inflation flotation

General Discussion
1

Hello,

I am looking for an inflatible stand up surfboard that is easy to transport (roll up put in small bag) and that is nearly equal in performance with a regular board.

I have seen the ULI boards but i don’t like the shape and i think they are not capable of carving in a wave because of the shape of the rails (you can’t realy call them rails) , or let’s just say doing a cutback, i bet they are a lot of fun at the beach but there should be a better product.

I guess better ones are not on for sale yet so i am seriously thinking of constructing one myself, so if anyone has information on how to do so, please let me know.

I have read the archives and it is mentioned that some people were at some point working on such surfcraft, maybe they could advise me in my quest.

The design i am thinking about would be something like this:

  1. shaped like a classic minimalibu, respecting all the dimensions, thin nose, thin tail, rails, etc.

  2. the material would be hypalon or some neoprene type of fabric.

  3. one of the main problems would be to achieve rigidness and to achieve that i was thinking of using an inner and outer lining where the inner tubes would be inflated under a lot of pressure (the way you inflate your tyres at a gas station, using the same kind of valve) and the outer lining being the actual shape holding everything together.

  • a first question is: would the weight of the compressed air necesary to maintain the shape inhibit flotation or cause excess weight (a bit heavier than a regular oldschool board would be acceptable but would that be doable?) ?
  1. also an option would be to work with a sheet of rollable plastic for the bottom like the material they use for bodyboards or more flexible material with low friction, and attach the neoprene outer lining to it, this way it would be easier to get the shape of the rails and it woul guarantee a flat bottom.

I hope i am making sense, english is not my first language,

Basicly what i am asking for is ideas and help on the type of materials that are best suitable for this project, i don’t want to be wasting to much time and money on prototypes, i never shaped a board before (only ding repair) but i own a couple of boards and so do some of my friends so for the actual shape i can copy from existing planks.

Thanks in advance, P.

2

Interesting ideas. I agree with you about the ULI boards, they are too thick (although my kids had fun on one). I don’t think you have to worry about the compressed air weighing too much! But I don’t know if you could get the rigidity you want that way either. Maybe another approach would be to use battens that run the length of the board, perhaps set in pockets so they form triangular beams? Even then I’m not sure you could stand on it without the result being shaped like a banana…

Dale will have some thoughts for you, I suspect.

3

As Keith mentioned, Dale is the real expert on this, but a few things to consider -

Unless you have an inner structure of some sort ( compartments with the dividers in tension ) , the shape of the thing is going to tend towards a cylinder or sphere so thin rails may be difficult to do, though I think your idea of inner and outer deck membranes would help a great deal. Perhaps a rail compartment inflated to relatively high pressure that had a flat-triangle cross section before being heavily pressurised would adopt the shape - certainly it’d need experimtentation.

You’re aiming for something perhaps the size ( when rolled up) of a sleeping bag plus pad or something of that nature?

The Hypalon or similar fabrics sound like the way to go, I have had them suggested to me previously - see http://www.uretek.com/ and www.highlandindustries.com/ with particular attention to the adhesives and bonding processes so you can think about your seam design and such.

I like the idea of a semi-rigid planing hull that’d roll up, though it’d have to start rolling at the nose 'cos the tail, with whatever fin arrangement you used ( I think FCS plugs would work easiest, set in fiberglass or PVC ‘cups’ in the bottom, adhesive or maybe welding it there - some of the plastic sheets you could use are weldable with hot air jets - if you wanted a big center fin I think you’d have to invent the attachment system ) would have the least problems. Likewise, the varying radii as the board rolled up might allow you to make the rear of the bottom stiffer and thicker. Something similar in a deck panel might be a good idea too, it’d simplify things considerably and allow for the rather high pressure per unit area of somebody standing on the thing.

Weight of air would probably not be a real problem. To get a volume of compressed air to the same weight as the equivalent volume in a lightweight Clark foam you’d have to compress it to something like 20 to 25 ATM, far beyond what you’d need for a board ( which would probably be no more than 2-4 ATM at most - that’s about 300-350 PSI and 30-60 PSI for non-metric types.) . The volume of air involved would be beyond easy work with a bicycle pump, perhaps one of the small 12 volt compressors that are available for automobile use could be brought along when travelling?

Might be interesting to put in a kind of inflatable spine on a separate inflator valve, such that you could vary the longitudinal stiffness and rocker by working the pressure in that versus the pressure in the rest of the board?

Interesting project…

doc…

4

Hello,

Instead of inflating the entire craft, consider a framework held in compression by an outer skin (Like Aleutian and Greenlandic skin boats, tents, etc.) There are many manufacturers making folding, travel friendly kayaks in this manner. The frame may be wood, aluminum, PVC tubing, or similar medium. Although the industry tends towards heavy Hypalon style skins, most backyard builders utilize lightweight nylon or cotton duck. Zippers sewn onto the skin allow it to be pulled over the framework and secured. Excess slack in the skin is taken up by small air bladders placed longitudinally inside the craft.

A search for ‘Folding Kayaks’ should reveal a multitude of designs, while a search for ‘Baidarka’ will lead you to the home builders.

-Seamus

5

Hello again,

Thanks for the advice,

I checked out the foldable kayak systems but i feel more for inflation, the construction design will be equally difficult to achieve i think, and the result with inflation would be much more easy to operate, just imagine you step out of the airplane (no fees for oversized luggage) and you stop at the nearest gasstation to inflate your board and you are ready to jump in the water.

Indeed the best way to go would be to start rolling from the nose and to have a ridgid tail with the boxes for the FCS fins, this way most of the rails of the tail would be easy to shape and those are the most important for steering control i guess.

I also loved the idea of a kind of stringer compartiment with adjustable pressure to vary scoop and rocker making it suitable for a wide variety of waves!!

I think this also would be the spine of the board, it should be pressurized in such way that you could stand on it without it collapsing (i hope this is doable).

What does worry me a bit is the type of sheet of plastic i should use for the bottom of the board, it should be very flexible (totaly rollable) , strong , durable and low friction in the water, i have no idea which type of material i should use for it.

To make sure that it will not collapse in the direction of the width of the board i would first attach the sheet of plastic to the rigid (fiberglass) tail section and then every few inches put thin cross-bars attached to the sheet.

Once this is finnished it is just a matter of glueing/welding the inflatible part on top of it and finally covering it with a thin but strong liner.

What I didn’t really understand was the part of the triangular cross section, i do understand that the rail line should also be pressurised and also that triangles are a very strong construction design but in which direction to place the triangles leaves me a bit puzzled.

So, this is what i’ve got so far, once i’ve got the basic materials to use figured out and the basic design i will start with the actual shape, enough stuff to brainstorm about.

Thanks a lot, P.