Fixed or running backstays ?
 

Hi Roger,

Roger Long wrote:

Also designed the rig and spars (as well as everything else) for this
ship:

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

Although yacht rigs are pretty far off my radar screen except for my
own boat, I've thought about them a bit over the years.

What a beautiful classic ship! Too bad about the project outcome.

Don W.

Fixed or running backstays ?
 

Roger Long wrote:
Yes, but why store them on the cap shrouds when not needed and have
the chafe and useless weight? Why not have them functioning as
redundant lower shrouds with enough back angle to help keep the mast
in column against the inner stay?

Unless the inner stay is also removable, there are things other than a
sail that can put loads on it. Missing stays and going aback with the
headsail laying against the innerstay could put a big load on the mast
and put it out of column in an extreme situation. Having the
backstays stowed in a position where they provide some support could
be a rig saver.

I have a staysail stay and runners on my boat. The staysail stay is
removeable but quick to set up. When it is set up the runners are
needed in heavy airs but only to windward. The runners run down to a
slide on the deck that can be moved fore and aft so I could stow the
runners quit far forward with them still providing support. In fact I
have never been out where I needed them on this boat. All their use has
just been to prove the system.

Gaz

Fixed or running backstays ?
 

If the inner stay is removable and is only there to give you the
option of having a low, more inboard rig, for heavy weather, I would
probably go with just runners and set them up whenever the inner stay
was set. The original poster though said that his mast was pumping.
That indicates a serious need for some intermediate support. I
wouldn't make the inner stay removable in his case. It makes tacking
a bit of a pain with big jibs but also provides a great hand hold on
the foredeck and the ability to have a double head rig in lighter air.

The tracks you have are a nice refinement but not something I would
suggest in the "keep it simple, keep it inexpensive" department. It
takes a lot of structure and planning to support the full strength of
the backstays all along a track even though it does spread the load
out a bit.

--

Roger Long

Fixed or running backstays ?
 

Roger Long wrote:
If the inner stay is removable and is only there to give you the
option of having a low, more inboard rig, for heavy weather, I would
probably go with just runners and set them up whenever the inner stay
was set. The original poster though said that his mast was pumping.
That indicates a serious need for some intermediate support. I
wouldn't make the inner stay removable in his case. It makes tacking
a bit of a pain with big jibs but also provides a great hand hold on
the foredeck and the ability to have a double head rig in lighter air.

The tracks you have are a nice refinement but not something I would
suggest in the "keep it simple, keep it inexpensive" department. It
takes a lot of structure and planning to support the full strength of
the backstays all along a track even though it does spread the load
out a bit.

My reasoning was, since the rig is designed as a sloop, and sailed as
one for 25 years, the mast is going to stay up. Putting the inner stay
on is a bit of a gimmick that the previous owner did because he thought
the mast was pumping. I finished the runners to support the inner stay
and keep the luff tight. I don't think the mast will ever come down
now. It is a lttle extra insurance but not critical.

Fixed or running backstays ?
 

Whoa wait a minute here ......
The whole function of the rigging is to keep the mast in column thus
minimizing compression/buckling failure.
Yes, intermediate stays balance the set tension of the forestay on a
cutter rig; but do not equalibrate the tension balance when the
staysail loads the forestay with the resulant of tending to take the
mast out of 'column'. The functional advantage of runners is that they
are applied only with enough tension to restrain the mast deflection at
the foresty connect, not to 'preload' the forestay .... but yet
adjustable to variable tensions .... as needed - NOT so with
intermediates the set up tension is the tension you get!

With regard to weight aloft the modern 'super-polymers' remove most of
the disadvantage of mass and chafe (to the other wire shrouds) .... and
totally disregarding that they are a total pain in the ass when
tacking/gybing.

With runners, you can position them essentially anywhere you want on
the deck; but, knowing that the pin connection at the extreme aft will
affect the best intercept angles and least amount of adverse strain and
the lightest amount of weight (diameter) since at that position the
need for 'stronger' runners is lessened - again its all in the
trigonometry and the reactive forces.


In article , Roger Long
wrote:

Yes, but why store them on the cap shrouds when not needed and have
the chafe and useless weight? Why not have them functioning as
redundant lower shrouds with enough back angle to help keep the mast
in column against the inner stay?

Unless the inner stay is also removable, there are things other than a
sail that can put loads on it. Missing stays and going aback with the
headsail laying against the innerstay could put a big load on the mast
and put it out of column in an extreme situation. Having the
backstays stowed in a position where they provide some support could
be a rig saver.

