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I'm starting this topic to both log my experiments and to petition contributions and ideas from others.
The basic premise, to build a strong, inexpensive inflatable boat. If you look at the Zodiacs, you'll see they run into the thousands of dollars. Even the lower cost (smaller) inflatables at WestMarine sell for over a thousand and go up. My basic plan is to use some heavy canvas, and impregnate it with something to make it air tight. The canvas should add plenty of strength allowing it to hold a little bit of pressure and stay rigid. Everyone I've spoken to about this project has responded either that I'm crazy (possible), this is impossible (I'll never believe it), or both.
Lets start with the base material. I am really thinking of using a heavy canvas, like the kind available at the hardware store as painter's drop cloth. Purchased like that, I can get large pieces of canvas that are very sturdy and inexpensive. I've used this material to make bags, covers, and cushoins for my sail boat. So, I think its a good starting point.
Next up, a low cost way to make the canvas air tight and durable. An early thought was to use latex because its cheap and readily available. The problem is latex will not last very long exposed to the sun and elements. I have experimented with "PlastiDip" stuff used to plastic coat tools, and "liquid electrical tape" but, these two substances are hard to the saturate fabric with. Probably just as well, as these would be pretty expensive in the quantity required.
I really think that a liquid vinyl or some kind of vulcanizing compound would be ideal. However, I have no idea where to find such things.
The basic premise, to build a strong, inexpensive inflatable boat. If you look at the Zodiacs, you'll see they run into the thousands of dollars. Even the lower cost (smaller) inflatables at WestMarine sell for over a thousand and go up. My basic plan is to use some heavy canvas, and impregnate it with something to make it air tight. The canvas should add plenty of strength allowing it to hold a little bit of pressure and stay rigid. Everyone I've spoken to about this project has responded either that I'm crazy (possible), this is impossible (I'll never believe it), or both.
Lets start with the base material. I am really thinking of using a heavy canvas, like the kind available at the hardware store as painter's drop cloth. Purchased like that, I can get large pieces of canvas that are very sturdy and inexpensive. I've used this material to make bags, covers, and cushoins for my sail boat. So, I think its a good starting point.
Next up, a low cost way to make the canvas air tight and durable. An early thought was to use latex because its cheap and readily available. The problem is latex will not last very long exposed to the sun and elements. I have experimented with "PlastiDip" stuff used to plastic coat tools, and "liquid electrical tape" but, these two substances are hard to the saturate fabric with. Probably just as well, as these would be pretty expensive in the quantity required.
I really think that a liquid vinyl or some kind of vulcanizing compound would be ideal. However, I have no idea where to find such things.
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Signing UpStep 1Trival Math
This is trivial but, still something to consider.
The greater the airpressure in the inflated chambers, the stiffer the vessel will be. Determining the air pressure to use will come from a combination of material strength and size of the chamber. This will be modified downward with a consideration of material strength decline with age, consideration of forces from use (people sitting on it, waves, motor, etc) and a safety fudge factor.
Generally in the realm of inflatable boats, 5psi is considered high pressure.
So, for a 24 inch diameter tube, we get a circumference rounded up to 76 inches. So, 1 psi would equate to 76 pounds of force trying to tear it apart (2 would be 152). Since large tubes will be very hard to contain lots of pressure, a compromise could be to stack narrower tubes that could each have a higher pressure.
This asks for some pro/con cosideration.
Stacked Tubes:
A quick and dirty method of measuring the strength of the material is to cut a one inch wide strip to a length equal to the desired circumference, plus a little bit for hangers. Hang it up and start suspending weights from it until it breaks. Do it a few times and pick the low value for the weight that causes it to break.
The greater the airpressure in the inflated chambers, the stiffer the vessel will be. Determining the air pressure to use will come from a combination of material strength and size of the chamber. This will be modified downward with a consideration of material strength decline with age, consideration of forces from use (people sitting on it, waves, motor, etc) and a safety fudge factor.
Generally in the realm of inflatable boats, 5psi is considered high pressure.
So, for a 24 inch diameter tube, we get a circumference rounded up to 76 inches. So, 1 psi would equate to 76 pounds of force trying to tear it apart (2 would be 152). Since large tubes will be very hard to contain lots of pressure, a compromise could be to stack narrower tubes that could each have a higher pressure.
This asks for some pro/con cosideration.
Stacked Tubes:
PRO | CON" Higher pressuere (stiffer) | " Greater weight" More air chambers safer if | " More complex construction there is a puncture | " More material/expenseThe single tube is basically, the opposite of the above. If material costs are kept low, the cost part may not be a big deal.
A quick and dirty method of measuring the strength of the material is to cut a one inch wide strip to a length equal to the desired circumference, plus a little bit for hangers. Hang it up and start suspending weights from it until it breaks. Do it a few times and pick the low value for the weight that causes it to break.
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http://yostwerks.com/Inflatable1.html
This is the place the kayak guy recomends, but you might need to place a large order. They have hypalon fabric too, which is what whitewater rafts are made of.
http://www.mauritzononline.com/vinylcoat.html
Seattle Fabrics has a good selection too. And they have a $2 sample pack.
http://www.seattlefabrics.com/vinyl.html
They often sell PVC tarps at home improvement stores as tarps. That is where i got mine.
$120
I'm trying to figure out how to post an image from Sketchup here, but so far I'm unsuccessful. If you want to give me an email address I can send you the files.
Good luck and keep us posted.
I am also considering making a surf board from the pink 2 inch thick foam insulation covered with fiberglass and attaching a trolling motor.
http://www.fixallroofs.com/ssl/order/order.php
I'm having trouble finding info on the web of people who have created their own inflatable boats. Tom Yost has a small kayak on his website he made with vinyl-reinforced poly tarp material gluing the seams with hh66 glue. He references a south american gentleman that made one too, but that's about it.
I was either thinking of using 18 oz tarp material like Tom, or use that for the outer hulls and make inner tubes with 20 mil pvc pond liner (a stretchy vinyl). My thought was the stretchy pond liner expands and pushes against the reinforced vinyl to create a more rigid structure. 18 oz vinyl tarp material can be had for $3 /yard (62" wide) and 20 mil pond liner is about $3 a sq yard.
Looking for any thoughts, experiences, or links to more info on budget diy inflatables.
Below I've attached a Link to my latest homebuilt inflatable. Technically it's an Inflatable / folder hybrid as it combines sponsons with 3 aluminum stringers in a sort of symbiotic relationship to achieve both rigidity and shape.
http://www.yostwerks.com/SonnetPuebloE.html - Sonnet 18 ( 2 pages)
The advantages of this configuration vs a true folding kayak are the much simplified frame, quicker assemby as a result, and lighter weight. Conversely, the advantages over a pure inflatable are it's sleek shape, clean entry, and good performance.
I think that the easiest way to succeed in making anything is to stick with materials and methods that have proven succesful in the past vs trying to reinvent the wheel. PVC is a woven polyester core coated both sides with vinyl. it's completely waterproof, is quite durable, and is reasonably priced. I used commercial "Folbot" sponsons ( nylon core) to insure reliability in this critical area. For $20.00US each, they are reasonably priced and likely higher quality than anything you will make yourself.
The 2 page link goes into some detail on this kayak. Even if it's not the configuration you require, there may still be some ideas of interest for your project, assuming you are still working on it.
Regards,
Tom