Rig Tuning, Part 4—Mast Blocking, Stay Tension, and Spreaders

In Part 3 we set the rake and bend and tightened all the rigging up just firm, which is the core part of doing a good mast tune.

Now let's tidy up a few important details so we can get on with the sailing tune (Part 5).

  1. Six Reasons To Leave The Cockpit Often
  2. Don’t Forget About The Sails
  3. Your Mainsail Is Your Friend
  4. Hoisting the Mainsail Made Easy—Simplicity in Action
  5. Reefs: How Many and How Deep
  6. Reefing Made Easy
  7. Reefing From The Cockpit 2.0—Thinking Things Through
  8. Reefing Questions and Answers
  9. A Dangerous Myth about Reefing
  10. Mainsail Handling Made Easy with Lazyjacks
  11. Topping Lift Tips and a Hack
  12. 12 Reasons The Cutter Is A Great Offshore Voyaging Rig
  13. Cutter Rig—Should You Buy or Convert?
  14. Cutter Rig—Optimizing and/or Converting
  15. Cruising Rigs—Sloop, Cutter, or Solent?
  16. Sailboat Deck Layouts
  17. The Case For Roller-Furling Headsails
  18. UV Protection For Roller Furling Sails
  19. In-Mast, In-Boom, or Slab Reefing—Convenience and Reliability
  20. In-Mast, In-Boom, or Slab Reefing —Performance, Cost and Safety
  21. The Case For Hank On Headsails
  22. Making Life Easier—Roller Reefing/Furling
  23. Making Life Easier—Storm Jib
  24. Gennaker Furlers Come Of Age
  25. Swept-Back Spreaders—We Just Don’t Get It!
  26. Q&A: Staysail Stay: Roller Furling And Fixed Vs Hanks And Removable
  27. Rigid Vangs
  28. Rigging a Proper Preventer, Part 1
  29. Rigging a Proper Preventer—Part 2
  30. Amidships “Preventers”—A Bad Idea That Can Kill
  31. Keeping The Boom Under Control—Boom Brakes
  32. Downwind Sailing, Tips and Tricks
  33. Downwind Sailing—Poling Out The Jib
  34. Setting and Striking a Spinnaker Made Easy and Safe
  35. Ten Tips To Fix Weather Helm
  36. Running Rigging Recommendations—Part 1
  37. Running Rigging Recommendations—Part 2
  38. Two Dangerous Rigging Mistakes
  39. Rig Tuning, Part 1—Preparation
  40. Rig Tuning, Part 2—Understanding Rake and Bend
  41. Rig Tuning, Part 3—6 Steps to a Great Tune
  42. Rig Tuning, Part 4—Mast Blocking, Stay Tension, and Spreaders
  43. Rig Tuning, Part 5—Sailing Tune
  44. 12 Great Rigging Hacks
  45. 9 Tips To Make Unstepping a Sailboat Mast Easier
  46. Cruising Sailboat Spar Inspection
  47. Cruising Sailboat Standing Rigging Inspection
  48. Cruising Sailboat Running Rigging Inspection
  49. Cruising Sailboat Rig Wiring and Lighting Inspection
  50. Cruising Sailboat Roller Furler and Track Inspection
  51. Download Cruising Sailboat Rig Checklist
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Sam Shafer

John,
Great article and series. Question are you re-pouring the Spartite every time you step the mast? or are you using the Spartite blocking to help reset the mast in the correct location?

Sam

Dick Stevenson

Hi John,
Continues to be an excellent series. Thanks.
There are two other reasons besides boat movement to consider when tightening the rigging screw and you find the tension on the shroud/stay is not increasing that have come to my attention over the years. A couple of times I know of the mast base being corroded to a thin section (hard to see from the outside) and the mast was literally being ground into the mast step with the compression tensioning of the rigging screw. The other time, the shroud had a wire or two broken at the entrance to the swage at the top of the mast and tightening the shroud just was unraveling the shroud from the swage.
Lots to watch out for.
My best, Dick Stevenson, s/v Alchemy

Ernest

Hi Dick,
as clear as this sounds it leaves me clueless – so it should be prudent to get atop to check all wirings after finishing the tune? How are you handling this?

Dick Stevenson

Hi Ernest,
Thanks for pointing out the need to clarify. I was merely trying to say that I have bumped into other reasons for the lack of increase in wire tension when tightening the rigging screws. That said, it is always a good idea to eyeball all swages after the rig is tuned.
My best, Dick

Sam Shafer

John,
This is the problem that I have. There is a piece if 1/4″ aluminum plate in the bilge and the extrusion just sits on that. I think the plate is held down by a couple of machine screws. I have been trying to find a design for a butt fitting and an adjustable mast step. So far I have not found anything. So i have started to design my own. Any suggestions?

