Tag Archives: drop stitch kayak floor

TPU Inflatable Kayaks: the Mis ing Link

See also: Advanced Elements 2021 AirFusion Evo

Pictures from Zelgear and Marcin S

These days IK are mostly made from PVC, be it the hull or the bladders. Just three main IK brands still using old school synthetic rubber: Gumotex (CZ), Grabner (AT) and NRS (US). 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 had ever doing that. That’s why I persevere 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 entirely 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 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 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 left, right and centre. 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 (above) 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.

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.

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 just 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.

An IK needs to be a lot more rigid than a relatively short and squidgy packraft. A lot of that is down to the fabric as well as the psi. That’s one good thing about inflated PVC: it’s stiff. You’d think a TPY IK would require high pressures to support a long boat which would then require bombproof seams. But add a drop-stitch floor (left) in TPU 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 are on it.
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.

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 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

See also:
More about Hybrid IKs
Gumotex Rush

Since 2019 the Gumotex Thaya sits alongside the near-identical and 20% cheaper 4.1-m Solar 3 (aka: ‘Solar 2‘ or ‘Solar 019‘) 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. As you can see on the left, 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.

decpump

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 with barely any additional weight. The only drawback is that you need a more powerful high pressure barrel pump (above right). The old Bravo foot bellows won’t do anymore.

DS is normally PVC and made in China, but Gumotex have found a way to manufacture the 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’].

thaya-family

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. 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 tey run 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 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 pillows, 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.

thaya-red-l

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 is 2cm narrower than a Solar 3 and with the usual care getting in, stability is not an issue. Out at sea my Seawave will 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 20% more than the Solar 3 whose days may be numbered.
One assumes this

Full Dropstitch (FDS) Inflatable Kayak Buying Guide 2021

See also
Book
Other IKs
Full review: Shipwreck ArrowStream Full DS
Guest review: Aqua Marina Tomahawk Air-K 375
Paddling with a Yakkair Full HP2
• Preview: Advanced Elements AirVolution
• Preview: Decathlon X500
Preview: Gumotex Thaya
Preview: Gumotex Rush
• Preview: Advanced Elements AirFusion
• Preview: Aquaglide Chelan 155
• Buying direct from China

As predicted here years ago, eventually someone was going to find a way of making a decent inflatable kayak entirely from dropstitch panels. Something a bit more sophisticated than the three-plank bathtub on the left. As things stand, with some innovative exceptions, most Full Dropstitch (FDS) IKs are still made this way.
There’s more interest in FDS than ever, because buyers view them as superior to a traditional round tubed IK. Certainly they’re miles better than just about any low-end, low-psi Sevylor or Intex. And they don’t quite have the days-long drying issues of your shell & Bladder IKs (but see below). And right now you can buy a two-seat, obscure-brand FDS for just £600, including paddles and pump.

Solo/Tandem FDS IK specs

WeightLengthWidthPayloadPressureIncluded**Price
Allroundmarine
Force L
19.5
43 lbs
4.73
15.5′
86cm
33.8″
350kg
771 lbs
13 psi
0.9 bar
Pump€790
Aqua Marina
Tomahawk AIR-C
24.7kg
54.5 lbs
4.78m
15.7′
88cm
34.6″
260kg
573lbs
10
0.69
2 skegs
Pump
£1000
Aqua Marina
Tomahawk AIR-K
20.3kg
44.7 lbs
4.4m
14.4′
76cm
30″
210kg
463 lbs
10
0.69
2 skegs
Pump
£950
BIC Yakkair
HP2
15.5kg
34.2 lbs
4.1m
13.4′
85cm
33.5″
210kg
463 lbs
8
0.55
Pump£1300
Bluewave
Glider
18kg
39.6 lbs
4.73m
15.5′
85cm
33.5″
317kg
698 lbs
10
0.69
Pump
2 paddles
£660
DS Kajak
465 FLex
20kg
44 lbs
4.65m
15.2′
78cm
30.7″
250
551 lbs
10
0.69
Removable
floor
€1300
Kxone
Slider 410
15.5kg
34.2 lbs
4.1m
13.4′
85cm
33.5″
210kg
463 lbs
8
0.55
£1050
Sea Eagle
Razorlite 473
17kg
38 lbs
4.73m
15.5′
76cm
30″
340kg
750 lbs
10
0.69
Pump
2 paddles
£1490
Shipwreck
Arrowstream
25.4kg4.31m83cm340kg
750 lbs
10
0.69
Pump
2 paddles
£849
Story22kg4.7m82cm220kg10 psi
0.69 bar
Pump
2 paddles
£600
Shorter (solo) and longer 2-3 seat models also available • Prices will vary • Weights can be in-the-bag or on-the-water • Payload claims can be unreliable • **All come with a bag/backpack (some with wheels; quality varies) and a repair kit • You will need a high-pressure barrel pump.

