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Keep the jib to maintain stability in higher winds?

Discussion in 'Day Sailers' started by Shorefun, Nov 2, 2018. Add this thread to a FAQ

  1. Shorefun

    Shorefun

    Joined Sep 5, 2018
    89 posts, 7 likes
    Hunter 170
    US Northfield, NJ
    I was doing a occasional search for a used Baby Bob mast float.

    In a discussion about the baby bob on a 140 a guy mentioned he found the boat was more stable with the jib out but loose. He had furled the jib and went over.

    Can someone explain why? What is happening?
    I have read and think I understand why a boat that is not moving is more likely to go over. I am curious why keep in the jib but loosening the sheets offers a more stable boat.
     


  2. Crazy Dave Condon

    Crazy Dave Condon

    Joined Jun 8, 2004
    6,871 posts, 660 likes
    -na -NA
    US Anywhere USA
    Sail control. I will call if you send your phone
     


  3. BobbyFunn

    BobbyFunn

    Joined Apr 16, 2017
    404 posts, 165 likes
    Federation NCC-1701
    US Riverside
    Sail like a Laser, broach like a Laser.

    The main only scenerio results in rotation around the center of mass versus a balanced "headsail & main as one". Even a luffing jib can pull the boat and counter the main.
     

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  4. Shorefun

    Shorefun

    Joined Sep 5, 2018
    89 posts, 7 likes
    Hunter 170
    US Northfield, NJ
    I understand the balance of Center of pressure vs Center of Mass and maintaining a line under sail. I expect it will be a fun learning experience when I finally get out on the water :) On a nice day I am going to do my best to get the boat in and out of balance so I know the feeling.

    My question is how would this play into the boat more likely to turtle?

    Why would just a mainsail increase the likely hood of the boat going over? I have some ideas, but I am ever curious.

    I will add my degree is in applied physics so I kind of understand some stuff pretty easy.
     


  5. Will Gilmore

    Will Gilmore

    Joined Oct 19, 2017
    3,526 posts, 1,617 likes
    O'Day 19
    US Littleton, NH
    For a sailboat balanced to sail with main and jib, furling the jib throws the balance off such that more rudder is needed against a heavier weather helm. That can result in lift under the boat to windward. Past a certain point of heel, that lift to windward becomes left to bring the keel and rudder out of the water. There may be less sail area up, but under the conditions one might reef the jib in, less sail area is made up for by the increasing wind.

    -Will (Dragonfly)
     


  6. BobbyFunn

    BobbyFunn

    Joined Apr 16, 2017
    404 posts, 165 likes
    Federation NCC-1701
    US Riverside
    I have a minor in economics yet make a living managing databases so i really cant be trusted. :)

    Imagine you could place three lines on a boat.

    One line would be tied to the centerboard and then anchored to seabed on short rode.

    Line two would represent the forces on the main and would be attached to the main in the bottom third, about one third from mast.

    Line three would represent the jib forces and be placed on the jib about one third from leading edge, bottom third. Line two and three are basically attached on the average lifting surface of sails.

    If you pull the mainsheet line only the boat will spin around the centerboard anchor then heel. This is unstable, a backwards arrow. When sailing the rudder keeps the bow opposite the force and the bouyancy of bow keeps boat from flipping head over heels, to some point. The centerboard trips the boat and even too much force can overwhelm bow bouyancy.

    The same experiment but just pull the headsail line. The boat will rotate around centerboad line some, but instead of heeling will be kept up by bouyancy of bow.

    Pull both strings at same time and the main force is countered by the headsail force. There is less rotational force when both lines are twisted together and pulled as one.
     


    Last edited: Nov 2, 2018
  7. BobbyFunn

    BobbyFunn

    Joined Apr 16, 2017
    404 posts, 165 likes
    Federation NCC-1701
    US Riverside
    My kids have a video game called Kerbal Space Program. Players are supposed to make space ships and place them in orbit around the fictional star system using pre fabricated rocket parts.

    My kids and I instead make "space stations" that have sailboat features.

    The main, headsail, and keel are all engines on supports. We can twist the engines into various direction, and place them anywhere.

    Fascinating to watch the orbiting sailboats get into unusual spins and then spin apart in a fantastic high G explosions.

