In this article we will deal with the tuning of standing rigging of a typical sailboat. Speaking of standing rigging we have to open a parenthesis on the types of rigs possible for a sailboat.
Please note this article is a translation and may contain some errors for which I hope you’ll forgive us!
Standing rigging: the evolution of rig types and their tuning
Historically, the most traditional rig type is the masthead one. That is with the forestay and backstay attached to the masthead as fixed standing rigging that create traction in the opposite direction. The spreaders, in this case, are in line, perpendicular to the fore and aft axis of the boat. With a masthead rigged boat, the backstay can be used to increase forestay tension in high winds. At the same time, by vertical compression of the mast, tensioning the backstay causes a bending of the mast that flattens the main. The backstay is both an element of the standing rigging but can also be tuned.
Tensioning the backstay, the central part of the mast advances forward creating a slight “C” shape of the mast seen from the side. This curvature lets you bring the “fat” of the mainsail forward flattening the sail. Therefore, with a strong breeze, we can intervened on the backstay to reduce the forestay sag and flatten the mainsail. Both operations improve upwind performance.
For decades now, however, “fractional” rigs with swept back spreaders have been increasingly widespread. In this case the forestay does not reach the masthead but only up to seven eighths or nine tenths of the mast height and so do the attachments of the shrouds. The spreaders are not perpendicular to the fore-aft axis but swept towards the stern on the horizontal plane. The swept back spreaders ensure that the mast can stand up even without the backstay, which is no longer “structural”. That is, it is no longer one of the elements of the standing rigging (albeit adjustable). It becomes simply the means to adjust the mast bend and curvature and would be considered and its control line is therefore part of our running rigging.
This development has become more and more marked with boats with very wide spreaders and without backstay. The evolution started with offshore sailing boats such as the Mini 650s and Class40s and now it is very widespread also among cruising sailboats. By completely eliminating the backstay from the the list of elements constituting our standing rigging, which presented itself as an obstacle to increasing the roach of a mainsail, it is now possible to have all the roach we want and even “square top” mainsails.
Standing rigging tuning on fractional rigs with swept back spreaders
We will talk here specifically about boats with swept back spreaders. We have chosen a Class40, a sister-ship of the boat with which I competed in the Global Ocean Race 2011/2012. It’s a popular model of Class40, a first generation Akilaria RC1, designed by Mark Lombard, from around 2006. The rig of this boat is not particularly “extreme” or delicate, being the Class40s designed for great ocean navigation. The standing rigging is all rod on this boat.
Although the mast is made of carbon rather than aluminium, the rig is the same as that of a Mini 650 Pogo2 from Structures shipyard. The Pogo 2, designed around 2003-2004 is the Mini 650 with most boats built. This type of rig, nine tenths fractional, has two orders of spreaders. There is no backstay at all, which is common on many modern boats. By now, I would say, even on cruising boats it is one of the most common rig arrangements. It is adopted by shipyards such as Jeanneau and Beneteau, even for boats without oceanic ambitions.
This type of rig is fitted with a runner at the mast top and a checkstay at the height of the inner forestay. Runners and checkstays are not structural, therefore are not to be considered part of the standing rigging per se, the mast does not need them to stay up. I jibed without runners in 50 knots of wind and nothing happened. That said, runners and checks play a very important role in stabilising the mast and reducing its stress. When I run my training centre I used to say that they were not part of the standing rigging but that for good practice we would treat them as such.
Standing rigging and structural lazy jacks
As said, the backstay is simply not there, to make room for the “square top” mainsail. This is the same both on Mini 650s and on Class40s. There isn’t even a topping lift to support the boom when reefing. On a Mini 650, to avoid too many lines, and with a boom that weighs a few kilos, nothing replaces the topping lift. This means that when the main halyard is released, the boom falls onto the coach-roof. The boom will rise again when we tension the reef line and this rarely even needs the boom to be helped by hand.
On the Class40, even though the boom is made of carbon, we can imagine how much the boom plus mainsail would weigh especially if full of water. The problem is solved with the introduction of “structural lazy jacks”. What is meant when we say they are structural? Their role is not simply to contain the main when dowsing it. They replace the topping lift and support the boom. Usually they are made with dyneema and not just simple polyester. They are adjustable both to raise the boom in port and to put them at rest during navigation.
