Contessa 26 Tech Notes
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I was concerned as I had read in a book (The Sailor’s Assistant) a discussion of compression load on the mast step (PP96), and of shroud strengths (PP99) which give a shroud strength as (dispX1.4 /number of shrouds) and then discusses dividing the shroud load by a formula on pp102.
If I understand the drift of their thought, each shroud should be tensioned to a certain value and the load distributed according to a certain method. I had read somewhere that one should have tension equal to the displacement on the shrouds (divided equally between port and starboard). the tension should be about 25% of the shrouds breaking strength and , well at some point my eyes glazed over. Got a bit complicated and so I yelled for help. I have enjoyed the articles on the web site you are posting and like the down to earth approach you use. Yours aye, Patrick
In answer to questions on rig tuning, There are a few general rules for rig tension but I’ve heard of nothing that specifically impacts the Contessa 26.
First of all is the fact that we’re dealing with an common eight wire masthead rig that is relatively simple to “tune” and is inherently rugged. Keep in mind that stainless steel does not like to be under constantly changing tensile loads, so one objective is to maintain a degree of tightness that doesn’t allow this to happen. Most rig failures come from too light tension over a long period of time which causes fatigue in the wire and its connections. Race boats use flexible rigs with backstay adjusters and other wizzies to modify the rig underway changing mast bend and sail shape. Good stuff for the racer, but not appropriate for the lone cruising boat. The objective for the cruising rig is to fix the mast in position and keep it there under all conditions.
Many people have their boat yard tune the rig when the boat is launched. They then sail off for the season with no further concern for the rig. Actually, the rig will change during the first few weeks after launch. The boat assumes its in-the-water shape which may be somewhat different than its on-the-hard shape. The rig will subsequently change and further tuning should be done. Now down to business. There are three basic rules:
1. Opposing shrouds must have the same tension.
2. Tension order – The forestay must have the most tension (see note below). The upper shrouds come next, then the lower forward shrouds, and finally the lower aft shrouds and the backstay.
3. Tension the shrouds so that, when heeled to about 15 deg you can just feel some looseness…but you can’t see it. This is done at sea obviously and something that should be regularly observed.
1. Getting proper forestay tension may be just guesswork if you have roller furling.
2. Tensioning the forward lowers slightly more than the aft lowers should produce a slight pre-bend in the mast when the backstay is tensioned. You’ll see it if you sight up the mainsail track. It should be barely noticeable. This pre-bend just tells the mast in what direction to bend when loaded. It stops fore and aft “pumping” of the mast that can cause metal fatigue.
3. Although some Brits agonize about mast rake, the JJ Taylor boats carry a slightly different rig that is not particularly rake sensitive, in my opinion.
This is how I have tuned all my boats since the early sixties. Not much magic to it. Never lost any wire or spars. Merrill
Note From Nigel Charlesworth (UK) regarding accurate mast rake.
I have a measured drawing of Birgitta (Rogers CO26) which shows the original configuration and the modifications required to achieve a 2 degree mast rake. It meant chopping 125 mm off the backstays (dia = 4 mm) and increasing the forestay length (dia = 5 mm) by 110 mm. I used Staloks. No changes were made to the capping or the lower shrouds. The standing rigging was re-tensioned, using a “Sure-Rig” tension meter as follows: everything 10% of ultimate breaking strength except for the capping shrouds which were set to 15%. When this was all done, the main halyard was dropped to the deck into a bucket of water and the distance from its bottom to the mast step was measured and found to be 295 mm which gives a 2 degree rake. Birgitta was put on the water, sailed and the standing rigging re-tensioned. Prior to any of this we were tacking through 115 degrees. Post static tensioning we tacked through 90 degrees, and after the dynamic re-tensioning we achieved 85 degrees in a 15 – 20 knot breeze. What was interesting was that it was the lower fore shrouds that create an automatic pre-bend. Equally interesting is that the flatter the sails the better the tack. By just slightly loosening the main and genoa luffs and easing the vang the tacking angle increases to 95 degrees.