View Full Version : Spar size for Lateen rig

12-26-2007, 09:46 PM
Hi All, Great forum,
I'm putting together a lateen rig for an old sailboat. I built a Doug Fir 12'-6"mast that is 2 1/2" diam. The sail will be approx. 85sqft. I think I will taper the mast to approx. 1 3/4" at the peak. My question concerns the diameter of the spars. The boom will be 12'-6" and the yard will be 14'-6". How large should the diam. of these spars be? The sail is Dacron cut down from a larger sail. Should they be tapered at the ends?


Jay Greer
12-26-2007, 10:29 PM
An excellent source of information can be found in the various books by Uffa Fox. On line research for a book called "Rigs and Rigging of Yachts" might also be helpful. You are not dealing with a rig that is of much consequence as to strains. Therefore, you might wish to rely on your own sense of proportion in this respect. Trust your own instincts!

Todd Bradshaw
12-27-2007, 12:39 AM
I'm not sure anybody has ever figured out and published suggested diameters for lateen spars, but I suspect something in the 1.5"-1.75" max diameter range would be about right for the yard and boom. Tapering to maybe 75%-80% of maximum toward the ends will both reduce weight and may improve the in-use bent shape. In any case, it's not unusual to need to add 2"-4" to the luff and foot curves of a lateen sail to help allow for spar bend while sailing. Excessive spar bend robs the sail of draft and power, so whatever you can do to maintain maximum spar stiffness (even if it means carrying a bit more weight aloft than you might like) is usually well worth doing. It's also wise to avoid mid-boom sheeting, which tends to bend the boom and rob the lower half of the sail of draft every time you sheet-in hard.

12-27-2007, 09:35 AM
I recall that pictures of lateen rigged boats showed the yard made up of two pieces, lashed together with considerable overlap in the middle, which would make the mid part of the yard stiff. Most lateen rigged boats did not have booms.

12-27-2007, 10:13 PM
Thanks for the input guys. Todd , you answered my next question before I could even ask it as I was wondering if I should add some round to the sail at the luff and foot! I think I will use 1.75" diam. as a starting point and go from there.

Thanks Again

02-13-2008, 03:21 PM
sailboat 005.jpg (http://www.woodenboatvb.com/vbulletin/upload/attachment.php?attachmentid=306&stc=1&d=1202932413)

Todd and all forumites,

Please forgive the partially non-wooden boat pictured ( If you can see it in the tiny photo ) Im also building a wooden kayak for my boy. Todd, I've read your book 15 times or so in the last month. Fantastic stuff, Although, I think my girlfriend has had enough of it. Anyway the boat originally had a Marconi rig, 20 ft mast 85 sqft sail. The lateen I came up with is roughly 85sqft, mast is 12'-6", Yard 15'-2" and Boom 13'-8" i purchased a large sail on ebay and cut it down ( got enough dacron for about 5 more boats) The mast goes from 2.5" at the step to 1.75" at the peak, Yard and boom are are rectangles roughly1.75" x 1.625" the yard tapered a bit at the peak. i tried your spar bend test from the book using 30lbs and the yard bent 2.5" spar 2.75" I temporarily hung the sail with zip ties to see how it would look. Does anything bad jump out you from the photo? (aside from the fiberglass) I think Im gonna run a traveler across the stern then a block on the end of the boom to a block midboom down to the block and camcleat arrangement on the daggerboard trunk. Again, with your book I go through the different setups once every couple of days. I sewed the sail with an '86 vintage kenmore with a 20 needle and it worked quite well. I thank all in advance for any advice, constructive criticism etc regarding this little boat. Sorry about the little photo.


Todd Bradshaw
02-13-2008, 03:57 PM
Those are pretty decent figures for the bend. Sometimes they can get up into the 8"-9" range and it really presents problems. If you have to build for 8" of bend in high winds, your sail tends to be awfully baggy in light air when the spars aren't bending so much. The 2"-3" range is good and reasonably easy to work with. The only concern that I can see is the fabric orientation. Normally you build with the weave and panel seams either paralell to the line of the leech (vertical cut) or 90 degrees to the line of the leech (cross-cut). Keeping the weave square to the leech helps keep the leech from stretching out and flapping in time. Building as you have with the weave 90 degrees to the luff means that the thread lines strike the leech on a bias and this can increase fabric stretch along that edge rather dramatically. This is one of the big problems with making new sails from old sails. There can often be plenty of cloth there, but much of it may not be big enough chunks that also allow you to orient it properly for a decent sail lifespan. Anyway, try it and see. If needed, you can probably either hollow the leech more or open up a couple of seams at the back end along the leech for a couple of feet and increase the overlap gradually as needed to tighten up a stretched leech. Next time though, lay your panels with the leech in mind, even if some have to be pieced with vertical seams to make full-width leech-to-luff panels. Keep at it. That's how we learn!

The farther forward you can place that final boom block, the less your mainsheet tension will just be bending the boom and pulling the draft out of your sail. I might even put it on a little rope loop around the boom, duct-tape it in place and go sailing to see what block position yielded the best looking sail shape and the easiest sail handling.

02-13-2008, 08:52 PM
I originally was going to piece together a polytarp sail just to test the rig on this boat, but i got the sail so cheap on ebay I figured If the machine wouldn't sew it no big loss. To my surprise it worked great. On some portions of this sail there were 6-8 thicknesses of material and I had no real problems. One thing i tried was to take the machine out of the cabinet and mount it on little wheels so i could roll it along the sail edge on the floor. It didn't really work like i thought, i think it might work better with no wheels and a piece of carpet on the bottom of the machine so i can feed a couple of feet through, move the machine , feed a few more feet etc. So the plan now is to see how this rig sails and eventually sew a new one. My next book purchase is the Sailmakers Apprentice but If i start studying another book I'll be out of the house. Thanks for the advice


Todd Bradshaw
02-13-2008, 11:50 PM
Moving the machine is a new one, though I have heard of people putting the rolled-up sail on a skateboard so that it could roll along as the machine fed it through. Personally, I have a panel that comes out of the hardwood floor in my living room floor where I can plug in a different panel that's been routed out to hold the machine. The whole floor becomes a table with the machine's bed flush with it's surface and the sail just slides along on the floor as the machine feeds it. However, if you're already in trouble for having too many boat books, taking a sabre saw to the living room floor to do boat stuff might not be such a great idea....

I had a friend who managed to obtain a huge vertical slab of a tree trunk and decided to cut it into an oval about 12' long to make a new dining table. It was too heavy to handle and too thick for his sabre saw, so he built the base and put the slab on it at table height. Then he mounted his band saw on wheels and rolled it along, all the way around the table. as he made the cut. I was impressed.

05-22-2008, 07:04 PM
Todd Bradshaw and fellow Wooden boaters,

I finally got a chance to sail the Fiberglass (sorry) Manowar. Before I am chastised let me say I made the Mast, Boom and Yardarm out of wood, I cut the sail down from a larger one and sewed it myself. Using hints from Todds great book and this website I made rope grommets to hold the sail on, affixed brass grommets on the sail, fashioned a new wood daggerboard trunk, and built a new rudder and tiller. She seemed to go quite well although the wind was 15-25 mph and i was more than a little nervous. Just my luck it started to hail when i was halfway down the lake. All this of course is just preparing me for the eventual wooden boat build. I'm just trying to decide what to build, So many great boats out there.

Todd Bradshaw
05-23-2008, 11:40 AM
Congrats Joe, it looks good! Hail must be a rather interesting sailing experience. I haven't tried that one yet.