Category Archives: Tech

Packboat Fabrics & Construction

Sigma TXL • bow skeg and thigh straps

Sigma TXL main page
Glues and Repairs

Years ago I remember when the value of fitting packraft rear skegs was debated. Then the now common longer sterns (introduced by Alpacka) positioned the paddler more centrally and greatly reduced excessive bow yawing. On a packraft you’d think a skeg under the bow would eliminate the yawing endemic to short, wide rafts but turning agility would be lost. In fact, I wonder whether a packraft might yaw nearly as much at the back but you never notice. You’re actually pivoting from the middle of the paddle shaft, or perhaps a bit behind, at the centre of mass.

Rear skegs certainly improve tracking on IKs; you can manage without, but with a skeg you can paddle harder without constant micro-correctioning. On rivers I’ve found solo packrafts paddle fine without a rear skeg; or they’re too short to demonstrate noticeable improvements. There’s a b it of nodding as you move off which soon settles down with momentum. Even my symmetrical Rebel 2K (left; stern same identical to bow, not extended) paddled fine down the Wye without a skeg. But whengetting pushed around by the swell or on sea lochs (especially when sailing) fitting one was worthwhile.
Either way, rear skegs are a thing now with packrafts and you don’t have to fit them every time. Certainly on my longer TXL I like to think the stock rear skeg aids coastal paddles; though we found a brief stint with no skeg was only slightly noticeable, paddling into the wind in a sheltered loch (no swell). Anyway, I’ve been curious to see what effect a frontal skeg has, so on buying my TXL I ordered a spare skeg and patch which Anfibio also sell separately for €21 + €6.

Goop no good; Aquasure OK; Helaplast better

Gluing on a skeg patch
As stick-ons go, this is not a mission critical job but you want to line it up dead straight which I now see is better done with the boat inflated. I just used the rear seam, hoping it was along the middle line. Anfibio recommend Helaplast which they can’t post outside of Germany but which you can buy on ebay.uk (from Germany…) for €7 for 50ml.
There must be something similar in the UK, but the problem is identifying it against something that provenly works. I had some Goop contact adhesive, but whatever the ‘Automotive’ variant is, it did not stick at all. So I decided to try some Aquasure+FD, leaving it to cure for half an hour before sending in the roller. That seems to have worked.

Using stock TXL mounts sort of works

Thigh straps
Part of me likes to think I’ll be using my nippy TXL the way I use my IK: fair weather open water transits rarely more than a mile from shore. As this might require sustained periods of paddling I figured some thigh straps would help, as they do in my IK. It’s not so much for hardcore bracing or even rolling, the way they are used in white water, but just to fix the legs so the core is more responsive and you can get good drive, as with knees pressed up under the deck of a hardshell sea kayak.

Anfibio sent me their latest 5-point thigh straps which I tried and liked on the Revo (left). But to make full use of them would require gluing on up to 8 extra patches (if not ideally the ladder patch).

I decided my old Anfibio 3P straps which I’ve used in my IK would be OK for my low-tension, flatwater use and require adding just one pair of loop straps. If I was really lazy I could have got away with the unused flat patch by the seat, but the direction on tension was off centre and would eventually wear, stretch and maybe break. The small patches are not really designed for such loads and now my Helaplast has arrived I decided to try it. An old post on the Anfibio blog explains how to use Helaplast:

  • mark off area on hull
  • mix hardener 20:1
  • clean surfaces with solvent
  • apply a thin layer to both surfaces and wait 30 minutes
  • apply another thin layer and wait another 10 minutes
  • Position patch; it won’t adhere properly
  • Heat with hair dryer to reactivate glue and press down hard (it’s better if the boat is deflated to do this on a hard surface).

The heat reactivation trick was not one I’ve heard of before with glues (expect to loosen stuff), but you could see it worked. Where the positioned patch was lamely stuck to the boat, a bit of heat saw it bond down well with some some rolling. You can tell when something looks well glued and this feels like that, though I’m sure glad I didn’t have to do that another six times. Next task: go and do some actual packrafting.

Read this: floors on 3-panel dropstitch IKs

Full dropstitch IKs
Hybrid IKs

Broadly speaking, 3-panel FDS IKs are assembled by gluing the three DS planks into a wrap-around envelope of more PVC which holds the panels in a boat-like shape. Some floors are removable, a bit like a footbed slips into a shoe. 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. Much depends on where you live in terms of climate and storage space.

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 sealed off.

