How to Tune a Sailboat Mast

How to adjust a turnbuckle. Tuning the mastHere are some general guidelines for tuning your mast’s standing rigging. Please see our blog on how to properly adjust a turnbuckle before you begin. As always we recommend seeking the advice of a professional rigger for more specific tips and tricks regarding tuning your boat’s rigging.

Your boat must be in the water. Begin by just slacking off all of the side shrouds as evenly as possible, so that all stays can be adjusted by hand. Once loose, try and adjust all turnbuckles so that they are pretty much equally open (or closed) from port to starboard respectfully. Also go ahead and line up the cotter pin holes (if present) in the studs so that they are in a pin-able position. Now is also the time to balance out the threads, between the upper and lower studs of the turnbuckle, IF they are not even. Do this by unpinning the turnbuckle from the chainplate – BE CAREFUL HERE –  to ensure the mast is secure before unpinning any one stay. Lastly, loosen all halyards or anything that may pull the mast to port, starboard, forward or aft.

1. Check by sighting up the backside of the mast to see how straight your spar is side to side. You can take a masthead halyard from side to side to ensure that the masthead is on center. Do this by placing a wrap of tape 3′ up from the upper chainplate pin hole on each upper shroud. Cleat the halyard and pull it to the tape mark on one side, mark the halyard where it intersects the tape on the shroud. Now do this to the other side, the mark on the halyard should also intersect the tape similarly. Please note: when the mast is equipped with port and starboard sheaves, instead of just one center-line sheave, it will appear slightly off to one side. Just keep this in mind……

2. Using the upper shrouds as controls, center the masthead as much as possible using hand tension only. Some masts are just crooked. If yours is(are) crooked, it will reveal itself when you loosen all of the stays and halyards initially and sight up the mast. Although you should use hand tension only, you can use a wrench to hold the standing portion (the stay portion) of the turnbuckle. If for some reason the shroud is totally slack and you still can’t turn the turnbuckle by hand then the turnbuckle may need to be serviced, inspected, and maybe replaced.

3. Tune the mast from the top shroud on-down, making sure the mast is in column. Remember: as you tension one shroud by adjusting the turnbuckle, to loosen the opposing shroud the same amount.

How to tune a sailboat mast
Image courtesy of Berthon Marina, UK. Click image to link to their site.

4. Once the mast is fairly straight from side to side, tighten the shrouds all evenly using tools for tensioning. Typically, for proper tension, the shrouds should be tightened using these guidelines; uppers are the tightest, and then fwd. lowers, then the aft lowers and intermediates should be hand tight plus just a turn or two. ~With an in-mast furler it is recommended to tension the aft lower a bit more to promote a straighter spar (fore and aft) for better furling. 

5. Now you can tension the aft most backstay (s). If the backstay has an adjuster it should be set at a base setting (500-1000 lbs). If the backstay simply has a turnbuckle then it should be tightened well. After this has been done, in either situation (adjustable or static backstay), one should site up the mast from a-beam and notice that the masthead has a ‘slight’ aft bias. If there is no aft bias, too much, or the mast is inverted (leaning forward), then the forward most forestay (s) will most likely need to be adjusted to correct this. If a furler is present then seek the council of a professional rigger or refer to your furler’s manual for instructions on how to access the turnbuckle if there is one present.

Image courtesy of UK Sailmakers. Click image to link to their site.
Image courtesy of UK Sailmakers. Click image to link to their site.

6.  Finally, sight up the mast one last time and make any necessary adjustments. 

7. MAKE SURE ALL TURNBUCKLES AND PINS HAVE COTTER PINS AND ARE TAPED NEATLY TO PREVENT CHAFE!

Read HERE for how to use a LOOS & Co. Tension Gauge!

Here is a little vid from our friend Scott at Selden Masts (click the link then hints and advice for more info) on rig tune…..

Is your mast fractionally rigged, only has a single set of lowers or is just plain different? Be sure to leave any questions or comments below.

