I would like scrutiny and comments of an idea I had.

To provide stiffness, I wondered about a timber frame around the outside of an inflatable hull. The hull could be cradled by hammock-like ropes and strapped up against that hammock. The bending and sheering forces of sailing would mostly then be absorbed by the timber frame and the slippery bouyancy is then left mostly up to the inflatable hull.

I drew inspiration from Teh Pookie; I want to build something like that! It would be incredible to build a hull like that with relative ease and economy.
http://www.proafile.com/archive/article/teh_pookie

One thing I’m really unsure of is how to obtain an inflatable form like the one sketched. My only knowledge of working with PVC-coated polyester is from Tom Yost’s foldable/inflatable kayak site.
http://yostwerks.com/InflatableMain.html

http://www.jpwinc.com/products/products.php?cat=9

Thanks. They don’t seem to have a tapering cone option though; I think I may end up using an American football for inspiration.

Construction started on this experiment today. I’m planning on a 5 meter main hull, round in section, made of three tapering panels, joined using butt seams. I’m thinking 8 cm tape on both sides of the seams ought to be sufficient. 12 meters of fabric 2 meters wide will be enough for the entire project. I’ve chosen to use fabric that is 610 grams per square meter; I’m unsure what working pressure this fabric will allow in a tube that is 40 cm in diameter, though it was able to hold 35 kg with one 2.5 cm strip of fabric, so if my calculations are correct, it will be able to hold 3 psi without bursting (a common pressure for inflatable catamarans). Whether it can have some longevity at that pressure will remain to be seen.

The 3 panels were traced from PVC pipe under tension; sketchup rendering of the panels this created indicated a satisfactory final shape will be possible.

The cones needed to cap off the ends of this may end up being rigid PVC orange traffic cones; my method of construction will leave 7 cm holes on both ends.

Laminated 1x4s will be made to hug the curve of the hull for structural strength. These will be 3 meters long, and will have 1 meter bow projections somewhat like in the first post.

Adam, thanks for giving us updates on your fascinating project. I have no ability to give constructive engineering comments so I’m sorry for that, all I can offer is encouragement. What a cool looking boat!

Hi Adam,
may you get some inspirations at these websites:
http://www.ducky.com.ua
http://www.happy-cat.at
http://www.smartkat.org.uk
http://www.airkat.com.ar

Thanks for those links, Othmar. Some of those catmarans really have some good performance. Smartkat in particular seems fast; mostly because it planes well and is super light it seems. I wish I could get my hands on their aluminum masts that snap together from pieces.

I’m hoping my rigid bows will aid in cutting through the water somewhat like the Catapult catamaran.
http://www.catapultcats.com/bass.more.pics.html

Progress is halted for the moment as I wait for the humidity to drop here; the PVC glue requires low humidity to cure properly. So I worked on designing the rig I plan to use. I’m trying to maximize sail area and aspect ratio without using spars longer than 11’ to balance cost/robustness/transportability. I came up with the standing lug sloop.

Adam,

I love your project.  Any updates?  I am really excited to see the results.  I looked into building one similar myself.  There are one or two articles on instructables about building an inflatable catamaran.  not much detail though.  There also was an inflatable trimaran that crossed the ocean (big enough for 4 men)  You can get some ideas of how they attached the ridged structure to the inflatables.  Energy Diet is the name of it.  http://smalltrimarans.com/blog/?p=5052

There is also a episode of “How it’s Made” that shows an inflatable company making one of their inflatables.  It’s on youtube.

Why are you choosing to use wood for the frame?  it seems to me that using aluminum would be more convenient for portability.  You can also use telescopic Aluminum for the spars and mast like the ducky or smartcat, etc..

Keep up the awesome work!!!

Lenny

Lenny,

Thanks for those leads. There are very few informational resources for this project.

I’ve made the sails since I last posted; they total up to a more modest 90 sq ft as shown in this new render. The final sailplan is less prone to jib sag with the tack further back; important on this design I’m sure.

The biggest reason I chose wood is that a form-hugging curve can be made easily given my hull shape. I’m not sure how that part will work out yet though.

Best,

Adam

I like this rendering!  Any foils?  A leeboard?

cool,
chris

There has been an inflatable proa already built.  It is found in the proa_file yahoo group in the files area under “folding proa”  I am trying to attach a picture of it.

I tried to contact the poster but was unable to. 

Also it seems that the Russians and Ukrainians are well versed in inflatable technology.  I found a few websites that may help.  They look pretty awesome!

http://gik.fordak.ru/index.php?PHPSESSID=8locvmktnudj37207tsc48dq71&topic=9652.0

http://www.fordak.ru/

http://yachta-kotoyarvi.narod.ru/

Lenny

Found a further one, some detailed pictures

http://www.minicatamaran.eu/intro2.html

Now found a website with links,

http://www.drkoellner.de/  Some of the links are dead.

Also found this, all I know it was sailed in the 2010 Ultimate Florida Challenge by a ‘crazy Russian’ like the bow detail. He has posted some info at

http://www.watertribe.com/Discussion/DiscReadMsg.aspx?strThread=6853&strNumReplies=9

TINK

TINK - 30 March 2013 12:14 PM

Also found this, all I know it was sailed in the 2010 Ultimate Florida Challenge by a ‘crazy Russian’ like the bow detail. He has posted some info at

 

I saw the Crazy Russian in the 2007 Everglades Challenge, he’s as tough as his boat. Found out though some discussion on proafile last year with a Russian that their expertise with inflatables comes from the lack of regulation on inflatables. Evolution on a finite scale.

cheers,
Skip

Adam - 16 January 2013 08:56 PM

12 meters of fabric 2 meters wide will be enough for the entire project. I’ve chosen to use fabric that is 610 grams per square meter;

Adam
What is the material you are using usually used for? The material for boats is twice the weight and very expensive

TINK

There are quite a few amazing plastic infused fabrics around.  And some are pretty cheap.

TPU is the acronym for Thermo Plastic Urethane and that’s what I’d be looking for.  Its what’s inside a Timbuk2 messenger bag.  It comes as thick or as thin as you like.  The substrate is usally nylon or polyester.

TPU can be glued or heat or sonically welded.  It has great physical properties and its cheap, which is why its ubiquitous in sporting goods.

Just a thought.

Best,
Chris

Thanks Chris
Big help £450+ just on material was getting steep foe an experimental sheet.

TINK