Some sailors consider a backstay adjuster a "go fast" gadget for racing while furler manufacturers consider it "essential" for their roller furling. There is a third category I'd like to call "protection." A few years ago two of us motored a C&C 27' in really shitty weather. The weather was just above freezing, with very steep 4' waves in which the aging Autohelm 300 could barely maintain
a heading. We tightened
the backstay adjuster to save the mast from pumping itself to pieces.
Tightening the rig like this to save it was a first for me. Like I said, "Really shitty weather."
So you think
you don't need a backstay adjuster because you only cruise your
SJ23? Well think again. A forestay that sags when the wind speed
increases is bad for windward performance because it makes the shape
of the jib too full (draft moves aft). This means greater heeling force
and slower boat
speed. It's the reason why the jib and mainsail need to be flat in medium to heavier wind.
A full sail may
also be present in a partly rolled jib when the extra sailcloth in the belly
adds draft too far aft. For a roller furler, an excessively sagged (curved) forestay increases the friction, making the sail
more difficult to roll up under load. Although prudence would also have
you release the sheet to ease the strain of rolling up
the jib.
Don't be tempted to tighten the
forestay of a mast head rig to solve this problem. The
backstay can tighten the forestay with less force due to a slightly more
advantageous angle to the mast head
(greater mechanical advantage). A tightened forestay relates to approximately 1/2 knot of extra upwind speed. Not too shabby!
To avoid
straining the
rigging and jib, ease the backstay adjuster
and the halyard when sailing in light wind or when the boat is at the dock.
Shown
at right is a factory 8:1 backstay adjuster kit that was sold by Clark
Boats to those sailors wanting to do some racing.
The
factory design is quick to set and easy to release. Some SJ23s were
equipped with this option at the factory but most were installed afterwards by
the owner, including the second chain plate. The
part numbers
shown are early 1980s vintage so you will have to update them to today's
equivalent parts. Listed below are the parts used for Panache. Thanks to Art Brown for preserving this document
from the Seattle SJ23 Club.
CAUTION - The Clark backstay adjuster diagram above, shows only one Nicopress sleeve swaged at each eye termination. I copied this design thinking the 1/8" wire will not experience a heavy load. In 2023 Panache experienced a sleeve failure on the split wire of this configuration after only 5 years of service. The wire pulled out of the sleeve below the wire block with a very loud 'thwack', just as I pulled the line to tension the backstay. This left the mast dangerously close to going over the side. "I quickly tightened the mainsheet, then the boom topping lift so the mast was safe for the moment. Later I secured the spare jib halyard to the pushpit as extra insurance. Now I was safe to lower the mainsail and motor to the slip."
It's unnerving to see the mast arcing against the sky and you must act quickly to save it.
This incident was too close for comfort. You really don't know how well things are going until shit happens!
Aaaarch.
POST ANALYSIS - After a thorough investigation of 2 compression tools, types of sleeves, and swaging techniques I used with this installation I finally discovered that the 1/8" wire that pulled out of the single compression sleeve was a hair thinner than Imperial 1/8" wire. This was confirmed with my dial micrometer. A sleeve that is compressed on undersize wire
with a calibrated tool
cannot achieve it rated holding power. Eventually the two will part company as per this failure.
This difference in diameter is likely the result of manufacturing wire to an Imperial measurement in a metric country, but I can't prove it.
The replacement wire is a true 1/8" thick Imperial measure and is double swaged. Back to Tech Tip F34a.
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TEMPORARY REPAIR
- In the repair that followed, each single sleeve was cut off and replaced with two sleeves as recommended by Nicopress. Doubling the sleeves shortened the wire ~3" so I added a SS strap to restore the length. This repair allowed me
to continue sailing for the season without having to lower the mast.
See Tech Tip f34a for a permanent repair.
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Panache BACKSTAY ADJUSTER for ROLLER FURLING (2018-04) - With
roller furling now installed on Panache Tech Tip F10 the
length of the forestay is fixed, setting the rake of the mast.
