Lugsails: Vertical vs. Crosscut

[Marty J]

I'm currently doing some book learning to prepare for a lugsail project with a few other people. I've noticed that sail plan drawings almost always show vertical seams, but the actual sails I've seen are more often crosscut. As just one example, CLC's marketing materials for the Northeaster Dory show a line drawing with a vertical cut balanced lugsail, but photos of the balanced lugsail that CLC sells for the boat show crosscut construction.

The question is: what are the reasons for picking one orientation over the other? Does one allow for better draft placement control via broadseaming? My understanding is that the stretch of modern Dacron doesn't vary enough between the warp and weft orientations to matter for small sails, and it doesn't look to my eye like the bias angles along the luff and the throat-clew line vary significantly between vertical and crosscut.

Our original plan was to build a crosscut sail because that's what we have experience with, but all these vertical cut sail plans are making me think twice. The vertical cut sails (of any type) that I have seen in the wild are either going for the "traditional" look or are made of traditional materials. That isn't our goal here, so if it's the main consideration then I think we will move ahead with a crosscut sail as originally planned. Wouldn't be my first time overthinking something like this!

For reference, this will be an 80 sq. ft. balanced lug for a Hvalsoe 16. If you're interested, the Center for Wooden Boats is hosting Eric for a virtual talk on Friday, February 19. This boat is truly a work of art.

Thanks in advance for everyone's insights. I would also be curious to hear thoughts on the same question for gaff, sprit, and standing lug rigs, as we will be building sails of those types in the future.

[Todd Bradshaw]

Either can work fine. I think you will find that sailmakers who concentrate on traditional sails are more likely to cut vertically and those who tend to make mostly sails for modern designs (especially 3-sided sails plotted with a computer) feel more comfortable cross-cutting, as it is what they are used to. There are some potential pitfalls though, which you hope folks who usually make modern sails are aware of. Luff round, for example, as a draft creating means works great on Marconi sails, gaff sails, gunter sails, spritsails and just about any sail attached along the aft side of a mast. It does not work well on a lug sail. The amount of downhaul tension required to pull that round into working sailpower on a lug (as opposed to just hanging there wobbling back and forth as it tries to find a stable angle to the wind) is crazy and really hard on the sail. It does not take a seven piece downhaul to firm up a lugsail's luff properly (of any cut). It takes a proper luff profile (straight or slightly hollowed on longer ones) and reasonable luff reinforcement.

I have always cut nearly all of my lugs vertically. I think it looks more historically appropriate and many of the boats which I built sails for were antiques, where we were trying to mimic the basic look of the original cotton sails of that period. They are broadseamed, but at the head and the foot, rather than the luff. Given a choice, I build them loose-footed with some foot round and straight luffed up to about 6-7 feet of luff length. Longer luffs get slightly hollowed, which helps to firm them up in use. Doubled luff tape was used on small sails, with maybe a piece of Dacron webbing inside the luff tapes on bigger sails unless the luff is roped. Basically whatever it takes to produce a seriously no-stretch luff. Leeches get hollowed about 1" for every 8-10 feet of leech length. The heads have some round - a little bit for creating draft, but most of it to compensate for yard bend, which is going to be there.

This is what the broadseam zones look like for a vertically cut lugsail. I don't have measurements or formulas for it as I have broadseamed by eye on the floor since about 1995 or so. It's probably typically a rate of maybe 1/2" additional overlap per 30" or so of seam length.

lug-broads.jpg

I always wanted to try cutting a tri-radial lug, just for fun. It should actually work nicely, but I never got around to it.

Radial-Lug.jpg

I also usually cut spritsails vertically for traditional appearance, with luff round, foot round, leech hollow, and a dead-straight head (it will sag a bit in use, creating enough upper draft without round). If I'm building gaff sails, Marconis or gunters it is usually to some designer's plan and as long as it is sound sailmaking, I'll follow it. Batwing types are built with a spider web cut, the weave following the leech edges. Lateens both cross-cut, or vertically if it is going on a really old boat.