    The designer allow the player to see the center of mass, thrust, and lift before deployment. By managing the lift and thrust and center of mass we can get these to change orbit without too much spinning.
     

    Attached Files:



    Last edited: Nov 2, 2018
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  8. Will Gilmore

    Will Gilmore

    Joined Oct 19, 2017
    3,526 posts, 1,617 likes
    O'Day 19
    US Littleton, NH
    My father told me you can flip if you don't raise the centerboard when going down wind. "What?", I asked. He told me about a time he was crew on a small boat in a race. The owner turned to the downwind leg and failed to raise the cb. They then proceeded to flip over. When I asked my father to explain that, he sputtered and finally said, "I only know we flipped over."

    -Will (Dragonfly)
     


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  9. Joe

    Joe

    Joined Jun 1, 2004
    6,577 posts, 372 likes
    Catalina 27
    US Mission Bay, San Diego
    You're over thinking this. Go sailing asap. Take some lessons. Read a sail trim handbook... you can find a good one right here on SBO written by Don Guillette.
     


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  10. DrJudyB

    DrJudyB

    Joined Jun 25, 2004
    229 posts, 148 likes
    Corsair F24 Mk1
    003 US San Francisco Bay, CA
    The fellow has confused correlation with causation. He capsized when the jib was furled, not because the jib was furled. Furling the jib and proceeding under mainsail alone doesn’t contribute significantly to capsizing.

    Look at a text book on the physics of sailing and study the free body diagrams showing lift and drag from Sails and hull appendages. To understand capsize read how gravity acting on ballast and buoyancy due to hullform create a righting moment.
     


    Last edited: Nov 3, 2018
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  11. Will Gilmore

    Will Gilmore

    Joined Oct 19, 2017
    3,526 posts, 1,617 likes
    O'Day 19
    US Littleton, NH
    And with all the flapping, you might wish the boat just flipped and got out over with.

    -Will (Dragonfly)
     


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  12. DrJudyB

    DrJudyB

    Joined Jun 25, 2004
    229 posts, 148 likes
    Corsair F24 Mk1
    003 US San Francisco Bay, CA
    Hi Will,
    In my experience, rudders stall out and the boat rounds up long before the boat capsizes. Except when a gust hits, the apparent wind moves aft and you don’t ease the main on a dinghy or you don’t let it round up. Or you execute a dinghy racing jibe really wrong. (Been there, done that hundreds of times in 20+ kts on San Francisco Bay)

    And, as for your Dad’s claim that a centerboard will capsize a dinghy on a run, he too has confused correlation with causation. As I’m sure you know, we raise the centerboard while running to reduce wetted surface so the boat is faster. The cb doesn’t cause capsize..

    Cheers,
    Judy
     


    Last edited: Nov 3, 2018
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  13. Will Gilmore

    Will Gilmore

    Joined Oct 19, 2017
    3,526 posts, 1,617 likes
    O'Day 19
    US Littleton, NH
    Yes, Judy. I agree with every point you've made. The planing of the keel/rudder system is something I only know about in theory. I have never had it happen to me, but have heard that it happens. I think the correlaton factor you mentioned is often mistaken for causation because these systems are complex and there are usually dynamics that get ignored or are unseen. For example: One is sailing in high winds and wants to reduce pressure on the sails. They relax the jib and pressure is released so they stand up right again. They then furl in the jib and go over. They have a correlation for a one time event. They forget it was bloody windy that day and a particularly hard gust may have hit them just when the wave action was perfect for going over.

    -Will (Dragonfly)
     


  14. BobbyFunn

    BobbyFunn

    Joined Apr 16, 2017
    404 posts, 165 likes
    Federation NCC-1701
    US Riverside
    Take a peek at this video from the lab.
    Downwind with main only



    Here the keel is removed from a rc keelboat and replaced with wenches as railmeat ;) to convert the hull to a dinghy. The hull spins freely on the floor.

    The imbalance is noticeable. The pressure on the main causes rotation as described in earlier posts. In all downwind scenerios extreme rudder is required to prevent weather helm. The hull naturally wants to round up. Note how if the hull tacks the balance causes an immediate capsize. In a real world scenerio the missing jib causes extreme instability, which leads to "stuff" happening quick. Inexperience crew may be capsizing due to not expecting the sudden changes brought on by rapid changes.

    In this next video we add the headsail back.



