Backstay problem on Gunter rig

Could anyone help with finding out main dimensions of Passat hull? Some are listed in that German website, but not enough to recreate the whole hull. There are no cross-section dimensions or photos, as there aren't any indication of gunwale height above keel line. I'm now surfing through Google Images, trying to eye-ball it. If only there was a decent photo of hull profile... I could estimate cross-sections then.

If anyone could help with any information, it would save a lot of guessing. I'm now sure this is the design I should be aiming for. Since it appears that plans of this boat were never released to public, I'll make a rough re-design based on Passat, following it as closely as I can, making some changes in parts that aren't possible to homebuild (like specific metal mouldings and fittings).

 

The Klepper Passat was a series boat but is not in current production anymore. It was produced between 1962 and 1970. They are still available second hand in Germany for about 1000-2000 euros. It is said it was the best folding sailboat, followed by the MTW Delphin 150. All other designs are compromised toward motorboats an sail poorly. Even so it is not a great sailor by todays standards. The boat has 100 kg empty and was not designed as a planing dinghy.

If I would build one now I would not try to duplicate the Passat, but use some of the construction features. I would try something similar to Petros's 100 dollar boat, only folding.

http://www.boatdesign.net/forums/projects-proposals/challenge-100-boat-12176-7.html

To do that I would use 8-9 frames made out of 12mm birch plywood (that is what the Klepper uses also). You can even use the phenolic film backed one that is used in construction, it has waterproof glues. Remember to seal the edges with epoxi or oil paint.
The best wood for the stringers is ash. I know it can be hard to find sometimes so I would substitute with spruce (picea abies). In the Passat the stringers are round and I would duplicate this. Round dowels of suitable lenghts can be found at the construction market. 20-30mm diameter should be OK. To join them you need to use some form of tube connector. The problem is that it must be a tube in tube connection or else the you will never be able to take the stringers apart after the wood gets wet and swells. Suitable tubes can be found.
Connection of the stringers to the frames can be made with short polyester webbing straps or like in the films below.
The sides must be made as a ladder. Spruce stringers and ply webs. Connecting them is not a problem, also the connection to the frames. See the video.
The keel must be articulated in sections so that it can provide tension to the skin. Keel can also be a ladder frame or an I beam. Also on video.
It is possible to build a boat without the inflatable sponsoons, but it would not be wise. The sponsoons main function is to tension the skin, and it is the most effective and simple way to do this. Assembly is much harder without them, not to mention manufacturing the skin. Sponsoons are made from PVC or from automobile inner tubes in PVC skins.
For the mast you either find a used windsurfing one (best option) or use a wooden one. If you want to use a round one but do not want to build a birdsmouth mast use the thick round section sold for handrails. It's available in spruce and pine 50mm in diameter. For a segmented round mast you need tube connectors and shrouds, a rectangular mast can use a plate and bolt connector, but also need shrouds.

Be advised that the whole assembly procedure will take around 1 hour. I still advise you to make a inflatable catamaran or buy one from Russia. Or you could study take apart multihulls like this:
http://homepages.paradise.net.nz/garyd/wa_apa.html

Here some films. study the construction details carefully. The boats are completly homemade. First video is a Klepper Passat under spinnaker.

Happy hunting at Senukai!

http://www.youtube.com/watch?v=E4rPHrozoG4

https://www.youtube.com/watch?v=Xn1EDwaS6nc
https://www.youtube.com/watch?v=lTiSyM9TAEE
https://www.youtube.com/watch?v=rbo9kEmc51Y
https://www.youtube.com/watch?v=9PixexDfXv4

 

Thank you for extensive information, Rumars. It is strange to me that Passat was not designed for planning, considering it's flat bottom. I gather from the photos that the bottom had no rocker, is that correct?

Petros boat is very nice, he linked me to that photo some time ago. Petros, if you are reading this - maybe you have some plans of that boat, or at least some more photos? It would be very helpful for me to take reference, if you could share them.

Well, complete duplication of Passat would be impossible, that's for sure. But if I copy hull lines and general arrangement, I'll know that I'm using proven design. I only have to find replacement solutions for metal hardware. Links you've given for wooden SOF kayaks suggested several ways to do that.

A question - how to make these inflatable tubes the right shape and size? It seems extremely complicated to me.

Thank you for your suggestion on multihulls, but I already considered that, and decided to stick with monohull...

Assembly time is ok. I expected at least 2 hours.

Another question - if hull is made in a way that tensions the skin when fully assembled, how to make the skin itself? I mean, it is probably very hard to tension the skin around the hull with hands, and glue or sew while it is under tension. If the skin is made around the hull that is relaxed (not fully extended, without tubes inflated), then how estimate if it will be the right shape once tensioned?