All of these except the little one in the lower left corner are vertically cut.

assorted-lugsails.jpg

[Todd Bradshaw]

One of the strangest things I ever discovered making lugsails, and one that I had never seen mentioned anywhere, had to do with adding reef lines to a standing lug. Since the tack corner is at or very close to the mast, the typical slab-style reef lines were messing up the whole geometry of the sail and its relationship between the sail's center of effort and the boat's center of lateral plane (and helm balance as a result). You might be able to get one reef in reasonably decently, but the second reef was going to need you to re-tie the halyard to a different spot on the yard in order to maintain good balance. If it's bad enough out there that you need to put in a second reef, who on earth wants to stop and be required to also untie and move the hitch holding the halyard to the yard? By drawing out the sail plan with all of its reefs, and keeping in mind that the goal was to be able to reef twice without needing to move the halyard's position on the yard, this is what came up. The vertical position of the sails CE changes a bit, but the fore and aft position (which is what has an effect on helm balance) could stay about the same.

Although it is not the case on every standing lug perimeter shape, and doesn't usually apply to balanced lugs, it is a really good idea on any lugsail with reef lines to also draw out the reefed positions on the sail plan and check to see what you are going to encounter.

You will notice that I usually use reef bands (narrow strips of extra Dacron across the reef lines). It isn't required, but since that line will become the sail's foot when reefed, the solid band helps to keep the reefed outhaul strain from overly stressing the panel seams.

SL-reefs.jpg

st lug double reef 013.jpg

[Brian Palmer]

I had a standing lug (no boom) built by the same sailmaker who does work for CLC. It was a replacement for a sail that was 40 years old and built in England. Both the old and new sail were cross cut. That was my sailmaker's preferred method. He included a reef and as Todd points out, the reef points are not parallel to the foot. The sail sets very well and I am very happy with how it turned out.

[Marty J]

Thanks Todd, that's great information. I'll have to go look at our notes but I think we were going to put some round in the luff (and probably use a ~6 part downhaul), so you've saved us some trouble there!

I'm not sure I've ever seen reef points like those on your standing lugsail. Clever! I was taught to angle the reef points up higher as they go aft in order to raise the angle of the boom as the boat heels, but I figure that's more of a consideration for keelboats that are expected to dip the rail. We were focused on gaff and marconi sails at the time, anyway.

Getting it right is more important for the current project than getting it traditional, so I think we will stick to what we know with crosscut seaming. Sometime in the near future we will be making a new sail for a Woods Hole spritsail boat, which would be a introduction to vertical cut construction.

[Marty J]

Todd, a follow-up question for you on the straight luff:

Do any adjustments need to be made to the foot and head rounds or broadseaming in order to achieve sufficient camber? It looks like Marino's foot/head round and broadseaming guidance assumes a rounded luff.

[Todd Bradshaw]

I've never read Marino's writing on sail shaping. Is there some specific page number in there that I should be looking at? The amount of broadseaming along the head of a lugsail is very small, whether cross-or vertically cut, and this is due to the fact that broadseaming is done on a ratio of seam overlap increase to a specific amount of seam length. For example, a common amount might be 1/2" overlap increase for every 30" of seam within the broadseam zone. The broadseam zone at the head of a sail is generally pretty small, so the amount of panel seam length in the zone is also pretty small up there, and short broadseam areas result in small amounts of overlap increase. You also generally want to take it easy on shape in the throat area of four-sided sails. That area won't usually tolerate a lot of draft and set well.

What will absolutely make or break having proper draft (or any draft) up top is going to be the allowance you make for yard bend. You can't stop yards from bending. The vast majority of the round you add to the head of one of these sails is for bend allowance. When the yard bends, it tends to eat up the round and flatten the sail - to the point sometimes of the head being totally without draft (which though not necessarily ideal, may not be a horrible problem at times). However, not allowing enough for yard bend and a yard flexing beyond the amount allowed for in the sail's head shape usually distorts the top third or so of the sail, which isn't good.

