Conference unifix::sailing

    Ok, I have added the keyword rigging, as it seems to be most
    appropriate for this questions.  Stability might be better but
    it is not in the keyword list.
    
    Jeff
    

The mast adds significantly to the boat's roll moment of inertia. 
Without the mast, the boat is thus more likely to be capsized.

Alan

re .1:

I deleted the keyword rigging, added the keyword boat_design, and set 
the note back to write.

the Moderator

re .2:

The weight of the rig raises the center of mass. By lowering the center of mass,
dismasting improves righting moment, especially once the boat is knocked down. 

I think this is a "it depends" question. For example, the clipper "Pride of
Baltimore", which capsized in 1986, reportedly due to poor stability, would
probably have been less vulnerable without her rig. On the other hand, on
a more stable design, the moment of inertia might be the overriding factor.

--RS

    I once spoke to a sailor who had sailed on the old schooners around
    here.  We were speaking of this type of situation and his take was that
    if a schooner was in a storm and lost her masts, that was the time to
    abandon ship.  Up to then he described the boat as being like a
    pendulum under the top of the mast and that the mast helped her stay
    upright in spite of the higher centre of gravity.
    
    re. .2 isn't it the case that while the righting moment would be better
    on an unmasted ship, this is only important when the capsizing moment
    has passed it's critical point ?  I guess that is more humour than
    physics though.

Actual life is a lot more complex than the simple physics questions:

Certainly Alan's observation about roll moment of inertia implies that a
schooner without masts will start rolling a lot. Since these were cargo
carrying ships, the likely consequence is shifting cargo, and all manner
of associated life-threatening problems. In addition, pieces of the masts will
still be attached to the ship through the rigging, and moving around in
highly unpredictable ways. It's not surprising that a sailor might prefer
a lifeboat under these circumstances. Of course, the water temperature
might play a role in his decision as well...

Then again, even among schooners, dismasting is a lot more common than outright
sinkings.

I think you've got several different scenarios here,
with different possibilities, depending on the size of
the seas and whether or not they are breaking.

The crucial issue in most cases will be the extent to
which the seas excite the boats roll, and how closely
the wave frequency matches the roll frequency. With
the boat dismasted, and the roll moment of inertia
reduced, the roll frequency goes up. If the sea state
now more strongly excites the roll (if the frequencies
more nearly match), the boat will be more likely to
capsize. Also, with the roll moment of inertia reduced,
the energy to roll the boat to its capsize angle is
significantly reduced, and once again the possibility
of inducing critical angles of heel goes up. And another
contributing factor is that any damping of the roll
by air resistance of the rig (significant for fast
rolling) is now gone, so some of the means of dissipating
roll energy is gone. All this adds up to an increased
likelihood of reaching a capsize angle.

In addition, the boat is going to be much more
uncomfortable, with roll angles and angular velocity
increased. If nothing else, it's going to feel a lot
worse.

This is mitigated by the fact that the critical angle
should increase somewhat with the lowering of the
center of gravity. The weight of the rig is not great
(say 300-400 pounds for a 35 foot boat), but the lever
arm is the longest of any mass in the boat (say 22-25
feet, about 6-10 times the arm of the ballast). This
will have an effect on the critical angle (note the
effect on moment is linear and on roll moment squared,
so the loss of roll moment outweighs the reduction in
heel).

The main consideration here is the dynamics of the roll,
not the statics, and they're not good, but I would guess
for most boats that pass good offshore stability criteria
that they are likely to remain upright but very
uncomfortable. A dismasted boat which is capsized is
also more likely to turn upright again (as the inverted
stability is less), and if caught inverted will suffer
less flooding before inverted stability vanishes.

Boats in breaking waves may do either better or worse.
A gigantic breaking wave will find the boat acting
more like a raft, and thus more likely to go over.
Depending on keel configuration, some boats may be a
little more likely to remain upright (someone who is
ambitions can figure out what Marchaj would say about
this). At least a dismasted boat is less likely to
be caught in a knockdown by the rig in the water. 