41 thoughts on “How to Tune a Sailboat Mast

  1. I am trying to tune a Hallberg Rassy HR36 masthead rig. The rig has two in-line spreaders. The cap shroud is 3/8 inch and terminates at the lower spreader. From the lower spreader, the cable transitions to a 5/16 inch cable passing over the upper spreader to the masthead. A second 9/32 inch cable runs from the lower spreader to the mast (just below the upper spreader). The Selden rigging suggests that the “upper shroud” be at 15 percent of the breaking strength of the cable. In this situation, is it 15 percent of the 3/8 inch lower portion? If so, how should the upper 5/16 inch and 9/32 inch cables be tensioned?

    Thanks for your help.

    1. Hi Bryant, good question. Once proper alignment and centering of the spar has happened (static tune), and you are perhaps a hair tighter than hand tight on all shrouds, you can begin to tension things to a percentage of breaking strength. Do this by using the cables at the deck and use their diameters to determine the tensioning amount.

      The V1 (aka cap shroud) in your case is a 3/8″ cable which supports the two cables above ii, hence its large diameter. The 5/16 V2,D3 and the 9/32 D2 total 19/32. So if 15% of the 3/8 cable is achieved you will below that threshold for the cables aloft. Does that make any sense?

      With that in mind there is a range of acceptable tension from light air to heavy air. 15% sounds like a good middle of the road tension. Generally you do not want to exceed 30%. Sail tuning in ideal conditions is generally the best way to determine the right tension, but 15% of breaking strength sounds like a good place to start.

      Don’t forget your cotter pins and tape, especially aloft.

      Hope that helps and thanks for the question.

      ~T.R.C.

      1. T.R.C. Thanks you for the clarification regarding the V2,D3 and D2 load distribution. When I set the V1 tension to 15%, the tension on the V2,D3 was at 8 %. I then tensioned the forward shroud to 12 % and the aft shroud to 10 %. Then I tensioned the backstay to 14 %. After doing this, I measured the tension on the V1 to be 10 %. The only information I could find regarding tension on the D2 was that is did not have to be tensioned much. I tensioned it to 5%. The mast sights straight and I used a bossen seat on a halyard to measure to the lower part of the V1, which also indicated that the mast was straight. Did I overtension the fore and aft stays? Is the tension in the D2 too much or too little? Again, I appreciate your advice.

        Bryant

        1. When you tighten the backstay it usually induces a bit of aft bend in the mast which will soften the upper shroud (V1) a bit. You can just take up on it again to get it back to 15% if you like. As I said there is a acceptable range for all of the stays, which you are well within. Everything else sounds like you did a pretty good job. Next up sail tune and see if there is excessive waggling on the leeward side, but in moderate breeze. The shrouds will begin to sway as the breeze builds, this could be a telltale to either reduce sail a bit or you can add some tension to the shrouds all the way around.

          Should be all good as they say.

          Cheers,
          ~T.R.C.

          1. T.R.C., your advice has been invaluable. I took her out in 12-15 knots and was very happy with the sail luff and stiffness of the rig. Thanks for you help!😁⚓️

  2. Hi , can you provide any tuning guides for a Swan 38 Tall mast single spreader rig with baby stay, I am keen to set the rig up for new North sails and race her competitively. The mast is an exact Nautor factory replacement in 1998. She shall not have furling sails.

    1. Hi Peter and thanks for the comment.

      Unfortunately we do not have a guide for that boat. I would ask the sailmaker however to see what info he or she might have. Alternatively you can always start with a good static tune and then sail tune the boat as I describe in some of the comments below. This is the best way. I may use a Swan 45 Tuning guide as the template and then just fill in my own numbers over time. This is ideal, but infidelity start with asking the sailmaker you are working with, he should have some good info.

      ~T.R.C.

  3. This may seem like a silly question, but it has me perplexed. How long should my cotter pins be? Long enough to ‘jam’ against the surrounding body, to prevent rotation? Otherwise, I don’t see how they’ll prevent my stays from loosening.

    1. The length should be the minimum amount to just be able to bend the legs. Too long and they get caught up on things, too short and you can’t adequately bend the legs to keep the pin in place. The head of the pin is a actually providing the security.

      Does that help?

      ~T.R.C.

