Lazy jacks can be one of the most complicated rigging systems on a trailerable sailboat but they have a simple function. That is, to cradle the mainsail when it’s lowered so that it doesn’t spill onto the cabin and cockpit. If you usually have another experienced crew member aboard, that person can gather and tie down the mainsail and you don’t need lazy jacks as much. But if you often sail short-handed or are just plain lazy, lazy jacks can make coming to a dock or anchorage a smoother, more pleasant event for everyone and it helps protect your mainsail.
There are many lazy jack kits available, from simple stationary setups designed for boats that spend most of their lives in slips to complicated retractable systems that you can work from the cockpit. A certain online Catalina parts retailer offers a simple but expensive kit specifically for the C-22. The problem with most systems is that they aren’t designed with the trailer sailor in mind. Either the lines fasten to the boom, which needs to be removed while trailering or they fasten to the mast and you need to reeve the lines through fittings on the boom in order to set them up. Anything that takes more time during setup means less time sailing and is the enemy of a trailer sailor.
Rock a bye, mainsail
The only system that I’ve found that combines good function with trailering convenience is the Sail Cradle Mark IV from SailCare. It’s made partly of regular rope and partly of shock cord. The rope lines form an inverted Y at the top and fasten permanently to the mast like other systems. The unique part is the shock cords that form an M shape at the bottom. You temporarily attach these to hooks and eyes on the boom during use. When it’s time to haul out and go home, you simply disconnect the shock cords, stow the system tight against the mast, and the boom can come off without any dangling lines attached. For a video of the system in action, skip ahead to 3:10 in this YouTube video of the system installed on a MacGregor 26M. The design is so clever that I built a set myself on Summer Dance at a fraction of the price.
Geometry 101 revisited
The trick to this project is determining where to mount the hardware on the mast and boom and how long to make each line. The length and position of each line is important if the lazy jacks are going to catch the mainsail or just deflect it onto the deck as usual. It’s also important that the mainsail batten ends don’t catch in the system on the mainsails’ way up or down.
Thankfully, there are standard formulas that you can use as a starting point and then fine tune depending on the specific sail, its battens, and so on. Using the C-22 P dimension of 21′ and E dimension of 9.66′, here are the formulas:
Top of first segment: P * 0.70 = 14.7′
Height of first segment (and first cord length): P * 0.25 = 5.25′
Height of second segment (and half of second cord length): P * 0.25 = 5.25′
Mid-boom attachment point: E * 0.40 = 3.86′
End of boom attachment point: E * 0.85 = 8.21′
These dimensions basically divide the mainsail height into quarters with the lazy jacks spanning the lower three quarters. And it divides the mainsail width about in half with the lazy jacks spanning the whole width.
To obtain the shock cord length, I temporarily rigged the bottom segment with regular cord, measured the length of that cord and then subtracted two feet. With the shock cord that long installed, I stretch it about one foot to pull the middle of the M shape down to hook it onto the hammock hooks I show below. Depending on how stretchy your shock cord is, you might want to subtract more or less. Start by subtracting one foot and test the system for a while to see how well it works. Then if you want to make it tighter, you can shorten the shock cord more.
In the following pictures, the upper and middle quarters are made of blue rope and the lower quarter is made of white shock cord.
Shock cord and awe
On Summer Dance, I attached the top segments to the mast with eye straps angled 15 degrees down and aft (to bisect the lower segment). I tied nylon thimbles into the ends of the line segments with fisherman’s knots. Each middle line segment is one piece of line 10.5′ long. Each segment is able to run freely through the thimbles of the adjacent segments. This lets the system adjust to different boom heights, angles, and it lets the system stretch for storage.
I attached the stationary ends of the shock cords to eye straps angled up and aft on the mast at about boom height.
I mounted hammock hooks on the boom 4′ from the mast. This location seemed to hold the middle battens best.
At the end of the boom, rather than drill more holes for more hardware (on Summer Dance, it’s pretty busy there already if you look at this picture), I simply threaded a loop of cord through holes molded into the fairlead cleats that were already in about the right location. Hooks in the ends of the shock cords clip into the loops on either side. If you don’t have cleats at the end of your boom, install a pad eye on each side instead.
Tweaking with twings
During testing, the mainsail battens fouled in the lazy jacks more often than not since the lazy jacks were only a few inches apart to start with. So I rigged twings from the ends of the spreaders to the upper eyes to pull the lazy jacks apart about 2′. This forms a sort of funnel (as you can see in the first picture) and gives the mainsail plenty of room to flail around without the battens fouling.
The sail cradle/lazy jacks work well out on the water. I can point Summer Dance into the wind and drop the mainsail neatly into the cradle in seconds. When we’re tied off at the dock, the cradle makes flaking the mainsail properly easier than before because it’s partly done already.
The beauty of the system is really in the shock cords. For stowing, you can stretch them to hook onto whatever hardware you already have that is convenient. When I have the mainsail tied up and covered, I simply unhook the middles of the shock cords from the hammock hooks. This slackens the whole system so that it’s out of the way when it comes time to hoist the sail again and the lazy jacks don’t affect the sail shape. I can also pull the slack down for the night and loop it under one of the cleats on the mast to prevent mast ringing.