Ross Faneuf
Once a naval architect, but now it's all intuition

    According to my Westlawn naval architecture text the dismasted
    boat is considerably more likely to capsize because the leverage
    and inertia of the rigging resists the roll when the boat is 
    suddenly struck broadside by a breaking sea.  The leverage of
    the rig on the boat is suprising, on the order of 115,200 ft lbs
    with a 200 lb mast with a gyradius of 24 ft. 200 X 24 squared =
    115,200 ft lb.
    
    Obviously there will be cases where the dismasted boat remains upright
    while another similiar boat with rigging intact gets capsized in the
    same storm.  There are many variables.  The base note states the
    question in the theoritical context of IDENTICAL BOATS IN THE SAME
    CONDITIONS which is of course impossible.  The question was asked
    to illustrate the TENDENCY of a dismasted boat to more likely capsize
    than a rigged boat.
    
    Jeff

I've never read the Westlawn texts, but it sounds like the terminology
is a little confused. Your numbers are the usual ones for computing
the computation of the mast to the roll moment of inertia. The 'leverage'
I would to mean the roll moment contribution of the mast (mass times
gyradius), but that CONTRIBUTES to the roll rather than resisting it 
(unless your mast sticks out of the bottom of the boat :=)).

Ross Faneuf

    It would contribute to the roll once the roll was establish and the
    boat was trying to slow down to roll back the other way.  I think
    the point is that the mast creates INERTIA to the initial roll, which
    in the case of a breaking boarding beam sea allows the boat to 'buy' time
    resisting the wave until the wave is past.  The idea is that the wave will
    pass before the boat has TIME to roll over because the boat has been
    slowed in its roll by the inertia of the rig.
    
    Jeff

There is a lengthy and quite technical discussion of this question in 
chapter 14 of Marchaj's book "Seaworthiness: the forgotten factor". Even 
if you don't fully understand the mathematics, Marchaj's arguments are 
comprehensible.

Some of his views:

"..... all agree that the probability of capsize increases with 
decrease in roll moment of inertia, i.e, broadly speaking, with decrease 
in size of the boat." [Dismasting also decreases roll moment of 
inertia.]

"..... the capsizing process is largely, but not entirely, a contest 
between the wave impact moment (which tends to knock down the boat) and 
her inertia (which resists this action)."

"..... the displacement/length ratio of boats of identical length (LWL) 
may vary by a factor of five or even more. As a result, a heavy 
displacement type of yacht may have as much as five times greater roll 
moment of inertia than that of an ultra-light displacement boat of the 
same length."

"..... a boat in a gale is likely to encounter a number of waves having 
enough energy to capsize her ..... the boat which has lost her mast and 
rigging becomes more vulnerable to a second capsize ....."

"..... beam was found to be 'the most significant parameter in its 
effect on capsize'." [That is, the greater the beam, the more likely 
capsize becomes, and, the greater the beam, the longer the boat is 
likely to stay upside down.]

So it would seem that modern beamy, very light boats with light rigs are
significantly more likely to be capsized than narrow, heavy boats. All
in all, Marchaj's book is very sobering reading and should be studied
closely by anyone contemplating buying a boat for offshore sailing. 

    "The wider the beam the more likely the capsize"!!!  Seems as if a
    narrow beam would make it more likely, but I guess the book says no?
    For example a canoe which has a narrow beam is extremely likely to
    capsize.  The metacentric height/CG  also plays a big role and I
    suppose with a canoe vs a sailing yacht we are comparing apples to
    oranges they are so different.
    
    Jeff

(Alan please correct my memory as required).

I remembering Marchaj's analysis without the book in front of me, but here
goes anyway...

Roughly speaking, the 'beamier' a boat is (basically decreasing length/beam
ration), the more it behaves like a raft or a flat piece of wood in the
wavers. That is, the more the boat tends to remain parallel to the water
surface as waves pass by (that is, the wave surface). Any such boat
encountering very large breaking or near-breaking waves will tend to follow
the wave surface as it curls and breaks, and thus capsize. Boats with smaller
beam (and, hopefully, a high roll moment of inertia) will tend to resist
this and not capsize.

In some ways, the worst case is a multi-hull, which combines relatively
low roll moment with a very pronounced tendency to follow the wave surface.