What is Dropstitch?

For the full story on dropstitch (DS) click this
Short version: a dense mass of non-stretch ‘space yarn’ is magically stitched between two fabric sheets at up to thousands of stitches per square metre.
The dimples you see on an inflated panel surface are the space yarn under tension. Once the outside of the sheets are coated with PVC and sealed round the sides, on inflation you get an airtight flat, board-like panel.

When inflated via the usual valve, this panel can withstand much higher pressures than a normal round tubed IK. We’re talking up to 15psi (1 bar) which is four times more than even the firmest tubed IKs. In fact, on an FDS IK, half that is plenty, as you’re not standing on it like a SUP. The huge popularity of iSUP boards in recent years has helped advance DS technology and an FDS can be be nearly as stiff as a hardshell while packing into a bag, like a regular IK.

4.3m long and stiff as you like.

It is pressure – or the ability to make a stiff form from an inflatable chamber – which has long been the weak link with traditional tubed IKs, especially once lengths increase. Floors need I-beams (above left), to act like the space yarn to make a flat, wide floor. But I-beams are expensive to assemble and – without pressure release valves (PRVs, more below) – are vulnerable to damage or rupture if over-pressurised through neglect or when left out in the hot sun.
Running 8-10psi, dropstitch technology eliminates the longitudinal sagging commonly experienced under a single paddler’s central weight in a longer, old-style boat (below). This rigidity enables sea kayak-like lengths of well over 4 metres (13′) which adds up to more room inside as well as a much better glide (less effort). It’s the same energy saving gained by pedalling a pushbike with hard tyres instead of soft.

Most full dropstitch (FDS) IKs are made of three flat panels. In a way they resemble a simple, self-assembled three-board wooden canoe (left).
On a regular IK, round side tubes upto 30cm in diameter also take up a lot of space inside. DS panels are typically just 10cm/4″ thick while retaining all the benefits of tubed IKs: light weight and buoyancy. The only downside seems to be the bulk: there is up to 4000 metres of space yarn in a typical 4.5-metre FDS. Add stiff PVC which is hard to roll up, and an FDS ends up twice as bulky as a similar-sized tubeless rubber boat. Nevertheless dropstitch is far more effective than using metal frames to support saggy IKs. In my experience this is a poor solution.
DS in IKs actually started with easy-to-fit dropstitch floors (derived from iSUp boards) but retained the round side tubes. These are still popular and are now called hybrids; seen by some as the best of both worlds. But all the boats on this page are Full DS. See image below for the three types of IK: tubed (bladdered – can also be ‘tubeless’); DS floor or Full DS.

Floors: Read This

Broadly speaking, FDS IKs are assembled by gluing three DS planks into a wraparound skin of PVC which holds the panels in a boat shape and additionally protects them from wear and abrasion.
Some floors are removable, a bit like a footbed slips into a shoe (right). This makes the hull skin’s inner floor accessible for easy cleaning, rinsing and drying before storage – an important part of IK care.
Not everyone may see drying as the deal breaker I make it out to be.

Unless a glued-in floor is fully sealed along the sides, water and grit will collect in the side cavities. But for deflation reasons, this cavity cannot be airtight.

Less good but almost universal is a DS floor permanently glued to the floor skin but not fully sealed to the side panels. See the two images above: at the bow and stern where the tape stops, water and debris can get down in the cavity. Some sort of drain valve helps water to run out of the cavities when flushing before deflating. Sometimes there are several capped drains along the sides, which is odd as just one will do.
These multiple drains are not a self-bailing ports, no matter what clueless vendors may claim or owners may think. Open the drains when afloat and the boat will part-fill with water for sure. Until I realised this, I was baffled by these drains. So it seems were actual owners.
Bluewave Gliders are like this, so are Allroundmarin, Sea Eagle RazorLite, Tomahawk, KXone, Shipwreck and anything else with the telltale drain ports. Even hybrid IKs like the Aquaglide Chelan have multiple (but closeable) ‘self-bailing’/drain valves along the sides of the floor.