Less good but almost universal with three-panels 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 run down into the side cavities.
A drain valve helps water to run out when flushing before deflating. Some boats feature several capped drains along the sides, which is either odd or a ‘more-looks-better’ marketing gimmick. After all, unless you’re an oligarch, your bath has only one plug hole.
Don’t mistake these multiple drains as 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. Until I realised this, I was baffled by these drains. So it seems were actual owners.

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 cavities along the floor edge which you’ll 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, slime and odours. 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 gaps 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 impossible 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 inflated to keep water out.
Fyi: this is all hypothetical but an Italian chap with a BIC FDS told me he had just this problem: gravel and grit collecting in the cavities. One solution of his was to stuff the openings each end with a dense sponge. Water may still get in but bigger grit won’t. Good idea.
For the moment it seems most manufacturers are happy to settle on fitted floors with drains, just as some buyers are either oblivious to- or not bothered by this issue.

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

Actually there is a worse option: supposedly ‘self-bailing’ 3-panel 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.
A 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 FDS bargains come unbranded, badly designed and without guarantees.
As said above: not everyone may see drying as the deal breaker I make it out to be. Much depends on where you live in terms of climate and storage space.

Leaking pressure release valve (PRV; Gumotex)

See also:
PRV maintenance by Marcin

Durness beach

The other day we paddled the Seawave off Durness beach where the surf was bigger than I’m used to. Hitting a breaking wave as we paddled out didn’t help; the swamped boat needed tipping out at the next beach. It was a bit too offshore windy to roam, but it was still a thrill to be paddling on the very top of Britain, just 2175 miles from the North Pole (about the same distance south to the Canaries).
After the paddle I took care to dry, wipe down and roll the boat up on a sand-free rock bench, but lacking a hose back at the house, I had to rinse one bucket at time – not ideal. When I pumped up, the floor soon went flat: sand was in the seal of the floor’s PRV (what’s a PRV). It’s a thing that happens but in nearly 20 years of Gumotexing it’s never happened to me. Today was my day.

Seawave PRV

The design of the valve means that if the boat swamps in the surf, water laden with grit can enter via the six vents and pool in the valve body right above the seal. The next time it purges, sand grains can slip down onto the soft rubber seal surface and stay there, letting air leak out.
Because the chances of this are high, with a leaking floor PRVs are the usual culprit, not the nearby inflation valve with its sealed valve cap, or less still, a puncture. But don’t rule either out (the cleaning procedure for an inflation valve will be the same).

Fixing a PRV
Much of what follows is my take on Polishman Marcin S’s translated post linked above. It’s not how I actually did it, it’s how I would do it next time after quite a lot of trial, error and better ideas or procedures though up along the way.

Before disassembly, first try giving the PRV a darn good blow-through by pumping like billy-o and letting it purge. It will help to prise off the vent cap with a small flat screwdriver so grains blow away, not bounce back in. Pump up and see what happens. Chances are it won’t work.

Next I suggest putting the boat on a slope (to save water and weight) and flood the stern to establish the pace of the leak from the PRV. You will do it again at the end to see if there is any change. By dragging the boat around 180°, you can let the water slosh down to the bow while you remove the PRV at the stern at the high end.

Don’t plug in a manometer to try monitor the leak over a period of time; it cost me a few hours and a disassembly or two before the flooding idea proved my manometer was leaking from the base faster than the PRV. As we know, pressure gauges are plugged in briefly to get a reading, then as quickly removed. To test for a leak, water is best.

You now know for sure the PRV is leaking so will have to remove and clean it. Flicking off the vent cap exposes the valve body’s six splines. Fit your Gumotex valve tool (or eBay clones from £6) and unscrew the PRV. As Marcin says: the plastic one will do; you don’t need the expensive metal one Gumotex also sell. Expect the PRV to be very tight. Marcin pre-lubed his, I didn’t but it undid easily enough. My boat is less than a year old.

It’s easier to start unscrewing the PRV with the boat fully inflated, but separate the two parts of the valve only once fully deflated so there’s less chance of the backing nut inside the hull rolling away out of reach. Same with the loose o-ring on the valve body base; don’t let it drop into the abyss.

With the PRV in hand, you can see how it works: a spring-loaded valve opens upward when pressure from within reaches a pre-set level – on a Seawave supposedly 0.25 bar or 3.5 psi (but it might close as low as 0.20). As pressure drops it seals shut. At this point you might try rinsing under a tap while pushing the valve open, but you’re going to have to disassemble it anyway to check the state of the seal.