Standing rigging and runners and checkstays
On boats with swept back spreaders, runners and checkstays are not structural. Despite the absence of a backstay it’s not runners or checkstays that keep the mast up. That said, they play a very important role – they help provide additional support for the mast. For example, for ocean-crossing boats, runners and checkstays help stabilise the mast and prevent it from pumping or bending. In addition, runners reach the masthead. With a fractional rig they provide extra support, and become partially “structural” in reducing the workloads of the last part of the mast not reached by the shrouds.
That said, on a nine-tenths rig it is unlikely that you could break the mast tip under spinnaker just because you did not set the runner. I am not aware of any such cases among Class40s. Certainly distributing the tension between runner and checkstay greatly reduces the load of the standing rigging. The checkstay, on the other hand, usually points where the foresail forestay attachment is located. In addition to acting as a support for the mast in general, it allows you to decrease forestay sag without adding compression to the mast.
Standing rigging: how to proceed with tuning your standing rigging
After this introduction, let’s move on to a practical case. Let’s consider the mast of a Class40, with two orders of swept back spreaders and its standing rigging. Hence, we have non-structural runners and checks, no backstay and no topping life. When I arrived on this boat to check the mast, there were two problems noticeable with the naked eye. First of all, the mast was not straight, it pulled to the left until the first set of spreaders. Then it made a bend to the right and then back to the left between the second set of spreaders to the masthead.
Seen from the side, the mast showed excessive rake and pre-bend that needed correcting. So we had left-right and fore-aft problems. In addition to this it was clear that when the starboard runners and checkstay were tensioned, the mast deteriorated in shape. In particular, the curvature between the first set of spreaders and the masthead increased. To fix a mast like this, with multiple problems, you need to have a method to get to a satisfactory result.
As for the adjustments to runners and checkstays, I leave them last, as we will see there are various options on how to use them. First we wanted to take care of putting the mast straight and solve the problem of its excessive rake. The rake shifts the sail centre aft and the bend in the mast flattens the sail, both of which we do not want in light winds. Since this boat is sailed in the Mediterranean we must have a good light wind setup and be able to intervene on the shape of the sail as the wind increases.
Standing rigging: how to put straighten the mast
The boat was in the water, we first had to avoid the risk of unscrewing a turnbuckle and accidentally unhooking a shroud. Since it was not me who had mounted the mast, I could not be sure that the turnbuckles had been inserted correctly, i.e. be exactly level with the same number of turns on the upper and lower par. This means that the threads are not screwed in equally. The lazy rigger screws the turnbuckle on deck a few turns so that he has only to hook the vertical shroud, the V1.
So, in order to avoid any dangers, we set the inner forestay (to double up with the forestay). We also set runners and checkstays just for safety. These work laterally to support the mast. We also attached spinnaker halyards one to the left and one to starboard to an eyebolt.
With a bent mast the first thing really is to understand was why it is so. So we measured the total length of the left and starboard turnbuckle system for both the vertical shrouds (V1) and the low diagonals (D1). Differences emerged immediately, the D1 on the left was about 1cm shorter than the one on the right. This explained why the mast started veering to the left. The port V1 was 2cm shorter than the starboard V1. This explained why the head of the mast pointed to the left after the initial bend. The curve to starboard between the first and second set of spreaders was attributable to the upper diagonal D2 on the starboard side, which was tighter than the left one.
Standing rigging: resetting everything to zero
With the boat in the water and not wanting to take any risk, we didn’t want to get to unhook any turnbuckle. This is to avoid the unpleasant situation of having a hard time getting to re-attach one. This could happen if there’s something inherently wrong with the measures taken that would forced you to work at the limit of the available turns. However we had to make some assumption and one was that each pair of shrouds would be the same length. I.e., that the problems were only in the adjustments of the turnbuckles.
When riggers cut rigging in the workshop they are very unlikely to make pairs of shrouds of different lengths. Therefore, except in exceptional cases, starting from this assumption is more than reasonable. By measuring the total length of the turnbuckles and exposed thread, many things could be deduced. In our case it was evident that the port turnbuckle had many more turns than the starboard side, compared to the thread of the V1 above. That is, the turnbuckles had not been hooked and tightened at the same simultaneously on lower and upper thread.
First of all, we unscrewed the turnbuckles of the V1s, whilst holding the upper threaded part integral together with the turnbuckle. This is possible because the rod shroud is free to rotate inside its T-Cup at the spreader. If it does not rotate, spray some WD40 but never twist the rod rigging. With this procedure we were able to restore a situation where the two V1s shrouds were the same length and with the same adjustment. We repeated the exercise for the low diagonals D1s.
