Conference unifix::sailing

    On a small boat without a mainsheet travler the amount of main sheet
    tension, and thus the sail shape is restricted.  In other words the
    tighter you pull the mainsheet the more you pull in the sail. When you
    talk/read books by the master racers of our times one point freqently
    becomes clear sheet tension is critical to proper sail shape.  The idea
    with vang sheeting is to use the VANG to tension the main sail.  This
    will allow you to use the main sheet to control sail position. To do
    this you will need an easily adjustable VANG, and alot of
    experientation to get it correct.  This is a grossly simplified
    explaination.  Pick up a good book on dinghy racing for a more complete
    discussion. 
    
    
    Forrest

    
    Adding to .1, the vang will control the leech tension, thus reducing
    (when trimmed in) the 'twist' in the mainsail.  You WILL increase
    overall sail trim efficiency (assuming no traveler) with this technique
    when properly used.  Sometimes, you WANT twist (large seas, swells,
    chop) - sometimes you don't (flat water, good breeze).  That's the
    qualitative analysis.  Quantitative descussion depends upon the
    wind/sea conditions, hull/keel design, pointing vs speed needs,
    and a whole lot of other things.
    
    .1 is right - get a good book and then go try it and experiment
    
    
    

    Without a permanent backstay and traveler, the upper part of the
    mainsail is difficult to control other than through sheet tension.
    Cunningham and outhaul adjustments usually affect only the bottom
    two thirds of the sail.  As the air freshens the top of the main
    needs to get flatter and the angle of attack needs to decrease.
    But when the sheet goes out the sail gets fuller, the boat heels
    and weather helm increases.  Solution - crank on the vang until
    the upper mast bend blades out the main and ease the sheet for the
    best boom angle.  Control the boat in the puffs by easing and
    tightening the mainsheet which will control the boom position.
    The effect is the same as cleating off the main and playing the
    traveller.
    
    One thing to be careful of in heavy air is to let off a bit on the
    vang when falling off the wind.  Otherwise much of the pressure
    on the sail is focused on the vang attachement with a significant
    mechanical advantage due to the length of the boom.  

    Is there a rule of thumb for the placement of the vang attachmnet
    points? I ask because there is this thought in my mind that the
    attachment point on the booom should be 1/3 of the boom's length from
    the gooseneck. I don't know where I gotr that idea and wanted to
    check it our before driling holes in my boom.
    
    What seems to make more sense to me is to consider the triangle
    involved. Is there an optimum triangle? E.G., an isosceles rt triangle?
                           Boom                  
                    _______________________O|<--- Gooseneck
                             B              |
                                            |
        angle obm = angle omb?              | M
                                            | A
                                           M| S
                                            | T
                                      
                                       
    Ed                                 
                                         

    Re. .4
    
    Sounds OK if the configuration of the boat allows it.  More often
    than not OM will be fixed and the question will be how long to make
    OB.  If 1/3 of the boom length is possible without decapitating
    the occupants, terrific.  
    
    It's worth thinking about the hardware at each of the corners. 
    In a breeze the vang fittings will be severely stressed.  A failure
    at any of the points can be genuinely expensive if not outright
    catastrophic.  As OB increases, the ability to control the leach
    improves because the boom flexes less.  However, the force exerted
    by the vang to achieve this control also has to increase because
    of the its diminishing vertical component.  I never thought about
    this when sailing dinghies.  When the breeze pipes up, just crank
    on more vang.
    
    Then I bought a bigger boat.  In the first year, during the last
    race of the season on a typical gusty fall day, I give a yank on the
    vang line during a puff.  BANG!!!  The mast fitting, which is a
    U bolt attached through the long axis of the mast section, rips
    out severing the mast at the partners.  The good news was that the
    mast stayed up until we got back.  The bad news was the insurance
    adjuster wouldn't pay for it.  Then they cancelled me anyway.  
    
    Year two.  New mast.  Improved fitting.  Same conditions, same time,
    same last race.  Puff comes along, I don't touch the vang.  SNAP!!!
    The cheap shackle on the boom breaks.  On goes the spare shackle.
    A no nonsense 1/4 inch stainless steel bullet proof job.  Gingerly
    re-adjust the vang to get just the right sail shape.  But the sail
    still looks a bit baggy so a bit more vang.  Leach is a bit soft
    so just a hair more vang.  RIIPPP!!!  My 30:1 purchase vang has
    liquified the gooseneck and the mainsail which was holding the rig
    together has ripped three feet up the luff.  Then the resulting
    flogging breaks all the battens and tears off all the pockets.  Another
    embarassing tow in.
    
