Standing rigging - stress calculations
 

"RichH" wrote in message
...
The theoretical calculation is by determining the center of buoyancy,
the center mass of ballast and calculating the righting forces that
would react at the top of the mast ... when the mast is pulled over to
a heel angle of 45 degrees.
You can do the same experimentally by restraining the boat (so that it
can roll unimpeded) and by pulling horizontally (or calculating the
trigonometric difference for other angles) from the top of the mast
until the mast is at a 45 degree angle to the horizontal ... then
MEASURE the stress/strain in the wire (cap shrouds). The induced/
forced 45 degree heel would develope the maximum static loads in the
wire (by the magic of trigonometry).

snipped

It seems to me that to pull the boat over to 45 degrees using a line from
the top of the mast would put a much higher stress on the cap shrouds than
you would get by heeling the boat to the same amount by sail pressure, which
would spread some of the load onto the intermediates and lowers.

Standing rigging - stress calculations
 

On Jan 31, 6:07*pm, "Edgar" wrote:
"RichH" wrote in message

...

The theoretical calculation is by determining the center of buoyancy,
the center mass of ballast and calculating the righting forces that
would react at the top of the mast ... when the mast is pulled over to
a heel angle of 45 degrees.
You can do the same experimentally by restraining the boat (so that it
can roll unimpeded) *and by pulling horizontally (or calculating the
trigonometric difference for other angles) from the top of the mast
until the mast is at a 45 degree angle to the horizontal ... then
MEASURE the stress/strain in the wire (cap shrouds). *The induced/
forced 45 degree heel would develope the maximum static loads in the
wire (by the magic of trigonometry).

snipped

It seems to me that to pull the boat over to 45 degrees using a line from
the top of the mast would put a much higher stress on the cap shrouds than
you would get by heeling the boat to the same amount by sail pressure, which
would spread some of the load onto the intermediates and lowers.

Doesnt matter where the maximum stress comes from ... the shrouds dont
know the difference as they are in reaction to that stress
application. Doesnt matter if windloading heels the boat to 45
degrees or by a rope tied to the top of the mast heels the boat to the
same 45 degrees .... as if the boat is at 45 degrees over the stress
in the wires will be IDENTICAL. :-)

Standing rigging - stress calculations
 

On Jan 31, 1:12 pm, RichH wrote:
... Doesnt matter where the maximum stress comes from ... the shrouds dont
know the difference as they are in reaction to that stress
application. Doesnt matter if windloading heels the boat to 45
degrees or by a rope tied to the top of the mast heels the boat to the
same 45 degrees .... as if the boat is at 45 degrees over the stress
in the wires will be IDENTICAL. :-)

It isn't really required to do this. Under IOR a method was developed
for estimating a yachts stability from small changes in trim angle
when moving a weight a certain longitudinal distance. They are still
pretty good estimators of stability, particularly if you yacht wasn't
designed to fool them. Again, L&E discuss the methods and work and
example.

-- Tom.

Standing rigging - stress calculations
 

On Jan 31, 6:33*pm, "Roger Long" wrote:
I think you'd better stick to filters Rich.

--
Roger Long

Huh?

Standing rigging - stress calculations
 

On Thu, 31 Jan 2008 15:12:30 -0800 (PST), RichH
wrote:

On Jan 31, 6:07*pm, "Edgar" wrote:
"RichH" wrote in message

...

The theoretical calculation is by determining the center of buoyancy,
the center mass of ballast and calculating the righting forces that
would react at the top of the mast ... when the mast is pulled over to
a heel angle of 45 degrees.
You can do the same experimentally by restraining the boat (so that it
can roll unimpeded) *and by pulling horizontally (or calculating the
trigonometric difference for other angles) from the top of the mast
until the mast is at a 45 degree angle to the horizontal ... then
MEASURE the stress/strain in the wire (cap shrouds). *The induced/
forced 45 degree heel would develope the maximum static loads in the
wire (by the magic of trigonometry).

snipped
[Edgar]
It seems to me that to pull the boat over to 45 degrees using a line from
the top of the mast would put a much higher stress on the cap shrouds than
you would get by heeling the boat to the same amount by sail pressure, which
would spread some of the load onto the intermediates and lowers.

Doesnt matter where the maximum stress comes from ... the shrouds dont
know the difference as they are in reaction to that stress
application. Doesnt matter if windloading heels the boat to 45
degrees or by a rope tied to the top of the mast heels the boat to the
same 45 degrees .... as if the boat is at 45 degrees over the stress
in the wires will be IDENTICAL. :-)


I don't think so.... I'm with Edgar


Brian Whatcott Altus OK

Standing rigging - stress calculations
 

ummmmm Im a mechanical engineer and + some other stuff. A long time
ago I used to do stress-analysis for high mobile steel, cranes, etc.
all AIChE stuff (FS=6).

One thing Im 'not' going to do is sit and hand calculate all the
elastic strain at load. I'll take a whack at your explanation ....
and get back at ya.
:-)

Standing rigging - stress calculations
 

RichH wrote:

On Jan 31, 1:39 pm, "Roger Long" wrote:

wrote


Does anybody know how to go about calculating the stresses in standing
rigging?

Yes.

http://home.maine.rr.com/rlma/Boats.htm#Barque

--
Roger Long


So how tight did you set the cap shrouds on Dimillo's Restuarant???

Love the shear line of that barque !!!!! .... true art-form.


She's sweetly shaped, Roger.

You certainly have the eye.

Standing rigging - stress calculations
 

RichH wrote:
On Jan 31, 6:33 pm, "Roger Long" wrote:

I think you'd better stick to filters Rich.

--
Roger Long


Huh?

If the mast were perfectly rigid then what you said would be true.
But they are not.

If the rope is attached right at the shrouds, the opposide shroud
would take near 100% of the load.

If the rope is attached ABOVE the shroud, the mast will bend -
top toward the rope and away from the rope below that.

That would be the load taken up by the lowers and it could be
in the opposite direction even.

Were the rope attached BELOW the shroud???

Standing rigging - stress calculations
 

On 2008-01-31 18:12:30 -0500, RichH said:

Doesn't matter if windloading heels the boat to 45 degrees or by a rope
tied to the top of the mast heels the boat to the same 45 degrees ....
as if the boat is at 45 degrees over the stress in the wires will be
IDENTICAL. :-)

The loads aren't identical, but for the purposes of evaluating the
standing rigging, the differences aren't significant.

As another said elsewhere in the thread: Each boat designer will figure
out those loads and add what they believe is a proper fudge factor to
come up with a wire size. When a boat's been successfully sailed in all
sorts of conditions for 30+ years, you gotta believe that they were at
least in the right ballpark.

--
Jere Lull
Tanzer 28 #4 out of Tolchester, MD
Xan's pages: http://web.mac.com/jerelull/iWeb/Xan/
Our BVI trips & tips: http://homepage.mac.com/jerelull/BVI/

Standing rigging - stress calculations
 

On Jan 31, 5:13 pm, Jere Lull wrote:
... The loads aren't identical, but for the purposes of evaluating the
standing rigging, the differences aren't significant. ...

Well, I don't think that's right. I bet the scantiling rules require
that you consider the reefed condition for a reason rather than to
just make work for designers. Hey, have I mentioned that there's
this book...:)

-- Tom.