SJ23 Tech Tip F09, (Updated 2018-09-20) Art Brown, Bret Hart & Bob Schimmel
Back Stay with Adjuster -
A factory design that is easy to operate.
sailors consider this a "go fast" gadget for racing and others consider it
"essential" for 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 waves in which the old Autohelm 300 could barely maintain
a heading. We tightened
the back stay adjuster to save the mast from pumping itself to pieces.
Tightening the rig like this to save it was a first for me.
So you think you don't need a back stay 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 main 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 have you release the sheet and halyard 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 back stay can tighten the forestay with less force due to a more advantageous angle to the mast head (greater mechanical advantage). To avoid straining the rigging and jib, ease the back stay adjuster and the halyard when sailing in light wind or when the boat is at the mooring. A tightened head stay relates to approximately 1/2 knot of extra upwind speed. Not too shabby!
Shown at right is a factory 2(4:1) back stay adjuster kit that was sold by Clark Boats to those sailors wanting to do some racing. Thanks to Art Brown for preserving this document from the Seattle SJ23 Club. 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 shown in the diagram. 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 I used.
for ROLLER FURLING (2018-04) - With
roller furling installed on Panache (Tech Tip F10) the
length of the forestay is fixed and the tension is set by the back stay.
This is typical since all roller furling
manufacturers recommend sailing with a tight forestay as this allows the
foil to rotate more easily. This
even more important when you need to roll up sail in a gathering
For these reasons I equipped Panache with
a back stay adjuster as shown at left.
Clark's design (shown above) slightly by adding a turnbuckle and two
plates to set the
minimum rig tension via the safety wire.
This way the mast is not solely reliant on the
block and tackle
support and should therefore be more dependable like a squeeze adjuster.
Pay particular attention to the 1.5" wire block
where the back stay
MUST match or exceed the breaking strength of the 1/8" SS
wire. The sheave groove MUST also match the 1/8"
flexible halyard grade SS
wire so the strands don't flatten. The cheeks of this block can be opened to replace the
without lowering the mast.
While the Ronstan
fiddle blocks will handle
half the load of the back stay block, they
too must match or exceed their load. All wire ends were swaged with
copper sleeve with the wire tight around an eye thimble.
Crimp the middle first, then either end.
(Never use an aluminum compression sleeve for standing rigging).
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 to the transom block access to the starboard side. It was too cold at the time so I cut the port drain tube away but 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 as 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.
SAFETY WIRE and BLOCK & TACKLE - A good feature of this back stay 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 reversed Clark's design of this adjuster by considering the safety wire as the primary support and the block and tackle the secondary support to achieve the safety of a squeeze adjuster. Never compromise safety, strength and endurance for a "go fast" gadget.
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.
FIELD OBSERVATIONS of BACK STAY ADJUSTER
At the end of the first season of use I now feel it is fair to judge the performance of this
back stay 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:
|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 back stay 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 back stays, 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 back stay 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 back stay 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 mould 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" back stay 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.
For ultimate strength and peace of mind the split back stay adjuster system that squeezes the two split wires together with a couple of wire blocks is the strongest and most dependable. While there is enough space on the top of the transom to fit a 2" wide pad eye just inside each chain plate, the 2 pad eyes must be reinforced from below to offset a potentially weak fibreglass joint under the black corner moulding. It would be a daunting task to fit an angle reinforcement plate and tighten the nuts from below, considering the tight space. In any case, the squeezer design works best when the 2 split wires are about 300 apart which is impossible to install over the narrow spacing of the SJ23 transom chain plates. To give this design a fighting chance it should have ball bearing blocks to roll along the 2 bottom wires. For these reasons I rejected this system. Just thought you should know.
NOTE - A back stay adjuster is not
cheap since the hardware has to be strong enough to replace the bottom 5'
of the back stay.
Verify the strength of the blocks, etc when you buy. The two
systems discussed here cost about the
same with each
having its pros and cons.
See Tech Tip F10.
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