Tag Archives: drop stitch kayak floor

TPU Inflatable Kayaks: the Mis ing Link

See also:
Advanced Elements 2021 AirFusion Evo
Aquaglide Cirrus 150
Zelgear Igla 410 (soon)

Pictures from Zelgear and Marcin S

These days IK hulls are mostly made from PVC. Just three main IK brands still using old school synthetic rubber: Gumotex (Cz), Grabner (AT) and NRS (USA). PVC gets recycled, is made everywhere and so is cheap off the roll and easy to heat weld. But is it only me who finds something unpleasantly ‘plasticy’ about PVC: the stiffness, the texture, the smell and maybe the eco-stigma.

The only PVC IK I’ve ever owned punctured on the slightest thorn and went on to do that with the next owner. And this was supposedly quality ‘Mirasol’ PVC from Germany (to be fair, a mate with an older K40 had no puncture problems whatsoever). I can’t imagine any Gumotex or Grabner I’ve owned ever doing that, not even my many (TPU) packrafts. That’s why I persevered with synthetic rubber IKs, even if it’s becoming an expensive ‘dinosaur’ fabric.

Synthetic rubber coatings like Nitrilon and EDPM are derived from the original DuPont hypalon. Boats must be hand glued which adds to costs. But, just as nothing man-made has managed to beat the properties of leather for crashing fast motorbikes, compared to PVC, synthetic rubber remains more durable and more resistant to UV, lighter, more supple, easier to glue (where needed) and easier fold compactly. After 15 years there was no noticeable deterioration in my Sunny, (below) other than a decade and a half of paddling wear and tear. A synthetic rubber IK will easily outlive a similar PVC IK.

Packrafts, meanwhile, are mostly made from TPU (as well as a few from PVC), a different sort of polymer coating which has many of the benefits of synthetic rubber: odour-free, smooth texture, light, UV resistant, supple (crease-free), not environmentally toxic. But, like PVC, it too can be heat welded. Since Alpacka got the ball rolling, there are now loads of brands banging out TPU packrafts. In this time the fabric and seam technology have proved themselves to be as durable as PVC or rubber, and capable of running higher pressures too. As someone on the internet observed: ‘Thermoplastic Polyurethane (TPU) is the link between rubber and plastic’.
For inflatables TPU is clearly superior to PVC in all ways except price and stiffness (but this works both ways). “It has properties between the characteristics of plastic and rubber. So, it is flexible without plasticizers, and its flexibility does not affect the design or its strength and durability.” Link

In a way, my 3-metre MRS Nomad packayak (left) was as much a TPU kayak as a packraft. With just 2psi or so, it was able to hold its shape (under my weight), but now costs nearly €1400 in the decked version. In 2022 I got a similar Anfibio Sigma TXL (above) which works surprisingly well in IK environments while weighing just 4kg.

Advanced Elements 2021 AirFusion Evo with a PU shell.

The only PU (same as TPU; not sure) IK I know of was NRS’ discontinued Bandit series. It was made in China but was still dropped, I presume due to cost reasons before they started making many more models with PVC. Since I wrote that the Advanced Elements AirFusion Evo with a PU shell has come out. And so has the TPU Aquaglide Cirrus for 2023.

Zelgear TPU IK

While researching the Zelgear Spark 450 preview I found a 2018 ZelGear catalog. It states their now discontinued 5.2m PVC Igla IK can be requested in TPU (or the similar and much stronger Vectran which Alpacka use for their top-of-the-range packrafts). There’s more here. The weight of this long boat is said to be 15kg. The cost? $2000 I was told.

You may wonder if relatively thin and flexible packraft TPU could support a 5-m IK? TPU coating is also said to be more elastic than PVC, but it can’t be any more elastic than rubber. And anyway, a stretch-free scrim (woven core) takes care of that; the coating is primarily for impermeability.

A long IK needs to be a lot more rigid than a relatively short and squidgy packraft. And a lot of that is down to the fabric, not just psi. That’s one good thing about inflated PVC: it’s stiff. You’d think a TPU IK would require very high pressures to support a long boat which would then need bombproof seams. But add a TPU drop-stitch floor (above) to take the load and the tubed sides would be under less pressure, so to speak. This Zelgear blog post from 2018 mentions some “some technological issues are being resolved“. I’m told Zelgear were on it but then Putin made his move…
Pictures below by Marcin S from a boat show in 2018.

With all these Asian-made TPU packrafts knocking about, some using locally sourced fabric whose quality in my experience is as good as the Alpacka stuff, the cost of TPU fabric may drop to a level matching the few ‘hypalon’ IKs still available. The $1700 Aquaglide Cirrus is one good example.

