Backstay problem on Gunter rig

TBH that sounds like a more sensible idea.

 

I have sailed two on my laser -the first impression was two big guys on one surfboard. The hull is not optimized for the greater weight but with taller topsides and bigger cockpit I think it is good start for a "one or two" crew design. I have also sailed my Jet alone and honestly found it less pleasurable to sail a hull designed for 2 alone -tippy and sluggish. A canoe stern has been suggested to improve load characteristics and we have not quantified it yet.

About your opinion of the whole concept - I appreciate your candor -I suspected your negative opinions were not about the particular merits. Still I hope you can manage to keep your criticism factual and constructive rather then digress into an assault on confidence. Bigotry can be found all over the webblogs -we value this one for educated advice.

I OTOH see value in the development of boats that can be stored in small spaces and little or no value in producing more craft that don't since there are large numbers of such boats to be had for far less than the cost of building. Costs related to storage and transport are the largest contributors to cost of ownership in a sport not considered cheap. Demographic trends point to more of the same in the future. Population and earnings are increasingly urban. Sailing must deal with it or fade away.

 

the most common way to make a rigid frame skin-on-frame is to use uncoated and untreated fabric (called "gray" goods, before dying and processing) and than to stretch it over the frame. it has enough stretch and give to usually not have to put darts and to allow one peice of fabric from gunwale to gunal, bow to Stearn. Sometimes even to pull it over the deck too, without pucker or darts.

I have made a skin-on-frame folder this way, but using untreated fabric and making it fit my frame. Than once completed I painted it with hypalon paint, that sealed all the sewn seams and helped it keep it's shape. It can be done, it solves the fabric stretch issue nicely. It ends up costing about the same as buying coated fabric.

It can also be done with the coated or laminated fabric, but you must alter the design because coated polyester fabric has very little stretch (but it still has some that will allow you some compound shapes of shallow draft). Using a lighter weight fabric over most of the hull helps this issue since it will streatch more. To make it more durable you just add double layers to the keel area or other areas subject to wear. But you will end up with more seams, or a compromised hull shape; hence Yost's recommendation to have little rocker, it makes it easier not to have a center seam. Seams can be made leak-proof and very strong with the solvent type adhesives, but obviously the fewer seams, the less risk of a leak and much less work to make the skin.

If it were me I would not comprise the hull shape to eliminate seams, but I would find some way around having to have a lot of darts and keep the seams to a minimum. Careful design and reasoned compromise in design will result in a good hull no matter which fabric you choose to use.

I have wondered if you use a heat gun when stretching pre-coated polyester material over the frame if it will allow it to relax and get compound shapes.

If you want to have a better performing hull I suggesting buying the untreated heavy nylon or polester fabric, and than coating it after the hull is done. It is also easy to sew togther with a machine (you can use a much lighter sewing machine) and you can make much stronger and cleaner seams. Although the hypalon paint is expensive and toxic, sealing the over turned hull is fast and easy. You brush or roll it on (natural fiber brushes are required, the solvent will melt plastics!), several layers and than let it cure. all seams are perfectly sealed the the skin will make nice clean shapes over compound curved hull frames.

 

A canoe stern would reduce stability.

TBH one of the best single-or-double boats I've tried was the International Finn. You have to be a monster to race them competetively in a breeze, but they can be depowered enough to make them manageable for one normal human, and they are great with two normal humans (nice big cockpit and plenty of carrying capacity). Much better than trying to fit two in a Laser.

Helpful hint: it is somewhat contradictory to say you appreciate candor, and then effectively accuse the person in question of bigotry.

My criticism was factual and constructive, IMO. I do think a simpler solution would be better. It would be easier to build (therefore cheaper if production is a possibility). It would be stronger, or alternatively it would be lighter for the same strength.

As I said to the OP, carrying longer bits on a roofrack makes more sense to me.

 

Which is an amusing juxtaposition of statements because the Finn design was essentially a Swedish Canoe style boat with the stern truncated at a transom instead of continuing to the point.

 

Not really. If they change a boat of fixed length from Laser transom to canoe stern, it will reduce stability.

Cutting the pointed stern off a Swedish canoe had almost no effect on stability, and resulted in a cheaper and more manoeuvrable boat, that also had slightly less wetted surface.

 

My intent was to keep the conversation constructive by pointing out negative outcomes in other blogs focused on opinion. I had no intention of making any accusations and I apologize if that is how it came out.

The Finn is the obvious 'step up' in size and its sail area fits the plan when a jib is added. The beam presents a problem of a couple frames being larger than the target size -I am not sure how solid that requirement is. Then we get to rocker again. If you take take all the rocker out of the Finn it will drag the transom anyway. Laukejas got some drag figures from deltship that indicated the drag was not large but I suspect the software is too simplistic. Is there any accurate way of quantifying the drag from immersing the transom ? Petro has a skin plan that might relieve the concern about designing in rocker.

For my own purposes I am considering different storage size limitations -fold flat, full length, less than 8ft (upright in standard room), less than 6ft flat or nesting, as well as the 3ft of most folding kayaks today. The ~3ft size is a major challenge and it is hard to quantify without lots of work just trying.

 

TBH I wouldn't bother with a jib. A single sail with an unstayed mast is very quick and easy to set up, and will provide quite decent windward performance, and is easy to handle solo or two up. If you're going to have to put the whole boat together every time you want to go for a quick sail, it'd make sense to keep the rigging part of it as simple as possible.

The fewer parts are involved, the more time you can spend on the water. This is another reason to use longer sections and fewer of them. The OP's proposal runs the risk of creating a "solution" that in practice is so complex to assemble and disassemble that nobody will bother.

And don't try to design the hull without rocker. That's just silly. Just make it the right shape, and then figure out how to build it.