 

The boat had rocker, it's not flat. And the stern is pinched. In my opinion not designed for planing.

There are solutions for the hardware. If you don't want to work the wood so much as in the films (it's a lot of precision work) you can make Long Haul style connectors. They are easy to make, mainly cutting sheet metal intro rectangles, drilling and filing the edges smooth. Can be done with hand tools in a flat in silence if you like. (Powertools suggested).
Here is a film where you can see what I'm talking about: https://www.youtube.com/watch?v=Z8KINTygl-w

Tubes are made by making a pattern of the outside of the gunwale. The skin will force them into shape.

The skin can be made in several ways:
First you make the tubes and atach them to the frame (inflated). Then:
1. Make a pattern out of shrink wrap and paper then cut it open and use to tailor PVC skin.
2. Tailor skin directly: tension the pvc over the frame (with strings) then cut on keelline. Sew keelline, fit to frame to check fit, recut, resaw until satisfied.
3. Build a segmented skin. Fit bottom on frame, tension with strings, mark the skin. Fit side panels, tension with strings, mark. Now you either cut to mark and sew or cut with overlap allowance and glue.

In any case it is a lot of trial and error involved until you are satisfied and it fits.

I get you want a monohull. What I don't get is why you insist on a dinghy. Folding kayaks make good sailors. Buy a big double (second hand) and outfit with sails. The big ones like the Klepper Aerius (and the copy from Poland made by Wayland) or the Pouch RZ85 have sails as factory options. The East German Pouch RZ85 is very common in the former Eastern Block and sails very well with a few modifications (mainly bigger leeboards an bigger rudder). Sail warderobe can be extended with mizzen mast, bigger sails, roller furling gear, even canting keel if you like (not joking will search link to that). And you have room for a passager. I don't know what your budget is, but this is a lot simpler than building the whole thing and could be even cheaper.
I'll atach you some links to films where you can see how they sail. Pure monohull, no outriggers. At 85cm wide they can be sailed like that.

https://www.youtube.com/channel/UCkbohJev09ZoXO_oI0YWmFg/videos
https://www.youtube.com/watch?v=BMKXO3ewd2M
https://www.youtube.com/watch?v=Ymda60k2pkU

 

Here is a very impressive dinghy from Russia. As far as I know not a production boat. Maybe you can find a way to contact the designer (over his youtube account?)

http://www.youtube.com/watch?v=_3VFiQ7cFvg
http://www.youtube.com/watch?v=0loHYQQaonc

 

Russians again:

http://translate.googleusercontent....H.html&usg=ALkJrhgrAIvSP8_MvIPm93Wmdv-bKzJ_2Q

http://translate.googleusercontent....L.html&usg=ALkJrhhX11t9xWChg9MDhiTaJMi6hAPGAQ

http://translate.googleusercontent....47.htm&usg=ALkJrhjDyil-QUfXXmjjtQG3uU3sYlgQbw

http://translate.googleusercontent....v.html&usg=ALkJrhg-7WNoGAj0sWUgqxrAy2jA1GGCXA

http://translate.googleusercontent....c.html&usg=ALkJrhgNymAn-761Ci2nkXrSRBp_GxYRvw

Same problems (apartments, no garage, few marinas) force simmilar solutions.

 

I have been away from the forum since I was traveling for the last few weeks. I do not have plans really for my $50 sailboat, just some overall dimensions. I built the same way you build a skin-on-frame kayak, allow it to free from between the frames that are cut to fit the size you want.

here are some pics of the build:

 

Thank you Petros for the wonderful photos. Would you please tell us the dimensions?

I mantain my initial statement, that this is THE boat to duplicate. I'm tempted myself. I would do it folding but in a very crude way. Only one fold lenghtwise (means transporting the frame on the car roof but simplifies things), tube connectors in epoxy fiberglass made in situ, L brackets with machine screws on all frame to stringer connections (would need a electric screwdriver or some wingnuts). Floorboards fixed in place on the same screws and I bet it would be a stiff boat. Gunwale doubled with aluminium flatband inserted into skin also fixed with screws, some of them eyebolts.
Skin tension via screw driven false stem and inflatable lateral sponsoons. I even think I could keep assembly time under 1 hour.

 

I patterned the form after a K-18 sailboat, but scaled it down to 14' long, has 4' 8" max beam, and about 12" gunwale height above keel. I like the hull form, but if I was to build another one I would make the transom about 4 to 6" wider so the aft hull is more full.

I do not recall the rocker, not much perhaps 6", fairly flat bottom so it comes up on plane easy since it is so light.

