Ask the Expert: Slacking the Rig in Winter
Ed. Note: Oh the puzzles that our boats present. You’ve got questions, whether they’re about sizing a prop or (as is the case here) adjusting a sailboat’s rig to compensate for winter temperatures. Fortunately, we have a number of resources in the industry to give you the answers. If you have a question, send it and we’ll post an answer.
We were cruising in Alaska this summer and while in Seward (who knew there were such great people at the Yacht Club?) got into this discussion in the local watering hole about the upcoming winter. The gist of the conversation went from winterizing in general, to effects of El Niño, and then to what happens to standing rigging in times of extreme cold that can occur during that phenomenon? One party suggested easing off your standing rigging because when it’s super cold the wire contracts putting more tension on the standing rigging. Another party said not necessary and the bigger problem was with the wire terminals at the lower end of standing rigging. Can you sort this out for us?
Love the magazine and found it everywhere we went in Alaska and it’s great to have nwyachting.com online.
Betsy and Ernie Wilson
Hey Betsy and Ernie, The question is about the coefficient of linear expansion. I’ve used round numbers to simplify the example below to illustrate the point. Based on the multiplier for 316 stainless wire, if the temperature goes from 100°F to 0°F, then a shroud that is 50′ (600″) long will shrink 1/2″ or about 1/10%. This is measurable, but is probably not going to cause a catastrophic failure if your rig is healthy enough for an extended cruise. That contraction is a few too many turns on the turnbuckle, so the door to the head might not close properly. This may definitely call for backing off the turnbuckles a bit if the mercury dips significantly. Just remember to put the turns back on when it warms back up, so count the turns and put it in your log. Backing off the tension is a counter-clockwise turn if you’re looking down on the turnbuckle.
To give this some perspective, new rigging stretches 1/50% (called constructional elasticity) when it’s first installed on the boat. This would equate to just under 1/8″ on a 50′ shroud. The standing rigging will also stretch a bit over time (called working elasticity), based on the load. All of these factors will definitely add up to a rig re-tune every few years, especially after seasonal temperature cycles or significant change in latitude.
Standing rigging for newer or stiffer boats should be about 15% of the breaking strength of the wire, which is what a Loos gauge measures, and is readily available at your local chandlery. I’ve found that on older boats that tend to be less performance-oriented that 15% is enough to start to turn the boat into a banana. I’ve had to compromise especially on boats with bowsprits and/or boomkins to stop around 11% so as not to stress out the rig or fittings too much. Some of the large ketches I’ve tuned just get progressively more difficult to tune once you pass 10% and have required a “cheater bar” on the flat bladed screwdriver.
The question about the lower terminals is that they get much more salt water exposure than the ones up in the rig. Half an inch of contraction would put equal amount of stress on the top and bottom fittings, but once again if they’re healthy, it shouldn’t be too much of an issue.
Now that we’ve discussed the stainless wire rigging, let’s see how the temperature affects the mast. The multiplier for aluminum is 38% larger so an aluminum mast will contract faster than the stainless steel, therefore taking the stress off the rigging. This should cause a net effect of your rigging going slightly slack as the temperature plummets.
If your mast is wood, then the multiplier is 1/4th that of stainless, so you might need to take those turns off your rigging after all.
If you’re stopping in Seattle on your way south remember that Redden Marine has dock space on the Ship Canal just inside the Locks and if you bring the S/V Intrepid by, I’d be happy to take a quick look at your rigging before you head down the coast. Anyway, I hope that helps answer your question. Have a safe trip! BTW, I used to live in Pt. Richmond, CA!
Captain Chris Larsen, Certified Rigging Specialist Redden Marine Seattle