Set the o-ring aside and unscrew the 6mm locknut on the valve stem. Press on the sprung valve from the other side to stop it spinning as you unscrew the nut. But before you do this, count the number of threads or take a photo (above), as the position of the nut regulates the purge pressure; the more you screw down the nut the higher the purge pressure. I notice Marcin’s nut on his Solar was much less screwed in than mine (lower purge pressure). (At one point I tried screwing in my nut an extra turn to improve sealing, but it didn’t seem to make much difference; still closing around 0.2. Maybe a few more turns are needed, but of course you don’t want to go too far and compromise the floor.

Left: pliers to undo the nut; magnifying glass and torch to closely inspect the rubber seal. Right: the disassembled PRV. From top left: valve body, o-ring, valve stem with rubber seal, spring, spring cross-washer, 6mm lock nut.

Ooo-er, quite a lot of fine Durness beach on there.

I chose to clean the rubber seal with an ear stick and toluene solvent. (I tried, but decided not to remove the rubber seal from the stem). After carefully wiping off the grains on, around and under the seal, I dipped the whole thing in the toluene bottle cap (not too long as toluene is strong stuff on plastic; it dissolved the orange marker dot). Don’t forget to inspect and wipe the inside of the plastic valve body too.

A lovely, clean PRV seal. Reassemble and carefully screw down the metal nut onto the soft plastic valve stem to where it was – or what you prefer.

Marcin suggests sticking some sponge under the vent cap to catch grains in future. Sounds like a good idea. These are easily removed/rinsed/dried or replaced by flipping off the vent cap.

A quick Hail Mary to Saint Columba and you’re now ready to refit the valve. You shouldn’t need any lube other than a bit of water for things to reassemble smoothly, though I decided to lube the o-ring with some TiZip silicon grease.
I found as you start screwing in by hand it feels like it’s cross threading. It isn’t: the edge of the fabric is getting caught in the thread. Back up and jiggle the valve body and loose fabric around to make sure the body has slotted and centred its flange into the fabric hole.
Pump back up, tighten the PRV down some more, but probably don’t clip on the vent cap just yet as you may be going back to square one, as I did (partly because the fitted manometer was leading me astray).

Now flip the stern back downhill and let the water slosh back over the Seawave’s valves. I found the PRV purged for about a minute, then abruptly stopped with an odd underwater squawk … but carried on leaking slowly. Another removal and check and refit and there’s still a very slow leak – a 2mm bubble every 2-3 seconds, but with the floor now lying in the warm afternoon sunshine, that may be normal purging. I decide it’s as fixed as it can be. A few hours later, all was normal again and we are all much the wiser.

Moral of the story: if you think sand-laden seawater may have pooled in your PRV (most likely from crashing beach surf, not normal, deep-water paddle-splash), back on shore flip the vent cap off and rinse the PRV cavity with fresh water, ideally flipping the boat upside down, so any grains flush out.

Gumotex Slip-On Skeg Roller (kayak trolley)

The effort of portaging the dozen locks of the River Wey the other month wore me out. On some portages you can drag the boat along harmlessly on lush grass. Others involved narrow gates, or crossing busy or narrow road bridges. It all got quite effortful, especially towards the end as my energy faded like a dying salmon.

I quickly worked out what was needed: a simple and easily deployed alternative to the typical strap-on canoe trolley, like the 60 quid Decathlon example (left) with identical examples on eBay for nearly half that price. A closer look at some images shows them to be needlessly high (unstable) and the clip-out joints don’t look that sturdy in the long run, though the tyres are nice and fat and clearance is great. With these trolleys I think the V of the alloy frame would sit better in line with the hull, not across it (with bends in the tubes). But crossways simplifies the wheel axle set up. My idea was to use the IK’s own weight with the skeg to locate and fix a trolley in place. Quick to use; no strapping needed.

With workspace-and-tools mate Jon, we came up with a stable two-wheel folding platform with a drop-in skeg slot and hinged wheels which folded out to both roll and support the hull either side of the skeg. To portage, lower the boat’s skeg into the platform’s slot, pick up at the bow and roll it away.

On getting the trolley, the too-high sides were easily sawn down by an inch, and another inch got sawn off the bottom to improve ground clearance, as in the graphic. We hadn’t pinned down a way of stopping the hinged wheel plates folding inwards on the move. The trolley actually worked OK on smooth surfaces without any hinge lock, but eventually a bump would knock one side in. Until a neater idea springs to mind, the easiest way for me was stringing a loop of stretch-free Dyneema cord round the top to keep the wheel plates from folding in.

