Low-speed sailboat hull

http://iv70.narod.ru/IV/6/Mewa.html
http://iv70.narod.ru/IV2/Mewa/Mevva.html

It can be completely disassembled and placed inside the car.
So, no weight limits are applicable in this case.

 

Foldable RIB (rigid inflatable boat) + sail

E.g.
1) http://www.dinghygo.com/product/

2) http://winboat.com/sites/default/files/models/Catalog Winboat.pdf
Compact Foldable RIB WinBoat 460RF SPRINT SAIL

 

Great concept. I reckon it would suit the OP beautifully, even better than some of the other options.

 

Despite these boats were factory built, the boats are not really good.
Lack of stability, lack of mechanical strength. The production was stopped long time ago.
The only advantage - the boats are cheap. The typical price of a second-hand Mewa-2 is approx. $600 in Poland / Russia. With a new sail and new skin for the hull - more expensive.
And nothing to build - just buy and sale.

Typical advertisement: http://yacht-com.ru/board/read452.html

That's how the boat looks disassembled: http://gik.fordak.ru/index.php?action=dlattach;topic=11606.0;attach=71459;image

 

I would be interested to know why you discounted the Duo dinghy from your "possibles" list? It seems to match your requirements.

It is very easy and quick to build. You can certainly build it in a weekend. 2 sheets 4mm plywood and 2L epoxy. The plywood I used to build the one in the photos cost USD31 a sheet, epoxy was about USD40, glass tape about USD20. Cheap timber about USD10. So that is under USD150 for the complete boat, excluding rig

Maybe it is too small for you?

Richard Woods of Woods Designs

www.sailingcatamarans.com

 

Dear Richard

Duo is a great design! http://www.sailingcatamarans.com/in...ats-and-dinghies-/420-duo-10ft-sailrow-dinghy

I could never imagine it iwas possible to build a sailingboat from plywood with a such small weight.

 

(sighs) Well, I'm starting to consider this. I really wanted to go with monohull for my first serious boat, but it might be that I'll have no choice. Writing your advice down as one of possible options.

Petros, could you explain please, how exactly does catamaran like you suggested come cheaper to build and lighter than similar size dinghy? I mean, it's two hulls, then there are beams, two daggerboards, two rudders, stayed mast, and all major joints should be disassembling easily for folding the catamarn. It seems much more complex. How exactly does such multihull beat the practicality of dinghy?

Also, if I were to use 100% cotton, what tradeoffs does it have compared to polyester? I think it's heavier for the same durability, and susceptible to rot. Does it heat shrink? What density would be enough for kayak, and what for dinghy?

Made my day. Well, I never seen anyone transporting couch or anything on the roof. The use vans for that.

RS Terra looks lot like Laser. However, it's described as for one adult or two small children. Definitely not two adults...

I'll look into Snarks and Herreshoff designs. Maybe it's an option.

Nick, thank you for your idea and links. I had a folding design in mind a while ago, and ever worked half a year on a design based on Klepper Passat. However, I had to abandon the idea due to this limitation: skin made out of polyester/nylon/whatever and coated with paint, even polyurethane, would crack when folded, and possibly leak afterwards. If I made skin out of PVC fabric, which takes folding well, I couldn't accommodate proper rocker, because such fabric is not heat-shrinking, and has to be glued with heat gun. I'd have to go with darts or overlaps, which doesn't sound too good. I have only seen PVC fabric used in Tom Yost's designs for kayks with no rocker.
Also, it would be highly complex to build. It requires inflatable tubes and other skin-tensioning solutions that add complexity and cost. All joints need some hardware, which I could not find in my country.
All in all, it is a great idea, but way too expensive and complex for my first serious build.

I am sorry, I must have missed it, or not looked into it enough. I will do so now. Looks promising, thank you!

 

All right, I looked this Duo thoroughly. It is truly magnificent in it's efficient use of materials. Almost nothing is left of these two plywood sheets. And indeed, this boat is both cheap and light enough.

It looks a bit cramped and not very elegant, though. I think I could let myself build a bit longer and wider boat, even if it takes 3 sheets of plywood. Duo weights 20kg. I could push dimensions up a bit, until it weights ~30kg. Maybe 3.5m LOA and a bit wider. I don't fancy using these inflatable collars (I searched, and with little surprise, no one sells them in Lithuania). It is said that Duo costs around 300-400$ to build. If I upscaled it to 30kg, I don't think it would go over my budget.

Started sketching this, we'll see. By the way, what is density of these plywood panels in photos of building Duo? I calculated it to be about 500kg/m^3, which seems a bit on heavy side.

What do you think on building a bit spacier and heavier boat based on Duo?