    There are more of these but they're too painfull to recall.  A couple
    of items to consider.  When putting the attachement on the boom,
    try to avoid drilling holes below the horizontal axis.  The bottom
    half of the boom is under tension and any cracks that develope there
    will propagate fast.  For the mast fitting, try to find or make
    one that uses the sail slot as the anchor.  Again, try to keep the
    drilling restricted to the sail slot which is under compression
    and away from the structural section.  A large sail slug or eye
    strap with a backing plate which is slid into the slot works well.
    To anchor the fitting, drill and tap the slug or backing plate and
    put in a machine screw and washer through the sail slot.  Then use
    the cheapest, smallest, imitation stainless shackle available to
    attach the vang itself.  Even better, tie it on with old weather
    worn string.  Makes a great fuse and much cheaper than a new mast
    or boom.  Lastly, keep and eye on the gooseneck.  A little sail
    twist in a breeze will keep it healthy.
    
    Gene Ho

    I seem to remember 45� angle between boom and vang being the lowest
    recommended for block and tackle vangs. Something about the sine
    of the angle between the vang and boom representing the amount of
    the vang tension which acts to pull the boom down. Well, you can
    draw the curve and see the effect the various angles would have
    on a vangs effectiveness.
    
    Walt

A somewhat less convenient way of using a vang is to attach the lower 
end of the vang tackle to a padeye on the deck or genoa track. This 
makes the vang and mainsheet adjustments interact, but, for cruising, 
this isn't too important. On the plus side, the pull from the vang is 
nearly vertical, and if the vang is led forward somewhat it also acts 
as a preventer. We use two vangs, one to port and one to starboard, to 
avoid the necessity of tacking a single vang. Works well.

Alan

    I have been considering how to address the need for a boom-vang on
    Viking Rose.  The boom is quite long and heavy and is connected to the
    Hood Stowaway mast via a robust goose-neck.
    
    I have been considering the use of a hydraulic vang, but I understand
    that the Warner (?) Boom Brake may also be used as a vang.  Any
    comments on advantages and disadvantages of a hydraulic vang vs a boom
    brake?  Incidently, the primary use of the boat is cruising.
    
    Cheers,
    
          Howard

    They're not entirely equivalent products.  The Boom Brake reduces the
    speed with which the boom sweeps across the deck during a jibe.  A vang
    keeps the boom down when sailing off the wind to expose more sail area.
    
    A hydraulic vang uses an integral piston and, usually, a remote
    hydraulic pump to provide the purchase necessary to adjust the boom
    height when there is wind in the sail. It's hard to do this with a
    block and tackle vang unless the purchase is cascaded with a
    supplementary system.  But there are now lots of products that do just
    that.  A hydraulic vang does not dampen the speed of the boom during a
    jibe.  It's not the same as a hydraulic door check.  But it does seem
    like a good idea for a product.  Any enterprising mechanical
    engineering types out there?
    
    The boom brake may be more what is needed for cruising.  It will tend
    to hold the boom down somewhat when the boom is let out.  That's a nice
    little side benefit to its primary purpose of decapitation prevention.
    
    - gene 

re .9:

As Gene points out, the primary purpose of a hydraulic boom vang is to 
flatten the mainsail to gain area when sailing downwind. Necessary if 
you're racing, I suppose, but otherwise I can't see an adequate return 
on the investment. The other use of a hydraulic boom vang (or the 
non-hydraulic equivalents) is to support the boom so that a topping lift 
isn't needed. 

One of the negatives of a strong vang (hydraulic or non-hydraulic) is 
that it is quite capable of breaking your boom. Many/most booms and 
goosenecks aren't really strong enough to withstand the forces of a 
really strong vang. Another major negative is cost. A non-hydraulic vang 
will be roughly $1000 including all the necessary fittings and a 
hydraulic one even more. These gadgets don't even make it onto my "nice 
to have" list. 

The boom brakes (the Walder is the best) are intended to make jibing in
heavy weather safe. I've never used one, but I did talk to the Walder
folks some years ago. The speed with which the boom comes across in a
jibe depends on the tension in the control line. I was unable to get a
clear idea of how critical this tension is. The answer was basically
"experiment". In a jibe, the boom lifts, putting the control line under
considerable tension (strong deck fittings are obviously a good idea),
actuating the brake mechanism. As the wind load on the backwinded
mainsail fluctuates, the amount of braking varies, and the boom more or
less slowly comes across the deck. My understanding is that the brake is
strong enough to keep the boom from coming across at all if that is what
you want. I'm not at all sure that I'd want to depend on the boom brake
to keep the boom from coming across fast enough to be dangerous to a
crewperson in the way. I think that being in the way of a moving boom is
potentially dangerous no matter what. 

On our boat, we use two four-part mechanical vangs (the old fashioned 
block and tackle kind), one to each rail. Thus they function as both 
vang and preventer. They've kept the boom from moving even when we 
inadvertently backwinded the mainsail in a gale (ugh). When reefing, we 
bring the mainsheet traveler car to windward and pull the leeward 
vang/preventer very tight. The boom is then firmly fixed over the cabin 
roof, making reefing the mainsail relatively easy even in very rough 
seas. A boom brake will not keep the boom from moving when reefing.

