Attached at the bottom is the file for the Hobie 18SX main. The file is a .txt to upload to this site. Please change to a .sc3 file to open in sailcut
If you can't open the file here is a quick description of what I have.
Large square top sail. I want it pretty flat to make it easy to depower. I'm starting with max draft at 2% bottom of sail, 44% at mid, and 35% at the top.
The gaff length (straight part at the top) is 1/2 the boom length.
I have 2in seams on the sail. The only part stitched will be the luff cord everything else glued. Batten pockets glued on as well. (Tapered cedar battens. yes I'm cheap)
Why do you use Sailcut4.09 instead of the newer and supported SailcutCAD? If you could convert your design into SailcutCAD's .def fileformat I would enjoy looking at your design and perhaps comment (if I have anything useful to add).
Hey there is a new sail design program. Cool. Here is the Hobie 18SX main. Again it is a .txt file to post here Must change to .saildef to open in sailcut 1.2.4
I have just had a look at your work, and have some comments/questions.
1: I think 18deg twist is excessive in the design. I would think 8 to 13 to be better. We used 8deg on the Tornado main we buildt and that was about right, perhaps a litt much for our conditions. 2: 5% draft is very flat in my opinion. I would not go below 10% draft and probably build it with more draft for our crew weight and conditions 3: I would have pushed the draft forward a a fair bit to compensate for the rotating mast working as a leading edge of the foil. 4: You probably want to work some more on the luff curve. 35mm at 45% dont sound like a beachcat mast. You need to match the luff curve of your sail with how your mast bends when sheeting it in. Otherwise, your sail will not set very well and give poor speed. You can either suspend the mast between two points and hang 10kg buckets on to it before you measure, or hoist your old sail, sheet it in (take care to rotate it) and shoot some digital photos. Use Photoshop or Gimp (open source) to match the bending properties of your mast with your sails design. Either way you choose, you need to think about how the mast bends to make the luff curve of the sail match it. 5: If you decide to add some draft, consider how your jib will interact with the main. You probably want the main to have less draft further aft where the airstream from the jib influence the airstream over the main.
I always choose to work with a crosscut layout in sailcut, it makes it easier to see how the draft is positioned. Afterwards I switch to tri-radial or whatever cut I want to use. I'll try to attach two screenshots taken from 87deg above to demonstrate the differences in shape.
I'll try to attache the design file for Tornado mainsail we buildt. It should be a fair base to work on your Hobie18sx design once you alter the luff curve to match your mast and compensate for your overlapping jib vs. our selftacking. I would do some changes to the design if we were to build another one, but nothing major.
Thanks Rolf for your article on the Beachcats website. Because of you I have been playing around with the Sailcut program for some Hobie 18 sails. I measured my jib and have that designed. Starting to work on a squaretop for the mainsail. I still need a lot of dimensions to finish the mainsail. I don't have a cloth cutter but can plot out the panels on a large Cad plotter for the panel patterns. Keep up the information and discussion on sail design. <img src="http://www.catsailor.com/forums/images/graemlins/smile.gif" alt="" /> I would like someone to critique my sail designs. I can be reached offline at djanddale at charter.net
If you want feedback and ideas, how about joining the sailcut-users list or the saildesign list? Otherwise, you could post the design here, but it looks like not even the hardcore racers who frequent catsailor want to comment on designs. Strange, but that is my experience so far.
Plotting 1:1 templates before transfering the design to the cloth sounds like a lot of work. Perhaps it's OK for a jib, but for a radial mainsail.. Whew.. With the "new" cloths designed for laminate crosscut construction, hand plotting is good enough and quite fast in my experience. But for spis you need to team up with somebody who have a large scale CNC cutter as the cloth need to be laid out in a tri-radial cut.
Thanks, I'll try to sign up. A different computer runs the program vs the one I'm on though. <img src="http://www.catsailor.com/forums/images/graemlins/frown.gif" alt="" />
quick question: a flat top is nice to have because you can flatten it out to depower in the puffs using downhaul.
