GIS Lugs’l Design (and eventually, build)

[davlafont]

(subtitle: Pimp My Lug; or: I Want a Thread Too!)


Well, after many months of lurking and commenting, it’s time for me to jump into the party and start to build my own Storer Boat. The object of my obsession has been the lovely Goat Island Skiff. I plan to run a blog as well as posting to these forums. Right now, there’s nothing to show so I’ll begin with my purpose for this thread.


I want to make the boat AND the sail. Part of that is to be economical, but really… I just want to do it. I’ve read Emiliano Marino’s The Sailmaker’s Apprentice. I’ve studied the various pics of Goats in EUR, AUS and USA and noted details where they differ. And I know there’s at least one contributor to these boards that made his own lugs’l. Plus, the cold weather is setting in here (the US Northeast) and I’m pretty sure that I won’t be mixing epoxy for many months; sail making sounds like a good cold weather pastime. I also seem to recall someone posting that having his sail ready and waiting made building the boat go quicker. I realize that a sail making thread on a woodworking forum is a stretch, but clearly the Michael Storer Wooden Boat Plans forum is about so much more than just the wood…


My plan calls for some traditional touches and some actual hand sewing. But MIK’s design philosophy has been to combine traditional aesthetics with modern materials and techniques. I will continue in that vein; no cotton here. In fact, my lugs’l will begin its life on a computer screen. I have played around with the free software SailcutCAD and I think I’ve got the hang of it. I understand how its outputs relate to traditional lofting techniques and broadseam development. I think it will be great to use this forum as a sounding board, then take the feedback and make tweaks in Sailcut. That’s my hope anyway. But hope is not a method, so this is my plea for collaboration on my lugs’l development.

[davlafont]

Meanwhile, here are some preliminary specifications I’m considering:


Cloth: 4 oz., general purpose Dacron from Duckworks, 36” panel widths, oriented cross-cut (i.e. perpendicular to the leech).
According to Duckworks: “Challenge 3.8 Oz. Genoa is a rugged all around fabric designed for mainsails and jibs on dinghies and small boats, and all purpose genoas. With an actual weight of 4.0 Oz., 3.8 is "balanced" in the sense that it has equal total yarn fiber (number of yarns times denier or size) in both warp and fill directions.”


Edge Tapes: (luff) 5 oz., 6” width, quarter-folded to be 1.5” finished; (leech) 5 oz., 3” width, half-folded to be 1.5” finished; (Head & foot) 4 oz., 3” width, half-folded to 1.5” finished.
My thought here is that the luff transmits the lion’s share of the downhaul tension, with the leech transmitting a good share too. I would consider matching the weight of the tapes to the sailcloth and rely on the folds to increase tensile strength, but Sailrite.com carries 6” tape in 5 oz. weight. Maybe that’s overkill? The alternative is to slit my own tapes from the same cloth as the panels, but I think will add considerably to the yardage I would have to buy.


Corner lashings: #6 brass rings with brass liners (eyelets), hand sewn.
The rings are 7/8” outer diameter, so they should fit nicely within 1.5” of edging. This detail is a nod to Marino’s influence and in keeping with the traditional aesthetic of the Goat. I’ll use smaller press-fit spur grommets along the head and foot since there are many more of them and they are not as highly stressed.


Reefing: Two reef positions at 1/3 and 2/3 the length of the luff, with individual reinforcement patches, hand-sewn rings, and nettles.
I’m taking my cues here from forum feedback. It seems that MIK’s first reef might remove a bit too much area when two-up, and the “handkerchief” reef is only used in conditions that I won’t likely see. Again, the patches and nettles are for fun and tradition, and will help prevent what Callsign222 dubbed “pregnant foot syndrome” while reefed. I plan to at least attempt to form hand-sewn rings for placement in the sail’s panels where hard parts like brass would seem out of place.

[davlafont]

So, am I missing anything? Webbing? Rope? Window? Sanity? Keep in mind, my objective for the entire project is to have fun, both in the making and in the use.

Future posts in this thread will discuss technical aspects of the sail design—i.e. draft--as I fool around with Sailcut. I also took shipment of material for a practice project; I plan to make “house flags” for the family (my brother’s J24, my father’s Sunfish and motorboat, and my future GIS), so I’ll post/blog about my stitching experience as I learn.

Thanks for reading, and welcome aboard my thread!

[woodeneye]

Well, you have my interest, so go for it!. Have you contacted MIK? He has a sail plan that he'd be willing to send you I'm sure.

I take it you already have a suitable machine to handle the cloth?

