SJ23 Tech Tip F09, (Updated 2018-09-20) Art Brown, Bret Hart & Bob Schimmel

Index

Split Back Stay with Adjuster - A factory design that is easy to operate.
INDEX - Consideration for Roller Furling, Second Chain Plate, Safety Wire, Observations, Bret's Installation, Squeeze Adjuster.

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.

A CONSIDERATION 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 is even more important when you need to roll up sail in a gathering breeze. 
- They also recommend saving the gear by easing the tension on the jib halyards and the standing rigging when at the dock. 
- The thread of a standard turnbuckle (IE: factory single back stay) is not designed for continual adjustment for variable sailing loads.  It will eventually fail with catastrophic results. 

For these reasons I equipped Panache with a back stay adjuster as shown at left.  I modified 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 for support and should therefore be more dependable like a squeeze adjuster. 
With the turnbuckle adjacent to the block and tackle I can remove the barrel and ease the adjuster line to the knot to lean the mast 2" further forward from normal.  This creates the slack I need to pin the forestay while stepping the mast.  The stopper knot limits movement.

SPECIFICATIONS - Pay particular attention to the 1.5" wire block (Harken 304) where the back stay splits.  It MUST match or exceed the breaking strength of the 1/8" SS back stay wire.  The sheave groove MUST also match the 1/8" 7x19 flexible halyard grade SS wire so the strands don't flatten.  The cheeks of this block can be opened to replace the bottom wire without lowering the mast. 
NOTE - Since the back stay wire block does not swivel, it was swaged in line with the split wire to achieve a fair lead over the sheave.

While the Ronstan fiddle blocks will handle just under half the load of the back stay block, they too must match or exceed their load.  All wire ends were swaged with a Nicopress tin plated 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).  
NOTE - The flexible halyard wire was cut to length with the turnbuckle thread set to middle.  This allows for slack to insert/extract the forestay pin during mast stepping and to take up wire stretch under constant tension. 

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.

1. 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. 
   - Some SJ23s have a structural reinforcement running almost vertical on the inside of the transom.  That being the case, install the second chain plate beside it. 
2. 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. 
3. 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 back stay.  Bend this in a bench vice. 
   - Mark the plate so it is installed leaning forward!  Don't say I didn't warn you!!
4. 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. 
5. 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.
6. 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. 
7. 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.
8. 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.

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. 

• The back stay 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 back stay tension with the turnbuckle thread about 1/2 screwed in.  This leaves 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 triangle plate assembly can swivel up/down with the pull of the Dacron line and the bottom one 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 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.
 

• 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 going into a slip.  Tech Tip D07.  I've finally learned to remove my hat 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 back stay 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 back stay wire over the wire turning block is still very healthy after a season of use.  I originally thought the groove in the sheave might not be deep enough to support the wire but it does since there is 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 back stay adjuster.

BRET HART'S BACK STAY ADJUSTER

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.
 

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" back stay.  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 the 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.
Fig 5 - A variation of the Clark design is to terminate the shortened back stay to a 4:1 block and tackle on the port chain plate.  This eliminates the task of installing a second chain plate on the starboard side which is difficult with the cockpit drain lines blocking access under the cockpit.  On the other hand, you could install an inspection port on the starboard aft end of the cockpit.  See Tech Tip D03.  An access hole that you can also use to inspect the outboard bracket bolts.  "No, don't store stuff inside here!  Geez."   An advantage of this design is that it doesn't block access to the outboard or passage over the transom.  Something to consider if you board the boat here.

SQUEEZE ADJUSTER using WIRE BLOCKS

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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