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. 


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.

28 thoughts on “How to Tune a Sailboat Mast

  1. 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.


  2. 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.


      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!

  3. 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?

  4. 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.


  5. 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… 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.


  6. 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.


  7. 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.


  8. 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.


  9. 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.


  10. 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.



    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.


  11. 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.

Leave a Comment or Ask a Question, We Will Reply!

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.