Flatten Your Mainsail Foot With an Outhaul

You’re familiar with basic mainsail running rigging, right? The halyard hoists it up the mast and the main sheet adjusts the angle of the sail to the hull. Both lines are important but they don’t adjust the aerodynamic shape of the mainsail, which can make a big difference if you want to get the best performance out of your mainsail.

There are three potential control lines for your mainsail to adjust its shape. Each line controls the tension on one of the three sides of the mainsail. To control luff tension, you need a Cunningham or boom downhaul like I describe in Control Mainsail Draft with a Boom Downhaul. To control leech tension, you need a boom vang like I describe in Control Your Mainsail Shape Better With a Boom Vang. In this post, I describe a trimmable outhaul to control the foot tension.

Most first generation C-22s and similar sailboats came from the factory with a simple loop of line between the mainsail clew and an eye strap at the end of the boom similar to the picture below. It holds the sail in place but that’s about all. You can’t easily trim it while sailing. If it’s loose enough to make connecting the clew easy, then it isn’t tight enough for moderate to heavy winds. If you take the time to cinch it up tight, you’ll have to untie it to take the sail off if you trailer sail. By then, the knot could be hard to loosen.

BEFORE - Easy or tight, but not both
BEFORE – Easy or tight, but not both

The solution is to replace that crude loop of line with a trimmable outhaul that consists of:

  • (2) Harken 085 double blocks or equivalent, one with a becket
  • Fixed eye snap shackle or halyard shackle
  • (2) Harken 072 3/16″ shackles or equivalent
  • Ronstan small V-Cleat Fairlead or equivalent
  • 5′ x 1/4″ New England Ropes Sta Set or equivalent

The pictures in this post show a five part (five line segments) outhaul only because those were the blocks that I had on hand when I rigged the outhaul. You could use fewer parts. I recommend at least two. The line is white with blue flecks in keeping with the color scheme that I describe in Choose Your Running Rigging Colors Logically. Notice in the picture below that I spliced an eye in the end of the line where it attaches to the becket. You could also use a bowline knot there but I prefer the neatness of spliced eyes, particularly here at the end of the boom where four lines are attached (main sheet not shown).

AFTER - Easy to attach and trimmable
AFTER – Easy to attach and trimmable

Size does matter

The challenge in this setup is to get the overall length of the outhaul as short as possible. On a C-22, there’s only about 10″ from the mainsail clew to the eye strap at the end of the boom. If the combination of blocks and other hardware is too long when you tighten the outhaul, the blocks will meet in the middle before putting enough tension on the foot of the mainsail. To solve the challenge, use the shortest shackles you can find. You might also need to shorten the becket on the one double block. Another option is to attach the working end of the line around one of the sheaves of the block itself, but that will result in less mechanical advantage.

To make the outhaul as easy to attach as possible, add a snap shackle to the working end of the outhaul for hooking to the mainsail clew. Install the fairlead cleat on the same side of the boom as where the line exits the outhaul blocks (port side in the picture below). The fairlead keeps the line captured at the boom if it gets out of hand. A foot of slack on the end makes the setup easy to trim while under sail and to loosen when removing the sail to head home.

The two lines that you see hanging down from the aft end of the boom in the pictures above are the working ends of the topping lift and jiffy reefing lines that I’ve installed on Summer Dance. They’re held out of the way in the pictures for simplicity. I describe them in Make Your Boom More Useful with a Topping Lift and Single Line Jiffy Reefing Made Easy, respectively. To see how all four systems (including the main sheet) fit on the boom, see the pictures below.

Boom end with all rigging shown
Boom end with all rigging shown
All four lines sharing the end of the boom
All four lines sharing the end of the boom

Keep It Simple, Skipper (KISS)

If the outhaul shown above seems too complicated or expensive for you, a simpler version is even easier to set up.

For a three part (three line segments) outhaul, you’ll need:

  • Harken 083 single block with a becket or equivalent
  • Ronstan small V-Cleat Fairlead or equivalent
  • 4′ x 1/4″ New England Ropes Sta Set or equivalent.

Install the block on the boom eye strap, the fairlead cleat on the side of the boom, and reave the line as shown in the picture below.

Simpler 2:1 outhaul is also shorter
Simpler 2:1 outhaul is also shorter

In this system, the line runs through the clew grommet itself. The line isn’t as easy to trim as with multiple blocks, but it’s still easy enough.

For the complete collection of rigging projects like this one, purchase my ebook Do-It-Yourself Small Sailboat Rigging.

