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Masts & Rigging: Points of interest from professional riggers Allspars

by Andy Postle, Allspars 22 May 10:00 UTC
The Allspars team © Allspars

When a mast breaks, not only are the entire rig and the sails damaged, but also the hull. It is not uncommon for people to be hurt too. Keeping your rig in good condition is therefore essential.

  1. Age of rigging

    When should rigging ideally be replaced?

    This clearly will alter depending on the material rigging is made of, use of boat, type of boat and rig design.

    Some standard guidelines are as follows:

    Wire:

    • Family cruiser sailing around 2000 miles a year - 10 years
    • Cruiser/Racer, used 2 or 3 times per week - 6 years
    • Charter yacht, which could easily sail up to 5000 miles per year - 5 years

    Rod:

    Rod is generally on the more cruiser/racer orientated yacht, so would usually be in the 6 year bracket to start with, but rod can be re-headed pretty easily. This allows the end fittings to be re-used, and in some cases, where there is enough adjustment in the rigging screw, the rod can be re-used with new cold formed heads fitted. This keeps the cost of re-working rod to a minimum in comparison to wire, where everything will go in the bin. Every 10-12 years a complete rod replacement would be required, along with many of the fittings, which have a pressed or formed head (as opposed to machined parts).

    Bigger yachts or super yachts should have a rigging maintenance programme in place where rod and its fittings are checked every two to three years and various rods are replaced over a 4-8 year time scale.

    However, over-riding all these time scales is the 30,000 mile rule, which, if this comes sooner than any of the age recommendations, takes precedence. So any boats doing the ARC World rally or any other around the world trip, should definitely start with new rigging and it will need to be replaced on their return, even though it may only be 2 years old.

    Some rig types will require a higher level of rig tune to prevent premature failure of a fitting or cold head on a rod. Slack rigging will accelerate the cyclic failure rate for all wire and rod rigging. Particular attention should be paid to rig tensions on aft swept spreader rigs, where the tension is critical to stability of the tube also (too little tension and the mast could invert).

    2. Quality of masts

    What are the differences in different makes of masts?

    Clearly there are some grade of material differences and also design differences. Made up as follows:

    Alloy

    • Grade of alloy used in the mast tube
    • Thickness/quality of anodising
    • Quality of castings for mast fittings
    • Quality of design of fittings
    • How much stainless steel / alloy contact there is in the design
    Carbon
    • Materials used, pre-preg or wet layup
    • Filament winding or mould lay-up
    • Engineering detail
    • Safety factor used in design, (racing or cruising)
    The better the quality of materials and the better designed the fittings, the longer it will last and give a better level of performance through its life span. In short, you generally get what you pay for.

  2. Carbon or Alloy?

    Carbon has many advantages over alloy when making a mast, as you can put the carbon exactly where it is required, this allows us to design masts a little lighter, as we can reinforce a tube just where the load is, and leave it out, where it isn't needed. Clearly with an alloy tube, it is of constant wall thickness, so the tube will be equal to the strength required at the most loaded point, so will carry excess weight in other areas. This advantage though must have careful and accurate calculations carried out.

    We are seeing some carbon rigs migrating onto second generation boats or even different types of second hand boats. This must be very carefully considered, as the original loads for the carbon mast were probably worked out for another boat, so the loadings will not be the same. When a fitting is moved, the mast section wall will not necessarily be the same thickness or of a suitable strength, so may not take the loadings applied, resulting in a tube failure. The golden rule here is a Carbon mast should only be refitted into a boat with the same righting moment (stability) with the same dimensions for the rig.

    Interestingly carbon doesn't usually end up saving significant weight aloft, as most carbon mast manufacturers have used the advantages the raw material offers to make stiffer masts than the original alloy masts they replace. By the time all the rigging and halyards have been added to the package, a weight saving of about 25 - 30% would be normal.

  3. Safety factors at time of design

    This implication exists for all mast designs. When a mast is designed, a careful plan of the boat should be taken, which includes consideration of chainplate locations, hull form, displacement and ballast ratios and the sail plan. All of this is put into a melting pot to give a correct section size and wire rigging sizes to support it all. If during its later life any of these originally designed features change significantly there is a potential for a failure. This is most evident in displacement.

    Some boats, especially cruising multihulls are prone to being filled with owner's equipment, so that the displacement rises significantly. This will have an adverse effect on the righting moment, so reduces the designed safety factor. If the safety factor was set up for a race boat, clearly there isn't far to go before a failure can occur?

    On catamarans a 10% increase in displacement is roughly equal to a 50% increase in righting moment, so safety factor could be very low!

    Normal designed safety factors are:

    1. Cruising: 2.5 - 3 x expected loads
    2. Racing: 2 x expected loads
    3. America's Cup: 1.5 x expected loads (but with a significant drop in lifespan)

  4. Common Cause of Rig failures

    The biggest cause of rigging failures is wires stranding at the junction of the wire to roll swage fitting. This is caused by cyclic failure, where stainless steel has a known number of cycles before failure. The differences in lifespan are controlled by rig tune and correct alignment and toggling of the associated fitting and how often the boat is used (as discussed above).

    Second cause is rod head failure, usually from metal fatigue, but again this lifespan is directly proportional to correct alignment and toggling of the associated fitting and how often the boat is used (as discussed above).

    Thirdly, is the simpler problem of bad maintenance or poor rig set-up. This is much clearer to see, from the simple, lack of split pin in a clevis pin, to taping up rigging screws, so that water is trapped, starting off crevice corrosion in the encapsulated stainless steel.

    A more recent trend is the failure of toggles on the industry standard bronze bodied rigging screws. Historically, many riggers have been happy to re-use these rigging screws on a re-rig, as they don't suffer all the same thread deformation problems that the older stainless steel rigging screws suffer. It would have been normal to therefore expect this fitting to last up to 20-24 years. Although these bronze bodied rigging screws have solved the seizing thread problems of the past, fatigue of the strap toggle is now the issue.

    Our advice now is that all rigging parts from chainplate up to the mast fitting, be replaced.

    Clearly there are many more possible reasons of failure, but I think that this list probably hits the greatest proportion of failures.

    Find out more about the service the Allspars team provide at www.allspars.co.uk

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