The back stays won't do the full job in the forward position but it's
up to you to figure out when the rig needs the extra support. I would
size them to function in the aft position. With normal factors of
safety, they will still be able to do a lot in the forward position.
On thing to be wary of is how much load they can put on the mast in
that position if they, rather than the mainsheet, is taking the load
of the mainsail. This is an issue with all backstays and aft lower
shrouds, however.

BTW, I did the indeterminent structural analysis on the standing
rigging and spars for the Rose, (later the Surprise) in "Master and
Commander" for her U.S. Coast Guard certification. Very cool to watch
the computer bend everything farther and farther and see the shape of
one of these rigs at the point of probable failure.

Also designed the rig and spars (as well as everything else) for this
ship:

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

Although yacht rigs are pretty far off my radar screen except for my
own boat, I've thought about them a bit over the years.

Fixed or running backstays ?
 

There are other and better ways to prevent mast pumping. Mast pumping
is a frequency response 'harmonic' that excites the 'natural frequency'
of the mast.
How to stop mast pumping - change the natural frequency by either
changing the rig tension or change the natural frequency of the system
by 'prebending' (forward bow) of the mast.
Oscilations are better controlled by changing the mass (not on a boat),
changing the geometry (not possible) or changing either the rig tension
(causing a 'different' harmonic) or changing the 'natural frequency' of
the mast by pre-bending. Prebending so changes the inertial
characteristics and the natural frequency that the excitation
frequency (that causes mast pumping) to be so incredibly high that one
would need hundred of miles per hour wind velocity to begin such
oscilations. Typical prebend is 3/4" on a single spreader rig and
total of ~1 to 1-1/2" on a double spreader rig. Without runners or
intermediates what can one do to stop or lessen the mast pumping?
simple - tighten the forward lowers mechainically or simply tie a
lenght of line between them (parallel to the lowers) to temporarily
i9ncrease their tension which will cause the mast to bow forward which
changes the natural frequency. ..... or again touting hte
'adjustability of runners': simply apply a 'little bit' of tension
until the mast pumping (harmonic) disappears!!!!


In article , Roger Long
wrote:

If the inner stay is removable and is only there to give you the
option of having a low, more inboard rig, for heavy weather, I would
probably go with just runners and set them up whenever the inner stay
was set. The original poster though said that his mast was pumping.
That indicates a serious need for some intermediate support. I
wouldn't make the inner stay removable in his case. It makes tacking
a bit of a pain with big jibs but also provides a great hand hold on
the foredeck and the ability to have a double head rig in lighter air.

The tracks you have are a nice refinement but not something I would
suggest in the "keep it simple, keep it inexpensive" department. It
takes a lot of structure and planning to support the full strength of
the backstays all along a track even though it does spread the load
out a bit.

Fixed or running backstays ?
 

Who is cheating, me or Gary?

Actually, no one is cheating. This whole discussion is starting to
break down over lack of clarity of just what kind and configuration of
rig we are talking about. A stiff cruising rig has the same
underlying dynamics as a highly bendable and tunable racing rig but
the practical issues are very different. It's starting to sound a
little like the way individual poster's rigs behave is being presented
as gospel across the board.

I'll have to come back later and straighten this out.

--

Roger Long



"Rich Hampel" wrote in message
...
You're cheating.... runners apply tension and thus change the
natural
frequency of the mast. You are using them to correct luff sag and
as
a substiture as a backstay tensioner. I do it alll the time. But
thats NOT the purpose of runners .... they are primarily used to
apply
tension to change the natural frequency of the mast and dampen any
pumping ..... as a prime function.

In article cd5Pf.112815$B94.66779@pd7tw3no, Gary
wrote:

Roger Long wrote:
If the inner stay is removable and is only there to give you the
option of having a low, more inboard rig, for heavy weather, I
would
probably go with just runners and set them up whenever the inner
stay
was set. The original poster though said that his mast was
pumping.
That indicates a serious need for some intermediate support. I
wouldn't make the inner stay removable in his case. It makes
tacking
a bit of a pain with big jibs but also provides a great hand hold
on
the foredeck and the ability to have a double head rig in lighter
air.

The tracks you have are a nice refinement but not something I
would
suggest in the "keep it simple, keep it inexpensive" department.
It
takes a lot of structure and planning to support the full
strength of
the backstays all along a track even though it does spread the
load
out a bit.

My reasoning was, since the rig is designed as a sloop, and sailed
as
one for 25 years, the mast is going to stay up. Putting the inner
stay
on is a bit of a gimmick that the previous owner did because he
thought
the mast was pumping. I finished the runners to support the inner
stay
and keep the luff tight. I don't think the mast will ever come
down
now. It is a lttle extra insurance but not critical.