4oz cloth sounds right. Mine is 5oz dacron in cream. It's very nice as far as holding the sail shape in a blow (low stretch) but prone to be very crinkly and shows up the creases that come from general use and storage.

One day I'd like to make my own sail, mainly to get an understanding of what is to me, a black art.

[Boatmik]

Well, here I am. This is a great thing to be doing Davlafont.

Meanwhile, here are some preliminary specifications I’m considering:


Cloth: 4 oz., general purpose Dacron from Duckworks, 36” panel widths, oriented cross-cut (i.e. perpendicular to the leech).
According to Duckworks: “Challenge 3.8 Oz. Genoa is a rugged all around fabric designed for mainsails and jibs on dinghies and small boats, and all purpose genoas. With an actual weight of 4.0 Oz., 3.8 is "balanced" in the sense that it has equal total yarn fiber (number of yarns times denier or size) in both warp and fill directions.”

Yep

Regarding the book resources. Some of the traditionally oriented books recommend "roping" the outside of the sail, which is stitching a rope along the edge. This is a traditional feature that is the kiss of death for sail shape as it will prevent the leach edge stretching but the cloth immediately adjacent to that will stretch fine. The result is the leach gets badly cupped.

Edge Tapes: (luff) 5 oz., 6” width, quarter-folded to be 1.5” finished; (leech) 5 oz., 3” width, half-folded to be 1.5” finished; (Head & foot) 4 oz., 3” width, half-folded to 1.5” finished.
My thought here is that the luff transmits the lion’s share of the downhaul tension, with the leech transmitting a good share too. I would consider matching the weight of the tapes to the sailcloth and rely on the folds to increase tensile strength, but Sailrite.com carries 6” tape in 5 oz. weight. Maybe that’s overkill? The alternative is to slit my own tapes from the same cloth as the panels, but I think will add considerably to the yardage I would have to buy.

the luff is under quite a bit of tension and is also cut partially on the bias - so the tape has to provide the resistance to stretch. With my lugsail version I just use an extra large patch of sailcloth folded around the luff - it is a straight edge, so no probs with geometry. Another solution I've seen used is to use a headfoil luff tape. On bigger racing boats they don't use hanks for jibs, but have a grooved extrusion thingy up the forestay. My BEth lugs used the lightest one for this purpose. But am just as happy with an appropriate weight folded cloth.

Corner lashings: #6 brass rings with brass liners (eyelets), hand sewn.
The rings are 7/8” outer diameter, so they should fit nicely within 1.5” of edging. This detail is a nod to Marino’s influence and in keeping with the traditional aesthetic of the Goat. I’ll use smaller press-fit spur grommets along the head and foot since there are many more of them and they are not as highly stressed.

cool

Reefing: Two reef positions at 1/3 and 2/3 the length of the luff, with individual reinforcement patches, hand-sewn rings, and nettles.
I’m taking my cues here from forum feedback. It seems that MIK’s first reef might remove a bit too much area when two-up, and the “handkerchief” reef is only used in conditions that I won’t likely see. Again, the patches and nettles are for fun and tradition, and will help prevent what Callsign222 dubbed “pregnant foot syndrome” while reefed. I plan to at least attempt to form hand-sewn rings for placement in the sail’s panels where hard parts like brass would seem out of place.

Traditional reefing methods are crappy as things have marched on.

The main eye at the front and back of the reef carries all the load and often I have sailed BETH without doing anything about the intermediate points. This fits with racing practice and they won't tie up the middle part of the reef unless the wind and seas are really building.

If they do want to lace it down they don't use individual ties. Just have two or three intermediate eyes and put a shock cord (bungee) from the front of the boom to the back going spirally around the boom and catching the two intermediate eyelets.

Only one knot to undo. Also if you main reefpoints let go the lacing just stretches and won't rip the middle out of your sail.

Great project - and I hope you can put some images up here if the program generates images. If you are using a PC you can get a free PDF virtual printer like PDFcreator. Then you can just select print for any document in any program and instead of your real printer select pdfcreator from the same menu.

I actually have a paperless business because I don't have a real printer. HOpe I never buy some PDF plans!!!!

MIK

[callsign222]

Uh OH! You're going for the Goat! HA! Oh the madness that will ensue!

[Boatmik]

And that's a good thing of course!

[davlafont]

I plan to run a blog as well as posting to these forums.

As promised above, I've created a blog for my sail project. If all goes well, I'll create a separate blog for boat construction too.

Here's the link: Dave's Lugs'l Chronicles which I will also add to my signature.

[davlafont]

Some of the traditionally oriented books recommend "roping" the outside of the sail, ...that is the kiss of death for sail shape as it will prevent the leach edge stretching but the cloth immediately adjacent to that will stretch fine. The result is the leach gets badly cupped.

