Standing Rigging Do Over

This is a 1993 boat (boat #11), but the rigging was completely replaced in 2004 (mast and rigging #738). The previous owner could not say why the rigging and diesel engine were replaced at that time, only that it may have been a warranty issue (?). 2004 is better that 1993, but it still means the rig is over 20 years old. 

Catalina 320 rig #738

I looked into the cost of new standing rigging and was a little astonished (a lot). I paid the local rigger for an hour to look over the rigging and check the original stem/forestay fitting (that has been known to fail). He said that mine looks fine and doesn't need replacing - phew! 

I decided to inspect the rig and check the rig tension myself. The first step was to buy a mast climber. The thing works fine, but you need to get used to the descent sequence as it is quite slow. Anyway, I have now climbed up and down the mast many times. 

I visually inspected every fitting in the rigging and did not find any cracks, flaws or excessive corrosion. I rented the two correctly-sized Loos gauges from Catalina.org to measure the rig tension. As a starting point I read various other accounts of correct rig tension by sail makers (https://c320.org/article.php/20040828173431380), other owners, and based on the working load specifications of the standard wire gauges. 

At the top of the mast on the ATN Mast Climber

I found that the rig was overly tight, particularly in the forward shrouds, and had too much induced mast curve. To cut a looong story short, the numbers I ended up after several re-tensioning sessions with the Loos gauges and wrenches was: Main cap shrouds #24 (5/16 Loos) 11% 1300 lbs; Forward lowers #33 (1/4 Loos) 10% 840 lbs; Mid Uppers (1/4 Loos) #31 8.5% 720 lbs; Aft Lowers (1/4 Loos) #29 7.5% 600 lbs; Back Stay Bridle #31 (1/4 Loos) 8.5% 720 lbs, or 1440 lbs x2 total back stay tension. Note that the percentages are estimated percent of breaking load. I could not check the forestay tension because of the roller furling, but get an approximate load from the back stay measurements.

NOTE WELL: I AM NOT ADVOCATING THAT ANYONE USE THESE RIG TENSIONS. The safest solution is to pay a professional rigger to tension your rig, though you may be subject to a hard sell on new rigging.

Then followed months of sailing and minor re-tensioning of both sides of the rigging on the fly while sailing to windward in different wind strengths to take out any leeward-shroud slack - mainly slightly tightening the aft lowers.

This range of tensions conforms to Mark Yeager's (Quantum Sails) claim that the main cap shrouds should be tightest, followed by forward lowers, then mid uppers, then aft lowers. It also conforms to the Loos guideline of a general starting point of 1300 lbs for 5/16" 1x19 316 wire (i.e. 11% of breaking load), and up to around the 20% of breaking load (i.e. around 2,000 lbs tension). The back stay measurement of 1440 lbs combined tension on the 5/16" single section (which reflects the tension on the forestay) is about 13%, and thus more conservative than indicated in the Seldon rig tuning guide which suggests 15% of breaking load for the back stay (https://support.seldenmast.com/files/595-540-E.pdf). Finally, all of the indicated loads based on the Loos Gauge ratings are well within the recommended safety factor of 20% working load to breaking load for 1x19 304 stainless rigging wire.

All of these numbers are conservative, given that race boats crank their rigs right up to the 20% of breaking load, and well over, to stop any rig movement. At these tensions, the mast is now perfectly in column, has a slight induced mast bend, the shrouds do not excessively slacken going to windward in 20 knots, and the mainsail has a nice flat shape.