    Same wind. I did need to add additional rail meat.

    The hull is much more stable and is almost balanced in a wing on wing configuration. There is still some weather helm but note that the rotation stops at a beam reach.

    In a real world scenerio the jib even though not trimmed creates enough drag to balance out the force on the main. The stability prevent wild swings and makes for better control with rudder. Inexperienced crew can react
     


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  15. DrJudyB

    DrJudyB

    Joined Jun 25, 2004
    229 posts, 148 likes
    Corsair F24 Mk1
    003 US San Francisco Bay, CA
    @Shorefun
    Are you asking specifically about sailing dead down wind with your sails “wing and wing?”
    Judy
     


  16. Shorefun

    Shorefun

    Joined Sep 5, 2018
    89 posts, 7 likes
    Hunter 170
    US Northfield, NJ
    Judy, I am only taking a comment someone had made and I do not have enough background. He just stated that the boat goes over easier without the jib.
    BobbyFun's video kind of shows that seems to be the case. I am still working through all the concepts and I will probably need to reread the stuff several times till it sinks in place.
    I also have to add that I am still getting my Hunter 170 ready and have barely 2 hours with a lesson I took. So I have no practical experience. I am in NJ so it is getting kind of cold to be out on the water with a 170.
     


  17. DrJudyB

    DrJudyB

    Joined Jun 25, 2004
    229 posts, 148 likes
    Corsair F24 Mk1
    003 US San Francisco Bay, CA
    @Shorefun,
    From my perspective, The video doesn’t reflect the real world. The RC boat is sailing on concrete (no buoyancy from water) and the hull form is too narrow to contribute to stability. And nobody would steer like that.

    From my perspective, the video of a narrow hull without a keel and sailing on concrete is missing some important variables that must be considered in any analysis of the physics of a sailboat’s stability. The crew doesn’t shift its weight to help right the boat. There’s no center of buoyancy to help right the boat because there’s no water. The angle of vanishing stability on theRC without its keel looks to be less than 45 degree. That’s not a realistic representation of a Hunter 170 or most dinghies.

    In the real world the Hunter 170 has a significant of stability generated by the wide fullform. Crew can to move to increase the righting moment.

    To illustrate my point: how often does the RC boat capsize in the water as long as it has a keel. Would it capsize in water with the keel removed with or without t jib. I believe it would.

    I would suggest you look at a technical discussion of stability. For example
    http://www.wavetrain.net/boats-a-gear/471-modern-sailboat-design-quantifying-stability

    One more salient point:

    1. I am assuming that a loose jib means an unsheeted jib. Otherwise this topic would be about explaining why sailing wing on wing dead down wind requires less skill than with just a main in conditions that are dangerous - such as in high winds and swaves that can cause a “death roll”

    2 if we are discussing capsizing after an uncontrolled jibe in high winds, I can assure from personal you that having a flooring jib won’t prevent capsize. Neither will having a sheeted but eased jib. You need to release the main sheet.

    I’ve sailed catrigged boats and unballasted sloops for decades and raced them too. I seriously doubt that there’s much validity to the claim that an unsheeted jib makes a a significant contribution to stability.

    That’s my story and I’m sticking to.

    Judy

    Ps. Please note that I am not arguing that a novice can’t capsize a Hunter170. He can if he steers the boat through an uncontrolled jibe with the tiller locked over, and stays on the low side, all in strong winds . One can, of course, capsize a Hunter 170, but you gotta do a lot of stuff wrong to do it, like sail in high winds before you learn how to do a controlled jibe. And if the skipper is doing that many things wrong, s/he shouldn’t count on an unsheeted jib to save him.
     


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  18. BobbyFunn

    BobbyFunn

    Joined Apr 16, 2017
    404 posts, 165 likes
    Federation NCC-1701
    US Riverside
    The keel for the RC model was removed and replaced with wrenches on one side only. When using both sails an additional wrench was inserted in the battery area. You can see them on the videos.

    The rig is set up for starboard tacks. When the rig tips over too much its unrecoverable. When the wind changes to port the rig flips because the "crew" doesnt change sides.

    Bouyancy isnt really part of the test, but the rig spins on what is pretty much right where it spins in water (with the keel).

