IKs are fabricated or assembled in two ways: either with airtight ‘inner tubes’ which inflate inside the floor and side compartments of a (sometimes porous) protective fabric shell to make a rigid form, like a bicycle tyre inner tube.
Or sections of hull fabric are assembled to make fully airtight chambers and a load-carrying monocoque. I call this ‘tubeless‘ (which is also found on the very cheapest heat-welded vinyl IKs) and the pros and cons of both are explained below.
An IK’s hull can be a shell with three chambers (two sides and the floor) made of PVC, woven nylon or both and into which are fitted light, removable sponsons or air bladders, made either from stiffer vinyl, more durable and flexible urethane, or just PU-coated nylon. Examples include Aire, Aquaglide, some Sevylor, Intex and Decathlon Itiwit, or Advanced Elements.
Pictured right: vinyl and urethane may all be just ‘plastics’, but might be compared to Platypus water bladders (vinyl, stiff, slippery) and the blue Camelbak (softer and rubbery). That is why in bladder boats like Aire, tough PVC is good for the outer shell and urethane makes an ideal, slightly stretchy bladder. Cheaper Aire Tributary IKs use vinyl bladders.
Compare that to the Gumotex, Grabner, Sea Eagle, NRS and Incept style of fabrication which involves the perfect gluing or heat-welding of the hull sections into an airtight monocoque.
I notice my ‘tubeless’ analogy was adopted by Innova, the US Gumotex importers, except that they try to make out that ‘tubeless’ is superior. It certainly is for automotive tyre use, but with IKs it’s more down to manufacturing ease and therefore, costs. PVC (welded is best, like Incept or some Aires, not glued like Advanced Elements or sewn like Tributary) is stiffer once pumped up, less durable, doesn’t abrade so well on grit (out of the water), but is less expensive than synthetic rubbers, easy to weld or sew, and is slipperier in the water.
The difference between the ‘tubeless’ or ‘tubed’ construction style is principally down to manufacturing costs and materials.
On boats with air bladders the shell doesn’t have to be airtight, It’s just takes form as the bladder is inflated. Shells can be heat welded, sewn or glued, and can have sleeve openings or zips to access and repair or replace bladders, if necessary.
But the robustness and durability of the shell is a factor, as it takes all the knocks and abrasion. Reliable heat welding of quality PVC is best, certainly compared to vulnerable stitching or laborious gluing. The green shell of the boat above was ripped on its second outing (possibly over inflated then left in the hot sun). I also read that on cheaper IKs, sponsons can get twisted in the sleeves during unrolling and inflation can get to be a faff.
The big drawback with bladders is that it’s normal for some water to seep inside the hull shell in the spaces between the bladder and shell. Result: the boat takes ages to dry properly. This may not matter in your villa in Acapulco, but it sure does in Scotland or Scandinavia or Seattle. Coming back tired from a long paddle and then packing a wet boat is as undesirable as packing a wet anything, not least if it’s seawater. Mildew may develop, grit may get in and who knows, something may rot and shorten the life of your boat.
If your boat is in and out of your car boot or motorhome, tubeless is the way to go. If you’re more into multi-day trips and have time and space to dry it later, a bladder boat has no disadvantages.
Tubeless construction seems to be the original or ‘European’ method and, if well made will last for decades as rafters know well (left, a hypalon Semperit from the 80s). Our Nitrilon Gumotex Solar looked as good as new when I sold it some nine years on, and had my Incept K40 been made from the same material and not PVC, I’d have probably kept it. No matter what they tell you (‘easy repair’), bladdered IKs are about ease of assembly and cost-saving.
I like the simplicity of tubeless IKs: a tough one piece shell. There is no cheap way of doing it and so any tubeless IK like a Gumotex, Sea Eagle (heat-welded PVC) or Grabner ought to be a well-made IK.
In my experience in the US, IK rental outfitters tend to use tubeless Hypalon IKs like NRS or Hyside, even if most recreational IKs sold are bladdered. Tubeless will cost more but they’ll last much longer, especially if made from synthetic rubber.