Adventure Island Jib and Lee Helm

Ok, looked up "high aspect ratio". You mean keep the jib small relative to it's lenght. I was not going to go past the mast, I think they refer to those as working jibs. Do you think it can be shorter yet and still remain as functional?

Greg

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Greg

2016 AI - Spinn & Jib

“Out of sight of land the sailor feels safe. It is the beach that worries him.”
– Charles G. Davis

Extreme examples...a spinnaker is a low aspect ratio sail. It has a foot length about the same length as the luff. A glider wing is very high aspect ratio since the wing is very long but not very wide. I'm suggesting that you make the foot of the sail about one meter long and the luff about 3.5 meters. If you don't have those lengths available, use the ratio of foot:luff of 1:3.5 or so. A high aspect ratio sail typically has less tip losses (drag). Everything is a trade off, though. You do sacrifice some power in very light wind, but your boat will generate apparent wind to make the sail "see" more wind than is there, so I think a higher aspect ratio will serve you better than a lower aspect ratio sail.

I was suggesting that the jib block on the loop could be used to move the tack back toward the mast (not furled). This will bring the center of effort of the sailplan back toward the mast (and the center of effort of the underwater foils) which will reduce lee helm.

Wikipedia has a good dissertation on forces on sails. It's probably more complicated than it needs to be, but the parts I've gone through seem to be more or less accurate (it gives only "some" of the lift explanations being mostly Newtonian and ignores medium viscosity). http://en.wikipedia.org/wiki/Forces_on_sails

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R/Thom
SeaRail 19
Triak
BMW C600
Formerly Getaway with Custom Spinnakers
Formerly raced F24 Mk II

That would be a jib with a shorter chord than originally planed. I may need to put another padeye further aft by about 20 inches on the bow to make the leech line up with the mast. This is to be a 100% jib. The leech should stay parallel to the mast correct?

Greg

_________________
Greg

2016 AI - Spinn & Jib

“Out of sight of land the sailor feels safe. It is the beach that worries him.”
– Charles G. Davis

I wouldn't put in any permanent mods to the boat until you have tried and are happy with size and functionality. You will have some difficulty in keeping the luff taut and a taut luff is what will help keep the jib functioning correctly, giving you forward drive to weather. Also (I didn't think of this yesterday when I suggested a high aspect ratio sail), the jib won't help as much off the wind with it smaller; so you may want to fit it into the foretriangle like you had imagined originally. You are correct, the jib leach should drop straight down either vertical or parallel to the mast. The sheet point should split the angle at the clew. You might find that the jib is small enough that you can hold the sheets by hand without any blocks at all (but it might get fatiguing). Basically, have fun. On another note, if you don't want to buy a tarp to cut up into a sail, tyvek works well-especially if you are going to glue it together and it is even cheaper (free if you can find a housing development going up around your neighborhood).

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R/Thom
SeaRail 19
Triak
BMW C600
Formerly Getaway with Custom Spinnakers
Formerly raced F24 Mk II

Checked out Tyvek and it was going to cost $65 just to get a piece big enough to create a test high aspect ratio sail so I settled for drop-cloth and grommets. For $13 I can create both a high aspect ratio jib and a standard 100% jib extending to the forestay. I want to test both because I still have some concerns about changing the center of effort resulting in lee helm. No jib is worth it if I have to fight to keep the boat on a straight course. I believe that I understand your recommendations on creating camber and will give it a go. Many thanks for all the advice.

Greg

_________________
Greg

2016 AI - Spinn & Jib

“Out of sight of land the sailor feels safe. It is the beach that worries him.”
– Charles G. Davis

The rigging of this jib system all but complete. The sail is on order and I'm using a test sail for now. I made some modifications to the setup shown on the previous video. Without using a halyard or any hardware that would furl under the mainsail, you can now "snuff" the jib completely with less than one turn of the mainsail. Not true snuffing but it best fits the description of what I'm doing. The jib is "snuffed" within the main so the main's aerodynamics should not suffer greatly when the jib is snuffed.