On a mast with a comptip and square top, when you yank on the downhaul, wont that just make the tip bend more and in fact, put more draft in the sail where you don't want it?
On the downhaul question. The 18 ft. skiffs tie their main on the top and have realy big square top sails. It works on that boat. The new I-14 do as well. Sorry these are not catameran examples but the only differance is a rotating mast. It is the same thing you put on more downhaul, the mast bends like a bow. The sail flattens. It has more to do with the shape of the luff in the sail. A coach taught me this: If you take a piece of paper draw a sail shape with it make sure to draw an arched luff. (Coach used a bar napkin) Then cut it out. Grab the top and bottom and pull. you should notice the flat piece of paper froms a nice bowed shaped sail. This is your mast straighting out the luff curve in your sail. Now stop pulling, this is downhaul the mast bends to follow the luff curve in the sail. and the paper goes back to being flat. MAybe this demonstration works better at the bar. I shouldnt matter how the sail is attached to the top of the mast it is the luff curve of the sail and the bend of the mast that creates shape in the sail.
Here is the latest redition of my Hobie18sx Main The luff curve I'm not sure on. Just went over how important it is.HA hA I have offsets from the original sail. Held a taught line in the center if the head and the tack. Measured the distance from the taught line to the edge if the luff rope. Well I have the measurements not sure what to do with them yet. Working on a jib too. Here is the main need to convert to .saildef to open with sailcut
Just bought 30 yard of 3.5 oz Carbon Kevlar Sail fabric. Batten pockets look like they take up lots of fabric. Will use "Standard sailmakers glue" to assemble. Still not sure what brand the glue is. Fabric should be here next week then it's cutting and glueing.
yes, aren't you asking too much from a comptip with a giant gaff like that? also the luff round on the sx design and the tornado design look to be not enough. i would think a mast could bend more than a couple inches. perhaps i am mistaken. certainly a quick look at an existing sail would tell us. that project is on the list. here is my current result from this fun little program. i didn't research the actual #s from my current modified tornado sail that is on the modified H18sx thatwe sail theses days.
Just bought 30 yard of 3.5 oz Carbon Kevlar Sail fabric. Batten pockets look like they take up lots of fabric. Will use "Standard sailmakers glue" to assemble. Still not sure what brand the glue is. Fabric should be here next week then it's cutting and glueing.
Where did you buy the fabric? Of all the things you can find online, can't seem to find a place to buy raw saIlcloth. Not that I am making anything, just curious.
That sailmaking CAD program is sweet. Does anyone have a book that they would recommend for designing/cutting sails? Something that would be cat friendly?
Also...I am doing a good job of getting the program to quit itself. How do you make the gaff angle more than 90? Either you have less than or equal to 90 but thats it.
The best work available is "The art and science of sails" by Tom Whidden. It is not aimed at beachcats, but it is the best there is. There are very few books about saildesign available. If you want to learn about saildesign you are more or less forced to work with an sailmaker or go trough the trial and error route. "Maximum sail power" is also relatively good if you can not get Tom Whiddens book.
About luff curve. There are two ways of giving a sail draft. Either by using broadseaming between panels or by adding cloth to the luff. You can distinguish between the two by laying the sail on a level surface. If the sail lies flat, cloth is added to the luff. When the sail is hoisted the extra cloth has to go somewhere which gives the sail draft. If you measure the luff curve of such a sail and enter it into Sailcut, you are giving the sail too much luff curve! The consequence is that the sail will have too much draft and it will be slow with poor pointing. The luff curve on the Tornado mainsail design (which btw. is based on a Marcus Towell design) is pretty much correct. When I adapted it to our weight and conditions I gave it a little bit too much luff curve, so we had to compensate with increased diamond tension. Luff curve is a direct function of how your mast bend, which again is a direct function of materials, profile, spreader rake, diamonds tension, boat, crew weight and predominant sailing conditions. With a composite tip the upper part of the mast will bend more than the lower section. We know that square top mains require higher sheet tension, so this would need to be compensated for in the design. I have no experience with composite tips, so I dont know if the idea of a square top is out of the question on such a mast.