- The forestay tension is then set by the backstay. This is
recommended by all roller furling
manufacturers since a furler rotates easier on a tight forestay. Easy rolling
is
really important when you need to furl or roll up a jib in a gathering
breeze.
- Many manufacturers also recommend saving the gear by easing the tension on the standing rigging and the jib
halyard when at the dock.
-
The
thread of a standard turnbuckle (IE: factory single backstay) is not designed
for continual adjustments for variable
sailing
loads.
The thread will eventually fail with catastrophic results.
For these reasons I equipped Panache with an 8:1 backstay adjuster as shown at left. In this conversion I shortened the factory backstay to 24' and terminated the adjuster portion with 7x19 SS wire crimped with two Nicopress oval sleeves at each eye. The wire block was bolted to the backstay eye.
I modified
Clark's backstay adjuster
(shown above) slightly
by adding a turnbuckle to the safety wire
(shown at left)
to set the
minimum rig tension. This way the mast is not solely reliant on the
block and tackle
for
support and should therefore be as dependable as a squeeze adjuster.
The safety wire is connected through two custom fabricated triangle plates
to which the 4:1 block and tackle is connected.
With the turnbuckle parallel to the
block and tackle I
can remove the barrel and ease the adjuster line out to the stopper knot to lean the mast 2" forward from its normal angle. This creates the required slack to pin the
forestay while stepping the mast. The stopper knot limits the forward movement.
SPECIFICATIONS -
Pay particular attention to selecting the 1.5" wire block
over which the split backstay turns. The breaking strength
MUST match or exceed the breaking strength of the 1/8" SS
backstay
wire. The profile of the sheave groove MUST also match the 1/8"
7x19
flexible halyard grade wire so the strands are fully supported (can't flatten). The cheeks of a
Harken 304
block can be opened to replace the
7x19 split wire
without lowering the mast, a feature that is important for servicing. Although you MUST secure the mast aft with a spare line
during this procedure.
Since a Harken 304 wire block cannot swivel (fixed is stronger than swivel), it was
double swaged on the backstay in line
with the
flexible
7x19 wire to achieve a fair lead over the sheave without torquing the backstay. While the Ronstan fiddle blocks will handle just under half the load of the backstay wire block, they too must match or exceed the load requirement.
- If you cut the split wire to length with the turnbuckle
twisted to mid position and the mast at the correct rake, it allows for a bit of slack to
set the forestay pin during mast stepping.
- Wrap wire tight around an eye thimble to maintain wire strength. Match the thimble size to the wire.
- Use
zinc plated Nicopress
oval sleeves on SS wire.
- NEVER use an aluminum sleeve on SS wire since the metal is incompatible with SS. It cannot flow around the strands, is too brittle and will fail.
- Crimp the middle of the sleeve first, then the thimble end and finally the wire end.
- Crimp the second sleeve ~1/8" away from the first. (2 sleeves = 100% wire strength).
- Leave 2 cable diameters (about >1/4") of wire protruding from a sleeve. This helps to lock the wire to prevent creep.
- Always crimp with a calibrated compression tool.
(3 crimps / sleeve = 100% max strength).
- For more info see How to Select and Crimp a Swage Sleeve.
SPLIT BACKSTAY and ADJUSTER PARTS. |
PARTS |
SPECS. |
24' Backstay wire,
1/8" (1x19) 316 SS |
- BL 1780 lbs, SWL 356 lbs. |
7' Split stay wire, 1/8" (7x19) 316 SS |
- BL 1670 lbs, SWL 334 lbs. |
3' Safety wire, 1/8" (7x19) 316 SS |
- BL 1670 lbs, SWL 334 lbs. |
4 Split stay & safety wire eye splices. |
- Two 1/8" (3MM) Nicopress oval sleeves (tin-plated or copper) per SS eye thimble. |
1 Backstay wire block, Harken
304 |
- BL 3000lbs / 1361kg, SWL 1500lbs / 680kg. |
1 Top
Fiddle Block, Ronstan S40
RF41500 |
- BL 2200 lbs, SWL 880
lbs. |
1 Bottom
cam/fiddle/block, Ronstan S40 RF41530 |
- BL 2200 lbs, SWL 880 lbs. |
1 clevis, starboard. |
- Heavy duty. |
12' Control Line. |
- 5/16" Dacron low stretch. |
1 Chain Plate, starboard. |
- 316 SS (1/4 x 1 x 10)" strap. |
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SAFETY WIRE and BLOCK & TACKLE
- A good feature of this backstay adjuster is the
1/8" 7x19 SS safety wire
that
supports the mast in case the tensioning line releases from the cam
cleats or breaks. I reverse engineered Clark's design by considering the safety wire
as the primary support and the block and tackle
the secondary support to achieve similar safety of a squeeze
adjuster. I don't like compromising safety, strength and
endurance for a "go fast" gadget.