  4. Great article to get me started, thanks! I just have a few questions…

    I originally owned a Tanzer 7.5. Her mast was rigid and simple to tune with a LOOS and an eyeball. I however now own a Mirage 33 (1982) and things are a bit more complex (but not too much). When I bought her the mast was already stepped and the owners said they replaced the forestay (inside the furler) 1 season ago. I went about the boat tuning the rig as best I could but I started second guessing the rake. I found noticeable rake in the mast with virtually no backstay tension on. So I think my forestay stretched (being “new”) and I need to bring it forward.

    How do I measure how much rake (at rest on the tensioner) is enough? With my rig as is I felt worried that if I pulled down on the backstay tensioner I might buckle my mast by bending it too far. It seems to me it’s ALOT of downward pressure on the column when you pull down on her especially if the mast was already raked or maybe in my case leaned too far back to start? She has a babystay too, I wasn’t sure how far to tension that other than to assist adding bend\rake but since I had too much already I just lightly tightened it and hoped for the best!

    1. Hi Jer,

      Thanks for the question. With the backstay tensioner completely off, you should be able to adjust the static/ base tension of the backstay with a turnbuckle (s). Loosen the Baby Stay so that it is completely loose, sloppy, to take it out of the equation. Then mark furling line spool direction and remove the line. Next, open the furler up to gain access to the turnbuckle inside, if present. Remove all cotter pins or locking nuts to free the turnbuckles on the headstay and the backstay. You should then loosen things so that the headstay and the backstay can be adjusted by hand. Close the headstay turnbuckle and open the backstay turnbuckle to reduce rake, and vice versa if wanting to add rake.

      You can measure rake by hanging a small mushroom anchor from the main halyard, with the boat floating on its lines, if you wish. Then once you achieve the desired mast rake go ahead and tension the forestay and backstay a few turns equally with tools; not too tight, but a good base light air setting, or as loose as you can imagine the headstay ever needing to be. Lastly, tension the baby stay a bit until it just starts to tug on the mast, helping induce bend. From here the backstay tensioner will do the rest: wind it on and it will tension the headstay and induce mast bend via the baby stay. You may have to take the boat sailing and adjust things as you find out how it performs at various degrees of rake and bend.

      I hope that’s not too wordy, but helps explain it all a bit. Feel free to email or call with further questions.

      Regards,
      ~T.R.C.

  5. Can you provide some specific information regarding rig for 1980 C&C 32. Looking to purchase new main and want to get the most from it for Wednesday nights. Boat currently does not have a pony stay, it has been removed. Can replace that track/car.
    What should initial bend look like, keel step is fixed so assume I need to some chock aft of mast at deck? Have rod rigging but no Loos gauge for same, should I acquire one?
    Love this site, very helpful
    RayK

    1. Hi Ray,

      Thanks for the compliment. This may be less technical than you might expect. I would start with the basic guidelines given in the article to ensure a good base, static tune setting. A Loos gauge is good but not needed. If you focus on getting the spar straight, side to side, with a slight aft bias and then the tension is set so that it feels fairly tight. I know that sounds vague, but keep this in mind: if you are anticipating heavier wind make things a bit tighter, and loosen things up if less windy. The order of tension, in regards to the which shroud (upper vs intermediate vs lower) is important; more so than the amount of tension. Make sure nothing is so loose it is just flapping about.

      The headstay should have some good slack to it with the backstay adjuster totally off. Adjust the backstay and headstay turnbuckles, with them in the slack position until the masthead is favoring a slight aft lean or rake, but only slight. From there, tension the backstay adjuster very tight and see what the headstay tension feels like, should be very tight.

      PLEASE NOTE: if the backstay adjustment is totally bottomed out at this point, the backstay needs to be shortened a bit. Just pay attention to how this affects the rake.

      This part is where the pony stay or the baby stay will play a critical part, for mast bend. You may even find the pony stay to be good for mast pumping in light air and waves. Making this baby stay removable is a good idea, as well as, we’ve found that Dynema rope is the best choice here.

      So… a centered mast head, side to side. A straight, in column mast from the top on down. A slight aft rake to start with…and as you begin to wind on the backstay and the baby stay you will add some rake but also a good bit more bend.

      Take this set up for a few test sails and see how things act, in different conditions. After that you can make some adjustments here and there as needed: weather helm, shroud tension, mast rake, pre bend, etc…Moving chocks and using a Loos gauge.