Such a boat is nearly as much of a pain to dry properly as the bladdered IKs I go on about. There will always be moisture in the long, inaccessible side tunnels along the DS floor edge which you will struggle to dry properly. Proper rinsing and drying matter, if you want your IK to last a long time, especially after you’ve been at sea when sand and other debris can get in the boat. Seawater causes mildew, staining, odours and possibly rot, so does trapped organic matter, while in the long term trapped grit might rub unseen against the soft PVC until it wears right through (this will probably take years).

Tubeless rubber IK: dead easy to dry

A theoretical way to eliminate these issues is by fully sealing or ‘wallpapering over’ the floor DS panel gaps: usually the bow and the stern as shown in green above. To drain and dry such fully sealed boats, you simply flip them over to shed the excess water, then deflate, spread out and wipe dry, just like the round tube Grabner on the left.
A boat modified like this would have no crud-trapping, moisture-retaining cavities. The flaw with this idea would be the air trapped in this sealed-off cavity would make the boat difficult to pack compactly: like trying to roll up a partially deflated inner tube. It needs a breather hole: a simple plug would work. Pull out the plug when deflating, plug up once pumped up to keep water out.
Fyi: this is all hypothetical but an Italian chap with a BIC told me he had just this problem: gravel and grit collecting in the cavities. One solution of his was to stuff the openings with a sponge. Water may still get in but bigger grit won’t.
In 2020 Advanced Elements introduced the innovative two-panel AirVolution FDS IK which seems to have no crack between the upper and lower panels. Good for them because, apart from the added labour, sealing the insides is not exactly complicated. For the moment it seems other manufacturers are happy to settle on removable floors or fitted floors with drains, just as some buyers are either oblivious or contented with bladdered IKs, despite their greater drying issues.

Protracted KXone cavity drying instructions using what seems to be a hidden floor drain valve (6, 7).

Actually their is a worse option: supposedly ‘self-bailing’ FDS IKs which have little side cavities on the edge of the fitted floor and simple drain holes in the outer skin. There are no closable drain valves.
The tellingly unused and unbranded FDS IK (left) I saw on eBay was like this. I had to check with the seller as there were no photos of the floor. Within an hour it sold for £700, but once on the water the new owner will find their boat filling up from below. It may only be a couple of inches but that water will slosh back and forth as you paddle along, adding several kilos of weight and upsetting stability. You could easily tape up the holes in the outer skin, but this is why what look like ‘bargains’ come unbranded and without guarantees. No brand would risk doing it this way and get rightly hammered by negative customer feedback.

Keel tubes

One benefit of having the floor panel separate above the PVC outer skin is you can stick a thin inflatable tube in there to give the hull more of a V-shape. The AirTrek FLex 465 by DS Kajak (and possibly the same-but-different KXone FLex) have these optional shallow inflatable keel tubes (‘AirBone‘) under the removable but clamped-down floor which you can easily inflate via a loose hose. It changes the hull shape from flat to V. More speed and a bit less stability is what they claim, and you can easily deflate the keel tube on the move if conditions get iffy.
An FDS IK’s barge-flat floor is one of its less good features, so this sounds like a clever idea. And as said, the floor is removable so it can all be cleaned and dried easily. Sounds like a win-win to me. See the video below or here.

Tracking (going straight)

Just about all of these FDS IKs come with an easily fitted slot-in skeg or tracking fin that’s often as tall as Flipper’s flipper. Like a fixed keel or rudder, the help the boat go straight. Some even have two under the dumb assumption that more must be better. A tall skeg will drag in the shallows and the boat can’t easily be sat on flat ground without stressing the fitting. But a skeg is easily trimmed – or you can buy a spare and cut it down for shallow conditions which need it. More about skegs here.
FDS boats also feature rigid moulded bow and stern pieces (below right) to help slice through the water. This is typically a weak point on broad-nosed tubed IKs (below left).

Hardshells and conventional tubed IKs can also have a curved hull in both axes: lateral and a bow to stern curve which is called rocker. The more banana-like the longitudinal profile the more rocker and the easier the boat turns and rides over waves.
With the formed bow and stern pieces, box-like profiles and plank-floors, an FDS IK has zero rocker, meaning these boats track well but are hard to turn without a rudder. Many owners report that indeed, they glide as straight as an arrow. One French KXone owner admits that after a year of use… ‘It always wants to go straight, even without the skeg‘ and he’s thinking of installing a rudder. Another reviewer from the US says: ‘The 393 RL tracks very well, almost too well. I trimmed 3″ off the skeg for better clearance in shallow water and it still tracks straight and true. It’s easier to turn now as well, another nice improvement.’ Here’s another short review from the UK.
This was my experience too with a DS-floored Moki II and the FDS Shipwreck, but on the latter it was much improved by removing the skeg. The boat’s firm hull innately tracked well enough

Hull profiles

FDS IKs are still crude box shapes because, excepting the Decathlon X500, making anything other than flat DS boards is too complicated and expensive. The design and handling of these FDS IKs are limited by these constraints: high sides, flat floor, no rocker. Add the fact that the rock-hard floor can make them as uncomfortable as a hardshell, but adding a well padded seatbase, stability can take a knock.