Rob Gill

Hi John,
By chance I had the mast out of the boat when your articles were first published, so it was very interesting and helpful thanks. I thought our production boat experience might be helpful for others as it also lead to some head scratching on my part as we have no butt fitting in our Z-Spar mast. The mast rather sits in a solid cast aluminium shoe that is bolted in place to a cross girder – and I gather this acts as a “female” plug and mast base in one. There is almost zero play once the mast is in its shoe and no way to adjust the mast base position when in there. The partners are formed by an opening in the deck above with a bolted on alloy mast collar, also with very little play around and no adjustment. With the mast in place, it is almost perfectly raked and centred with the stays slack (as in your instructions). I know that with moderate pre-bend settings we are so balanced (small to moderate amount of weather helm in most wind strengths) when sailing upwind or reaching she will usually sail herself with no autopilot – I guess one blessing of a well worked out production boat (Beneteau 473).
Anyway, following your article I questioned our rigger who was replacing the stainless rigging (after 15 years) and he said ours was the most common set-up and they seldom see boats here (production or otherwise) with a mast plug. Given we have little play fore and aft (nor seem to need it) and there was no visible wear or damage on the mast butt, there seemed little point fitting one. The rigger’s advice was to leave it as designed.
We did have corrosion in the aluminium mast shoe, but this was around the stainless tie rod that ties the mast collar to the shoe and prevents the deck from working from halyard loads.
So please excuse a different kind of “plug” – we decided to replace both the Z-Spar shoe and collar which arrived by courier with some other rigging mast parts in just 4 working days from the USA to NZ. It seems every single part for our 16 year old mast is available (almost entirely ex-stock) at a very reasonable price from their web-site: https://www.usspars.com/boat-information/?vendor=Beneteau&model=OC+473#section-display.
Our rigger was mightily impressed – great service US Spars!
Rob

Dick Stevenson

Hi John and everyone,
I am sure I have seen mast butts, but I do not remember having done so in all the boatyards I have walked around, nor have I ever owned a boat where the bare mast extrusion did not sit directly on the step. And the same for all the friends I have helped with their work over the years. So, I am intrigued and wonder what the benefit/drawback would be of a retrofit. Mine is a quite dry boat, so I have little corrosion. I would also have to see whether the turnbuckles could tolerate whatever the length the mast butt would add to the overall mast height.
My best, Dick Stevenson, s/v Alchemy

Marc Dacey

I’ve seen them, but only in the context of some sort of depression in a deck-stepped “tiny tabernacle” where the mast butt, often a chamfered sort of rectangle, fits into a matching “female” spot on deck, after which a pin is put through a second extrusion.

We have a very large tabernacle (over a metre high) for our deck-stepped mast which allows the mast to pivot down for canal transits and related service or transport. But we do not have a fabricated mast butt; the mast sits on a rubber pad to keep it from metal on metal wear, but it wouldn’t be too hard to have one made and to remove whatever length of mast it augmented to leave the mast height at zero. Thanks again for getting me to consider something I had never really thought of!

Ernest

Regarding Spartite I found a nice 3-part series on youtube showing how the Spartite tightening is done: https://www.youtube.com/watch?v=PTakwY3JcY8&start_radio=1&list=RDPTakwY3JcY8

Lee

Just hope you have thoughts to share on how to tune a solent rig. Can get the forestay to have no appreciable sag but not the solent stay. Also we have a removable inner stay for our storm jib. It’s only set up for passage. At present set it up to be tight and not deflect beyond 1/2” when pressed on at shoulder height but clueless as to whether this is good thinking. Doing so does seem to put a bit of pre bend in. Finally uncertain as to how to handle the hydraulic backstay when using the storm jib. Would seem more tension would give more sag. Have noticed with the solent you flatten things initially but then get nothing by going further.

Eric Klem

Hi John,

Another good post. A few thoughts in reaction to it:

I agree completely on Spartite. I have been that guy trying to put wedges back in. It is not that I think wedges don’t work, they just need to have a very low taper angle which also makes them quite long so that you can get a good fit which often interferes with stuff mounted on the mast above the partners. Spartite is also much quieter which is a big deal for me at least.