A more technical way to think about it is to consider the initial stability,
and look at what contributions are made by form rather than weight.
Multi-hulls and dinghy-style (beamy) modern racers try to get as much of
their initial stability as possible from the form (geometry) of the boat -
to get significant buoyancy creating a right moment with as long a lever
as possible (as opposed to traditional cruising boats, which rely much less
on form and much more on lead ballst). Initial stability achieved through
these forms can also be considered a measure of tendency to follow the
wave surface. Marchaj, as I recall, quantifies this, although I've now
forgotten the correct terminology.

So, to bum out those of you who like such boats, you should note that the
forms are well-designed to capsize (and remain inverted) in survival seas.
Thus I remain content with my lead lugger.

Ross Faneuf

In a way, initial stability measures the tendency of the boat to follow the
wave surface. The higher the initial stability, the more likely to follow
wave surface. Multi-hulls and dinghy-type racing hulls attempt to raise
initial stability 

re .11:

Remember, a canoe has no ballast (and it is very light). If it did, it
would be much less likely to capsize. Ross' memory of Marchaj (.12) is 
about what I recall.

See also Note 193 on capsizing. 

Alan

Canoes follow the same laws as sailboats - they're all oranges, if you like.
A canoe gets virtually all of its stability from its form, and thus is
quite capsizable in large waves. Here, though, with an open boat, you have
a limiting condition which is very different - the wave size which will
swamp it, or the wind condition which will either make it unmanageable or
blow it over. Anyone operating a canoe in the kind of seas where the
conditions we've been discussing occurs is way, way over the edge of the
envelope.

Ross Faneuf

    Ross is quite right...multihulls are more likely to capsize in survival
    conditions.  If you follow the multihull press these days, there is a
    great deal of attention being paid to drogues and sea anchors, and the
    relative merits of each.  A consensus is forming that a proper drogue
    or sea anchor rig of sufficient strength (a whole-number multiple of the 
    boat's displacement!) and the knowledge of when and how to effectively
    deploy it is absolutely essential aboard any offshore multihull. 
    Interestingly, those multis most easily capsized according to Marchaj's
    analysis are also those which perform best under drogue or sea anchor,
    as they tend to be light and have little frontal area for waves to
    impact.
    
    John.

I would expect a drogue or sea anchor to be helpful for any boat,
including monohulls - thus the prescription to trail a drogue or warps
in the folklore of dealing with survival storms. In fact, if the
multihull world is coming up with numbers and quantified recommendations
I would like to see them for application to lead luggers.

Ross Faneuf

re .15:

This raises an "interesting" question. In conditions in which a drogue
is likely to be needed to prevent capsize, how do you deploy it safely?
One's natural tendency is to have great faith that matters won't worsen
to survival conditions, which will lead to having to deploy the drogue
in probably rather frightening circumstances. 

There is evidence that drogues are helpful in preventing monohull 
capsizes, too, and the deployment question of course applies to them as
well. 

Alan

    We knocked off a few miles a bunch of years ago on a 37 ft Brown
    designed three wheeler.  Leaving New Zealand in the middle of (their)
    winter afforded some interesting opportunities to observe behavior
    under sloppy conditions.  Old monohull sailors all, we learned quite a
    bit about handling the boat as we went along.  One evening we were
    about 50 miles east of Port Moresby  with 30 kts up our tail and a good
    sea running.  We wanted to slow down  to make port in the morning, so
    we heaved a few lines off the stern. Bare poles and still making 6+
    kts, surfing right along.  So we hauled (and this wasn't easy) the
    lines and attached a couple of tires to two of the lines, this time
    using the primaries so we'd have some advantage if we need to haul the
    lines in again.  We slowed to 3+ kts and made our landfall mid-morning.
    We did find the boat tracked very well (even without the tires) and the
    tendency to broach was significantly reduced.
    
    Now these were pretty mellow conditions.  The forces on any drogue in
    survival conditions would be incredible, so you'd need to ensure that
    1) you had something that would actually slow you down and
    2) you had somewhere you could attach the lines and some way of getting
       them in if needed.  We needed power assistance to get bare lines
       back to the boat, and it was very difficult to get the tires back
       even with power assistance.
    