      ADDT’L TIP: Chocks and mast step position affect bend and rake properties. Want more rake? Chock mast aft in collar and move step forward. Want more bend? Chock mast forward in collar and move mast aft. As all things, there is more to it than that, but that’s the gist of the whole chocks and mast step thing…

      “Sail Tuning” is a blog we are in the works of, but the punchline is that if hard on the breeze, and the leeward shrouds are excessively loose, and you are sure you aren’t over canvased…then go ahead and take turns on the leeward side until they just stop waggling, count what you’ve done, tack and mirror the turns on the other side.

      Once the boat is set up for that specific condition, and you return to the dock, you should take your loose gauge and record these settings…creating a tension gauge setting for various conditions.

      :-0)

      Hope that helps.

      ~T.R.C.

  6. Hi, Thanks for your information.
    I have a Dehler 34. 1986… How much mast prebend and rake is recommended?
    The boat is new to me in March. Raced ok but I want to get a new main and want it to fit a well tuned mast. What do you think of a 2 degree rake and 4″ prebend at the speaders?
    Also, I have a Harken furler, How do you measure the forestay tension?
    Thanks, Duke

    1. Hi Duke,

      This answer isn't going to be as technical as you might have imagined. 2 degree's of rake and 4" sounds like a pretty good start with the backstay off of course. The manufacturer or spar builder may have better insight into their vision, to give you some more exactness. 
      

      The answer, this boat is pretty sporty so it should show some rake. The spreaders are swept slightly aft so this will produce some natural bend just to tension the headstay.

      Head-stays are always tough to measure with any sort of gauge, there are some class specific tricks for using a gauge in funky ways in order to get data, but they aren’t really reliable in my opinion. If you live in a typically windy area, go for bit more shroud tension, headstay tension and mast bend, and see how the boat feels. This will take some trial and error. If the forestay feels too stiff, slot too tight, loosen the uppers a bit, thus reducing bend and slackening the headstay.

      Once the boat is sailing well in the ideal conditions, record that bend and those tensions. This is where I would leave things set, record it, and then just adjust shroud tension to affect bend and headstay in order to compliment different wind strengths and sea states. It takes quite a bit of back and forth, and documentation to get it right. One designers have already worked all of this out and then they share it for others…..very helpful. The rest of us will have to be the trailblazers for this type of information for other boat owners with the same (similar) boats to benefit.

      Hope that helps, thanks for the kind words, and good luck. Once you figure things out post a link here for others with the same boat…..would be helpful.

      ~T.R.C.

  7. Hello,
    Thanks for all of this great info. I just purchased a 37′ boat with a 3/4 fractional rig and a tapered mast. I was wondering if there were any special considerations when tuning the fractional rig?
    Currently the stays and shrouds are a little loose and can be wiggled (borderline flopping) by hand although the mast stands and is visually centered. (We are in SW Florida and the boat went through a direct hit by hurricane Irma like this and still stands tall!)
    Also is it advisable to increase shroud tension in small increments first on one side and then do the same on the opposing side?
    Thanks so much for any info

    1. Hi Nathan. There are some thoughts, so fractional masts are usually fitted with aft swept shrouds and spreaders. If so, this means that the uppers also tension the headstay and create mast bend. The lowers then also act to reduce mast bend, so the tighter you make them you are actually reducing mast curve, thus powering the mainsail up. So be conscious of these two thoughts when tensioning the shrouds. The rest is fundamentally the same as the guide suggests. Loose or wiggling shrouds (excluding the scenario where we are talking about the leeward shrouds under sail), should be tightened. Doing things in increments is definitely a good idea.

      Hope that helps. Thanks for the questions.

      ~T.R.C.

      1. Thanks!! Now that you say that about the swept spreaders helping create mast bend it makes perfect sense. I had an ‘oh duh’ moment. I’ll probably err on the side of looser lower shrouds knowing if we need more power we can always tighten them up. Thank you again this helped immensely!