Standing rigging: loosen everything
To bring everything back to zero tension, I went up to the first set of spreaders and loosened the D2s which I would then adjusted last. For the moment I wanted to see the mast without no tension in the D2s. Their role is to prevent the mast from bending to leeward between the first and second spreader levels, especially upwind. As we were stationary in port and without sails, I could totally ignore the D2s until the end.
After that I went back to looking at the mast track and, no wonder, the mast was perfectly straight on the left-right axis without any curvatures. This is not to say it was already set right, but we had zeroed the lateral tension errors.
Standing rigging: rake and pre-bend
The rake depends on the relationship between the length of the forestay and the shrouds as a whole. On this boat only the V1s on deck are adjustable, the rest of the shroud is of fixed length. So the rake is controlled by adjusting the stay length and the V1s. The bend instead arises from compression of the mast given by the tension of the V1s, these pull down the mast that bends forward. The tension of the low diagonals D1s controls the angle up to the first set of spreaders of the overall curvature that the mast takes up to the masthead.
To reduce the bend we had to reduce tension of the V1s but also monitor the tension of the D1s. That is, if the D1s are too tight and the V1s too, we can even force in an inverse curvature. I.e the mast will go backwards to the first level of spreaders then stard bending forward from there to the masthead. This especially with loose D2s that do not prevent the section above from bending forward.
We therefore started by loosening the V1s by two full turns, observing a reduction the bend. The overall rake was still excessive. This can be measured by hanging a full bucket of water on the main halyard and letting it hung just above the deck. The distance between the halyard and the mast at the boom is your rake. We had no option but to intervene by shortening the forestay, which in this case was adjustable.
Standing rigging: adjusting the forestay
The forestay turnbuckle in this case, and like on many other boats, was inside the furling drum. Once the sail was lowered and the retaining bolts were unscrewed, it was possible to raise the drum and access the forestay turnbuckle. Before tightening the forestay, however, I wanted to loosen the the V1s a little so as not to induce further compression in the mast. To preserve the left-right adjustment symmetry, we unscrewed the V1s turnbuckles two full turns each side. We took then tightened the forestay by the same two full turns on the turnbuckle.
Each complete turn corresponded to approximately 3-4 millimetres in length. Two full turns lengthened the V1s by 7-8mm and the impact was visible to the naked eye. I could measure the rake with a bucket, but I had somewhat of a historical memory of the setting of that mast. In fact, I had sailed on an identical boat for a total of about 60,000 miles. So in all fairness, I was trusting my eyes. We removed two more turns from the V1s and took them back at the forestay. A change of about 1.5cm that was well noticeable at a height of 20 meters.
For example, when setting the runners, it was noticeable that the working points of the control lines had moved by about 20cm. The de-multiplication of the runner pulleys obviously amplified the effect on the control line. It was clear, however, that we had moved the mast head forward several centimetres and the excess rake was gone. We gave the forestay one more turn and removed a turn from the V1s and we were satisfied. The amount of rake optimal rake is usually provided by the designer so you can do this job with absolute precision.
Standing rigging: pre-bend
The pre-bend, at a given a setting of the V1s, is controlled by the tension of the D1s and D2s. The goal is to give the mast a beautiful shape that does not have strange kinks in its curvature and especially any inversions etc. In our case the mast bent too far forward and the forestay was particularly soft. This meant that the V1s tension encountered no resistance to mast compression. With the D2s completeley loose, the D1s were obviously too soft too. All the vertical tension turned into compression and bend.
By giving the D1s a few symmetrical left-right turns we were able to straighten the lower part of the mast. The curvature was accentuated between the first spreaders and the masthead so I went up to the D2s to give a first rough and symmetrical adjustment. Once on deck I noticed that the mast was much better already, the forestay was tighter, even though we hadn’t touched the V1s at all. But, the overall curve of the three “sections” of the mast was not yet regular. I therefore decided to tighten further the D1s by a turn and the D2s by two.
Looking at the mast from the side you could see a beautiful shape without irregularities that gently curved back. I was satisfied with the shape and only the sea trials could have confirmed the correct setting of the D2. If these are too soft the mast will sag to leeward between the first spreader and masthead. If they are both too tight the mast becomes straight like a telegraph pole losing its beautiful shape.
Standing rigging: the overall tension of forestay and V1s
For a rod of the size we were adjusting we needed a large and very expensive tension measurement tool. The spring-loaded ones suitable for adjusting the shrouds of a Mini 650 are useless. So, I resorted to trusting my “sensorial” memory. Taking V1s and D1s and shaking them, hitting them, you get a feel for their. Shaking the furled headsail gives an idea of the tension of the forestay. I relied on my historical memory and everything seemed to me in order.