    The test is actually accurate. I sailed that for years in all sorts of innappriate rc weather. Its important in that boat to manage the mainsail size per wind. The jib almost is never reefed. This test matches the real world on water in that i need to adjust the joystick rudder trim to compensate for weather helm as i change tack. Wing on wing is somewhat stable, but as soon as a jibe happens the rig spins to beam reach. If i sheet in, the jib dominates and if im not careful the rig is locked in an upwind tack. If this happens too often i put a smaller main on. This weakens the jib to have more control.

    The real lesson when i watch those vidoes is to go upwind and downwind with both sails. Fractional rigs without an asymetrical spinnaker are incomplete half-a$$ arrangements.

    If single handing...get a keel. My rc boat with a keel has a better chance of sailing to the Azores than my 170.

    The 170 is not stable at all. If i sit on the corner of the cuddy cabin by the jib sheet cam and lean back, its over in about 2-3 seconds. Thats not hyperbole.

    My friend was out with me on slow afternoon. The topping lift was too tigjt and interferring with the battens. I gave him sheet control while i jyst let the rudder go lose. The boat changed direction and heeled unexpectly for the guest. His immediate response was.."you really cant just take this out by yourself can you, really unstable." He couldve been putting shade on my skillz :)

    I think the dude in the 140 is flipping on main only when not paying attention and in rounding up scenerios. The jib slows down rounding up. Thats the only explanation.
     


  19. Will Gilmore

    Will Gilmore

    Joined Oct 19, 2017
    3,526 posts, 1,617 likes
    O'Day 19
    US Littleton, NH
    This is, in fact, a very increasing and important discussion to sailboat handling.
    Judy points out that the RC model doesn't represent actual sailing conditions. True. It does, I think, illustrate a condition that shows how a lack of jib effort can make some boats less stable.
    If this discussion is limited to the 170 and/or the 140, then the model is not helpful. However, for the purposes of answering the question posed about how a boat (in a generalized concept) could become more unstable with the jib furled, the model, at least, illustrates that such a condition can be the case. I don't think it explains it, but it does suggest it is feasible.
    Keep in mind, the 170, as Judy points out, is a wide boat. Width adds to inherent stiffness and initial stability, but when a wide boat heels, the keel or CB has more tendency to come out of the water because the center of flotation moves outboard. This means a greater chance for planing the foil under the boat and increasing the heeling moment. It would be a different story with bilge boards or lee boards. Boat shape and configuration has an affect.
    I honestly don't believe the 140 or the 170 is significantly more likely to flip without the jib. I suspect there is a factor more related to the captain at work, but I also think there is reason to believe the idea has merit.
    I would like to hear from more sailors and would be interested in reading what @Jackdaw has to say on the subject.

    -Will (Dragonfly)
     


  20. DrJudyB

    DrJudyB

    Joined Jun 25, 2004
    229 posts, 148 likes
    Corsair F24 Mk1
    003 US San Francisco Bay, CA
    I'm going to give some real world examples of how to loose control of your boat while sailing below a beam reach. These happen so often that sailing instructors and racing coaches teach how to prevent, anticipate and respond to the situation. In all my 55 years of sailing and 30 years of accumulating technical expertise in sailing, I've never seen any discussion this "loose jib" technique for preventing capsize. I infer from that information that it must be rare.

    Here's the gist of some very well known advice about how to prevent and regain control of a boat if you lose control while sailing below a beam reach.

    On a broad or deep reach, if you are fighting the helm to stay below a beam reach, the mainsail it trimmed too tight or you have too much mainsail area. There will be a lot of pressure on the helm, I would suggest you need to ease the main so you can steer your course, especially on a fractional rig with a big mainsail and a small jib, or a cat-rigged dinghy. If easing the mainsail and vang dont reduce weather helm, you should have reefed the mainsail earlier.

    A broach is a scary version of a "round up" that starts while the boat is sailing on reach or deep reach because the rudder loses control. As soon as the boat is on a beam reach, the boat heels dangerously far, the and puts the boom in the water. That pins the boat down, preventing it from rounding up, head to wind.

    It can be caused by the boat heeling so far that the rudder is out of the water, or by a wave that lifts the stern and rudder out of the water or a sudden wind direction change that puts the boat on a beam reach. The time-honored technique to regain control when a broach starts is to immediately ease the vang (if the boat has one) and/or to totally release the mainsheet. This works for both a centerboard boat as well as a keel boat.

