October 6, 2016

Rig tuning the cheaper way

HOW DO YOU TUNE your standing rigging if you can’t afford those expensive tension gauges? Well, there is a way.

It just so happens that the elastic stretch of stainless-steel wire increases in rough linear proportion to the load, up to about half the wire's breaking strength. Therefore, stretch is a good indication of load.

Thus, when a 33-foot-long 1 x 19 stainless-steel wire (of any thickness) is loaded to half its breaking strength, it will stretch 2 inches. Little wonder, then, that the leeward shrouds sometimes look a little slack.

Nevertheless, you can use this principle to tune your rig. Here's how:

Take all the load off a wire and mark on it as accurately as possible with tape or a marking pen a length of 1,980 mm.  Do this anywhere along the wire, where it's most convenient.

Now tighten the turnbuckle and measure the length again as you do so. You will find that every extra millimeter of stretch (up and above 1,980 mm) induces a load in the wire of 5 percent of its breaking strength.  In other words, an increase of 2 mm, with a space between your marks now of 1,982 mm, indicates a 10 percent load.

You can find out the breaking strength of the wire from the manufacturer's or retailer's catalog, and from that you can calculate the load in actual pounds or kilograms if you like. But it's just as easy to reckon that a moderate pre-load for the average rig is about 25 percent of the breaking strength.  In which case, you need to stretch your marked length by 5 mm to 1,985 mm.

That's it.  No need for expensive tension gauges. All you need is a tape marked in millimeters and you’re good to go.

Today's Thought
Often ornateness goes with greatness;
Oftener felicity comes of simplicity.
— William Watson, Art Maxims.

“Doctor, I think I’ve got water on the knee.”
“No problem, Mrs Jones, I’ll just give it a tap.”
(Drop by every Monday, Wednesday, Friday for another Mainly about Boats column.)


Unknown said...

Does the same math apply to rod rigging?

John Vigor said...

Sorry, DR, but I just don't know. Intuitively, I doubt it.
John V.