Space between mizzen mast and mainsail

Discussion in 'Hydrodynamics and Aerodynamics' started by sanantonnio, Dec 7, 2017.

  1. DCockey
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    DCockey Senior Member

    On most sailboats the luff (forward edge) of the jib is fastened to the forestay, which is in a fixed position. When the jib is reefed the center of the jib moves forwards, not aft as in TANSL's drawing.
     
  2. TANSL
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    TANSL Senior Member

    It is clear that my drawing is a fudge to the point that I had drawn the bow to the right and you, apparently, have interpreted precisely the opposite. I have tried to draw a very powerful jib to force the CoE forward. But, apart from my mistakes, the variations I have shown in the position of the CoE, can they be close to those that occur in reality and, most importantly, represent an important imbalance for the boat?.
    I'm representing the global CoE, not just the jib. And I understand how you tell me that the jib is reefed. Consider, if it seems appropriate, only the cases of the left and the center, to answer my question.
    I also suppose that in the event of a storm some will prefer to sail with only one sail. But that, I think, takes us away from the case raised by Gonzo.
     
  3. DCockey
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    DCockey Senior Member

    TANSL, with the bow to the right the luff of the jib should stay on the line between the bow and the top of the mast, not move aft.
     
  4. TANSL
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    TANSL Senior Member

    Do you mean somethig like
    Clase-J_08.jpg Clase-J_01.jpg

    Forget, then, my horrible drawing. In your opinion, a movement, forward or aft, of the CoE by, lets say, 8% of the total length, does the ship become very unbalanced?. If this were so, what could we say when the ship sails only with the main sail and, in addition, reefered.
     
  5. rwatson
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    rwatson Senior Member

    Exactly TANSL, you are right. There is NO problem trimming sloop sails.

    Gonzo is just trying to talk up dual mast benefits, and better balance is not one of them.
     
  6. TANSL
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    TANSL Senior Member

    That was what I thought. That is why I tried to do some small calculation that would guide me in this regard. There are many people who make very serious statements without justification and that can lead to very wrong conclusions.
     
  7. rwatson
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    rwatson Senior Member

    Oh, and by way of a PS, lots of boats have two forestays , so when they mount the smaller heavy weather jibs, the DO move the sail closer to the mainmast
     
  8. gonzo
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    gonzo Senior Member

    How do you make the jib halyard get its attachment lower in the mast? The drawing makes no sense. I think you may not have any sailing experience.
     
  9. gonzo
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    gonzo Senior Member

    That is called a cutter, not a sloop.
     
  10. TANSL
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    TANSL Senior Member

    I have very little experience in sailing but I can design boats. According to what you want us to believe, you have experience in sailing, but you can not, you do not know how to design a boat. Given your experience I do not know why you say things, apparently incorrect, regarding the effects of trimming the sails.
    My drawing makes no sense, Ok, I do not care at all but what you said in posts #5 and # 11, does it makes sense or it is a great nonsense (nonsense said by a person with great experience in sailing)?
     
  11. TANSL
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    TANSL Senior Member

    Whatever you call it, what you say in posts # 5 and # 11, apparently, is not true. Could you prove that it is?. Thanks.
     
  12. rwatson
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    rwatson Senior Member

    I think that Post Number 5 is correct. With two masts, you can lower the main to reduce sail, and be well balanced.

    But post 11# " setting a deeply reefed main and a storm jib unbalances the boat horribly. It won't point at all."
    This IS just nonsense, as 1000 racing yachts per weekend prove.

    Reefed.png
     
  13. PAR
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    PAR Yacht Designer/Builder

    All boats, if well thought through in the design process can sail well with various sail combinations, reefs and wind strengths. Sloops and cats tend to get "hard mouthed" in a big blow, even reefed down. If the reef is deep enough, this can be manageable, though often times it's not and sail changes are in order. This is one of the problems with racing sloops; they need a large inventory of headsails to match wind strengths to keep them in the groove. Going to windward on a sloop rigged with a trisail is a butt kicker, though generally a little better with a deeply reefed main and a storm jib. These are two different animals. The trisail is the last option you have before carrying on under bare poles, so you're going to take a beating anyway. I've sailed in hurricane force winds under trisail and it's a hold on a see situation. Your tied to a berth, cockpit seat or tightly strung harness, praying you'll hold out long enough for the wind to abate. Your fear is exhaustion, not so much the boat, assuming you're not seeing seams open up, etc. I've never sailed in these condisions under storm jib alone, as this was just taken in, before the trisail took over the full compliment role.

