Conference unifix::sailing

The (I hope) obvious lesson here is that replacing a fitting that failed 
under load with an identical fitting will almost invariably result in 
an another failure. I trust that this time you will replace the broken 
part with something stronger. 

Why, though, is the fitting failing in such light winds? Keeping initial 
costs low by using marginally strong fittings is common practice, but
this is ridiculous. 

Years ago a friend had a fitting on board his ketch which failed under 
far less stress than windstrength alone would indicate.  Turned out he had 
his mainsheet rove through all the boom and traveler blocks, but not in 
the correct configuration.  As a result, significant twisting loads were 
added to the obvious tension loading, and it failed dramatically underway.  
Close examination of the part showed the twisting that had led to it all.

Any chance your leads might be fairer?  Or some analogous alternative? 
Just a thought....

J.

    the d ring is the largest that would fit using the current blocks
    which i should be the factory setup...i will be looking at changing
    that setup..also if the load distribution is correct..
    
    thanks
    jfk

You can dramatically affect the loads on your mainsheet traveller by your
choice of positions for the traveller. If you keep the traveller centered,
and you pull in the sheet all the way, the boom (and sail) has a tremendous
mechanical advantage against the traveller, since the mechanical advantage
for lateral boom motion is proportional to (1/sin(theta)) where theta is the
relative angle between the mainsheet and the mast.

You can avoid this worst-case loading by moving your traveller to windward
and using a looser mainsheet. This reduces the loading substantially,
although it will allow the boom to rise somewhat, so your sail will not be
as flat.

--RS

    Re: -.1  Which is why you have a vang in the first place.  I do,
    however think that any main sheeting system should be able strong
    enough to survive forces greater than you can ut into it by further
    sheeting.
    
    Dave
    
    
    

re .4:

What you recommend will reduce the loading on the mainsheet, sheet 
blocks, traveller, etc. I assume that you are not offering this as a
permanent solution, however. Prudent seamanship suggests that everything
on the boat should be strong enough to withstand whatever load is
applied in whatever conditions are encountered. One should not have to
worry about anything ever breaking because someone could easily be hurt
or killed if something does break. Mistakes can be and are made and
unusual conditions do occur. You cannot depend on always keeping loads
reasonable. The more disastrous the consequences of a failure are, the
more important it is that the failure not occur. 

    This discussion reminds of a rule I heard for trimming the main
    in a good breeze (before heeling becomes a problem):
      
    Put the traveler on the centerline and haul on the mainsheet until
    you think something will break - then haul it in some more
    

    this is my first full year with the boat...the d-ring was one of
    the items replaced after the survey because he found it to be bent.
    when i replaced it i looked for something larger, but i could only
    replace it with the same size ring...it failed 2mi outside the golden
    gate...i thought we checked everything this spring...i will now
    recheck again and again..
    
    jfk

I am inclined to agree with Alan's comments about replacing gear that is too
small. However, I think you need to be careful when making gear changes to
understand the full ramifications of what you are doing.

The D-ring failure is a fairly benign failure, since the ring doesn't fly,
and boom, etc. tend to fly away from anyone that might be hurt. If you
upgrade the D-ring, or some other subset of the mainsheet system, you must
satisfy yourself that you are not simply moving the failure mode to the next
piece of undersized equipment. If some other piece breaks, the potential
for injury may be much greater.

Ideally, you would upgrade the entire mainsheet system to a larger size,
judging from the fact that your existing gear won't accept a larger d-ring.

--RS

re .9:

You make the excellent point that merely strengthening one fitting (the 
D-ring -- which I assume is a D-shaped shackle) may cause another 
fitting to fail. Every fitting must be strong enough. If the traveller 
or mainsheet block won't accept a larger shackle (or D-ring), then it is 
all too likely that the block or traveller lacks adequate strength. 

But I disagree that the shackle failure is not dangerous. People do sit
on cabin tops, and a boom flopping around could well bash someone in the
head. On our boat, we lean against the boom when reefing. A sudden
mainsheet system failure while reefing would most likely result in a bad
fall and possible serious injury. I think that any failure is
potentially dangerous. Of course, some failures are potentially much
more dangerous than others. 

One of the not obvious dangers of sailing is that the loads on blocks, 
shackles, etc, are not well known and one must guess at the loads much 
of the time. Undersized fittings may survive for a time, but since 
strength decreases with fatigue (use), they are likely to fail sooner 
rather than later. Plus, shock loads may be several times static loads, 
and a fitting that is able to carry the static load may fail under shock 
load. For example, the shock loads on the mainsheet system, boom,
rigging, etc from an uncontrolled gybe are tremendous. 

    Somewhat off the subject, Alan's response reminded me of something
    else to remember.  We encourage very strongly our crew to not situate
    themselves on the inside of a vector made by a line going through
    a turning block.  When one of those blow up, inside the "vee" is
    not the place to be.  The forces are strong enough to kill.  Our
    headsail trimmer was seriously injured when the line holding the
    genny car let go and it slid back into his leg.  And that is not
    a complete blowup.  Also, I can't think of a whole lot more dangerous
    than a boom flopping around in heavy air.  How do you grab it to
    control it without high risk of injury?  I guess I'd lower the main
    right away whereever it it ended up.
    
    Dave

    re: .4, "Prudent seamanship suggests that everything
             on the boat should be strong enough to withstand 
             whatever load is applied in whatever conditions 
             are encountered..."
    
    As our moderator himself discusses in other notes, prudent 
    "seamanship" has more to do with understanding your boat's 
    capabilities and then sailing within that envelope.  Otherwise, 
    we'd all be sailing around in North Sea life boats for fear of 
    rogue waves.  Well, not me of course.  I'd take my chances in 
    a stock Catalina with a beefed up d-ring.
    
    ;)

re .12:

I think that the following more accurately reflects my position:

      Prudent seamanship suggests that everything
      on the boat should be strong enough to withstand 
      whatever load is applied in whatever conditions 
      one may reasonably expect to encounter .....
    
The definition of 'reasonably expect' is the problem here, and, as I and 
others have said, depends on one's aversion to risk. I would suggest 
that a coastal ocean sailor should certainly expect, say, to encounter 
sooner or later winds gusting to at least 30 knots and should choose a
boat and equipment appropriately. A coastal sailor should not reasonably
expect to have to survive sailing in a hurricane. 

    I certainly support the comments about keeping people away from
    the `sweep' zone of any item which is liable to break.  I was once
    sailing through Sydney Heads at around midnight when the boom/mainsheet
    shackle broke (Murphy's law).  Anyone standing on deck to leeward
    would have been in a black sea with a badly cracked head.
    
    On a more pleasant note on Thursday I fly to the U.K. to take a
    H. Rassey 35Ft to the South of France. 

    Sorry I didn't get to this sooner . . . on the road and all.
    What year Cat 30 is it?  Is it one with the curved traveller?  They had
    some loading problems a few years back and subsequently went to a
    flat traveler.
    
    I'm trying to picture which "D-ring" you're referring to.  Do you mean
    the one on the traveler car?  I regularly take my Catalina 30 out in
    30 knot winds with no (knock knock) gear failure problems.  I have the
    tech notes for Catalina 30's dataing back ten years.  I'll look through
    them and see what I can find.  If not, there's a guy in Jacksonville,
    FLA who will answer any question on the boat for a SASE.