To make it a folding hull I highly recommend minimizing the number of screws or loose fasteners (zero would be best, there are none to lose that way). And reducing the number of parts as much as possible, saves build time and assembly time. I would go with fixed frames at about 2 ' spacing, and fewer but stronger stringers. If you can tolerate the length, one piece stringers (full length) would be simplest, though using hollow tube with inserts and cord or elastic line down the center would make assembling folding stringers fast and easy. except for the keel and gunwales, you could attach all stringers with short elastic cord or bands that wrap over small knob on frames. the keel and gunwales should have solid attachment to frames since they form the main structure of the frame.

As a rule: keep it simple, keep part count down as much as possible, minimize the number of fasteners required, and preferably no loose small parts (like screws). This will make it fast and easy to assemble, and more reliable since there are less joints to fail.

 

Petros you are of course right, assembly should be ideally without fasteners. The problem I see is flexing. In a traditional SOF the skin is under great tension and the whole lot flexes as one. In a folder the skin can not provide that much tension and the frame has to resist this forces alone (well the skin contributes a bit, but by far not like in traditional SOF). This is solved by having beefy gunwales and keels in the form of I-beams or ladder frames. In effect the stringers are only there to define the underbody shape. In my folding kayak the stringers are 15x10mm and are held in place only by the skin. People retrofit straps or other devices to better hold them in place because they move around in choppy waters. In a narrow kayak it's not that much of a problem, but for a planing dinghy I would want a secure connection to the frames to obtain maximum tosional rigidity. In a non planing dinghy I would not bother with it and secure them with straps.
Mechanical fasteners are a pain to use and keep count of and everybody has some replacement wingnuts in the first aid kit (bolts are fixed in the frame so no loosing them).

IMHO such a boat would be for holiday use only and as such not a frecvent assembler like a kayak. Folding is only to avoid having a trailer and space to park it. In East Germany (probably the biggest producer of folding dinghys) people normally transported the boat to the lake at the beginning of the season, assembled it and left it there on the water until they got it home for winter storage. I would expect a simmilar user profile. Even if weekend usage is expected it's not such a big deal.

 

Avos'ka (Stringbag) is pocket cruiser with internal ballast. I think it is not exactly the boat topic-starter looks for.
Other boats from Igor Vygovskii site (iv70.narod.ru) look more suitable.

 

Thank you for replies, sorry for my late reply, as I had some gale winds in my studies, and didn't have time to thoroughly look into the information you all provided.

Well, dinghies appear to be much more stable due to wider shape. It also allows better hiking. More people can come onboard, and even with 1 or 2, it is much more comfortable than in kayak (I have a lot of experience with kayaks, and I know how much it hurts after 8 hours of sitting in it with no way to change position). Also, more things can be stored onboard for a few days trip.
From the construction point of view, it is known that the strongest shape is a sphere, and the least strong - a stick. Kayak is closer to the stick, being long and narrow, while dinghy has fuller shape, being more close to sphere. Therefore, it seems logical that for sailing needs dinghy should be easier to build strong. Correct me if I'm wrong.

That sounds awfully complex and time consuming. On the other hand, I guess there isn't any other way...
Just a thought - I was planning to make hull skin from one piece of PVC fabric, so I don't have to cut and glue it (reduces risks of leaking, saves time and money on glue). The only things that have to be glued would be deck fabric, transom, and bow. And maybe some reinforcements.

Well that is really interesting. It appears very fast and rigid.

Speaking of Russian designs, from all the links you gave me, they are made out of metal alloys, while these German folding boats (like Passat) are made out of wood and plywood, except for hardware. I wonder why is that. These Russian designs are homemade. It seems to me that acquiring metal sheets, tubes, and other materials, and working with them (cutting to shape, bending, smoothing down, soldering) is way more difficult than working with wood. For example, in Lithuania, I never ever saw a raw metal sheet being sold (one that these Russians use for centerboards, for example), and believe me, I looked. Metal working tools, like drills, saws and so on are very expensive, and looking at these designs, I can't imagine then being made without electric or even workbenches.

For that reason, I tend to prefer wood-based design, since I can acquire timber and plywood, and most of the shapes I saw in Passat and similar dinghies appear to be possible to cut with hand tools or simple electric fretsaw.

However, Rumars, you helped a lot with these links. I got some very good ideas from these Russian designs. For example, this centerboard design is fantastic. I always wondered how could centerboard box fix with the skin without leaks, and here is the most simple solution - no box.

Petros, I also thank you for these photos. I can't imagine how you managed to make the boat this cheap. Salvaging materials, you said... Well, you must have had a lot of salvage to choose from! Not to devalue your work, but I don't believe it would be possible in my country... Nice work!