-
The backstay wire block is 6' up from the transom which is 1.5' above the
horizontal boom, making
it
convenient to secure the boom to at anchor or possible to pass
through when boarding via the transom boarding ladder. Be prepared
to shorten this bottom wire as it stretches. Mine stretched 1"
in 2 months from new.
- The top fiddle block is positioned 3' above the bottom block which
leaves plenty of line to adjust rig tension.
- The
combined length of the split wires (safety & fixed) was chosen to
restore the factory backstay tension with
the turnbuckle thread about 1/2 screwed in. This results in the turnbuckle tightened
to
the light tension required at the mooring. Don't be tempted to set the tension
less than this as it will
promote shock loading in the rigging when the mast flops. Just millimetres with each roll of the hull
can induce fatigue that can break metal rigging with disastrous results.
- I incorporated a SS triangular plate
assembly
at the top and
bottom of the safety wire to support the mast. (SS plates = 2"
face with 1/4" spacers at each corner).
The standard nuts shown were changed to nylock and locked with a dab of
silicon sealant for extra security. Using the safety wire is a strong
and secure way to support the mast and has shown no
problem after 3 seasons of use on the water.
-
The top triangle plate
can swivel up/down with the pull of the Dacron line. It limits the amount of tension the line can exert on the backstay.
-
The bottom triangle plate can tilt fore/aft,
duplicating the function of a turnbuckle toggle for
stepping the mast. In practice the bottom block rotates very
little.
- The 14' of control line
is
low stretch 5/16" Dacron line to prevent shock loads into the
rigging.
-
The top fiddle block is a (Ronstan S40
RF41500 at left) and the
bottom fiddle block is a (Ronstan S40 RF41530
at right).
-
The turnbuckle thread is shown almost released, having just stepped the
mast. In sail mode it is tightened with half thread showing.
The turnbuckle is adjacent to the block and tackle so the barrel can be released or removed and still support the mast with the line.
This is a useful technique to pin the forestay when stepping the mast.
RONSTAN block Smart Feature - A sliding post on these fiddle blocks can be pushed to
one of two stop detents to fix the swivel
pin at 00, 900 or disengaged for free turn.
No tool required. Its perfect for this application. These are
set to full swivel.
CAUTION - When releasing the
control line DON'T just let it go. This shock unloading,
plus forgetting to tie a stopper knot, is a
recipe for loosing the mast over the bow. Instead, ease the line out
with your hand for a soft landing at the stopper knot.
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INSTALL SECOND CHAIN PLATE (2018-04) - I've been wanting to do this job for a long time but held off because the cockpit drain tubes blocked access to the starboard side of the transom. It was too cold to twist off the port drain tube so I cut it. But I still couldn't quite reach the top of the starboard transom. So I used an offset box end wrench with a dab of butyl rubber on the nut to hold it against the bolt so my buddy could start threading it from the outside. (I never dropped a nut this time and wish the technique always worked this well). The alternative was to install a 6" inspection port in the aft end of the cockpit as per Tech Tip D03. Something I didn't want to do.
-
Note the location of the port chain plate then inspect the inside of your starboard transom (under the cockpit) for a similar clear area. Mark the location through the top of the transom for the second chain plate.
- If your SJ23 has a structural reinforcement running almost vertical on the inside of the transom, install the second chain plate beside it.