    A few days later, we were in the Port Moresby Yacht Club, several
    sheets to the wind, and the talk meandered around to use of drogues. 
    An old rummy made an interesting point: What happens when your
    resistance is on one side of a wave and your boat is on the other side
    of the wave?  The crude diagram below exaggerates the potential
    problems you'd be looking at.  One of the things I always liked about
    getting smacked by a wave was the ability to yield or roll with it.
    
              /\   |
            +/--\+++++
            /    \
    
    A drogue complicates this situation somewhat.  Yeah, you might not
    pitch-pole, but you are set up for getting your deck swept, maybe
    repeatedly.  Not a particularly pleasant thought on a thin-skinned
    trimaran.  So what we deduced from this temporarily sobering
    discussion was to be darned careful about inducing any significant amount
    of drag using drogues.
    
    Dave

    RE: .18,  
    
    You raise a very importnt point.  Since water within a wave moves in a
    cyclical motion, one must be sure to deploy a drogue or sea anchor to a
    distance that matches 2 or 3 or 4 wavelengths as closely as possible. 
    The goal is to get the drogue or sea nchor to be riding on the same
    part of the wave as your boat is, separated by one or more waves.  That
    way the forces on each are similar, and you avoid having a suddenly
    slack line that can take up very violently as the two try to move
    apart.
    
    This diagram oversimply illustrates the point:
    
                      DIRECTION OF WIND & WAVE TRAVEL
                              ------------->  
    
                   __                __                __
                 _/  \_            _/  \_            _/  \_
               _/    A.\_........_/......\_........_/......\B
             _/          \_    _/          \_    _/          \_
           _/              \__/              \__/              \_
    
             (A=Anchor or Drogue, B=Boat, ....=connecting rode)
    
    J.

    
    	If waves in a storm were that well ordered, I'd try to steer. Also,
    if I'm falling off of a sharp one, I certainly would like the drogue
    NOT to be falling off (read ripping out) of the wave or so behind me.
    Probably just keep adjusting till the violence settles a little. But
    then I've been lucky enough to not get caught in that kind of stuff for
    days on end-
    Scott.

    
    The issue of heavy weather sailing is very interesting and has filled
    books.  An important thing to remember is that what worked in one storm
    may not work in the next- even for the same boat.  As an example, the
    nastiest conditions I've encountered were based on a combination of
    wind, tide, water depth, lee shore (Beating around the north end of
    Great Barrier Island, New Zealand in a trimaran, into a northeastly
    gale with a jagged lee shore and the tide flowing against the wind out
    of the Firth of Thames).  The biggest seas I've seen (a couple of days
    in 55+ kts off of Samoa) were actually fairly well-mannered and
    predictable and would've maybe even been predictable enough to try the
    suggestion in .19 as the periods were regular enough to leave a drogue
    in a relative position- but then because they were predictable *and*
    because the boat (45 ft Block Island ketch) was in no danger, we didn't
    need drogues.  Bare poles did the trick there.
    
    But none of the weather-related conditions I've seen were what I would
    call survival conditions.  Sometimes you're just gonna lose.
    
    Factors to consider, not necessarily in order of importance:
    - Do you have sea room?
    - What's the condition of the seas?
    - What's the experience of the crew?
    - What is the physical and mental condition of the crew?
    - What the sailing characteristics of the boat?
    - What is the condition of the boat and its gear?
    - What is the depth of the water?
    - What is the wind strength?
    - What is the estimated duration of storm?
    
    Strategy changes as answers to each of the above questions varies.
    
    The good news about heavy weather sailing is that the more you do it,
    the better you learn how to read your boat.  Under the proper
    circumstances, and with the right crew, it is an exhilarating
    experience. 
    