No roping for me then (whew!). Would you expect a similar result from my idea of a 5oz. tape on the leach? It's close in weight to the panels' cloth, but will add two additional layers. Plus the leach's weave--unlike the luff--is oriented along the path of strain just as the tape will be.

The main eye at the front and back of the reef carries all the load and often I have sailed BETH without doing anything about the intermediate points. This fits with racing practice and they won't tie up the middle part of the reef unless the wind and seas are really building.

I think I don't have the same competitive drive. I'm more concerned with Callsign and Alzuger's experience with the "foot-as-pillowcase" effect. I suspect my skill at flaking the sail neatly will prove inadequate. But I do like the following technique...

If they do want to lace it down they don't use individual ties. Just have two or three intermediate eyes and put a shock cord (bungee) from the front of the boom to the back going spirally around the boom and catching the two intermediate eyelets.

Sounds easy enough. Plus, if the holes are built, nettles can be added or omitted (if attached with knots, not sewn).

Great project - and I hope you can put some images up here if the program generates images.

Ask and ye shall receive...

[davlafont]

So this is a 3D solid view. The sliders left and bottom rotate the image which is very help to "feel" the shape. I used the dimensions in the GIS plans and have already begun to shape the design. A touch of hollow in the leech, a touch of round in the head and foot, etc. The effect of those tweaks are best viewed in the wireframe view. (...coming up)

[davlafont]

So what follows is a series of views from the port side (leeward as far as the shape goes), beginning with straight on, zero degrees of rotation. Then imagine yourself floating up and over at the following intervals (d=degrees): 45d, 60d, 75d, 80, 85d, 90d (directly overhead) and finally 95d (slightly windward):


^0d


^45d


^60d


^75d


^80d

About this time it might be good to note that I specified a 10 degree twist to the head. This explains why the yard is not directly over the boom in the 90 degree shot. Is that a reasonable estimate of how much twist to plan for in moderate breezes?


^85d


^90d


^95d

[davlafont]

This series rotates around the front of the rig, from port to the bow to just a bit over to starboard.


^0d


^45d


^60d


^75d


^80d


^85d


^90d (Dead on from the stem; The boom is over the centerline of the boat for the purposes of this analysis, but the software also allows a sheeting angle input as well.)


^95d

What thinks ye?

[woodeneye]

Hi Dave

Thanks for the perspective views!

I have a couple of comments. This sail is looking a bit flat in the lower half to me. I notice you haven't added any luff curve and I think this is the reason that its so flat. This is where you need some drive in your sail, so maybe play with that.

Is there a reason you are making the leach hollow or concave? This is fine if you are looking for a traditional shape, but with modern sail cloths that don't stretch like the old cotton sails it's not really necessary. A very slight roach does look cool, but you will need battens of course. Have a look at this sail...

https://www.woodworkforums.com/f169/g...ml#post1050100

[davlafont]

Correct: I have the luff flat, or straight, right now. I think I pulled that notion from Todd Bradshaw's discussion on WBF. As I understand it, the rounding at the edges will help develop draft under load if that edge is supported by the spar. If not, fabric is not "pushed" into the body of the sail, it just flaps in the breeze; hence the need for battens along a roach. With firm to heavy downhaul tension, any material forward of the line between the tack and the throat would be under-stressed. (Mind you, this is only me thinking through the concepts, not speaking from experience.)

However, the panels are shaped in a manner similar to broadseaming to provide for the draft you do see. There is also a touch of round in the foot--50mm based on MIK's estimate of spar bend--but I don't believe the program shifts that amount outward as the wind would. So the shape displayed here is likely what would result from a full tightening of the downhaul, bending the boom (as well as the yard) by 50mm. I'll have to play with the parameters a little to confirm or deny.

The hollow leech may also have come from my reading of Bradshaw. I'll have to check the thread I printed when I get home tonight. But the purpose was to avoid flutter in the absence of any battens.

Thanks for the feed back Bruce, exactly what I was hoping for!

[Boatmik]

I remember Todd saying (and it makes complete sense) that it is a good aim to have a seam coming in to meet the throat. That becomes a really useful place to put some broadseaming - if you are doing broadseaming.

I'm giving Brian Pearson a yell in the background as he dug up a lot of the sailmaking information including the above.

That position is the maximum broadseam which continues with all the panels seams that meet the luff - because you can't have any round in those areas.

Personally I dont' like roach on lug sails - I really like the simple shapes of the traditional sail.

But I won't stop you if you think you like it.

MIK