib. You can also set up a preventer going downwind. Most cruisers have one of these, so there really isn't and extra expense for a cruiser. If you decide to go with the split sheet, I recommend you mount 4 hardpoints and use snap shackles on the bottom of the tackles.

    How low is your boom. I understand the rope traveller might not fit. You might need 30" above the deck if the entire thing is a boom-end, 4:1 using fiddles. (assuming 7/16 line and 3" sheaves for the main, 2" sheaves for the traveller arrangement. If you are inclined toward the little micro hardware and 3mm lines, I can't help you with space rqmts.
     
  4. redreuben
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    redreuben redreuben

  5. redreuben
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    redreuben redreuben

    Might need OS7 to translate the text though ! I couldn't read it.
     
  6. PAR
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    PAR Yacht Designer/Builder

    A double ended sheet isn't all that common any more, though some newer designs still use this arrangement. It does mean about twice the tackle and line requirements though. I've seen some with the sheet continuous, instead of two tails. This wouldn't be the go fast setup.
     
  7. aussiebushman
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    aussiebushman Innovator

    Thanks Guys

    Just a few points:

    I 'm only interested in slow cruising, never racing
    The main-sheet tackle will be at the boom end
    That point is about 1400 mm (55") above the cockpit deck level

    BUT - the outboard tiller as well as the steering arm that connects the twin rudders are on the centre-line, one above the other leaving access either side. A conventional traveler would therefore have to run right across the cockpit at seat height and this means climbing over it to get on board or vice versa whereas with a split sheet there is room to get under it and no climbing to get on board. (I have to consider my not too-active lady, also my German shepherd - try lifting that on board)

    Yes, the cost is higher than a single sheet setup but unless someone tells me I'm plain stupid (highly possible) I'm yet to be convinced to go the conventional way

    Please comment

    Alan
     
  8. aussiebushman
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    aussiebushman Innovator

    Par
    Your comment "I've seen some with the sheet continuous, instead of two tails" makes a lot of sense. I guess this means a double block and becket one side, a double at the boom and a double with a cam cleat on the other side. However, surely there would less control than the two-tail arrangement and harder to control a gybe.

    Does that sound right?
     
  9. Corley
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    Corley epoxy coated

    The Lightwave catamarans use a twin mainsheet arrangement which seems to work ok in the cruising context. I went looking for a photo of their setup but was not able to find a clear photo that showed any detail.
     
  10. PAR
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    PAR Yacht Designer/Builder

    Aussie, I've used both arrangements and once you get used to the double tail, it works, but race setups wouldn't bother with this (yep, your assumptions are correct). Personally, I'd use the "up and back" tackle arrangement. This places a blocks on the corners of the transom and a single line reeves through (up to the boom, down to the block, up to the boom, etc.), eventually to land on a cleat somewhere. It's less tackle, a single line, reasonable purchase from the rail and simple enough. On a performance oriented boat, you'll want the traveler, to get a better purchase and sail twist control, but on this cruiser, I'd kiss off the traveler and just use the up and back setup.
     
  11. cavalier mk2
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    cavalier mk2 Senior Member

    Tom Speer described his Chris White system in thread here somewhere and we rigged ours up in a similar fashion. The vang/preventers run out to the beam/ outer hull sides from the boom and back to the cockpit like a double mainsheet but without the tackle. A secondary winch can be used for power but I found it unnecessary, using a continuous line only one cleat was needed. The mainsheet itself is conventional tackle to the centerline, 4 to 1 is fine for my boat. I found it easy to control the twist by positioning the boom with the v/p and using the mainsheet tackle for the power. After a short time the amount of v/p to set became natural. Jibing we found it easy to leave the main sheet out and just pull and brake the boom with the v/p. Short tacking is easier to set than a double mainsheet as you just leave the v/p slack and set the mainsheet. Twist control is excellent, we picked up power over the old conventional vang we used previously. We tested on a cruise and will be keeping this one.
     
  12. aussiebushman
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    aussiebushman Innovator

    Thanks to all of you

    I'm now convinced the "double tail" system is the answer and for cruising only, I can live with the loss of performance.

    I have now constructed most of the cockpit components with 3 mm thick welded angle plates bolted to the corners of the transom and the top with 10 mm eye bolts and keeper plates under them to take the load.

    I'll post some pictures when the project is bit further along

    Thanks again

    Alan
     
  13. cyclone
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    cyclone Junior Member

    I use dual mainsheets on my Constant Camber 23 trimaran. I have nothing to
    compare them to performance wise. I use a continuous mainsheet and two Harken 7:1 sheeting systems (because I had them already). I switched to Salsa rope this year which works better than the old dacron sheets. Jibing and tacking are probably more involved. A sheet bag is planned to tidy things up. A side benefit is that the dual system combined with a topping lift really stabilizes the mast when moored or when running with jib alone. There are no foreseeable plans to change to another system. I think the L7 tri uses dual mains as well.
     

  14. aussiebushman
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    aussiebushman Innovator

    Thanks Cyclone

    Very useful information. I certainly agree with the sheet bag idea to prevent falling over the sheet-ends all the time. Not familiar with "Salsa" though - it may have a different name here in Oz.

    Your topping lift comment is interesting too This is a small trailerable boat where the mast goose-neck and boom will stay in position all the time because they are bolted to a tabernacle. If feasible, I intend to fit lazy jacks to collect and stow the sail, then only the mast itself get unbolted at the hinge. This assumes the geometry works out as planned!
     
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