Tuning standing rigging

The proper way to tune the standing rigging is a much discussed question on sailing forums across the Web. Most of the posts center around the use of a Loos guage. I personally don't advocate a Loos guage because it typically involves adjustments based upon the percentage of breaking strength of the wire when I feel that a specifically designed tension is more appropriate for a well engineered hull/spar interplay.

With the development of composite and alternate materials from the now traditional twisted steel cable, the ability to reduce stay diameter while increasing cable strength may render the "breaking strength" standard a dangerous or, at least, damaging measure to base rig tension upon.

Why do sailors find it so hard to use the mast as a tension guide, when there is an obvious connection between mast bend to the tension in the rig?

For a typical fractional rig, tensioning the rigging based upon the bend in the mast seems very obvious. For the small B&R rig, a prebend is almost always a condition and it takes a specific tension to achieve a specific bend.

From a design stand point, the wire size is relevant for efficiency, cost, and application. A daysailer doesn't require the strength of a blue water sailer or racer. Does it seem appropriate to, therefore, base a tension guide on the breaking strength of the cable? Is this a design consideration that should be passed on to the user?

Thoughts, please.

 

Tuning the rig is directly related to the cut and material of the sails. Adjusting the bend or pre-bend will be related to it. The sailmaker should either indicate how much is needed, or cut the sails to the existing bend.

 

Most of the boats I have owned and sailed did not have "bendy spars". There might have been mast rake, but the shape was mostly dictated by sail cut. The exception was the Nordic Folkboat. Basic 3 stay fractional rig, with the backstay on a purchase. All my other boats were "masthead" rigs.

 

How did you determine the correct tension on the stays when tuning?

Yes, but...
Racing or performance sailing often calls for inducing bend or relaxing it to adjust for wind direction and conditions. Adjustable backstays are designed for such trimming.

The sailmaker will certainly take those things into account. However, that doesn't say much about tuning technique.

-Will

 

If anybody really needs to know the tensile loads being applied,it isn't so hard to find out nowadays.You just equip the boat with these at critical points Load Pins - Cyclops Marine https://www.cyclopsmarine.com/products/load-pins/ .Whether good use can be made of the information that is generated is a slightly different matter.I would think that if the data could be combined with a synchronised video recording of the rig it could be a useful tool.

 

"Tuning" kinda infers the rig was set up with some intent of precision, and it was not. The boat had already suffered from a leaky garboard in way of the keel foot from excessive winding on. I do try to keep a well tension forestay, but not at the price of forcing the boat apart. At some point, a boat built in 1947 needs a sympathetic owner. Generally there would be some slack in the lee-shroud under full main in a breeze, and i hardly ever wound the backstay up tight. The Nordic Folkboat racers are obsessive about mast bend and tension/tuning, as i guess anyone hoping to win races should be, but i have no need to obtain the last fraction of a knot out of a boat and halving the lifespan of sails, let alone the hull.
A friend with an IF glass Folkboat had stays that where bar tight, a 12-1 backstay system and non class fully battened mainsail. He did a fast run from the UK to Tenerife in the Canary Islands in snotty weather, but he would "press on" when most people would be reefing.
Rod rigging is an entirely other beast.

 

I think you have put your finger on the biggest issue. What can be made of knowing this information if you're not a designer?

I've always set my stays much the same way @skaraborgcraft seems to; by feel. I was taught early on that over tightening can result in changing the shape of your boat. I remember seeing old wooden sailing boats with hogged shears and being cautioned about the dangers of over tightening shrouds while on one tack or the other.

Apparently, the modern sailboat can put up with much higher loads on their standing rigging.

-Will

 

I have a 1954 Star Class wooden and a Sitka spruce mast and boom.

Historical articles that appeared in Stardust about half way down the articles is some information on the history of the Stars thin mast types and how it rigging would be bend in the different types of mainsails over the years of innovations.
- edited by David Bolles -
Star Boat Design and Development https://starclass.org/classic/history/star_boat_design_development.shtml.html

 

A 1947 boat would have a pretty slack rig. I have sailed and raced many vintage boats, and the rig is completley slack on the leeward side.

 

Even with 3 stays?

Old cold moulded boats like the fairy Atalanta could handle higher tensions than clinker built. Though my old Koster had a galv steel ring frame under the mast, so little tension was put into the planking compared to a short shroud plate.

 

Yes. The hulls were not as stiff as modern racing boats have. Cotton sails also stretched a lot.

 

Not as stiff stiff in way of structure you mean? Folkboats have 55% ballast ratio, the standard sails do not even come with reef points in the main.

 

Very interesting. I didn't realise that the Loos adjustments were based on breaking strain and I can see your point.

In the classes that use a Loos guage that I know of, I think just about everyone uses the same guage of rigging and therefore the purpose of having figures that can be compared from boat to boat, the Loos seems to work OK.

Like you, I tend to use actual mast bend and forestay sag as the measure.

 

Regarding rig tension and older boats and rigs, it's interesting to use modern sailcloth and consider its effect on rig tension. With typical older dacron (although perhaps not CYT sails when new) one was often using high halyard and forestay tensions to combat the tendency of the sails to stretch and become fuller in strong winds.

With modern sailcloth (like Doyle D4 carbon) the stretch is minute and the depth didn't increase and move aft as the wind increased. Increasing backstay tension acted directly to reduce sail draft as the wind increased, rather than struggling to control the increasing stretch-induced draft. The rigging loads on my 28' 1970 timber boat appeared to be significantly lighter and the boat went better. I notice the same thing on our balsa sandwich '80s 36 footer when we went from a cruising dacron genoa to a modern laminate; less rig tension, less work, more speed.

Of course, design can mean that modern sails require enormous tension (as in some windsurfer and beach cat sails) and in very heavy conditions when the boat is bouncing modern sails and lines may transfer more loads to an older hull, but in general it seems to be a win/win.

Sort of on the same topic, apparently some of the top Sydney-Hobart boats are now carrying racing storm jibs made of laminate and fully battened. I can see how much better they would be than the standard dacron storm jib, in terms of handling and performance when it's really needed. The standard storm jib must still be carried under the rules to the racing storm jib is extra weight but judged to be worth it, and having played with storm jibs on the foredeck at night racing across Bass Strait I can see that it's another area where modern tech could be a real boon.

 

I think we must differentiate between three stages of tuning. First is the initial loading, wich can actually be calculated. To function properly most masts must stay in compression at all times and the standing rigging shouldn't go slack for fear of inducing shock loads. This is like using a torque wrench on a bolt, you put it in tension so that all subsequent loads are lower and the bolt stays the same lenght.
Second we have tuning to optimize sail shape, this is done however you like (by eye, sailmaker data, etc.).
Third is maintaining those optimum settings, this comes into play when you deal with material strech or re-rigging the boat. This is the stage where any kind of gauge is most useful, you just match the last known good settings.

There are of course cases where this theory of mine seems overcomplicated. Most commonly those are boats with massively overstrenght masts that don't actually need the compression to function. Usually they don't have a lot of standing rigging, and prebend isn't a topic. This are the rigs where "bar tight" on both tacks is all that's needed.