A few years ago I predicted that full drop-stitch IKs would become the new thing. This has happened and has driven IK design and sales a long way forward. But, PVC aside, I’m still not convinced by the boxy profiles and packed bulk of FD-S IKs. Until FD-S forms can evolve (as the Itiwit X500 has shown), I think hybrid, drop-stitch floors (D-SF) are certainly the way to go, if an IK is to stay undecked, unlike the X500.

There will always be a demand for cheap vinyl or PVC IKs but I predict the next big thing in high-end IKs will be TPU, including removable D-S floors in TPU. TPU is now well proven with packrafts and blends the heat-welding benefits of PVC with nearly all the better attributes of ‘hypalons’.

Preview: Gumotex Thaya IK

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Since 2019 the Gumotex Thaya sits alongside the near-identical and 25% cheaper 4.1-m Solar on which it’s based, but with a drop-stitch (DS) floor to greatly improve rigidity. The Solar was not unlike my old Sunny, running just 3psi (0.2 bar) all round. That can get a bit saggy with a well-fed solo paddler. This was the first of Gumotex’s DS-floor boats, but a basic exercise in simply replacing a floor rather than trying anything more fancy like the Rushs of 2020.

Drop-stitch fabric now makes the complicated hand assembly of pressure-vulnerable I-beam floors (left) redundant. A DS floor is a flat panel with effectively 3-4 zillion ‘I-beams’ (see top of the page) all spreading the pressure load evenly to constrain the form into a plank shape, but at a much higher pressure than an I-beam floor can safely handle. In an IK, high pressure = a more rigid hull = better glide/less effort for barely any additional weight. The only drawback is that you need a more powerful high pressure barrel pump (above right). Your old Bravo foot bellows won’t do anymore.

DS is normally PVC and made in China, but Gumotex have found a way to manufacture threading and bonding a D/S floor with their durable, flexible and environmentally right-on Nitrilon rubber fabric. It can’t be that hard. The regular, normal-pressure 3psi sidetubes ought not need the higher pressures I ran on my adapted Seawave because the 7psi (0.5 bar) DS floor greatly aids rigidity (see action video below). Gumotex’s new tag line rubs it all in:
‘Made in EU [read: ‘not China’], made from rubber [read: ‘not PV … spit … C’].

The promo video below suggests something revolutionary, but combining DS with Nitrilon can’t be that much different from doing the same with PVC. It will certainly simplify or speed up assembly. One assumes drop-stitch floors supposedly don’t need a PRV necessary to protect I-beam floors from internal ruptures when they overheat in the hot sun. Some UK outlets where claiming the Thaya has a “Safety relief valve [PRV] in the bottom of the boat” but it’s probably just a copy and pasting error from the Solar. I can’t see one in any pictures and have yet to see a DS panel with a PRV until the AE AirVolution came out in 2020. The assumption is they don’t need it if it runs a modest 7psi, but some claim high-pressure DS floors won’t last as long as I-beams. Without a PRV, that may be true and much will depend on running the correct recommended pressure, the quality of manufacture/assembly and where possible, leaving the boat in the water on hot days so the large water-contact area keeps things cool.

One positive thing about old-style I-beam floors is the parallel I-tubes (left) probably don’t hurt tracking (even without a skeg). They also enable the desirable curved hull profile of a boat rather than the flat floor of a barge (for the moment DS panels can only be flat or maybe with a slight curve).

Payload ratings seem to have settled at 230kg and the movable seats are also made from DS panels. Initially I thought why? For the backrest and footrest that makes sense but who wants to sit on DS seat base on a DS floor? Of course you don’t have to pump DS up to the max to get its flat form constraining benefits and it looks like valves are regular twist-locks so you’d couldn’t get more than a couple of psi in there. Footrests are the usual inflatable pillow rubbish, but possibly also DS? I’d replace them with a section of sawn-down plastic drainpipe so you get a solid block to brace against. It makes efficient paddling much easier.

I’ve never tried one, but I do wonder how a flat-floored DS IK might handle in windier, choppier conditions where an IK isn’t exactly a hydrofoil at the best of times. A flat, raft-like floor will be stable, sure, but it will roll and pitch about more. Also, according to the specs (left) at 89cm the Thaya is a disappointing 6 or 9cm (3.5″) wider than the all-tube Solar 3 (Actual verified width seems to be 34″ or 86cm). Great for family-friendly stability; not so good for solo paddling speed and efficiency. My Seawave was 2cm narrower than a Solar 3 and with the usual care getting in, stability is not an issue. Out at sea my Seawave would swamp long before I’m tipped out. But then again, the near-rigid floor may cancel out the drawbacks of the greater width. At 18kg the Thaya is heavier than a Solar 3.

For most recreational, flatwater users the Thaya ought to be a nice family boat, but then so is a Solar 3. The Thaya costs 30% more than the Solar 3 whose days may be numbered, but it’s 2022 so maybe not.