At 1.7kg it’s not that light, but as a prototype it was dead easy to make and the thing needs to be durable. Something similar out of alloy tubing (like the Decathlon trolley above) might be half the weight, but is less easy to fabricate in the front garden.

After a few miles…
By chance, I was left car-less during a few days of great weather. In either direction it’s less than a mile and a 50-metre drop along a quiet road to the seashore: an ideal trolley testing scenario. What extra weight there is sits best over the wheels, and at the bow I tie a shoulder loop into the mooring line, leaving me hands-free to check my messages. Coming uphill for a mile from the beach, I could walk at normal speed with much less effort (and time) than carrying the deflated IK.
By chance it seems the width and height proportions are pretty good for stability, and the cord works well enough to keep the hinged sides up. A couple of times over rough stony ground the cord came off and the trolley folded up, or on steeper side slopes it just fell over. So maybe another 10-15cm of width would be good, but without much added height. And there must be a simple latch or lock idea for securing the sides.

The solid plastic wheels (£12.50 for two pairs) make a racket or hard surfaces and will transfer shocks and eventual wear to the wheel mounts. Some near-identical rubber wheels cost about the same and ought to feel less harsh. But first, I may waste some time wrapping some spare motorbike inner tube around my current wheels.

Having a trolley makes an IK nearly as versatile as a packraft: a boat you can start here, end there and easily transport back across the difference.

Wax your paddle blades to reduce drips

See also:
Paddles for inflatables

IKs are mostly undecked and drips from the swinging paddle can be a bit of an annoyance on a chilly day if you’re not wearing waterproofs. A solution in three words: Wax Your Blades.

More than three words
After watching the vid above I found some Nikwax Solarproof (left) under the kitchen sink. As well as being a UV protectorant (like the Aero 303 spray I’ve used for years), it adds water repellency to outdoor fabric gear like tents and jackets.
Now that it’ll be out for weeks, I sprayed my Seawave 2 and noted the boat was slipperier than usual when we lashed it to the car roof to go for a paddle. Should glide better on the water, too.
I also sprayed Solarproof on one paddle blade and in the sink noted the unsprayed blade took over twice as long to dribble dry (4-5 secs), but the coated blade still brought some water up with it.

Out paddling on the water, I can’t say the coating made that much difference because, as in the video above, your paddle is typically out of the water and swinging forward for a second or two – not long enough for the Solarproofed paddle to shed its water.
However, his wax version did seem to shed near-instantly. So I beeswaxed the untreated blade and noticed wax sheds water as fast as the sprayed paddle did alongside the untreated one.
Conclusion: water repellant spray works and has UV benefits, but wax sheds water better and probably lasts longer, too.

Seawave 2: improving the SoT backrest

Seawave Index Page

As soon as I received Seawave 2 last year I ditched the heavy and squidgy Gumotex seats (right), and implemented my proven packraft inflatable seatbase + SoT backrest idea (left and below right) at a fraction of the weight and bulk.

The seatbase is fine of course; it weighs next to nothing and lifts you off the unavoidably soft floor for a good ‘raised-bum’ paddling stance. I’ve been using it for years, but sometimes I think I could use more back support than the SoT foam backrest. It presses nicely into the small of the back, but like a low-backed chair, is not something you can lean on. You could say in a kayak you shouldn’t be leaning on anything, but sitting bolt upright, knocking out a series of ‘searchlight beam’ torso rotating powerstrokes. But after too much of that you just want to lean back on something.

I picked up a used BICSport Power Backrest (for an SoT; right) which looked like it might be more comfortable. At 37cm, it was tall but lacked a hand rear pocket and instead had a centrally positioned adjustable bungy to counter-tension the back and keep it upright. Using it for the first time on the Wey last week, it started well but after a few hours collapsed as the pull from the front and back straps crumpled the backrest.

The problem: lack of stiffness. A backrest needs to be stiff like a chair back, while a seatbase wants to be soft like an armchair. One provides support; the latter takes your weight. The best way to fix the backrest was to insert a firm plastic plate. It just so happens I kept that very part from a rotting old Aire Cheetah seat bought 15 years ago for my Sunny.
I got that boat back last year, did it up with new seats and sold it. How’s that for recycling!

To be honest I’m beginning to think separate backrests and seatbases are a bit of a faff to fit and especially getting the seatbase just right under you when getting in and out a lot (did someone say ‘Wey‘?). It was ot that hard to attach the packraft seatbase to the BIC backrest, and like all these mods I do, is easily reversible.