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13 Comments Add yours

  1. Dave Larson says:

    Have been reading your posts with great interest since purchasing a ’74 in February. Planning to do the topping lift and outhaul as soon as I repair the forestay reinforcement. I’m curious about your costs. For this project, the cost of the 085 and 086 blocks alone is in the $90+ range from the two suppliers I checked. Can you recommend a less-expensive source for hardware? Thanks,

  2. kbilling says:

    Hi, Dave

    Yep, they’re pricey little buggers! The main reason that I used that size of blocks was because I got the pair of them on eBay for around $25, so it was a no-brainer. If that had not been the case, I would have used something like the Harken micro blocks 227 and 228 at around half the cost. Those are also the size that Catalina Direct uses in their kit. Another benefit would be that their combined length is even a little shorter, which might make the difference with a long-footed mainsail.

    When I need to buy parts at retail instead of eBay, I like defender.com. They don’t offer free shipping but their prices are among the lowest for most things and they have a great selection, which means I can usually get several things on the same order to spread the cost out and still be less than most other retailers.

    Good luck with your improvement projects. Hope to see you here some more!

  3. Dave Larson says:

    Thanks, $tingy. I figured you had to have done something like that. Just started the topping lift project today: bought a piece of 7/64″ Amsteel and put an Brummel eye in one end and another Brummel eye with a thimble in the other. Will have to wait till the next time I drop the mast to install it. I think the necessary hardware is already on the boom. Was thinking about attaching it to the main halyard for a quick check of the concept, either with or without the mainsail. I know the lead won’t be quite the same as attaching it alongside the backstay on the masthead truck, but it should be close.

    1. kbilling says:

      Glad to hear you’re going for it! I think you’ll like how handy it is to just reach up and hoist the boom up whenever you need to.

      Must be kinda tricky splicing line that small. I’ve only done as small as 1/4″ so far and that was tough enough. Did you make a core to core splice?

      1. Dave Larson says:

        Had to look up core-to-core splice, but no, that’s not the technique I used. The Amsteel line is single-layer, not cored. I used these instructions (http://www.l-36.com/brummel2.php and http://www.colligomarine.com/docs/misc/splicing_instructions_for_web_rev_1_2.pdf) modified to account for the fact that the smaller line is 8-strand, not 12. {I can’t find any sites that call the 7/64th rope as 8-strand, but that’s what I have.
        It wasn’t hard to work with at all.

      2. kbilling says:

        Interesting splice and it looks faster to make. I might try that on the lazy jacks I’m making. They don’t need the full strength of a conventional eye splice and I don’t want to have to make 8 of them!

  4. The most no-nonsense, comprehensive forum I have found for our boats. Thanks. 1987 Cat. 22 SK #14218

    1. kbilling says:

      Thanks for your comment, John. We could all gain from less nonsense and more common sense.

  5. Nic Reid says:

    Hey $tingy!

    My name is Nic Reid. I’m over in Bend, OR. I just bought a Tanzer 22, and I’m SOOOOOOOO excited to get going with some projects. I stumbled across your blog last night when I was looking for info on how to do projects on the cheap, and I can’t believe how awesome it is! You’ve done a stellar job, my friend. I’m working through the Mast Step post at present.

    I noted that you said there is a downloadable checklist with mast step coaching and a boom crutch document as well. Call me thick, but I’m not finding those. Any help would be appreciated.

    I’m excited to follow your posts. Are you still actively sailing in N. Idaho?

    1. Hi, Nic

      Congratulations on your new-to-you Tanzer! You’re in for lots of fun.

      There’s a trailer sailor launch checklist and a dimensioned drawing of a mast crutch on the password protected Downloads page. The password for the page is in the confirmation email that you should have received when you subscribed. If it’s not in your Inbox, look for it in your Spam or Junk folder. If you can’t find it anywhere, use my Contact page to send me an email and I’ll send you the password.

      I sail weekly on awesome Lake Pend Oreille in north Idaho. I’ve been coming here for years and still haven’t explored it all. Bend is pretty cool place too!

  6. Ed in Gig Harbor says:

    So, testing my understanding of pulleys used in combo like your initial project above… if I modified your second 2:1 example using a single block at the sail and a single block at the boom end, it eould just give a bit more leverage on the outhaul line, but less than the double block arrangement, right? Is it possible to pull the foot too taunt and harm the sail?

    Thanks for sharing all your projects…great inspiration to make some modifications and maybe even get my V21 to sail ‘better’.


    1. Hi, Ed

      Two single blocks wouldn’t give you any more mechanical advantage, it would still be a 3-part tackle. But it would reduce friction considerably. You could try it that way and see if you like it and if it’s not strong enough, replace one of the blocks with a double block to increase the ratio.

      It would take a LOT of leverage to damage the foot your mainsail with an outhaul, especially if you have rope in the foot. The only time that you would want it as tight as possible is in the highest wind conditions, which most skippers don’t want to brave anyway.

  7. Cookie Monster says:

    Thanks Stingy. I implemented option 2 due to space constraints on my gulf coast 18. My only change was to use a horn cleat. Love the system!

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