    Ketches on the other hand are much less hard mouthed in a blow and have many more hoist and shortening options, before fighting uppercuts from the boom as you hoist a trisail. A performance oriented sloop is changing down headsails nearly continuously in building wind strengths over SCA's and this is the real butt kicker in a sloop, unless it's a Tahiti ketch or similar, which doesn't seem to care much about the wind strength until it's 30 knots. Of course, most can't live with the other compromises these offer, like needing 10 knots to leave the slip, a 1/4 mile to make a 180 turn and the speed of a sea horse.

    As a typical production sloop is reefed down, the CE moves forward and down, which is good in a blow, but increases helm pressure, which is bad for a tired skipper fighting the tiller for hours on end. With a short handed crew this means they're carrying more headsail area than they likely need, because it's hoped the pressure will pass by and they'll out live the strain, without having to go up on that foredeck and wrestle with headsail changes. Head sail reefing other than rollers is a challenge for a short handed crew. Crewed boats have less difficulty in this regard and will change down. FWIW, I've never seen an around the buoy's fleet under storm jibs and deeply reefed main, let alone trisails. They call it a day long before these wind strengths and run for shore, under their #5 (or whatever was their bed sheet number was) and a deeply reefed main, cussing about the heavy helm the whole way back, as they sucked the life from the their last downwind beer.
     
  14. CT249
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    CT249 Senior Member

    Gee, I dunno PAR, my experience is very different. As an exampl, I think in my last Hobart (which was rated among the worst 15% by many of the top sailors) we only used three headsails and at no stage upwind, even when the boat was fully pressed under storm trysail, was the helm a two-hand job. In fact even reaching, when a main-only boat is often rather ornery, going across Bass Strait in literally freezing conditions under storm trysail only was actually rather a blast in some ways, much like a high wind dinghy race.

    It wasn't an easy sail - one crew with 7 Fastnet class wins and 200,000 cruising miles (including long spells at the Horn and Alaska) rate the seas as the worst they have ever seen - but the boat was very nicely balanced at all times.

    My current two boats have short overlap headsails and fractional rigs. They've basically got a tw0-headsail inventory; the 105%ers, a "3.5" (ie smaller than a 3, bigger than a 4) plus a storm jib each. On one we just routinely used the 105 up to 20++ knots; on the other we use the 3.5 when cruising because it can be furled. By the time you can't hang onto those sails under max mast bend and vang, with the headsail and traveller both out wide, cruising under main only is easy and fast enough - any quicker and you get too wet from spray.

    The only time I did a deep ocean passage on a ketch, I found that dropping the main lead to an annoying job of furling while standing high in an exposed position. Dropping a headsail, which can be done while kneeling or crawling, seemed much safer.

    YMMV.
     

  15. PAR
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    PAR Yacht Designer/Builder

    Now that's just not a fair comparison. The Hobart is one of, if not THE most notorious sailboat races going. 99.99% of sailors will never attempt anything approaching a Hobart run, though I would, if only to just to say I'd finished. I'll also bet your boat was more carefully setup for big wind, deep water and keeping the crew safe too. If the ketch you were on was setup similarly, you wouldn't have struggled with the main. On my small ketch, I use two side by side topping lifts, which are bungee corded back to the mast when not needed. When released, they capture the battens and the sail all but flakes itself onto of the boom. Additionally 99% of sailors don't do deep water racing either, so it's difficult to make companions. Most are around the buoy types or casual coastal skippers. These boats are setup quite differently and big winds to them, might be a good slosh to windward to you.

    I think we're talking to different things; a quick douse and/or reef to avoid a 1/2 hour of a fast moving squall or a fully prepped and battened down commitment, to a day or two or more of rough deep water work. Boats will be setup differently, likely with many being unsuitable as delivered from the production line and also differ with crew expectations and job requirements. I remember a race to Hawaii a couple of decades ago, where the crew and I made so many headsail changes, we wore out the cheap bags we had some of them in. By contrast, the last regatta I was in, we made no headsail changes, but wind strength only varied by 5 knots across the 5 races. The "jib and jigger" technique is a short term approuch to a small, fast moving system and does keep the boat well balanced, if of typical proportions.
     
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