I don't mean to be a units Nazi, but I really don't believe you were
working in kpsi. I can get behind your numbers at 500 psi, 1 kpsi and
1.5 kpsi. Though I do understand what you were conveying, just the
engineer in me.
Neil Schiller
1970 Redwing 35, Hull #7
(C&C 35, Mark I)
"Corsair"
Whitehall, Mi
BSME, MTU 1977
On 6/5/2016 4:01 PM, Ainslie via CnC-List wrote:
I recently did the procedure Alan describes on my 35-3, using the main
halyard and a six-pack for weight. With the boom slightly off to
starboard, I used tape as markers on the boom for each of my
‘soundings’. I started with no tension on the hydraulic backstay, and
progressed to 500 kpsi, 1000, and 1500 kpsi. Each of those increments
moved the masthead aft 2 to 3 inches. From the no-tension position to
1500 kpsi, my beer-bob weight moved aft a total of 10 inches. I didn’t
notice a difference in the beer-bob with the babystay tensioned or not
(which makes sense because the babystay won’t affect the masthead),
but it was easy to see the bend in the mast. If you stand at the mast
with any amount of tension on the backstay, and you flex the babystay
by hand, you’ll see how the mast flexes. Not hard to see how this is
an important control in sail trim.
Jason Ainslie, Spirit
C&C 35 Mk III
Port of Bayfield Ontario
------------------------------------------------------------------------
*From:*CnC-List [mailto:cnc-list-boun...@cnc-list.com] *On Behalf Of
*ALAN BERGEN via CnC-List
*Sent:* June-04-16 2:35 PM
*To:* cnc-list-requ...@cnc-list.com
*Cc:* ALAN BERGEN
*Subject:* Re: Stus-List Adjustable backstay?
The babystay doesn't go slack. The whole mast moves back, but more at
the top than at the middle. If you want to see the effect of
tightening the backstay, look at the forestay, and sight up the mast
from the side while the backstay is not tensioned too tight. Then run
a weighted line (or even your main halyard if the main is down) from
the top of the mast to the boom. When you tension the backstay, the
top of the mast moves back; the middle of the mast moves back (less
than at the top); the weighted line will move aft along the boom; the
forestay will be straighter and you'll see the bend of the mast when
sighting from the side from the boom to the top of the mast.
Alan Bergen
35 Mk III Thirsty
Rose City YC
Portland, OR
On Sat, Jun 4, 2016 at 10:14 AM, Ronald B. Frerker via CnC-List
<cnc-list@cnc-list.com <mailto:cnc-list@cnc-list.com>> wrote:
Sam, like you said, the mast is more or less fixed, but not
completely. As you decrease backstay length the mast has two motions,
bending and rotating from the deck pivot point. As it rotates
(pivots) backward it tightens the forestay. That's about all I get
with my tree trunk of a mast; no bending, but more than an inch back
and down. The thinner sections with multiple spreaders
and/or babystays will get more bending. Both motions move the tip of
the mast back and down since the forestay is mostly fixed (it does
lengthen slightly since it's a bit of a catenary and more tension
takes some droop out). Since systems seek an equilibrium which
reduces overall tension, the babystay will loosen slightly with the
bending, but will assist the bending motion until equilibrium.
Frac rigs get a lot more bending of course by geometry alone. And
tuning them starts with lighting a candle by the hollow stump at
midnight! Those with multiple spreaders are the devils own design.
Ron
Wild Cheri
C&C 30-1
STL
------------------------------------------------------------------------
*From:*Sam Salter via CnC-List <cnc-list@cnc-list.com
<mailto:cnc-list@cnc-list.com>>
*To:* CNC-LIST <cnc-list@cnc-list.com <mailto:cnc-list@cnc-list.com>>
*Cc:* Sam Salter <sam.c.sal...@gmail.com <mailto:sam.c.sal...@gmail.com>>
*Sent:* Friday, June 3, 2016 9:50 PM
*Subject:* Re: Stus-List Adjustable backstay?
Looking at this as an engineering problem (I don't have a 30-2) -
explain what I'm missing:
Top of the mast is more or less fixed (fore and aft) by the forestay.
Sure, it will move back an inch or two when it takes up slack in the
forestay, but mostly it's going to stay put.
Baby stay puts pre bend into centre of mast or at least fixes it in
space, fore and aft.
When backstay is tensioned won't the top move mostly down and push the
middle of the mast forward, slackening the baby stay?
Tensioning the forestay and taking draft out of the main.
Do you guys see the baby stay go slack or am I full of it???
sam :-)
C&C 26 Liquorice
GhostLake Alberta
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what we do, please help us pay for our costs by donating. All Contributions are
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