  8. I want to buy a tension gage. Most familiar with Loos. But do I need Pt 1 or 2? (Pretty sure I don’t need 3 or Pro.) I have two rigs to tune: a 1972 Morgan 27 and a Catalina 22, I think 73 or thereabouts. The Morgan 27 is mine, fresh water for life, and 99.9% most likely factory wire. The Catalina 22 is a borrower in the Gulf, but pretty sure the owner has never tuned it. My problem is I can’t find the gage of wire for either standing rigging anywhere! Any help?

  9. I just purchased a 1980 C&C 40. I was told that I need to replace the rod rigging as it is “too old”. The mast is down and the rod rigging seems ok but I have not done any penetration testing. Does rod rigging need to be replaced due to age?
    Thanks Rigging Co.

    1. Hi Bob,

      Not replaced, but re-headed. This can mean that some stays need to be replaced as a whole, but not typically not the whole set. There are instances where you’ve almost replaced all of it anyways, so full replacement just makes sense. Other than those scenarios, full replacement is due after a certain mileage with rod…60,000 NM. Please keep in mind these standards are very general recommendations. It sounds like in your case, you should send in the rod, tangs, and chainplates for service and inspection. once we receive everything we will make a quote for the recommended services and/or replacement.

      Hope that helps and give us an email for more info.

      ~T.R.C.

  10. I have had a problem with securing the spreaders to the shrouds, resulting in the spreaders dropping. I am using stainless wire to seize them but still having a problem. Any tips on how to do this properly?

    1. Hey Jerry,

      Seizing the wire onto spreaders with hinged spreaders is a bit of a trick of the trade that requires some practice. We use the X’s and O’s method. The end result should be something that looks like this…https://theriggingcompany.files.wordpress.com/2011/11/2012-06-07_14-26-09_899.jpg?w=900. A trick to make the wire bite into the spreader end a bit more is to wedge a small piece of leather between the spreader and the wire before seizing. Also parceling and serving the wire where it intersects the spreader will help create more bite too. Lastly, and I don’t like this method but you can install a bull dog cable clamp beneath the spreader, nuts facing in, to keep it from dropping when slack.

      I hope that helps a little. Thanks for commenting.

      ~T.R.C.

  11. I am struggling to get enough rake into my mast. 33 foot Charger 33 keel stepped. Have loosened forestay and moved mast foot forward by about 10 mm. Should the chocks in the collar be adjusted? Runners and 2 spreaders, and check spreader. Spreaders do not have much aft angle. Move mast step more forward? Outers are tight with inners looser. Thoughts?

    1. Hey Bernard,

      Yeah, it sounds like chocks are the last thing. Maybe remove the chocks with the rigging slack and see if you can get the mast to sit where you like it with just hand tension. Then chock it where it wants to sit. It sounds like you are on the right track everywhere else, perhaps add a toggle into the headstay and shorten the backstay is next. Good luck and I hope that helps somewhat.

      ~T.R.C.

  12. Hi, We have a Lagoon Catamaran with fractional rig, upper and lower shrouds, fore stay and upper and lower diamonds. No back stay. The mast has a degree of pre-bend. I do not plan to drop the mast.

    I may have to do some work on the port side upper diamond. Is it as easy as just undoing the turnbuckle? Or do I need to loosen the starboard one at the same time. If it needs replacement should I also replace the starboard one even if in good condition?

    As a further question, what happens if a diamond breaks, does it result in mast failure?

    1. Hey Steve,

      You would need to loosen the other counterpart to that stay for sure. It is just good practice, will keep the mast straight, and also make your life easier for removal install. Now, do you replace both? I don’t know. How old is the standing rigging? Why are you replacing the one? If it is not all due for replacement and you are just replacing due to damage, just do the one, but loosen both sides to do this.

      Hope that helps and thanks for the visit.

      ~T.R.C.

  13. Hello! I recently purchased a keel-stepped 1982 Goman Express 30 which came with an Alado Furler. I have been sailing it since May of this year. My question is this: Despite relocating mast wedges at the cabin roof to bias the lower mast aft about 2″, I still have a pronounced backward bend (10 degrees or so) just above the highest spreader. When sailing on jib alone, most wave action causes the mast to pump right at the bend point. I have a split backstay that is as un-tensioned as possible and the forestay only has another inch of adjustment left. There is no baby stay.

    How can I get the bend out of the mast? How concerned should I be that the mast might break at that point?