-
Drill and smooth a hole through the top of the starboard transom, similar to the port plate. The chain plate should fit a bit loose so sealant can go down the hole to do its job.
-
Determine the location of the bolt holes through the transom then mark and drill the holes through the chain plate. I drilled 3/8" holes for 5/16" bolts, allowing for a bit of misalignment in the installation.
- The top 2" of the chain plate should be bent forward about 100 to be inline with the backstay. Bend this in a bench vice.
- Mark the plate so it is installed leaning forward!
Don't say I didn't warn you!!
-
Temporarily place the chain plate in the transom hole at its intended angle and use a ruler to transfer a parallel line from the plate to the outside of the transom as in fig 2 below. With the chain plate held against the outside of the transom (a
spacer at the bottom of the plate will stabilize it parallel to the hull) and lined up squarely to the top hole, draw a line on the transom. Mark the 3 mounting holes on the transom with a transfer punch.
- Drill the holes slowly so it doesn't punch out on the inside. All measuring and drilling must be done perpendicular to the transom so the holes line up.
-
Lower the chain plate through the transom hole till the 3 bolt holes line up. Insert the bolts and large washers coated with butyl rubber sealant behind each head.
-
On the inside, tighten each nylock nut to just prevent movement. This is definitely a two person job. It helps to have the arms of an Orangutan!
-
Seal the deck hole and wipe away any excess. Make it look pretty. Then vacuum the drilling dust from under the cockpit.
- Its not necessary to add sealant between the chain plate and the fibreglass but it will prevent movement. Your choice.
PANACHE SECOND TRANSOM CHAIN PLATE |
Fig 1 -
Panache's transom showing the planned second chain plate in red. This is closest to a symmetrical installation without a huge amount of rework of the thru hull fitting. The installed 1/4" thick SS chain plate actually extends 6" below the red line so the mounting bolts would be well below the thru hull fitting. Unfortunately the nut of the thru hull fitting interfered with where the plate was installed so a 1/4" thick spacer was required around the fitting. I used a hole saw to drill through 1/4" thick vinyl "puck board" creating a doughnut spacer to slip over the fitting. This created a uniform flat surface to tighten the nut against. Problem solved.

By the way, that is ice nestled in the orange tarp at top right. Fortunately Mother Nature
blessed us with "warmer" temperature the next day. This is February.
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Fig 2 - I drew a pencil guide to outline the chain plate on the hull. This guide is required to position the plate for an exact alignment to mark the bolt holes for drilling. Use a center punch so the drill bit doesn't "walk". After all, this exacting work. 
|
Fig 3 - Mounting holes drilled but the nut of the thru hull blocked the 1/4" thick SS chain plate. This is where I slipped a 1/4" thick spacer over the thru hull fitting and tightened the nut against the common surface of the chain plate & spacer.

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Fig 4 - The finished installation sealed to the deck. It's quite a reach to the top of the transom but my box end wrench holding the nut with butyl rubber did the trick. It helps to drill the chain plate holes 1/16" larger than the mounting bolts.

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FIELD OBSERVATIONS of BACKSTAY ADJUSTER
-
At the end of the first season of use I now feel it is fair to judge the performance of this
backstay adjuster.
I installed a lot of things at the same
time and had some growing pains as a result, hence the delay.
Keeping in mind that Panache has a split pushpit, I have noticed the following
since the installation:
- It is now more difficult to board
the boat via my transom hung boarding ladder. While "little
people" can go through the split bottom wires, "big people" step over the pushpit.
Dock or dinghy
boarding on Panache is usually done through a cockpit side gate.
Tech Tip
B21.
- In the beginning I found it more difficult to
reach the side of the outboard to push the starter or kill switches.
I've learned to lean overboard between the
wires and its better. Although I added the extension handle on the shifter
for the delicate task of motoring into a slip.
Tech Tip
D07. I've finally learned to remove my hat and take stuff out of my pocket before
bending over the transom!
- While I haven't tried yet,
it would be more difficult
to pull start the engine. With a single backstay it was relatively
easy.
