Go with running backstays ....
They are a royal pain in the ass as they need to be readjusted on each
tack BUT the wide base angle (distance from the bottom of the mast to
the attachment point on deck) is large so that the mechanical
efficiency is much more efficient (in comparison to fixed intermediate
stays), can use less strong tackle & wire/line, etc.
The 'nice' thing about runners is that they can be slacked and stored
on either the cap shroud or the lower aft stays when not needed.

With fixed intermediate stays the base angle is too small (the
intercept angle of the stay with the mast) to be of any significant
structural support strength, etc. needing *humongous* strength in the
deck/base and significantly stronger 'wire' than a runner. A fixed
intermediate stay add unecessary 'weight aloft', doesnt do a good
structural job (because of the low interc ept angle with the mast
attachement).
Its all about the 'trigonometry' of the attachment points. and the huge
forces generated by the small intercept angles.
Choose Runners if possible inspite of their being a PITA
;-)


In article , Len
wrote:

I want to install a cutter-stay and two back stays on my 50ft alu
sloop, 1) to add a cutter-jib to my sailing options and 2) to stop the
annoying pumping-motion of my mast.

So my options a

1) Running backstays, which are relatively hard to install reason why
I would prefer:

2) Fixed backstays, to be installed on the existing puttings of the
lower stays and the other end on the exsisting mount of the
intermediates. When fixed like that, there will "room voor the boom"
on downwind courses.

Problem is the very small angle the fixed backstays will make compared
to the mast. They will be fixed to puttings one meter before the mast.
The other end will be mounted 14 meter high in the mast.

What do you think about the forces such an installation will cause
when using a cutter stay in heavy weather?

Regards, Len.

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.

--

Roger Long



"Rich Hampel" wrote in message
...
Go with running backstays ....
They are a royal pain in the ass as they need to be readjusted on
each
tack BUT the wide base angle (distance from the bottom of the mast
to
the attachment point on deck) is large so that the mechanical
efficiency is much more efficient (in comparison to fixed
intermediate
stays), can use less strong tackle & wire/line, etc.
The 'nice' thing about runners is that they can be slacked and
stored
on either the cap shroud or the lower aft stays when not needed.

With fixed intermediate stays the base angle is too small (the
intercept angle of the stay with the mast) to be of any significant
structural support strength, etc. needing *humongous* strength in
the
deck/base and significantly stronger 'wire' than a runner. A fixed
intermediate stay add unecessary 'weight aloft', doesnt do a good
structural job (because of the low interc ept angle with the mast
attachement).
Its all about the 'trigonometry' of the attachment points. and the
huge
forces generated by the small intercept angles.
Choose Runners if possible inspite of their being a PITA
;-)


In article , Len
wrote:

I want to install a cutter-stay and two back stays on my 50ft alu
sloop, 1) to add a cutter-jib to my sailing options and 2) to stop
the
annoying pumping-motion of my mast.

So my options a

1) Running backstays, which are relatively hard to install reason
why
I would prefer:

2) Fixed backstays, to be installed on the existing puttings of the
lower stays and the other end on the exsisting mount of the
intermediates. When fixed like that, there will "room voor the
boom"
on downwind courses.

Problem is the very small angle the fixed backstays will make
compared
to the mast. They will be fixed to puttings one meter before the
mast.
The other end will be mounted 14 meter high in the mast.

What do you think about the forces such an installation will cause
when using a cutter stay in heavy weather?

Regards, Len.

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.

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

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

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.

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.

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.