    Thanks in advance for your reply!

    Eric Hassam – Delta Flyer

    1. Hi Eric,

      Thanks for taking the time to comment on our site. It sounds like you are on the right track. So one other adjustment that you have is the mast step position. This greatly affects mast bend on keel stepped masts. For a stronger bend and less rake, move the mast butt aft. For more rake and less bend (probably what you need to try), move the mast step forward a bit. If neither of these help, you may be off to have your headstay shortened and this means it is too long. This is likely not the case, but it is a possibility.

      Keep in mind….A mast should have a slight aft rake bias along with a small amount of mast bend. This is quite normal. You can send us a picture if you’d like a second opinion on if it is over-bent. Having said all of that, even if you remove all of the mast bend, the mast may still pump. This is a design flaw in many spar designs that lots of end users have experienced. This can be remedied by redesigning the stay lay out. Is there a place for a staysail stay and/ or runner backstays? If so add them. Is there a place for a baby stay? If not, that may be a consideration.

      Thanks again and I hope that helps.

      ~T.R.C.

  14. Hi, I have a 48 foot yawl with a 7/8 fractional rig, is the tuning procedure the same as a masthead rig? I seem to have trouble getting aft rake and proper headstay tension. Also, is there a particular tension number the upper shrouds should have? many thanks in advance

    1. Hi Bill, thanks for taking the time. 7/8 is very close and I would treat it like a masthead rig, especially if the none of the spreaders are aft swept. Tesnsion the headstay using the backstay(s). This should pull the top of the mast aft. If there are any other forward stays, i.e. stay sail stay, forward lowers, or anything else that could be holding the mast forward, go ahead and loosen those completely. You then may need to tighten the Tri-attic (the stay that connects the top of the mizzen and top of the main) if present. OR if the mizzen needs more rake too, then lossen all forward stays and pull it back using the available aft stays for this as well.

      Hope this helps and please email us and send some pictures if you need more help.

      ~T.R.C.

  15. I have a 1972 Morgan 27, which has both forward and after lower shrouds. I wish to remove the forward lowers so I can trim a 110% jib inside the stays. I see a lot of boats without forward lowers and think this will work OK, but wonder if I should increase the size of the aft lowers and beef up the chain plates. Any suggestions?

    1. Hi John,

      Unless there are other owners of the same boat that have experience in this I would NOT remove them. Boats without forward lowers are usually using aft swept spreaders. This type of rig has a different dynamic altogether. They are also usually fractionally rigged. I think the result would be sever mast pumping if not worse along with other potential issues. You can still utilize inboard sheeting via some different jib lead arrangements. I think this would be time/ money better spent. Look at Catalina 27's....
      

      Hope that helps.

      ~T.R.C.

      1. THANKS FOR YOUR INPUT. I AM GOING TO REMOVE THEM ANYWAY AND SEE WHAT HAPPENS. “HOLD MY BEER, WATCH THIS….” FAMOUS LAST WORDS.

  16. I have rod rigging on my Beneteau 32s5

    Any other guidance on tuning them vs wire rigging

    1. Hi and thanks for commenting.

      Just follow the guidelines in the write up. The over all goal is that the mast needs to be straight and in-column when looking at it from side to side.

      Fore and aft, the mast should show a very slight lean aft. Depending on whether or not the spreaders are in-line or aft swept; you should also see some slight bend if there is any aft sweep to the spreaders just from the tension of the uppers.

      A Rod stay tends to run a bit tighter than wire, so keep that in mind.

      For racing, ideally once the static tune at the dock (the part we just talked about) is done, go out and sail tune. Do this by going hard on the wind and checking to see if the leeward shrouds are just starting to dance, this is ideal. If they are swaying about they are too loose for the current conditions. If the leeward shrouds are tight, they may be a touch to tight. Tension and loosen as needed; count what you did and to what shroud, then tack and do the same to the other side.

      ALWAYS secure the turnbuckles when you are finished adjusting them.

      Hope that helps.

      ~T.R.C.

  17. Wow, I would hate to be charged by her for three trips up the rig and forget the screw driver the rubber plugs that are sacraficial and replaced everytime removed just to clean the stainless 1×19 rigging.

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