SJ23 Tech Tip B25, (Updated 2004-08-09) Bob Schimmel

Index

Stem Head and Tack Flange Fitting.
The SJ23 standing rigging chain plates and stem head fitting are built very robust to support the mast.  In fact there's enough strength designed into them to lift the entire hull from all four fittings.  This was a requirement for the manufacturing process as the hulls were slung from these fittings to move them inside the factory.  It should be obvious that this strength is of great benefit out on the water.  The stem head fitting is bolted to the stem with three 1/4" bolts where it simply cannot give.  Short of the hull sliding over the edge of the world, it will probably never let go!

The flange for attaching the jib tack is welded to the back of the stem head fitting with excellent quality welding and the end of the flange is through bolted to the bow cap and deck with a 1/4" bolt.  While the fitting is very robust, upon close inspection I discovered that the tack flange flexes quite easily.  I discovered this when I had the fitting off the hull to replace my bow cap.  See Tech Tip B12. While I was mindlessly bending it by hand one day I found that it flexed quite easily, much to my surprise.  In fact it flexed about a 1/16" from rest.  My strength doesn't even come close to the force of the working jib in a 10 knot breeze.  To understand the extent of this I flexed it with a 12" wrench and discovered that I could easily deflect it 1/4."  I didn't flex it beyond that, thinking the bend might become permanent.

 

 

 

Given the flexible flange there are two short comings in the mounting technique of the stem head fitting;

  1. The small area of deck under the bow cap has only minimal strength as it is pop riveted to a 1" wide fibreglass flange at the side of the hull. (It could be said that the reverse might be true in that the stem head fitting supports this portion of the deck). At right you can see the underside of the fore peak.  The hull flanges are visible along the port and starboard sides, with the tack flange bolt hole close to the stem.  The two sets of triple holes in the foreground are the forward pulpit mounting holes.  The white area at the top of the picture is the end of the cabin head liner.
  2. There is an air gap under many bow caps that creates questionable hold for the 1/4" flange bolt.
Since the flexible tack flange and the minimally supported deck can be pulled up under the load of the jib, the bow cap will loosen with time.  For those of you who are into micro improvements of sail performance, the jib will slacken along the forestay as the flange lifts with increasing wind strength.  Something to take into consideration if you have a backstay tensioning device! 

SOLUTION - Install a strap between the end of the flange and a stem bolt.  Since the anchor locker is an extremely difficult and tight hole to crawl into it is essential that the strap you are about to make can easily slip into place, the first time.  I suppose there are variations of this strap that can do the job but the difficulty of sliding into the anchor locker means that it really should work the first time.

  1. Flat Stainless Strap - Fabricate a strap from 1/8" thick 3/4" wide stainless steel that fits between the tack flange bolt and the top stem head bolt.  Drill a 1/4" hole near one end of the strap and bend the strap 90 degrees.  Then insert a (1x1/4)" bolt, thread up, and weld the head to the strap to prevent the bolt from turning.  Loosely fit the strap in place to determine the position of the strap's bottom hole that fits over the top stem bolt.  Once the hole is drilled fit the strap in place, tighten the bottom nut, and then tighten the top nut.  DO NOT over tighten the top nylock nut to the point of pulling the deck down; not even the slightest amount.  If this is the case then insert spacers to fill the gap. 

Once in place the tack horns on the flange will be absolutely rigid making it impossible to lift. Go ahead and use it to step the mast. 

INSTALLATION - Panache is not equipped with a deck anchor locker as described in Tech Tip B11 so I crawled into the locker through the cabin door that you see on the right.  The reach to the forepeak is unbelievably far so I stretched out on a long (2x6)" to save my kidneys and other soft body parts.  This way I could spend some "quality time" in there to get it right.  As awkward a reach as this was, the strap must fit perfect and I'm getting too old to fiddle around with parts that only just make do.  So take a head light or flashlight with you!

NOTE: The tack horns shown in the stem head image above are bent down about 100 from horizontal to keep the jib attached.  If you intend to bend these with the fitting still bolted on the bow, pry them down with a long bar or other leaver.  Don't use a hammer.  The impact blows will damage the fibreglass deck.

 
CAUTION: Many people temporarily attach the hoisting lines to the tack hooks to step the mast, leaving the stem head fitting free to attach the forestay.  This is a very dangerous practice as the weld may let go, possibly ruining the rest of your day!  Despite the fact that the stem head fitting is welded very well, you are straining the joint across its weakest dimension.  Just because you got away with it all these years is no reason to continue this dangerous practice!  I addition, the diagram in the SJ23 manual (Tech Tip h06) shows attaching a line to the fore deck mounted cleat to pull the mast up.  This is also a very dangerous practice as the cleat bolts may pull right through the deck, again ruining your day!  Neither of these is a strong fitting.  Check under the deck to confirm this for yourself.

THE SAFEST PROCEDURE is to temporarily attach your lifting line to the forestay hole in the stem head fitting:

  1. stand the mast up
  2. support the mast
  3. remove the lifting line
  4. and finally attach the forestay to the stem head fitting.

 

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