|SJ23 Tech Tip F09, (Updated 2018-01-14, Bob Schimmel, Art Brown & Bret Hart)|
sailors consider this a "go fast" gadget for racing and others consider it
for fast cruising. 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 cold, shitty weather
with very steep waves that the Autohelm could barely deal with. We tensioned
the back stay adjuster to save the mast from pumping itself to pieces.
Tightening the rig to save it was a first for me.
So you think
you don't need a backstay adjuster because you only cruise your
SJ23? Well think again. A head stay that sags when the wind speed
increases is bad for windward performance because it makes the shape
of the headsail fuller (draft moves aft). Wind flowing across a full jib
translates to greater heeling force and less forward drive than a flat
sail which means the boat
can't point as high. This is why the jib needs to be flat in medium to heavy wind.
A full sail may
also be present in a partly rolled headsail when the extra sailcloth in the belly
adds draft too far aft. In addition, an excessively sagged (curved) forestay increases the friction inside a roller furling foil, making the sail
more difficult to roll up under load. Although prudence would have
you releasing the sheet and halyard a bit to ease the strain while you roll up the
Shown here is a factory 4:1 backstay 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. The part numbers shown are early 1980s vintage so you will have to update them to current period. The diagram gives you a good start to search for equivalent parts. Pay particular attention to the Schaefer wire block. It MUST match or exceed the breaking strength of the wire. The sheave groove MUST match the 1/8" wire and the opening should be able to pass the nicro-pressed thimble. Clark's design requires 1/8" 7x19 halyard grade wire to be used over the large block. While the fiddle blocks handle half the load of the Schaefer, they must also match or exceed their load.
A good safety feature of this design is the stainless steel safety wire that supports the mast in case the tensioning line breaks or releases from the cleat. Never compromise safety, strength and endurance for a "go fast" gadget. The length of the safety wire can be set for minimum backstay tension required for downwind sailing or to relax the rigging while at the dock. Don't be tempted to relax the tension too much as it will promote shock loading in the rigging as the mast flops (millimetres) with each roll of the hull. Metal fatigue will break rigging components with catastrophic results. Use low stretch Dacron for the control line to prevent shock loads into the rigging.
INSTALLATION - There is no getting away from it, the second chain plate is difficult to install due to the tight space below the cockpit. I crawled under the cockpit the other day and without some super reach tool (that can hold a nut without dropping it) I cannot reach up high enough to tighten the nuts on the back side of this chain plate. So I might take a lesson from Bobby and Bill in (Tech Tip D03) to install a 6" or 8" diameter inspection port in the aft end of the cockpit. Fairly easy to install. Just have to protect the gel coat from the jig saw using some tape. Some SJ23s have a structural reinforcement running almost vertical on the inside of the transom. That being the case, install the new chain plate a couple of inches outboard from it. Once you determine where to install the chain plate, cut the hole through the top of the transom. Then hold the chain plate against the outside of the transom, lining it up to the hole, and drill the 3 mounting holes through the transom. Use the chain plate as a drill guide. Slip the chain plate through the top hole, insert the bolts then slip on the large washers and spin a nylock nuts on from the inside. Two people make this job a lot easier. Its not really necessary the add sealant to the face of the chain plate but it will prevent vibration movement. You definitely must seal the top of the chain plate where it goes through the deck.
NOTE - For ultimate strength and peace of mind the split back stay adjuster that squeezes the two wires together with a couple of wire blocks is probably the best. This design requires 2 pad eyes installed on the transom that must be reinforced from below. There is enough space to fit 2" long pad eyes just inside the chain plates. It is a daunting task to fit the reinforcement and tighten the nuts from below, considering the tight space. However, this design works best when the 2 split wires are about 300 apart which is impossible to install over the narrow spacing of the chain plates. To have this work effectively 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.
Both systems cost about the
same with each
having its pros and cons.
|Bret Hart's 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 an
adjustable back stay adjuster and would probably use the 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 would be greatly appreciated." Bret.
A - "If you want to be successful in racing or fast cruising, you must have a backstay tension adjuster. 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 really well on the SJ7.7 with its fractional rig. To understand this you have to realize the mechanical advantage that makes it possible to bend the 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 bend the mast and flatten the mainsail. 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 Sta-Lok fitting for the block at the bottom of the new
5/32" back stay. This is the smallest wire size a Sta-Lok can fit
to. He ran the free end of the control line into the cockpit to a
cam cleat so it is easy for the helmsman to pull and release the line when heeling
hard. Below are the photos of his installation on Cosmo.
|The control line lead to the helmsman.
||Looking aft from the cabin.
I like the different colour line.
|The all important, extremely
strong wire turning
block held with a Sta-Lok fitting at the
bottom of a new 5/32" back stay. This is a good place to clip the
end of boom line for mooring storage.
||The overall view. Very nice
"In the future I will change the purchase ratio from a 3x1 to a 4x1 as drawn in the tip. I can add a lot of tension with the 3x1 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.
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 new chain plate on starboard which can be
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."
BABY STAY - Another go fast gadget you could try is a
from the spreaders to a deck fitting, forward of the hatch. Equip the bottom end with a six foot long roller tube over an 8:1 block and tackle.
I installed one of these on my previous Venture 222 and it worked
wonders for flattening the mainsail. What makes this gadget work so well is that it doesn't take
much effort to pull the middle of the mast forward to flatten the
NOTE - The underside of the deck MUST be reinforced with a substantial cross beam to support the load under the baby stay. In addition, you MUST have a stopper knot on the line to limit the amount of pull. There are lots of deck apes out there who don't know their own strength and under the rolling motion of the boat it is easy to overdo an adjustment like this. The stopper knot makes the operation idiot proof! This is no reflection on the apes!
REMOVABLE INNER STAY (Food for Thought) - While not a go fast gadget,
a removable inner forestay can keep
you going by maintaining a balanced sail plan; a small jib with a double reefed main centered over the
hull (IE: The
center of effort over the center of resistance). The top of the stay is attached to the mast where the top of the mainsail
is when double reefed. This way the forces on the mast counter balance each other, a
bit. The bottom of the inner forestay is attached to a pad eye on the deck
positioned where the
inner stay is
parallel to the forestay. Use a very strong adjustable pelican hook
(or equivalent) to clip the stay to the pad eye, then hank a small jib to the
stay. This can be done more easily in worsening weather since
you are closer to the mast on a wide portion of the deck. Having the
sheets attached to the sail with a cow knot speeds up the job. When not in use the
stay can be clipped to the bottom of a shroud.
NOTE - The underside of the deck MUST be reinforced with a substantial cross beam to support the loads under the inner stay.