The mast of the Class40s are, pass me the term, quite “ignorant”, and don’t it is not about fine tuning that last half turn. These are boats where you usually an average setting and not touch it before a specific event. This is because upwind mast is fully loaded at just 15-16 knots after which you need to reduce sail. So unless you had to do a short inshore event with light airs predicted changing the setting for each and especially longer races makes no sense.
We had created a perfectly straight mast track, an adequate rake and a pre-bend. It was time to move on runners and checkstays to decide if something needed changing. Before adjusting them, however, we could use them to do a test on the adjustment so far of our mast. I.e. tension them and observe the effect on the mast, which for this type of boats does not have to be significant (I’ll come back to this point). Tightening the left runner-checkstay pair seemed more or less ok. Starboard we clearly had a problem, the mast would bend to windward at the height of the second set of spreaders.
Adjusting runners and checkstays
On this Class40 the runner was attached to the first pulley and therefore its length was a given and could not be adjusted. The checkstay, instead, was tied to the first pulley with a lashing so that it could be adjusted in length. As mentioned, runners can be used in different ways. On some boats a loop with T-bone is is used to shorten the checkstay lashing by a few centimetres. With this expedient you can shorten the checkstay relative to the runner to the point that you set the checkstay and the runner remains effectively loose.
When the T-bone is undone, the runnner has more relative tension than the checkstay as by undoing the T-bone we have effectively lengthened the checkstay. This allows us to run high and increase mast bend with a full mainsail. Once the wind increases and we take the first reef, the runner is no longer needed (especially upwind). So we can put back the T-bone that shortens checkstay and use it as a counter cable for the inner forestay. The inner forstay and the staysail come up in about 16 knots of wind.
This system with T-bone on the checkstay give you maximum flexibility and is obviously suitable for those who know how to use it. However, in long race, especially single-handed, offshore, it has some “human” contraindications. Having to remember this T-bone day and night in every situation is not the best of proposition. We have also said that the mast of a Class40 is not quite so bendable and adjustable. The t-bone extra adjustment will not give you extraordinary gains and advantages upwind as there’s only so much extra bend you can put in with a runner and loose checkstay. All in all it will probably only change your solent to staysail switch point by a knot of wind or two.
A setting for inshore events and one for offshore racing
My personal opinion is that when offshore racing it is best to avoid easily avoidable risks. This T-bone, if forgotten closed, supports the mast only at the level of spreaders, leaving the masthead free. Imagine bearing away, removing the genoa and hoisting a large spi. Suddenly you run the risk that with enough wind the checkstay could even cause the mast to reverse its curvature with the masthead going forward and the lower part held back by the tight checkstay.
Balancing the risks and benefits, at the end of the day, on my boat I decided to eliminate the T-bone and seek for a medium setting. To do this we tighten the runner with the checkstay lashing very short to start with. We progressively lengthen the checkstay lashing until we get to a setting where, when tightening runner and checkstay there is a similar tension on both. If we observe the mast we will also notice that this setting will mean that when tightening runners and checkstay there isn’t much change in mast shape. We forego some fine tuning for safety offshore.
The very fact that the mast remained straight even when runner and checkstay were tightened gave me good confidence that I had already adjusted the D2s correctly. In fact, if the D2s had been too soft, when tightening the checkstay the mast would bend to windward. I can do the reverse test and see if the opposite set causes bend to “leeward”. If the D2s are set correctly setting each pair of runners and checks in turn should not produce any curvature either side from the first spreader to the masthead.
Standing rigging: sea trials
Having worked and checked with runners and checks the sea trial was more for the pleasure of ending the day with some sailing. The wind was not much but enough to load the mainsail close-hauled and verify that the mast remained straight. We had no doubts having already simulated the effort with checkstays. Everything was in order throwing in a few tacks confirmed that the boat made sailed the same angle to the wind on both tacks. This was not the case before, with a perceptible difference of several degrees.
Standing rigging: conclusions
Adjusting the rigging of a sailboat is less complicated than you imagine. But I have seen many badly adjusted masts and not by just a little. If you put your hands on the standing rigging without following a sequence and without knowing what you are doing, you end up like a dog chasing its tail. It is important to understand the influence of stay-V1 on the rake. The influence of forestay-V1 and D1 on the bend of the mast up to the first spreader. Finally, the role of the D2s in counteracting or favouring the bend between the first set of spreaders and the masthead. This on a mast with two sets of spreaders.