ETA: I'd suggest taking a serious look at this before getting too carried away with complexity: SOF boat, can be sailed confortably with one or two people, light enough to throw on roofracks, cheap and simple to build.

http://gentrycustomboats.com/Annabelle.html

 

All right, since I see that majority here says that fit-in-trunk idea is too complex, considering I have very little experience at sailboat building, I decided I'll go with roof rack idea. So, the only limitation now is that no part should be longer than around 2m, and that the total of these long parts wouldn't exceed 35kg. I guess that won't be a problem.

Petros, your suggestion about untreated fabric sounds very sensible, however, I really do not trust that I can handle this. I have yet to find a fabric suitable for this, and, more importantly - the paint that would be flexible enough not to crack while folding boat and still remain waterproof over the years, also, it sounds like one hell of a job to do. You see, I found reasonably cheap PVC fabric, and I know it's good for this task, it is tested, truly waterproof, good anti-chafe properties, all good except for stretch.
In other words, it sounds very risky to me. I understand why a professional like you would do it, but I don't really think I can manage it, considering lack of materials in my country.

That is also what I aim for. If I can manage with one width of PVC fabric for hull and one for the deck, it would be perfect.

I have made a small approximate model of Laser hull, and then tried various materials. Paper wouldn't do it, but some fabrics actually stretched enough for rocker without creating excess material.

So, the main question now - how much of a rocker can PVC fabric handle? For example, if I would go with original Laser hull rocker, would treated PVC stretch enough?

I really need to know this before I start building, because if I find out that PVC can't stretch enough, the whole project will be doomed. I'll have to cut out excess PVC, and that means additional seams, weaker spots, more problems with tensioning skin, worse hydrodynamics, and so on.

If anyone could give a reliable figure of how much rocker can be stretched with PVC, it would be very helpful.

 

My intent with the paper exercise was for you to find that a small amount of rocker is beneficial to getting stiff fabric to fit smoothly, and that a dart or two in the sheer, aft of the maximum beam to the second chine max, are all that is necessary. I will be putting a new tarp over my laser for the winter -much stiffer than the reinforced PVC. I can mess with it a bit and show you how it would fit.

The bottom line is that it is far from a showstopper. The transom joint is larger, takes the same stress, and is below waterline -more so without rocker.

I am uncertain about post treating fabric but I think it is something I should learn about. The last time I looked at hypalon the factory treated material was very expensive, the post treatment rubber cost less but was still more expensive than PVC over polyester. Maybe I shop in the wrong places.

I was interested in working out the 1M or 1.3M breakdown to the point of a plan and cost estimate but I have to say that my own favored plans are for a 6 ft breakdown size. My trunk is larger than yours. 6 ft avoids premium shipping and makes viable triple nesting, fold over, or a skin over plywood or plastic floor.

 

I suspect that if you set your frame on some sturdy saw horses and than heat the coated PVC fabric you should be able to make it work on a Laser type hull (as long as there are no hollows on it). You could either put the fabric in a large heated tub of water, or use some heat lamps on it (like six or seven) to warm it up an soften it.

 

I have been wondering about that but I am concerned about the pvc pulling away from the polyester. They should stretch quite a bit near the glass transition temp which is much lower for PVC than PBT. I have some color samples I can mess with -no loss. I think we only need 3 to 5%. I will stretch it that far and check under the microscope for separation.

 

if it delaminates, clearly you got it too hot. PVC is a thermoplasitc and should respond well to reforming it with heat (they use heat to weld the seams without delamination, no reason it can not be used to give it some shape).

The object is to heat it just enough to get it to shape over the hull without puckers or wrinkles. you will need to put a seam at the bow and transom, keep them to a min and you will have less places for it to leak.

 

You don't need to reinvent the wheel. Just have a look at these and admire the solutions:

http://faltbootbasteln.de/fbb-klepper_passat.html
http://faltbootbasteln.de/fbb-delphin150.html
http://faltbootbasteln.de/fbb-umbauten-am-d150.html

Use google translate if not able to read german.
Skin is PVC. No need for heat to form anything. You cut and sew the skin to shape an apply a glued patch ower the sewing. Sewing is not done by overlapping but edge to edge. Or glue it directly like yost does (overlapping). Glue can be Uhu Kraft thinned with acetone or any other suitable glue for flexible PVC. Tension of the skin is provided in two ways, longitudinal by the keel and lateral by the inflatable sponsoons.
You can use one of the specially formulated PVC's for boats like Valmex ( http://www.mehler-texnologies.com/EN/products/boat-pool/valmex-boat/index.php ) (it is available in Lithuania price should be around 12 Euros per square meter) or other cheaper reinforced PVC's like the ones for truck trapaulins. If you still speak russian you can check the russian forums about foldable and inflatable kayaks building and operating, for various reasons they are the biggest market in the world for this type of craft and have the most producers.
My advice is not to build but buy (second hand would be best) a either a foldable kayak, put outriggers on it and a sail or a inflatable sailing catamaran.
Here is a link to a russian producer (there are many more): http://triton-ltd.ru

 

Rumars, thank you very much for the links. That 430m Klepper Passat is EXACTLY what I want to build. It would be absolutely perfect.

However, even with translation, I couldn't find exactly - is this a series model that is sold? It appears so, but I couldn't find any buy links to check the price.

Any idea how much would it cost to build such a boat, not including sails? Are there any plans available? (Still looking into this myself, but thought maybe you already know)

EDIT: I found that there is also that Klepper Master boat. 1m shorter, but still very acceptable, even though it has leeboards instead of centerboard. Any idea if it is possible to buy it in Europe?
I'm considering to re-design Passat so that it doesn't need inflatables... I really hope I can get away without them.