    Dave
                          

    The Fastnet Storm of 79 was especially bad according to my reading
    because of the period and steepness of the seas.  The period was
    mixed and the seas were STEEP.  The wind strengh 55-65 knots was
    misleading, in that the seas were far more severe than one would
    have expected.  BREAKING steep seas led to the capsizing of many of
    the vessels.  I also noticed that many of the crews took to life
    rafts.  Later, many of the boats whos crews had abandoned them were
    later found afloat.  That suggests that many of those boats were
    inappropriate abandonded, i.e. the boats were not sinking.  Its
    easy to shoot from the hip as I am doing not having been there, but
    it does suggest that state of mind of the crew is as important as
    the reality of the sea condition.
    
    Jeff

In 1979 I was crewing on a 44 foot ludder yawl.
The boat was a dinasour then... lucky for us.

During a rather nasty bit, a WALL of water from
behind lifted the yawl up rearend first and flipped
the boat upside down. I was throw into a buklhead and
was just a bit dazed as the water began to pour in.
The boat finished with a reverse death role and righted.
Wet, dazed, and black and blue....but alive we managed
to bail our little fingers off and stayed afloat.

It was the closed I had felt to death in my life. I 
figured it was all over for the home team.

Our Skipper  kept his head and we kept our boat.

Seems I will never forget that moment and also
under the most severe conditions I have ever sailed
in out boat made it and still floats today.

I guess thats why, today as a skipper and occasional
profession captain I always have a man-overboard drill
at the beginnig of any cruise and tell this story with
the ending that....
If worse comes to worse.. NEVER NEVER NEVER leave a
floating boat.... Wait until its half underwater and
going fast before jumping into a life raft.. and even 
then keep the life raft attached until you MUST MUST
cut 
the line. Its ok to be worried and get everything 
together and even inflate the raft and tie it off... its
ok to look silly the next morning... I'd rather look
silly with an intact crew and boat,  than, 
 looking cool and dead.

At least IMHO anyway....

					Georgia

				Navigator, & cook
				1979 Fastnet race...

    I also read that boats in the same Fastnet Storm but in slightly 
    different areas faced markedly different conditions.  Boats which
    were over Labadie Bank (shallow water) faced worse conditions than
    the boats over deep water.  This helps explain the markedly different
    descriptions of the storm from different boats.  Where you were in
    the storm and the type of boat you had of course made large
    differences.
    
    The trend of yacht construction in the late 70's was toward lighter
    faster boats (read, light scantlings) and it sure showed that more
    rugged traditional construction paid off under severe conditions.
    Can't have it all I guess, that is, a strong AND light fast boat.
    
    Re. last.  Glad you came out of it ok... must have been quite an
    experience.
    
    Jeff

    
    As Jeff has stated the course and locations did make a difference.
    Also, for instance, our boat was a VERY HEAVY OLD TUB... we were in
    the race mostly for fun and experience.  We didn't stand a chance of
    actually winning. But it *DID* turn out to be an experience...  ;)
    Most of the boats badly damaged were of very light construction and
    had little or no addional reinforcement. A lot of the boats were
    shipped over to the race because they were not built for trans-atlantic
    or heavy weather sailing... Although some of or crew and support 
    personnel flew over, our boat was sailed over from the US. 
    There is still a lot of discussion as to whether or not the race should
    have even been started. Additionally, a lot of boats were abandoned
    and picked up later by other crews that claimed salvage rights....
    The lawsuits went on for years ...  
    
    							georgia

    Even if a little bit late I wish to thank all the contributors to
    this note for sharing their experiences that prove very useful al-
    so to a Snipe would-be racer as I try. You`ve all been very inte-
    resting and useful; really thanks, I anyway learned a lot.
    
    What I would only add is very simple and I hope it will raise a fur-
    ther discussion:
    
    IMHO I don`t think sea and sail were created for speed; offshore races
    should be raced ONLY with really sea-worthy sailboats as I`m still con-
    vinced that sea is and will always be stronger than any kind of boat.
    I think Georgia has stated it very well: maybe a very heavy old tub
    will not win but her crew will probably survive and come back to sea;
    John Rousmaniere was sailing a Swan (i.e. not a typical IOR design) and
    he understood what had happened only when he was back.
    
    Good points I have read about phisical/mental state of the crew and
    the skipper, even if this sails very far from the base-note.
    
    Bye you all and safe sailing.
    
    Arrigo