Replacing Wire Sidestays with Composite | Part 1
We noticed it during a routine look: one of the outer strands on Paikea’s sidestay had popped. A single broken wire in a 1×19 stay doesn’t sound like much, but it’s the kind of thing that changes your whole season. This is Part 1 of a series on how we diagnosed the failure, why we’re not putting the same wire back up, and what we’re replacing it with instead.
It’s Never Just One Wire
The instinct is to ask why we don’t just replace the one broken strand and go sailing again. We could. But when we first got Paikea, a rigging inspection turned up three broken strands on the opposite side stay, and we replaced all three stays on that side at the same time. That means every stay on the boat has done the same miles, seen the same loads, and aged through the same conditions. If one has failed, the other two are sitting at exactly the same point in their life. Waiting for them to fail one at a time isn’t a plan, it’s just delaying the inevitable and sailing on borrowed time in the meantime.
Age Isn’t the Real Number
Insurance treats a 1×19 wire stay as good for ten years, which is a tidy number and not a very honest one. What actually wears a stay out is cycle loading, not the calendar. A boat that never leaves the marina could sit for a decade and barely touch its rated life. A boat like ours, doing more miles in a year than most boats do in ten, is putting far more load cycles through the wire in a fraction of the time. Our stay was well inside its ten-year window on paper. In terms of actual work done, it had been pushed a lot harder than that number suggests.
There’s also a mechanical side to it that has nothing to do with mileage. Water, salt, dust, and general marine grime all find their way into the swage terminals over time and start corroding the wire from the inside, slowly reducing how much load it can actually carry. Plastic covers over the terminals make this worse, not better — they trap moisture against the metal and hide the corrosion from view at the same time, so you don’t see it coming. Then there’s the accident side: a bad gybe, a boom slamming into the rig, running downwind with too much sail up in a breeze and shock-loading everything when the boat rounds up. Any one of those can pop a strand on its own, age aside.
The Real Driver: Weight
Overloading a stay is directly tied to how much the boat weighs, and on a multihull that relationship is brutal. More weight means a higher righting moment, which means more stability — which sounds like a good thing until you realise it’s also driving load straight into your rig. It’s a genuine catch-22: an overweight multihull feels safer because it doesn’t want to heel over, but that same weight is quietly increasing the chance of breaking a stay. On a monohull, extra weight mostly just makes the boat heel less. On a cat, it goes straight into the standing rigging.
We modelled Paikea’s righting moment across a range of weights, from the 8.5 tons we weighed in at in Valencia down to the 7-ton target we’re working toward through the interior refit. At 8.5 tons, the righting moment comes out around 27 tonnes per metre — territory you’d associate with a 70-foot monohull. Bring that down to 7 tons and it drops to roughly 21 tonnes per metre. Still a serious number, but six tonnes per metre less load being generated in the first place.
Running the actual stay loads against that showed our cap shroud carrying just under five tons at 7 tons displacement, and closer to six tons at 8.5 tons. Compare that to the breaking loads of common 1×19 316 wire — anywhere from roughly 10.4 to 12 tons depending on the brand — and the safety factor at our heavier weight worked out to around 1.8:1. For a cruising boat, you want to be sitting at 2.5 to 3:1. We were sailing well outside that margin, which goes a long way toward explaining why a strand potentially let go inside what should have been a safe window.
Deciding Not to Go Like-for-Like
A straight swap to the same wire, one size up, would fix the numbers. But we’re already pulling weight out of the boat everywhere else in this refit, and putting heavier metal back up the rig runs against everything else we’re doing. The options in the synthetic world are wire, Kevlar, PBO, and Dyneema, and each comes with real trade-offs. PBO and Kevlar aren’t UV or moisture stable, which is not an ideal property for a boat that lives outside permanently. A braided rope-style Dyneema stay is genuinely appealing for anyone doing remote passages, since you can carry a spare and splice a repair yourself if something breaks. But braided construction has to trade away stretch and creep performance to get that flexibility, because the fibres sit at an angle to the load path rather than running straight down it.
That left continuous filament, unidirectional Dyneema — a uni loop cable rather than a braided one — as the option that actually improves on the original wire rather than just replacing it. Within the Dyneema family we went with DM20 over SK78 or SK99. It’s the softest and lightest of the three, has the least creep of the group, and — on the theory that Dyneema gets stronger the more it’s worked — still has most of its working life ahead of it, rather than having already been strength-built through years of use the way the higher-spec materials have.
Sending It Off to Fabrica
We worked with Fabrica, a smaller rigging house we’d dealt with before on other projects, rather than one of the bigger names — mostly because of how responsive they were to our specific questions and needs. Their quote came back with a max working load of 6 tons against a minimum breaking load of 24 tons, working to a 4:1 safety factor for synthetic rigging. That’s more than double the breaking strength of the old wire, for a stay that weighs a fraction as much. The one trade-off is diameter — the new stay is nearly double the diameter of the old wire — but for the weight and strength gain, that’s one we’re happy to make.
Next up: we head to the Fabrica factory to see how these stays actually get built, and go deeper into the safety factor question and the different Dyneema grades — there’s more on that in the Library for members.
In the Library
Want the full breakdown on rig loads and tuning? Should Sidestays Break? walks through this exact failure mode in more detail, and Why Weight Is Critical on Your Multihull covers the righting moment math behind everything here. For the whole picture on how Paikea’s rig is set up, start at the Performance Sailing Hub.
More indepth discussions on our sidestays on our Members page and Forum.