So the relationship between the amount of round added to the sail's head and the scantlings and bend characteristics of the yard are generally far more important in the quest for nice shape up high that the small amount of broadseaming present up there. In an ideal world, the wind would be steady, the yard would bend a bit and the sail would be cut for exactly that amount of bend, plus have a small amount of round left over and broadseamed along the head to create the perfect draft up there. Reality is a very different picture and we are forced to compromise on all those points. The sail's shape will be "righter" sometimes than at other times and any info that we can get from the customer about the conditions they are most likely to sail in and certain particulars about the spars and rigging will help us adjust the cut. I don't really know of any simple formulas for this stuff, and from what I can tell it is mostly a product of experience and testing.

I will often dictate what I believe would be good scantlings for builders who are making their own spars - scantlings that should work decently with the way I plan to cut the sail. I have had good luck roughly following Iain Oughtred's spar diameter guidelines from his "Clinker Plywood Boatbuilding Manual". For a lugsail's yard he suggests "Diameter 1:64 to 1:60 of length, and tapering to 82% at the heel and 62% at the peak. I like to stick the maximum diameter at about 45% aft of the heel.

If you are cross-cutting without luff round you still want to work from a typical cross-cut-style broadseam curve, and you want a well positioned tack seam. Generally that seam (which ends right at the tack corner or very close to it) will be broadseamed at double the rate used elsewhere on the sail. It will be the most powerful shaping seam on the entire sail. Depending upon your tack angle (luff angle to foot angle) you may want to move the tack seam up the luff a few inches if it's a situation where the tack angle is less than 90 degrees. It's hard to explain without seeing it, but it gives you a little more room to work with down there. It's just one more of the little tedious details that sailmaking tends to be full of if you are going to do it well. I probably wouldn't increase the amount of broadseaming just because I left the luff round off unless it seemed like it was generating an awfully flat sail.

The foot round, at least, can usually be pretty simple if it is a loose-footed sail. Keep it moderate and make it a good looking curve with a fairly straight run-out toward the clew corner (not too curvy back there). If needed for cross-cuts, you can stick a couple of vertical broadseams in the foot panel to give it just a slight cupped shape on the bottom. Not too much though. We want a little bit of endplate effect (helps keep air from sneaking around the bottom of the sail and robbing us of our high pressure and low pressure side to side differential) and it gives us a firm foot that doesn't flap, but we don't want to hook the foot too much.

[Ben Fuller]

On RANTAN's standing lug I took deflections on the yard and gave them to the sailmaker. And even then it had to go back because there was too much draft at the yard. It was complicated by doing the non traditional and making a sleeve for the yard with an opening for the halyard. A very high aspect ratio sail on carbon sticks with full battens and the foot cut to vang it a bit. Experimentation was needed to get the bottom batten to be the right stiffness. Seems to be quite efficient.

[WI-Tom]

For my boomless standing lugsail, Dabbler Sails had me do a simple spar bend test with the yard before he made the sail. Easy to do, instructions here:

http://www.dabblersails.com/blog/blo...id=43&pic_id=4

I'm no expert, but my sail seems to set pretty well:

DSCN3310 (2).jpg

[Todd Bradshaw]

Yep, that's the bend measurement system taught by Jim Grant at Sailrite back in the early 1980s and though it is a fairly rough estimate of real in-use performance, it's still about the best method we have to get a feel for what we will be seeing out on the water. In addition to selling sail kits, and before they got their computer plotter for designing the sails and cutting out the pieces needed, Sailrite also sold a comprehensive home course to teach sailmaking. The Sailmaker's series of six small booklets that they still sell were some of the texts included in the course. They are still among the most valuable texts you can buy for clear instructions for designing and building a sail.

[FF]

I was never really happy with the Sailrite recipes for small lugsails and incidently met Robert Laine on the Amsterdam Boatshow in the nineties. He had developed a program that he called later Sailcut 4, probably because it was for 4 cornered sails. I used it a few years for many sails and then went to another sailmaker with a plotter/cutter, and he cut the panels for these sails more recently. I like a slight roach and they need short leach battens. And you better make the luff straight. Frank
You can se more of my sails on www.oarandsail.nl

[Todd Bradshaw]

That's a good looking set of sails!

My "plotter" is pretty basic, and the efficiency of the "software" that runs it kind of depends upon how much Scotch it had the night before and how my knees are feeling. Some days it's really soft.

plotter.jpg

And some days I even have help!

RS-2.jpg