Back(stays) at last

In the last article we covered stays and mastbands. To complete the picture for staying the mast, I’ll now look at chainplates, shroud tensioners and backstays.

Shrouded in mystery

As far as the connecting lugs on chainplates go, they should be at least of the same dimensions as those on the mastbands - see previous articles. It is also helpful if you reduce the work that a toggle has to do by bending the lug to align with the stay if the lug lies fore-and-aft.

But how big should the chainplates be? Well, in the words of a famous London actor, not many people know this, but chainplates are held onto the hull not just by their fasteners, but also by the friction between plate and hull which is generated by the fasteners. As in the case of the spars, the amount of friction you can generate is limited by the crushing strength of the wood. Plug in a few numbers and for each tonne of shroud load, you need 60mm2 total bolt area acting on 4500mm2 of plate area against the hull, and a plate cross section area of 120mm2. As an example, 4mm galvanised wire would therefore need a chainplate about 25mm wide x 200mm long x 5mm thick, held on with at least 2 6mm bolts. In an ideal world, one would fasten chainplates with bolts because they can be tightened up positively. In practice, it is often the case that the uppermost fastening hole has to be fastened by a screw because of the beam shelf or rubbing strake in that area. It is probably safest to discount the effect of this screw when totting up the fasteners required.

Keeping the Standing Rigging Standing

Keeping the Standing Rigging Standing

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In the last article we got as far as putting terminals on to wire ropes. They are only any use if we attach them to the things they are meant to be supporting, so let’s look at attachments to spars.

All Standing - a quick look at standing rigging

I reckon that you have by now had your fair share of esoterica, so let us start getting down to the practical aspects of standing rigging. What I am going to do over the next two or three articles is to develop consistent sets of equipment based on the strength of the wire being used to keep the spars in place. There are two main objectives for doing this. Firstly, the standing rigging is not an area of the boat where guess-work or aesthetics pay dividends; we need to be talking engineering here. Secondly, there is no point in re-rigging using stronger wire “just for good measure” if the attachment points on your spars and hull are not similarly upgraded. Doing so adds weight, windage and cost for no benefit. The guide-line I’ll be using here to develop these consistent sets is that the attachment points and tensioners for the wire should be 1.5 times the strength of the wire. This means that the first thing to break is the wire itself, which is sensible because it is one of the more easily inspectable and replaceable items in the system. As we saw in the last article, sizing the wire includes factors of safety anyway, typically about 2 to 4 times the design load, so I’m not looking to shave things too fine here. But I am going to have to assume that by some means you know the size of wire that you actually need.