On how much tension to put in the backstay/forestay, I am not sure that all 40′ boats would do well to have a strong person really crank on a set of 12″ wrenches. On our boat with a 5/16″ backstay (often found on 40’ers) and corresponding 5/8″ thread size in the turnbuckle, I can get to 20% of wire breaking strength quite easily with a set of 8″ wrenches. I do a good job of cleaning and lubricating the threads and have a lot of experience dealing with highly torqued fasteners. If you assume a k factor of 0.2 (which is really like using loctite on clean threads, grease will be even lower) on a 5/16-18 thread, it only takes about 26 ft lbs to get to 2500 lbs of tension which is 20% of breaking strength. This would only be 26 lbs of force at the end of a 12″ wrench which is not a whole lot if you have good body position. I suspect that many people have poor threads and don’t lubricate appropriately which leads to very high k factor and resulting difficulty in getting to tension but if done right, it isn’t that hard. I suspect that part of the reason for the results you posted are also likely related to diameter, as diameter goes up, you need more torque for a certain tension and I would assume your backstay turbuckles are significantly larger diameter than what you would find on a 40’er.

We do use a tension gauge in 1 place which is to set forestay/backstay tension. Due to geometry, our forestay has slightly more stress so we put the gauge on it and adjust until it is at 20% of breaking. If we had hydraulics, we would just look at the gauge there but we do not. This results in more tension than ideal in lighter air but seems to be the best overall compromise.

One other silly thought is that I find it much easier to use the vice grip style crescent wrenches for tuning although I have never seen them in large sizes so it may not apply to boats over about 40′.

Eric

Eric Klem

Hi John,

I noticed that in one place in my previous post I said a 5/16-18 thread where I meant a 5/8-18 thread. The numbers should otherwise be right. If the thread were 5/16, it would take about half the torque for the same load which would be very easy to get into trouble with.

I have not previously given much thought to your question about graphing load versus displacement on the backstay, thankfully I have always sailed sufficiently stiff boats to not run into that. I have no special knowledge in this area so my comments are only educated guesses. My initial reaction is that if you are only finding the stiffness of the hull, that is not a big deal as stiffness of a structure tends to be relatively constant across its stress range (this is why you see the Modulus of Elasticity) and relative deformation doesn’t tell you anything about stress, only absolute. However, if you truly get to a point where there is no backstay tension increase at all with displacement of the ram, then there is an issue as that would imply you have gotten into plastic deformation which is not reversible. Telling the difference between these can be tricky as the slope can be low but not zero and you can have no plastic deformation. One thing that would worry me is if I slowly needed additional piston displacement to get to the same loads over time. This wouldn’t be a valid measure on new rigging but once it has settled, you could measure piston extension and if you had less over time for the same pressure, that would worry me (I am assuming that creep of the fiberglass hull is small enough that it would not be an issue with this but I haven’t actually tried to check that). Of course, shock loading while sailing can get higher than the load that you set things at and if you were actually plastically deforming structure, you would expect to see some amount of slackening. Regardless, your suggestion to not keep cranking if the load isn’t increasing seems valid.

I suspect that the designers of lightly built racing boats have had to give this some thought so they probably know what it means much better.

Eric

Marc Dacey

Eric, we have 12 5/16″ stays and it takes some time to tweak them. I use either a long screwdriver (with a lanyard around my wrist!) or vise-grips of the pointy kind. I agree that if the threads aren’t galled, it is not hard to get them to the state where the deflection suggests they are in the desirable 20% zone. Still, as I used to use the simpler Loos Gauge for my old boat (1/4″ wire size), I feel I should invest in its bigger brother just to be sure I have even tension on opposing sides of the mast. I know to look for slack on the lee shrouds, but “slack” is a very imprecise term! I prefer foot-pounds or Newtons or whatever I can verify.

Eric Klem

Hi Mark,

Ah the days of sticking a screwdriver through an open body turnbuckle. I found a crescent wrench with long jaws that I used to put across the turnbuckles. This spring when we got new rigigng, we went with the Stalock supajust ones which have a proper flat for a wrench.

I am someone who is a big believer in knowing exactly how to tighten or adjust every faster and/or adjustment. In my production designs, I specify how to tighten and what thread treatment on every single fastener or other adjustable feature, usually with some form of bolt torque although most designs have a few items that use a different method. Of course, torque is the poor man’s bolt tension. In this case, I am with John that measuring tension is not necessary to get what you want as you won’t know what tension to set to other than for the forestay/backstay. Regarding getting the two sides equal, I am pretty sure that the mast is effectively very flexible compared to the rigging so if you have the mast properly straight, tension is equal side to side. In the end, what we want is a mast that has the shape we want and rigging that doesn’t flop around when the wind gets up. Tension is certainly one way of looking at this but knowing what tension to set to is the trick, an engineer could calculate it but it would be extremely labor intensive and require very good correlation of the design drawings and the actual boat. Since we don’t have this, the first time tuning is done sailing and then there are easy ways to get back to that tune that are position based although tension would be an acceptable way of doing it. I suspect John’s next section will be covering exactly how to do this.