Now when sailing, you have a choice to quickly furl both sails simultaneously or suff the jib only. Snuffing requires you to release one quick release and to make one knot before furling the main about one rotation. Appears that this should give me the flexibility I'm looking for without needing to separate the jib from the mast during use or storage. Will test when the sail arrives and try to get some video.

I am torn between the sailmaker using a light Dacron or the material spinnakers are made of to make the jib. Any one have any experience making a jib with spinnaker type material? The spinnaker material would facilitate the snuffing but I'm sure suffer on performance to some degree.

Greg

_________________
Greg

2016 AI - Spinn & Jib

“Out of sight of land the sailor feels safe. It is the beach that worries him.”
– Charles G. Davis

You "can" make a jib out of nylon. It will hold its shape until the apparent wind reaches about 12 kts or so (true wind of 8 and 4 kts of boatspeed for example (yah, I know it's not accurate because of that additive vectors, but I'm lazy)). Once the wind blows faster or the boat goes faster, the jib shape will stretch to less aerodynamic and have more drag plus you'll lose some pointing. Big boats make big jibs out of nylon for really light conditions--they are classed "windseekers". My own experience with both windseekers and a nylon jib bears out their utility until the apparent wind is in the 10-12 kt range.

I'd stick with a polyester fabric since it doesn't stretch as much. Dacron is a very nice material for a sail and is readily available. If you want something as light as nylon but as non stretch as dacron, there is stuff called "code zero" fabric which is a polyester with twaron reinforcement. http://www.kayospruce.com/index.asp?sel ... %20Fabrics The material cost is nothing compared to the labor cost of having a sailmaker make a jib.

What treatment do you plan for the luff of the jib? Most jibs aren't designed to take much load along the luff since they typically have a forestay that they are hanked onto. You might consider reinforcing the luff with some 1/4" polyester or better line...could get away with 1/8" if you use a high tech line. All you want is something to take the halyard load instead of the fabric. The luff has to be really taut for the jib to work well. First few times out with this system, keep an eye on your mast and mainsail. You'll be pulling aft with your mainsheet along the leach and pulling forward on the mast from the middle (plus doubling the compressive force driving the mast down into the mast support). I don't anticipate a problem, but I'd watch it until I'd be sure of that.

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R/Thom
SeaRail 19
Triak
BMW C600
Formerly Getaway with Custom Spinnakers
Formerly raced F24 Mk II

Greg: actually a lot of spinnakers are rip stop nylon, very light and very strong. You main sail is made from Dacron, but it's not lightweight Dacron your jib material will likely be a little lighter. I make all my temporary sails from rip stop nylon that I get at Joanns fabric stores, I buy so much of it they know me by name in there (kind of a joke in the family, Bob the seamstress). I buy about a half dozen spools of Dacron upholstery thread there every time I go and usually buy them out of it.
Good luck
Bob

Thanks guys. I'll call the sailmaker Monday and see what materials are available.

I have the jib sheet blocks set just to outside the aka knuckles where there is an opening in the tramps. Is this the ideal angle or do I need to run these blocks further out to the ends of the akas or to the ama handles?

Greg

_________________
Greg

2016 AI - Spinn & Jib

“Out of sight of land the sailor feels safe. It is the beach that worries him.”
– Charles G. Davis

Your sailmaker will design a specific entry angle into the leading edge of the jib. That will determine what is the best angle off the midships which will make the boat point best. It is usually around 10 degrees. Ideally, when both jib and mainsail are trimmed for beating, the leach curves of both sails will be identical. Folks who race boats tend to have "twings" and "barberhauls" that can be set to get the jib clew in exactly the right position. Where you are planning may be a little outboard for my sensibilities. Personally, for my jib I don't use blocks at all, I hand hold the jibsheets; if it is a long beat I can secure the sheet outboard the cockpit on a small cleat that I mounted there (but then, I steer with my feet in the Triak). Talk it over with your sailmaker and send him photos.