For the back I bought another Chinese cheapie IK seat (left and below right; with back pocket; about £25) as I did for the refurb’d Sunny. The seatbases on these one-piece seats are just an inch or so thick; OK of a molded SoT but too low for the flat floor of an IK. So I attached a packraft base to it which provides the all-important raised position. The backrest is just more bendy foam so may need stiffening but we’ve found works fine as a second seat as the Mrs who never paddles like a Maori raider anyway.

Looks a bit messy but works great


The Case for Open Boats (SoT, IK, SuP)

…The sit-in vs sit-on saga is complex and deep because it doesn’t just involve design, seaworthiness and technical stuff such as stability and comfort. You’ve got to throw tradition, experience, pride, machismo and credibility into the mix.

Lone Kayaker

I came across Rupert K’s Lone Kayaker blog, an intrepid Devon based chap who has an uncanny knack in spotting and photographing marine life from his kayak. I tracked his online adventures from the Southwest up to a sail-boat assisted visit to the Western Isles, including a nail-biting solo lap of St Kilda. Even in a spell of good weather, that’s still pretty out there.

I assumed all this had been knocked out in the usual high-end hardshell sea kayak, but looking more closely at the few photos, it seemed to be some sort of Sit-on-Top I’d not seen before: long and low and slim like a proper sea kayak – but with the legs airing off under the breezy sky. Well I never.
Just as people write-off IKs on the basis of gaudy, vinyl beach toys seen flying past in a gust of wind, I too had made a similar assumption that ‘all SoTs’ may be fun, easy to paddle and cheap, but are wide and heavy.

Not a 22-kilo, 5.5m, 22-inch-wide Cobra Expedition with something called a kick-down venturi bailer*. They don’t make the Cobra X any more, but it looks like it and similar touring SoTs are based on the surfski idea (left): long, narrow, tippy but fast ocean playboats popular in the warm waters of South Africa and ANZ, but not a thing you’d go touring in. A rudder is vital to keep on top of things, but unlike a typical surfski, the Cobra had hatches to enable storage in the sealed, unsinkable hull.

* A kick-down venturi bailer is some sort of heel-operated cockpit water dump valve which opens a backward pointing drain spout. It derived from small, racing sail boats and moved on to surfskis – probably. Kick the valve open and as you move through the water, any water in the kayak’s footwell or cockpit gets sucked down and drawn out in a few seconds (the venturi effect), after which you close the valve clamp to reseal the footwell. With the valve open at a standstill, the low footwell might partly fill up with water. You will see in the Cobra reviews on paddling.com that some owners complain about leaking seals on their venturi valves.
Self-bailers – certainly IKs like the ROBfin or most Aire IKs – need to have the floor well well above the bailing drain holes and general water level if the paddler isn’t to be sitting in water most of the time. But seating a super-slim surfski needs to be as low as possible if there is to be any chance of not tipping out. You get wet anyway in a surfski or SoT, but a valve like this enables a low floor plus hands-free bailing on the move. I imagine a slim surfski is like a bicycle: you need to keep moving to not fall over.
You do wonder if these valves might eventually find their way on to fixed-floor drop-stitch IKs. As we know, many have floor plugs anyway to aid draining and drying of unreachable cavities. The thing is, SoT’s and surfskis have basin-like floor and seat wells which drain easily. The idea will work less well with a flat D-S floor.

Like me, he’s enjoyed owning a lot of boats over the years to find what suits him best and listed a Top Ten here. It even includes a couple of Gumboats and also lists many of the SoTs: RTM Disco, Scupper Pro, Prowler – which I briefly considered after reaching the limits of my bendy Sunny in Shark Bay. Then I discovered the K40 – like the Cobra, another Kiwi design – and a whole lot of other IKs better suited to my kind of paddling.
There are more provocative SoT vs Sink thoughts here (quoted top of the page) which, depressingly, references the occasional snobbery of SINKers, especially towards IKs. As I say here, my theory is this contempt is initially based on the appearance of the cheapest IKs: there sure are some hideous Bloaty MacBloatface IKs out there!

It’s worth reading his summary at the end of his Scottish trip (quoted below). I couldn’t agree more and is why I can never see myself buying a hardshell, even if they perform better most of the time. There’s more to paddling than that. As an avowed packboater, I won’t get getting an 18-foot SoT either, but it’s good to now know such things exist and as Lone Kayaker proves, enable SINK-like exploration.