Well this is what occupies my thoughts at the moment. How many stringers, how many ribs. Passat uses total of 10 ribs, keel, 3 stringers on each side, a panel on each side behind which are the inflatable tubes, and gunwales. That is quite a lot, I think I would lower ribs to maybe 5-6, but keep the stringers and panels as it is.

As I understand, the lesser parts there are, the stronger joints have to be, the stronger the materials, and skin also has to be stronger, due to less support from structure.

I'm really not qualified to make a balanced guess here. As I mentioned, Passat looks very well made boat, but I would replace metal hardware with wood where possible, transfer centerboard idea from Russian designs, and try to use simplicity of Petros' design. Aiming for about 4m LOA, what would you say is the optimal number of ribs, and how thick plywood for them?

Well, I want the boat to break down to 2m meter parts at most, so basically there would be only 1 joint - amidships. Maybe that isn't too bad...



Thank you all for the extensive help. I really appreciate it. I'm also sorry for taking so long to decide on basic design principles. Maybe I'm aiming too high, I don't know. If I were to find a used SOF folding dinghy, buy it for up to 500$, and refit if needed, it would be easiest, but closest used such dinghies I can find are in Germany, and the trip would cost about as much as the boat itself...

 

In Russia Al tubes, profiles etc. are quite available. It's easier to find suitable Al tube than good wood. And here exists at least 50-year tradition of building SOF boats using Al, both production and home-made. USSR produced huge amounts of Al for aerospace and shipbuilding, so enough left for SOF boats.
And for freshwater boat you have no need to protect aluminum frame from water, not so for wood.

BTW: http://www.sapagroup.com/lt/sapa-profiliai-uab/ms-pasilymas/

 

Thanks, Nnnnnnnn, I know some of these sites like the one you provided, however, as I understand, they only deal in wholesale. Also, they don't provide prices, so it's hard to estimate how much would the boat cost to build, comparing to wood.

Anyway, assuming I can get my hands on any necessary materials - what design, wood or metal based, would be preferred for my project? What are cons and pros of each choice?

The way I see it:

Wood-based:
Pros:

-Relatively cheap
-Easy to work with
-Only basic tools required
-Boat would have more buoyancy in case of capsize
-Better looking and more comfortable

Cons:
-Epoxy required
-Painting or varnishing is a must
-Not as strong in small parts, such as joints
-May still require some metal hardware

Metal-based:
Pros:
-No varnishing or anything required whatsoever
-Maybe better strength/weight ratio
-Easier to assemble
-No wooden parts required for anything

Cons:
-Extremely hard to work with
-Requires expensive tools
-Requires soldering
-I can't imagine how to make certain shapes even with proper tools

Of course, this is my un-educated guess. Maybe someone could please shed some light into this important decision?

 

There have been some enlightening links lately. I only knew of one folding sail dingy but it turns out that there were several and the one I had seen was the 'runt of the litter'. About buying used -in the US I occasionally see dilapidated ones for sale and they are cheaper than the wood because the skins are trash. There are more of these in europe than here but it certainly does not pay to travel to buy them -you would have to buy based on photos and trust.

The video about assembling a Longhaul kayak taught me a lot about how the structure works. The keel and the gunnels are wide boards that are hinged and can provide most of the structure (all of the torsional structure and almost all of the longitudinal stiffness). The other key is seeing that there are two kinds of stringers -the kind that need a constant stiffness to be bent into a "fair" shape, and the ones like the keel and gunnels that are built to shape, solid, but not constant stiffness. The Longhaul kayak has only two stringers that are constant stiffness (the round ones) and if you look at them they are metal tubes at the joints. I would venture to say that it is as easy if not easier to make good constant stiffness stringers from metal tube rather than wood because of the joints -more joints more strongly favors tubes.

Aluminum is not hard to work with. Hardened steel or carbide cut it and it can be bent riveted and glued.

Even in the wood designs there is a large amount of metal in the fasteners and joints. On the Longhaul kayak there were lots of metal fasteners with pins. If I was following their method I would buy a long length of brass "piano hinge" -hinge you buy from the hardware store in long lengths of 3 to 6 ft and cut to whatever smaller sizes as needed. Then I would mount short lengths in place and push the pin out to disassemble. Then I just make a new easy to handle pin for long term use. bending drilling and filing will drive you nuts if you build these parts from scratch.

The Russian dingy in the utube video with tubing going in many different directions (we call it a space frame) is interesting because it is strong, stiff and light, but it doesn't even try to make a smooth fair bottom.