When it comes time to put Summer Dance on the trailer, I unhook the ends of the shock cords from the boom, clip them into the lower eye straps and loop the slack under the mast cleats. This holds the whole system neatly out of the way until next time.
Without the expensive blocks or cables used in other systems, all the parts of this design (about $30) are easily and economically replaced as needed.
Reliability update
I’ve been using this lazy jack system continuously for six years and I still like it. I have replaced the shock cord once but the rest of the system hasn’t experience any noticeable wear.
I also made one modification to eliminate the top segment entirely and instead secure the middle segment to eye straps mounted at the midpoints of the spreaders. This simplifies the system a little and it solves one small annoyance. It simplifies the system because it eliminates the need for a top segment and the twings are no longer necessary. The spreaders hold the lazy jacks open instead.
And the annoyance is that, after raising or lowering the mast and when walking the mast forward or backward, the top segment wouldn’t pass through the mast crutch without manual help. That meant that another crew member had to help out or I had to lay the mast down, pass the upper segment around the mast crutch myself, and then resume stowing the mast. Eliminating the upper segment also eliminated that problem.
But other than that modification, I wouldn’t change a thing.
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The $tingy Sailor 
Hi Ken, I like your lazy jack system with the shock cord. I would like to do the same thing with my 1974 Ranger 20. My question is on the size of the shock cord you used and size and type of the line. Any info will be appreciated. Allan
Hi, Allan
I used 1/4″ marine shock cord. For the lines, they’re currently some cheap 3/16″ utility cord that I got for about $5 for the bundle. I wanted to rig the lazy jacks up with something disposable first so that I can adjust the lengths, if necessary, without wasting more expensive line. I have some 1/4″ Sta Set that I’ll replace them with when I want to make them permanent, probably at the end of this sailing season. I’ll splice eyes in all the ends at that time. Those should last a lifetime. But you could just as easily use 3/16″ line or even 1/16″ vinyl coated cable with rings instead of thimbles. They don’t have to be very strong. I’ve found that having them a different size and color than my running rigging helps to distinguish them when setting up the rigging.
Good luck with yours. Let me know how they work out for you.
Ken
Hi Ken, I just found your site. I’m a DIY guy as well and love your site! I would like to add this system to my Catalina 25. Question.. How long is your shock cord, and how did you go about
determining the length of it?
Thanks,
Warren
Hi, Warren
I don’t have the length of shock cord handy right now, but the way I calculated it was to temporarily string the bottom section tightly with regular cord and then subtracted a foot or two for stretch. I recommend starting with one foot and testing. You can shorten it more if you want it tighter. I shortened it a little too much, so the shock cord is pretty tight getting it into the hammock hooks from the cockpit with a boot hook and actually raises the boom a little when the main sheet is slack. But hey, it’s like having a built-in boom kicker! I’ll revise the post to make this point. Thanks for bringing it to my attention.
I hope you find lots of projects that you can do on your C-25. If I ever get a larger boat, that is one that’s on my short list to consider.
Thanks for visiting and hope to see your around here again in the future!
Hi Warren, I’ve also got a Catalina 25 that I’d like to add this to. I often sail single-handed and this would be loads of help. Did you ever do it? How’d it work out? Thanks,
Mike
Ken!
Thanks for this idea. I am rigging a similar system to my Compac – 16. I have found much of your blog to be enlightening and entertaining! Hope to see more to come!
Ken, I love your innovations. I also have a C22 & I am about to employ your lazy jacks, but I was considering doing away with the top segment and securing the middle segment to the spreaders through an eyelet riveted to the top of each spreader about a foot from the mast. Any thoughts about this “tweak?”
That would probably work fine. Since the lazy jacks would be pulling downward, I would rivet the eye straps to the bottom of the spreaders instead, similar to the eye strap for the flag halyard that you see in the second picture. Doing that modification would put the lazy jacks more in the way of a flag halyard so you’d probably want to use one of the other options that I describe in Make a Flag Halyard to Fly Your Favorite Colors if you want to fly a flag.
Good afternoon Ken, i have a mac 25 that i’d like to incorporate your ingenious system to,however, i want to eliminate the top segment & install something about a foot out on each spreader but am wondering if i need to use swivel blocks on the spreaders or will eye straps work ? also do you think that 3/16″ shock cord & lines will be ok ?just out of curiosity what is the swivel block shown in the 2nd picture down, on the starboard spreader on your boat used for ? i can’t see where the lines run to.thanks in advance for any reply & thank you for sharing your info, Great Site !! I’ll be looking forward to hearing from you.
Mick Hodapp
Hello, Mick
Eye straps will work just fine on the spreaders. The top segments of the lazy jacks are stationary and don’t rotate much at all. Smaller lines and cord will work too, it just might be a little harder to see and to handle. The small block that you see in the picture is for a flag halyard. Make sure you run your lazy jacks inboard of it if you add one.
Thanks for your questions and have a Happy New Year!