- There is less forestay sag
from an observation I made from the pulpit, although I've never actually measured
this while I had hanked jibs.
- The boat sails faster with
the backstay tightened. In fact it sails very well with the
110% working jib that was converted to roller furling.
- I'm happy that I moved the safety wire with the turnbuckle
to the same side as the block and tackle. It allows me to release
the barrel so the mast can lean further forward with control while I pin the forestay when stepping
the mast. Pinning is more arduous with the weight of the furling
system drooping the forestay. See
Tech Tip F10.
- The flexible backstay wire
over the wire turning block is still very healthy after several seasons of use. I
originally thought the groove in the sheave might not be deep enough to
support the wire but it supports it well with no flattening. In
addition, there isn't even a bend in the wire showing where it went around
the sheave so the radius is correct for the wire size.
- All good stuff. So go
ahead and install a backstay adjuster.
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BRET HART'S SPLIT BACKSTAY ADJUSTER |
Q - "I do
a little racing now and then and I noticed that I have some head stay sag
that is affecting my upwind performance. I've thought about installing a backstay adjuster and would probably use the
factory design you've posted
here. I wonder how well this would
work with a mast head rig and deck stepped mast. It seems to me it
could put a lot of extra downward force on the deck and compression post
and I wonder if you see it as a potential problem more than a benefit. I
have a friend who has a deck stepped fractional rig and the pull results in bend rather than a downward force. I have seen some
SJ23's with adjustable backstays, in a split configuration, and it didn't
look like the deck was damaged or anything so I wonder what the factory
design looks like. I tend to worry
about the small things too much so maybe it's only a quick answer for you! Your
advice is greatly appreciated." Bret. A -
"If you want to be successful in racing or fast cruising, you must have a
backstay adjuster to tension the forestay. It's one of the best gadgets for pointing
upwind as
high as possible. For downwind sailing you slack it off and away
you go with fuller sails to grab the wind. This adjuster works even
better on the SJ7.7
with its fractional
rig. To understand this
you have to realize the mechanical advantage that makes it possible to bend
a fractional rigged mast with less effort. On a mast head rig it is less beneficial, but still useful. I added one to my
previous Macgregor
Venture 222 with mast head rig and it helped a lot going upwind. I
also added a baby stay adjuster that could flatten the mainsail by bending the mast
forward. A baby stay can bend a mast very easily so use a stopper
knot to limit the pull. Don't overdo it."
If I were to install a backstay adjuster on an SJ23, I'd install
the Clark design shown above. An adjuster can
increase the loading on the bottom of the mast, as you suggest, but this force is NOTHING
compared to the load when the boat is knocked down on her side. Panache is one of the earliest hulls out of the
mold and she survived two
knock downs in 2000 without damaging the original standing rigging.
So don't worry about damaging the deck. The forces are well distributed
through the tabernacle and supported by the compression post under it.
If
you are concerned about the deck see
Tech Tip F03." Bob.
Construction - Bret modified the original Clark design somewhat
by installing a new 5/32" backstay with Sta-Lok fittings for the wire block. This is the smallest wire size a Sta-Lok can fit
to. He ran the free end of the control line to a
cam cleat so it is easy for the helmsman to pull or release the line when heeling. Below are the photos of his installation on Cosmo.
Fig 1 - The control line lead
directly to the helmsman. Speed of operation isn't that critical but
convenience for the helmsman is.
 |
Fig 2 - Looking aft from the cabin.
I like the contrasting coloured line. Makes it easier to identify in
the flurry of activity.
 |
Fig 3 - The all important, extremely
strong Ronstan wire turning block held with a Sta-Lok fitting at the bottom of a new
5/32" backstay. The free shackle is probably a good place to clip the
end of the boom for storage.
 |
Fig 4 - The overall view. Very nice
work.

"In future I will change the purchase ratio from 3:1 to 4:1 as shown in
this Tech Tip. I can add a lot of tension with the 3:1 but the pull gets pretty
hard towards the end. I use 1/4" Yale Warp Speed for the running
line since it is very strong and low stretch. The safety wire around
the blocks will be added shortly as backup." Bret.
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