If I were planning extensive offshore cruising, I'd probably get a
Walder boom brake to control the boom when intentional jibing. I'd still
use our vang/preventer tackles for controlling the boom during reefing
and to prevent unintenional jibes, most especially when anyone is
outside the cockpit. 

Alan

Alan,

since you've tried the "backwinded in a gale" approach :-)

What's your opinion on the relative dangers of a backwinded mainsail
held by a preventer, vs. an uncontrolled gibe, assuming that the
gibe doesn't put crew's heads at risk?

I.e. if you're in the cockpit, running in a gale, is it worthwhile
to go forward to set a preventer? Or should you just keep your head
down?

--RS

    When running in a gale it is most worthwhile to take the main down
    altogether and rely on a small jib (if that) to maintain way on.
    
    If the boat's layout allows it, I like to lower the boom to the deck,
    strap it down, and use it as a handrail.
    
    If, for some reason, the main must stay up, a vang to the rail will
    increase the angle the wind has to shift for an accidental jibe to
    happen.  But be prepared to blow it off instantly.  I prefer to
    tape open or otherwise inactivate the self cleating mechanism on the
    vang and lead the tail to a winch which can be released easily under
    tension.   And keep your hand near the tail!
    
    - gene

re .12:

We always have our vangs/preventers rigged. The lines can be easily 
reached from the cockpit so that there is no need to go on deck to set 
them. That aside .....

An uncontrolled jibe in heavy weather, regardless of the risk to the 
crew, can quite easily cause severe damage to the boat, eg, anything 
from breaking the mainsheet blocks, shackles, or traveler up to breaking 
the boom and bringing down the mast. Backwinding the mainsail with the 
boom firmly held by a preventer is definitely to be preferred to an 
uncontrolled jibe, in my view. 

When running in heavy winds, we always have chosen to run on a broad
reach rather than dead downwind to minimize the chances of backwinding
the mainsail. In big seas the boat will slew off course, and broad 
reaching allows a bigger off course excursion before the mainsail 
backwinds. Though we've not yet been in conditions bad enough to require 
doing so, dousing the mainsail and setting the trysail (which does not 
use the boom) would be a good option. We have also survived running 
downwind in a bad gale with just a reefed working jib set (I described 
this experience in another note). Running downwind on a broad reach may 
require tacking (jibing, actually) if the course you want to sail is 
actually a run. Here is where a boom brake would be very nice. 

By the way, our mainsail is cut so that the boom is above our heads when 
standing in the cockpit. I absolutely refuse to have the boom any lower 
than this. An unexpected jibe is always a possibility, and it doesn't 
take much of a blow to your head to kill you. I am appalled by the 
number of boats (usually of the racing ilk) with mainsails cut so that
the outer end of the boom barely clears the deck or cabin roof. While 
I understand the reasons why it is done, doing so is, in my opinion, 
not a very bright idea. 

Alan

    Alan,
    
    Using your double vang system, what is the procedure for doing a
    controlled jibe in heavy conditions?  
    
         Howard

re .15:

The procedure is roughly as follows. Note that our mainsail is only 
about 200 sq ft. Our preventer/vangs are Schaefer 4:1 vangs, and the 
mainsheet traveller car (not a recent low friction design) has a 4:1 
purchase on the control lines. The mainsheet winch is a Barient #19 
self-tailer. What works for us may not work with a larger sail or with 
different gear. 

Initially, the mainsheet traveller car is all the way to leeward, the 
mainsheet is well eased, and the leeward preventer is tight. 

Slowly ease the leeward preventer and center the traveller car. Continue 
to ease the leeward preventer and bring in the mainsheet on the mainsheet 
winch. If the mainsail hasn't backwinded by the time the boom is
centered, change course enough to backwind the mainsail. Since the boom
will be centered or nearly so, the shock loads from backwinding the
mainsail on the preventer will be within reason. Also, as the mainsail 
backwinds, the mainsheet will go slack and the preventer will now act as 
the mainsheet, which implies that a strong preventer tackle and 
attachment points are necessary.

Once the mainsail is backwinded, slowly ease the now windward (previously 
leeward) preventer until the load in on the mainsheet again. Now ease 
the mainsheet and take up the slack on the leeward preventer. Finally, 
move the traveller car to leeward. 

With some care and practice, all of this can be done by a single 
crewperson on our boat, though having two crew do it is preferable. 
Adding a boom brake would make the process both easier and safer, I 
suspect. The most difficult part of the process is the easing of the 
heavily loaded preventer once the mainsail backwinds, but since the 
mainsheet is well in, even if the preventer is eased too fast, the boom 
can't travel far. It helps to have ample purchase on the traveller car 
control lines also. We've jibed this way with a full main in perhaps 20 
knots apparent and in higher winds with the sail reefed.

Alan