 

I have just skimmed this thread, but saw some mention of trimarans. This guy is very inventive and may have some good ideas for you.

http://www.diy-tris.com/

http://www.youtube.com/watch?v=C8kUq4BouS0

 

philSweet,

I am VERY interested in a boat that does what you described

Have been looking hard at options and have pretty much accepted that a pram/scow is a better solution than generally thought (maybe by the inexperienced, which included me).

I'm a Mini650 fan who loves David Raison's Mini #747 and plum crazy about his latest evolution #865.

Don't want to hijack this very productive and interesting thread - so if you have a link to any info showing your boat, or wouldn't mind discussing it off-thread you can PM me.

TomH

 

It seems that a real issue here is there are real limitations on materials that Laukejas can build his boat out of. So far I've heard that fiberglass tape is out. Dacron appears to be out as well. So too is marine plywood, it seems.

To come up with a real intelligent solution, it seems we need to know what materials he does have access to.

Apparently exterior plywood is one of them. But in what thicknesses?

Also, what kind of fasteners are available. Can he get hot dipped galvanized screws and or nails? Or stainless steel? Or brass?

And what about glues? Is epoxy available in his country? How about other glues that are at least water resistant?

Some pdracers have been successfully built using "PL premium(r)" and even "PL II(r)" with taped seam construction, using fiberglass wall tape.

Right now, I'm thinking of a double ended sharpie that would be about 4.0 m long and about 1.0 m wide. It would carry a sprit-sail of about 6.0 sm. The sail would look something like the attachment below.

The bottom could be made of plywood, but the sides could be plywood strips covered with canvas, to keep the weight down, if thinner exterior grade plywood is not available. The cockpit could be as long as 2.0 m but more likely 1.5 m long.

Just thinking.

Also attached below is a design I hope to build some day, which may be in your size category. It is 3.66 m long and 0.92 m wide. Just imagine it with a 6.0 sm sail, like the one in my first attachment, rather than the 4.36 sm one shown. The sides are dead straight and only the bottom and deck are curved. A flat deck might work on this design as well.

The waterline is quite short, when the boat is level. When it heels, the WL lengthens and the hull Whetted surface shrinks. In light winds, the sailor can induce heel by positioning his weight.

Pretty radical, I know, but it might work quite well in Laukejas' situation.

Another design to consider might be Jim Michalack's "Pickup squared". He can find it in the "plans" section of www.Duckworksmagazine.com. It's a little shorter and wider than my idea, but it requires no stitch-and-Glue to build.

 

Imaginary number, the trimaran you showed looks beautiful. I will look it up to see if it's within my possibilities.

Sharpii2, thank you for your ideas. Well, situation is not as bad as you say - I may have led you to misunderstand the material shortage in my country. True, Dacron, polyester, nylon, fiberglass cloth and marine plywood are nowhere to be found.

However, fiberglass tape is available, and so is epoxy (although somewhat more expensive than in USA). The hardware you mentioned is available, although I'm not sure what you mean by brass (other than material itself).

After long and hard search, I have found this laminated plywood (Dave Gentry says it looks like your MDO plywood, it might be the same) of 4mm thickness, and then it goes up every 2mm. Sold in 1250x2500mm sheets.


So, in other words, stitch&glue would be ideal in my scenario. All materials are readily available, construction is easy enough, and it will be well below my budget limit with proper planning.

So, right now, of all the options showed by generous members of this forum, I think Duo is the best fit. However, it seems a bit short and cramped for two persons, and watching the videos, I'm pretty sure the transom would go below waterline with any additional weight.

My idea is to make a design of my own, based on this Duo. It will be a bit heavier (Duo is 20kg, and I can go up to 30kg), and more expensive (Duo is 300$ to build, so even if build cost doubles, it's still within reach).

Since I have access to Delftship and SolidWorks software, I tried re-creating hull of Duo, increased waterline, beam and rocker to make it ideal for 200kg displacement and balanced with larger sail area.

Still working on it, here's three screenshots. They are very large, you can zoom in a lot.

http://static.dyp.im/EYKEs76Uc5/1584d30f2ae5684a3fc19f3f1f74a255.JPG

http://static.dyp.im/Ri6OfZtbGc/37a58af889c3bfff8693842df237720f.JPG

http://static.dyp.im/YEI6Wk20Yj/88d5020f866998f3d8eb7b3bc8a65b55.JPG

I removed one of the side seats to see what reinforcements I have in mind to support the thin plywood better.