… And of course hugely safe. If you have a spill you just climb back on. Or do you? In the same way as I would suspect that a average paddler in a conventional sea kayak could not roll up if they get tipped over in a big sea (and if they did, they would be subject to exactly the same conditions that just tipped them over, so they would probably go over again), I would worry that I may not be able to get back on my SOT. It’s fine if it’s flat, but conditions bad enough to result in a capsize (surf excluded) would be pretty nasty anyway.
However at least I would have the chance of a simple re-entry and not be struggling with a swamped kayak, pumping it out, etc.
The sit-on-top/sit-in kayak (SINK)  debate is potentially very long. I just like to keep things ultra simple. Simplicity means more time on the water and less time faffing about. Float it out onto the water.Sit on and go. No struggling with a spray deck on the beach and then scrunching across the stones it into the sea.
Yes OK you need a decent drysuit for all season SOT paddling, but apart from that, clutter is a minimum.
Considering my expedition round the west of Scotland as a whole, there were three or four occasions when I was concerned about my safety because of the sea state. Probably unnecessarily so, as I never came close to capsize. But paddling round the ‘dark side’ of St. Kilda I would have been in a state of severe anxiety if I was in a SINK. The unsinkable, unswampable feature of SOTs with their drainage holes provide a feeling of security.
I suppose it boils down to enjoyment. My expedition was probably 80% enjoyment, 20% worry. If I was in a SINK that would have been 50%/50%.
I could go on and on, and be a bit of a bore about the SOT advantages. Maybe it’s because they are so sneered at by most SINK sea kayakers.

Lone Kayaker

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’.

Tested: Tyre pump adaptor for inflatable kayaks

See also
Pumps

You may have seen these bayonet/car tyre adapters on eBay in recent months (left). The bayonet end clamps into your IK’s raft valve (won’t work on Boston valves). The other end is a regular Schrader valve like on your car/bike wheel. Attach that to your 12-volt Halfords tyre compressor and you can inflate your IK from your car battery. No more of that effortful, back-breaking pumping!

Me, I’ve never seen the value of electric pumps for IKs. (Packrafts are another matter). You can only use them near a power source, or the rechargeable battery will run out. And how hard and slow is inflating an IK with a good barrel pump anyway? As IKs catch on with more mainstream recreational users (whose cheap boats may come with a rubbish pump), some find manual pumping too tiring. What is this world coming too?!

The difference between tyres and IKs:
• a car tyre is a low-volume, high-pressure vessel (~30 litres @ ~30psi)
• an IK has high volume but runs low pressure (3 chambers of 50–160 litres @ ~3psi). Drop-stitch has less volume but runs much more pressure.

That’s up to five times more volume in an IK, but at a tenth of the pressure. I would guess the swept volume of my better-than-average car pump (left) is 3–5cc. My Bravo RED 4 barrel pump is 2 x 2000cc (it pumps on the up and the down strokes).
Even if my 12-volt compressor whizzes along at 1001rpm, it will still take a long, long time to fill a 160-litre IK floor. But for a fiver, I thought I’d prove myself right.

The Test
The easiest way was to pump up my Seawave’s floor to the point the PRV purged at about 3psi. The actual psi is immaterial but it’s consistent.

No surprise: it took less than a minute to pump up the 160-litre floor with the barrel. With my car tyre pump it took over 7 minutes.
And if you want say 4psi in the sides, or a 10psi drop-stitch boat, the duration of the tyre pump (or effort with the barrel pump) rises exponentially. It will take forever with the car pump adapter and I think the tyre pump would auto shut-off or burn-out before it reached anywhere near 10psi.

Just a tenner on amazon

I looked into rechargable or D-cell battery or mains/car electric pumps like above. They go on amazon from just £9.99, or even less for mains only or 4 x D-cell battery. These may be great for pool toys, air beds and other low-pressure items like slackrafts which just need a shape, not rigidity.
The Pumteck (left; £15) claims an obscure pressure rating of 4.5 kPa which sounds impressive but translates to just 0.65 psi or 0.045 bar. That is slackraft pressure; there is no worthwhile IK that runs such a low psi.

All these pumps do is save you the initial pumping which merely takes time (< 5 mins), not effort. The rechargeable ones will be spent in 10 minutes and then need hours of recharging. For a typical 3-psi IK you’ll still need some sort of manual pump to top off to full pressure; even more so a higher pressure DS IK.
If your back can’t handle a barrel pump (taller pumps work better for taller folk), consider a Bravo foot pump, but with any dropstitch IK there is no getting round the need for a high-pressure barrel pump or a very expensive SUP electric pump.