Eric

Eric Klem

Hi John,

I just looked at the “folded rule” method for the first time and in theory, it is perfectly valid. To carry a load, all structures must deflect. Another way of saying this is that stress is proportional to strain, the proportion being the modulus of elasticity. Stainless steel is one of the nice materials where this modulus is pretty constant over the stress range. All this goes to say that if you known the amount of deflection in a structure with known geometry, you also know the stress (actually, this is one of the best ways of measuring it). The numbers given by PBO are for 1X19 stainless wire but this method would work just fine for other constructions if you know what the correct displacement this corresponds to. I would think that 1X19 is consistent enough and there should be no other factors unless you have something like really severe corrosion.

The question that I have would be in how consistently it can be implemented. The deflections are quite low so you need to really have a stiff rule that is well attached to the shroud so that your setup is repeatable. Also, different people will start with different amounts of tension in the shrouds which will have some effect. In theory, you won’t end up putting exactly the same number of turns on each side but it will be pretty close and if you count, you could always even it out in the end. I believe that all of these effects will be pretty small but they will be there.

Overall, this seems like a reasonable method to me although I have never tried it.

Eric

Eric Klem

Hi John,

I am happy to try to help, I enjoy reading and contributing to your site and also learn a lot from it.

What you are proposing seems reasonable to me. 25% of breaking is a reasonable number. As you say, someone like you who has a lot of experience can probably do it without a measurement tool but for less experienced, some way of measuring tension for the forestay/backstay seems like a good idea whether it be a hydraulic gauge, tension gauge or the folding rule method.

Eric

Marc Dacey

I appreciate your comments. I also agree that if you get the important parts of tuning and mast bend correct, you are most of the way to a proper tune that allows the sails to work effectively without stresses the rig unnecessarily. I will still probably get that larger Loos gauge as I had a considerable improvement in sailing characteristics when I used its little brother to tune up my previous boat’s rigging.

Jan Rytenberg

Hi all,

I don’t see any referens to the “folding rule” method as described in the Selden rigging brochure. It is a simple way of measuring the actuall tension in a wire by measuring its elongation.

Jan

Douglas MacIver

Hi John, in the context of your hydraulic backstay adjuster notes, what formula are you using to convert from PSI to pounds tension? Are you basing the conversion on the cross-sectional area of the 1×19 wire? Working back from Harken/Navtec specs, I have 2.1 lbs. pull force = 1 psi, but I don’t know how they are calculating that.

Douglas MacIver

Thanks John. Without detailed specs of the cylinder it’s difficult to know the piston (ram) diameter, so I’m just going to go with the manufacturer’s pull-force specification, which in the case of my Navtec adjuster (and repeating what has been said), is PSI * 2.1 = pounds pull-force.

Arne Mogstad

Hi. I would like to ask about the use of the inner forestay (cutter-stay) and the runners, as I find it very confusing, and I really struggle to find information on how to use it. If anyone have any book or website, or knowledge to recommend/share on it, I would be very grateful!

My OVNI has a removable inner forestay. I can easily adjust it with a handle on deck. I also have fwd and aft lowers, and as you say, those are the ones to use to set the prebend (especially since my inner forestay is removable).

However, if I am to put any amount of tension on the inner forestay, it will immediately start bending the mast unless I have the runners tensioned. And to get a decent tension for the sail to be used in the stronger winds that I tend to use the staysail in, it will bend the mast a fair bit without the runners tensioned! I think I have realized that I’m mainly supposed to adjust the tension on the inner forestay with the runners (in the same way that you would adjust the “normal” forestay with the backstay).

I now want to go to windward, tacking, and that’s easy, because I can close haul with both runners tensioned. Bear off and I just slack/remove the leeward runner. Easy.

But now I want to do a gybe, and now I need to slack both runners to make room for the boom on the leeward side, AND the new leeward side after the gybe (or pull the mainsheet in quite a lot, which makes the boat feel very “skittish”).

Is it okay to not use any runners for a few minutes during a gybe, which will allow the mast to bend a fair bit?

And also, is it okay to tighten up the inner forestay to induce additional mast bend during sailing (with or without using the staysail or runners)? I do not have an adjustable backstay, so it won’t tighten the forestay, but as I see it, it will flatten the mainsail.

I feel like I am asking very basic questions here, but I have tried really hard to comprehend this. I’ve read all of the sail handling and tuning chapters many times over, and done countless hours of experimenting onboard, but I just struggle with this one. Sorry if I’m beating a dead horse here!

Kindly, Arne 🙂

Arne Mogstad

Hi, that is way better than I could have hoped for, and I’m happy to wait for it, well aware you got a lot on your plate with so many useful and big topics being tackled these days (and working on your own boat)! 🙂

Feel very free to edit my question for clarity and brevity.

Kindly, Arne 🙂