And the flat floor and box profile may make edging – leaning on one edge as you turn or to counterbalance on waves – trickier. You’d need thigh straps to do this, although I never got that technical with the Shipwreck. This Tomahawk owner said his boat’s initial (or primary) stability was a bit shaky, but once on edge was quite stable and took a lot to tip right over. This was on flat water. In more dynamic conditions things may happen too fast for you to react.

Pressure-release valves

It’s notable that there are no PRVs on most of these FDS boats, presumably because the very high density of space-yarn means they can handle over-pressurisation better than an I-beam floor where the forces are more concentrated. The two-panel 2020 AE AirVolution is one exception.
Otherwise, better branded FDS IKs have clear warnings at the valve not to exceed recommended pressures (below). Some claim DS panels without PRVs won’t last as long as I-beams with PRVs. Much will depend on the quality of the original manufacture/assembly, maintaining the correct pressure and where possible, leaving the boat in the water on hot days to keep things cool.
These boats’ smaller volumes also means they’re quicker to inflate than a regular IK, although the effort in reaching 10psi requires a barrel pump. Tall and slim barrels work better than short and fat: it’s this shape and not the volume which counts. A 4.4m FDS panel can be filled to 10psi in just a minute; allow a bit more time for the floor.

Footrests & Decks


Not for the first time I see my ideas adpoted by manufacturers. In Sea Eagle’s and Airkajak’s case it’s a simple footrest tube with an adjustable strap which I came up with a years ago! It’s so much simpler and more versatile and effective than the mushy pillows still used by Gumotex. KXone and Gliders and Shipwreck use a padded strap.
In any type of kayak, a footrest helps you connect with the boat, execute powerful strokes and not slide down the seat as you do so. And as an IK doesn’t have the benefit of a hardshell deck to brace knees off, a solid footrest is all the more useful.

The KXones may come with optional removable decks. Once you realise this boat is as rigid as a sea kayak, adding a deck (or at least some sort of deflector at the front) may be a good idea for managing bigger waves. A regular IK will bend up and over the waves; a stiffer FDS IK will cut through them and may swamp, especially if loaded.
IK World ran a comparison between her old style DS-floored Sea Eagle FastTrack and the 393 solo Razorlite, as well as giving a fuller review of the 393. You may like to scroll down and read some of the readers’ comments about issues and returns they’re having with early RazorLites (the very first FDS IK). She mentioned the FDS boat was less stable, but to me the stability of the yard-wide FastTrack is beyond the pale.
About 76cm on the 473 is still 30-inches and I felt quite safe in my 69cm-wide K40 right up to the point when it was coming in over the sides (thigh braces helped greatly, I admit). Then again, the 83cm-wide Shipwreck is actually more like 60cm at the waterline where it counts, and I (quite heavy and tall) found the 6cm-thick seat pad made me very tippy. Removing the foam from the seatbase resumed normal service.

You notice Sliders and the BIC are much wider than a Sea Eagle RL, for example. This is because they’re pitched as SUP IKs, in that you can stand in the boat (left). With the popularity of iSUP boarding, this is a clever gimmick. But sit-down paddling performance will suffer. Me, I’d sooner have as slim a kayak as possible.

Good on all these brands for upping the game with their takes on FDS IKs. It’s a big step in making IKs less ‘bloat’ and more boat. Many people commonly mistake them for hardshells.
Having spent years looking at loads of images and videos of all these boats, at the moment the 20-kilo DS Kajak 465 is the one I’d choose, except the massive bulk of these things puts me off. The removable floor aids proper drying and cleaning, it’s no wider but half-a-foot longer than my Seawave, and graphics-wise, it doesn’t give me a migraine. But €1200 is a bit of a gamble. The Shipwreck ArrowStream which I did actually try (review here) was a great deal but the price has now jumped to £850.

Spotted a mistake or have something to add? Your comments are welcome below.

Inflatable Kayaks: Hull Forms and Rigidity

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