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R/Thom
SeaRail 19
Triak
BMW C600
Formerly Getaway with Custom Spinnakers
Formerly raced F24 Mk II

Can a light dacron sail be stored in a bunched up fashion (snuffed)? Will it bunch up well and will you damage the fabric by storing it this way?

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Greg

2016 AI - Spinn & Jib

“Out of sight of land the sailor feels safe. It is the beach that worries him.”
– Charles G. Davis

Dacron is stiff. It will not snuff easily. When you bend new dacron fabric, you can make a permanent crease in it. The more you crumple dacron, the softer it will get and the easier it will crumple and snuff. But, the reason it makes a good sailcloth is the fact that the fabric is stiff, presents a smooth surface, and resists being tortured out of shape. If you are going to snuff a sail, it should be flexible to start with and not stiff. You can get the benefits of dacron without the stiffness by getting a different polyester fabric (it's the polyester that resists stretch--avoid nylon which will stretch 25 % or more). A light 300 denier coated polyester packcloth will make a nice lightweight and snuffable jib. It isn't made specifically for sailmaking, but will work well (I made one out of it). The trouble is, it is difficult to find for sale--most of the packcloth you see for sale is made of nylon.

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R/Thom
SeaRail 19
Triak
BMW C600
Formerly Getaway with Custom Spinnakers
Formerly raced F24 Mk II

You can make sails from ripstop nylon but it's much more work. As an example if you look at the videos of my wing jib which is rip stop nylon, I had to sew it together with many sections and with battons every 10-12 inches apart. The Battons prevent the nylon from stretching too much. Since my wing was designed to fill with air to make it rigid (it's about 6 inches thick and it fills up like a balloon to create the airplane wing shape). Which is the opposite of what you will want or need.
All my spinnakers are always made from rip stop nylon but are always made from a strategic pattern of small patches (usually 2-3 ft) that are all sewn together to make the parachute shape (it's a heck of a lot of engineering and work to make a good G2 spinnaker (IMO)), and rip stop nylon is my preferred material because it can be just bunched up and stuffed into a sail bag (you can't easily do that with any of the dacrons I have found).
If your into making your own sails a company called sail rite (www.sailrite.com)has all kinds of instructional videos on how to make the re-enforcing for the corners of the sails and such. There are also some nice programs out there like sailcut CAD that help design some of the stuff. It's actually kind of a fun hobby (designing and making your own sails).
Bob

Sailmaking can be a lot of fun. Sail design can be fun, as well. I don't use sailmaking software, though. I went back to chord math principles. The basic process is either adding fabric to create 3D from flat or subtracting cloth to create 3D. The typical spinnaker uses "adding" cloth to create the camber (3D). A typical spinnaker uses misshapen triangles sewn together (like a circus tent). A typical jib is made using broadseams (subtracting cloth) to create the camber. That being said...I have never been happy with my crosscut jibs or mainsails because they never seem to have enough camber at the head; so all of my recent sails have been made with radial tops. You bring an interesting thought to my head about your inflated jib design. I "could" go back and add kevlar kite string to my nylon jib. Kinda make my own 3DL sails. Trouble would be in "fixing" the kevlar to the nylon since few glues will work with either nylon or kevlar. But I might give it a try; thanks for the idea.

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R/Thom
SeaRail 19
Triak
BMW C600
Formerly Getaway with Custom Spinnakers
Formerly raced F24 Mk II

Downloaded Sailcut CAD for free online. Great program and the guide makes for a wonderful learning experience. May have found a new hobby. Thanks for the tip Bob.

Tpdavis473, my sailmaker has Code 0 material but it is a slight off white. He has heard they make a true white and he will try to locate it. It would be nice to have the jib made out of this.

Greg

_________________
Greg

2016 AI - Spinn & Jib

“Out of sight of land the sailor feels safe. It is the beach that worries him.”
– Charles G. Davis