    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Below is a article written 30 years ago, explaining what is going on, how to prevent one and how to recover from it if you are pinned down.

    Guide to Avoid Broaching


    By BARBARA LLOYDJULY 11, 1988

    Continue reading the main storyShare This Page
    • archive_feedback@nytimes.com.

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      VIEW PAGE IN TIMESMACHINE

      July 11, 1988, Page 00011The New York Times Archives
      DURING a New York Yacht Club regatta in Newport, R.I. in May, a fleet of racing boats encountered a cruise ship barreling along at about 15 knots. The ship kept bearing down, appearing not to change course. The sailboats had to move fast to get out of the way. And since they were all flying spinnakers, it was no easy task. Several boats broached in a mass of quivering rigs and thrashing sails.

      Other than sinking, broaching can create one of sailing's most hair-raising moments. Broaching is when the boat heels too far to one side, or capsizes. The boat falls on its ear, its bow driving into the direction of the wind. The mast tips sideways, forcing its sails to sweep the water's surface or submerge. A broach can shred sails and toss crewmen overboard.

      A keelboat usually will right itself because the keel acts as a counterweight; a multihull will stay upside down. In either case, there are ways to prevent a broach, or stop it before it gets out of control.

      Steve Colgate, founder of the Offshore Sailing School based in City Island, N.Y., said that students live in fear of broaching. ''It is probably one of the most frightening situations because they don't know how it's happening or why,'' he said. ''Knowledge helps to relieve much of the concern.''

      In broaching, a sailboat usually is moving through one of two points of sail: a run, with the wind coming from behind, or a reach, where the wind comes at the boat broadside. Most often, the boat is carrying a spinnaker and sailing on a close reach.

      On more sophisticated boats, such as those that carry additional adjustments for the rig, Colgate has these tips:
      A wave usually triggers a broach, but it can also come from a sudden puff of wind or change in the wind's direction. When the boat starts rolling from side to side under spinnaker, the next errant wave may disturb the delicate balance between the boat and the power in its sails. If the rudder rises out of the water in heeling, there is no steering left in the helm and the boat sails out of control.

      Preventive measures vary with the size and type of boat, but there are basic rules. Colgate suggests these guidelines: Let out the mainsheet immediately if the boat begins to round up into the wind; keep the boat as flat as possible in the water by having the crew sit on the windward rail; make sure you use the right size sails for specific wind conditions so as not to overpower the boat.


      If you're sailing in conditions that could force a broach - in rough seas or high winds - keep the backstay on downwind rather than letting it run free. This bends the mast and depowers the mainsail by freeing the leech.


      If the boat has a boom vang, release the vang to stop a broach rather than easing the mainsheet. This is a quicker adjustment. It allows the end of the boom to ride up, forcing the top part of the mainsail, where most of the power is in the sail, to fall off to leeward first.

      Select a flat spinnaker for reaching conditions rather than the fuller sail you would tend to use while sailing downwind. Keep the halyard tension tight to keep excessive fullness out of the sail. ''This is not the right time to start playing with halyard ease,'' said Colgate, referring to a racing tactic for getting more power out of a sail.

      Keep the weight of the crew aft in the boat. Weight forward tends to force the bow of the boat down, a condition that can contribute to broaching by creating weather helm - the tendency of a sailboat to turn its bow to windward.

      Richard Konkolski, an offshore sailor who has logged more than 150,000 miles at sea alone, cannot count the number of times he has broached by turning the boat on its side. Konkolski defected six years ago on a boat from Czechoslovakia and now lives in Newport, R.I.

      He pushes his boats hard, but he knows how to be cautious.

      ''You mostly broach because you are carrying too much sail,'' Konkolski said. ''The trick is to keep good control of the sails and good control of the steering. You have to pay full attention to the spinnaker - to the direction of the wind, to the gusts, and to the sea.''

      Konkolski considers the helmsman the most important person on a boat. An experienced helmsman will guide the boat down the face of the wave rather than letting it hit at an angle where the wave will roll the boat. He is then quick to steer back on course.

      A version of this article appears in print on July 11, 1988, on Page C00011 of the National edition with the headline: Guide to Avoid Broaching. Order Reprints| Today's Paper|Subscribe
     


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