Sailcut CAD works with a mathemathical model of the sail you design. So if you enter values for luff, leech and gaff which dont match up Sailcut CAD will let you know by setting the misbehaving value to the default. If you are unable to make the gaff angle larger than 90deg, try adding to the leech length.
Sailcloth can be bought directly from the manufacturer (Bainbrigde, Contender e.a.), just dont let them know you dont run a company.
While waiting for the fabric to arrive I ordered that book "The art and science of sails" from amazon. I feel I'm opening a bag of worms and will want to buils more sails.
My Bobie 18 is the family boat I have three boys 9,11,12 All want to sail, none understand how sailboats work. I want to set the boat up so I can single hand and the boys can trap. WIth the new square top main the I want to add a self tacking jib. This will be smaller than the original.
On the 18sx main I'm going to try placing the battens in the seams. I've enlarged the seams to 145mm. My battens are 1 in. cedar tapered strips. I have lots of carbon sleaving to cover the wood with. I plan to play with the taper to get the bend in the right place then cover with carbon to make stiffer. The top batten pocket will glued on cause there is no seam to hide it in.
I got the fabric direct from contender. Enough material for main and jib less than $200. The monofilm material won't last as long as other sail fabrics, but will allow a not so expensive learing curve.
I've just completed an install of a I-20 self tacker to my TheMightyHobie18 curved beam. Its really pretty simple but does require some cutting and alteration of the unit to make it fit the curved beam. Good luck with your enhancements!
I guess you are buying "The art and science.." used, as it is long out of print. Last time I checked it was really expensive on the used market. Sailrite.com also make some decent leaflets on how to manually lay out and cut sails.
I believe your battens will be very stiff (too stiff, possibly), if you add carbon or even glass to the cedar. Cedar is much stiffer in itself than foam, add some glass and it becomes really stiff. 4mm spruce with a light layer of glass on each side is strong and stiff enough for hull construction, just to put it into perspective. I would have tested it with one batten first..
At age 9, 11 and 12, might I suggest some bathing, capsize and righting exercise before you go wild (sailing)? Just to make sure you know how and are able to right the boat. Can be a real boost for your kids confidence on the boat and add to their perception of it.
Good luck with the project! Sailmaking is not rocket science, just a craft like any other. When you get around to installing the luff rope, let me know so I can tell you what we did wrong the first time. Please post some pics of the process and the finished result when you are done <img src="http://www.catsailor.com/forums/images/graemlins/smile.gif" alt="" />
Fabric arrived yesterday. Spent an hour learning the control system for the cutter. Cutter is from Gerber Garment Company and is primarily for making clothes. The manual is several inches thick very confusing and mostly useless as I am not making a run of clothes in various sizes. My main has only 9 sections and I'm wondering if it would be faster to lay them out by hand. This will probably pay off if I make more sails; And I'll be able to run a clothing sweatshop when I'm done.
I'm posting the "final design for the main." I took the mould from the tornado sail posted earlier. As I have been reading a little on sail design I figure to make the sail go up wind I need a high aspect with the draft forward in the sail. The tornado sail was better than my last rendition. Two differences between the tornado and the hobie sx are the hobie weight 475lbs and the sail is 15%bigger plus no vang control. I'm not sure if the tornado has vang but I think they should.
I'll post pics of cutting today'"if I get it to work" But if you see a guy walking around in a suit that looks like it's made of sail material... that would be me.
Finally on the whole sail plan The main and jib are designed to go fast and upwind, The current spin is designed to sail deep. I don't think they will work together. The main will drive over the spin.