The bottom and side panels are 4mm plywood. Transom is 8mm plywood. Cross-sections (by the seat, and in the bow) are also 4mm. Bow cap is 4mm too. The center seat is 2cm thick plank (or several planks joined side-by-side if I can't find a plank that wide). Invisible in screenshots, there are two 4mm plywood panels inside the center seat that act as centerboard trunk. The side seat horizontal panels are 8mm, and vertical panels are 4mm. The beams that support these seats are 10x30mm.

Estimating that MDO plywood has a density of 500kg/m^3 (correct me if I'm wrong), the total weight reads 24.6kg. Of course, there are several things missing, like mast step and partner, rudder attachments, maybe several more beams to support thinner sections of plywood. Maybe 1 more kilogram. Then there's epoxy and fiberglass tape, which may add another kilo or two. Same for paint. Hardware, another kilo.

All in all, it seems to come out close to 30kg in total, which is my limit. Of course, I need to determine exact density of plywood, as well as finish my model. But it seems possible. I haven't yet estimated how many sheets of plywood I'll need, but I try to stick to 4mm and 8mm only, so maybe it'll be 3 sheets of 4mm, and 1-2 sheets of 8mm.

Comparing to the Duo, I have extended side seats right up to center seat to add structural integrity (to minimize the twist of the hull due to thin plywood) and to increase buoyancy tank volume.

What do you think of this design? Took me only a day to sketch.

 

Hard to tell just by the sketches.

They are not ortho projections and you give no dimensions.

Apparently you have gone from a two sheet original to a four sheet plus expansion.

By the looks of it, it will be quite strong. You have a lot of box beam action going on. This will make the boat quite rigid, but it comes at the cost of a lot of trapped air.

Even on a wooden boat that is thoroughly epoxy encapsulated, this is not a good thing. You will need access plates on each separate box structure, which can be left open when the boat is not in use.

Have you figured out how much it will displace?

I see very little rocker in the bottom. That may be just because the way the sketches are angled.

Below is a sketch of a pdracer I drew back in the double aughts.

You may find the cockpit interesting.

It is to be made of four sheets of 6 mm plywood, including the rudder and the two boards.

 

Sharpii2, attaching several more screenshots for better view of dimensions:

http://static.dyp.im/z7EMgzHVHD/4f8d8ef90a0ae8726d39cab5770a5b48.JPG

http://static.dyp.im/3mEo12EsMe/e9da8555d0a91ae9e462f56107680b53.JPG

http://static.dyp.im/kcUCavzo8s/f53052533bac6cf06686461f9301fad0.JPG

Target displacement is 200kg in fresh water (the maximum load). Length is 3.75m, beam is 1.25m. Draft is 13cm, and at perfect trim, bottom edge of transom is coincident with waterline, while bow is submerged 1cm (to dig into waves better).

Here's a linespan exported from Delftship, it helps visualizing the waterline and the rocker:

http://static.dyp.im/KvTm7ab4rm/febd0a6a2a587b5557d4511dc1232696.jpg

I tried nesting all the plywood parts. It seems I can get away with 3 sheets of 4mm and 1 sheet of 8mm. However, I haven't yet worked on rudder and centerboard, so it might need another sheet. Of course, scarfing will be necessary. Here is how parts nest:

http://static.dyp.im/wMPuTGhEKg/fd7713b4d37dc6b06e7e487cbea6e70b.JPG

Why is that a not a good thing? If these compartments are watertight, they will help to float the boat if it capsizes. Of course, I can add a plug to each of them to ventilate the compartments when boat is ashore.
So what's wrong with trapped air? Or did I understand you wrong?

Your pdracer seems interesting. It seems to me that it's foils are quite small compared to large sail area. Maybe you have more sketches, or at least in higher resolution?

 

It doesn't look at all like a Duo to me!

I am working on a 4m long version, 2 man cruising sailing dinghy.

The inflatable tubes are primarily there for use as fenders when coming alongside the "mothership", remember the Duo was primarily designed as a tender. But they are also useful to add stability when sailing if you are a less agile sailor. They aren't essential

https://www.youtube.com/watch?v=IpPCZq5CuWo&list=UUhKTQtbKN5BaXFTg2BjcbqA

You can buy suitable inflatable tubes here, they ship worldwide

http://www.sailormall.net/pneumatic...350-kg-code-o1330125-15850-1?search=pneumatic

4mm ply weighs about 7kgs per sheet, so it looks like your boat will need about 25kgs plywood, plus 3kgs epoxy, plus maybe 10kgs timber. I doubt if you can build it to weigh 30kgs and still be strong and buoyant when swamped

My own Duo cost about USD150 to build. The two sheets of ply were USD31 each, timber was ripped down 2x4in that came from Home Depot, so was very cheap, maybe USD10 for all of it. The glass tape was USD21 and the epoxy was about USD30. St steel screws about USD6

Richard Woods