$tingy
Thanks for the info & the quick reply & ditto on the happy new year !
Mick, I did exactly what you are asking on my setup and it works just fine. I used the d-rings without any blocks and the line moves freely through the d-rings. Like Stingy said, there is minimal movement.
thanks for the reply,that is good to know !
Hi Stingy, this is an amzing setup.
I love the idea of attaching the jacks directly to the spreaders instead of the mast, leaving a wide opening.
I’m a bit confused about one thing though. I assume you ease the lazy jacks by releasing the shock cord from the mid-boom hook. But that will cause it to turn from an ‘M’ shape into a upside down ‘U’, where it’s strung across the two mid-height eyelets. It’s now out of reach when you go to harden the jacks again. How do you retrieve the midpoint of the shock to get it back on the hook? You must climb up on the cabin top?
Thanks!
Hello, D
You’re right. When released, they’re out of reach. If the wind is low, I often jump up there and grab them by hand and rehook them. If not or if I remember to get them earlier, I reach up with my boat hook and pull them down with that.
Thanks for asking,
$tingy
Hi $tingy,
Did you ever modify your lazy jacks to terminate at the spreaders instead of the mast? If so, any concerns about the lazy jack’s down force on the spreaders?
I’ve been using the same design lazy jacks on a MacGregor 26M for a couple years and am very pleased with them.
Thanks much your great website. It’s excellent!
Joe
Hi, Joe
No, I haven’t made that change yet but I might do it this winter while I have the mast down. I’m not concerned about them pulling down on the spreaders too much, there isn’t much force applied by the bungee cord and the upper shrouds will resist it.
Thanks for your question,
$tingy
Good morning folks, does anyone who has done this system from the spreaders on a C-22 or a Mac-25 remember the total amount of shock cord they used? Thanks!
Hi, Mick
If you build the lazy jacks like I describe here, with static rope for the upper segments and shock cord for the lowers, then the amount of shock cord is the same regardless of how you rig the uppers. After I measure it, I’ll update this comment soon with the amount that I used.
Thanks !
I posted a comment sometime back about your ingenious lazy jack system that i want to use on my Mac25 & am finally ready to take a shot at putting it together & have all of the materials & tools except for the pop rivet tool that i see you used to fasten the hammock hooks to the boom. My question to you is, could self-tapping aluminum or ss screws be used instead of pop rivets & if so what size & which metal would work the best ? the reason i ask this is that i have never used a pop rivet tool & don’t want to buy one unless it’s necessary. if pop rivets are the only way to go would ss rivets have to be used & if so, what would you have to do to prevent corrosion between the different metals ? ( we’re in the Pacific) Any input would be greatly appreciated & thank you ! Mick
Hi, Mick
Rivets aren’t required and you could use tapping screws with the same results. I just prefer to use rivets in aluminum to avoid the grief of galvanic corrosion that comes with using stainless steel. If you do decide to mix metals, I recommend applying a corrosion inhibitor like Marlube so that you can remove the screws in the future if you need to.
Thanks for your question,
$tingy
Good morning fellow sailor & thank you for the speedy reply & the information, hopefully i’ll put it to good use ! Iove this site, keep up the good work !
!!! 2 seconds ago, I need to figure out a lazy jack system if I plan to sail alone….<>. YOUR POST. Thank you, Carmen
I’m looking to install lazy jacks on a MacGregor Venture 2-24. I like this set up and watched the video of the install on a MacGregor 26 at the link you provided. I guess my only concern is the downward pull of the sail on the spreaders as the sail is being dropped and possibly luffing around in the wind, as others in the comments above expressed as well. I replaced the spreaders on my boat last summer, and while they are firmly attached at the mast with fairly hefty brackets and bolts, the pipes themselves are remarkably light and the upper shrouds are only held to the outside spreader ends by a pair of flimsy plastic caps screwed into the spreader ends. I’m afraid if any weight or force is applied to the spreaders, it might bend them or break the plastic in the caps, or both. I was wondering if anyone in the years since you first posted has tried your suggested mods, eliminating the upper segment, its connection to the upper mast, the twings and connecting the jacks directly to the spreaders? P.S. I’m a big fan of your posts. I took your suggestion, bought a Highfield lever and rigged up a new forestay. It made all the difference — so much easier — when raising and lowering the mast. Thanks.
Hi, Joseph
I’ve had several readers ask about the mod but I’ve not received any reports of anyone actually doing it yet. If you use shock cord for at least one of the segments, I don’t think it will transfer enough force to the spreaders to do them any harm. Sailcloth is so slippery that the sail falls easily onto the mast. I’ve doused my mainsail into these lazy jacks in tempests several times without harm.
Any of you other readers out there try them attached to the spreaders?
$tingy
Where did you get all your supplies, do you sell package?
I get them from various suppliers, Bob. Due to the many possible variations in sailboat rigging, I don’t offer a kit.
Hammock Hooks, where did you get them? I have or can get the rest of the stuff.
I don’t recall exactly where I got them but if you search for Sea Dog Hammock Hook, you’ll find multiple options.