I fitted over-rated 4.8psi Ceredi PRVs to my Seawave’s side tubes a few years back. I like the idea of not having to worry about the boat getting hot in the sun (and exploding), just as much as gaining some extra rigidity by fitting PRVs rated a little higher than recommended side tube pressures.
I bought a pair of unbranded Chinese PRVs off eBay (<£9 posted – about 30% of Ceredi/Leafield prices) to consider for my next IK. Some sold on eBay don’t even mention the purge pressure! These ones did: 4psi or 0.27bar, just a bit over the 0.25 of the boat I have in mind.
Out of the bag, the quality of the molding looked no worse than a Ceredi. I was a bit surprised they’re smaller than usual PRVs, (the listing gave these dimensions), but what does it matter as long as they work. I worked out a way of testing them by removing the backing ‘nut’ and screwing the ‘male’ PRV housing onto a rubber motorcycle throttle grip. The other end of the grip I jubileed to the barrel pump nozzle. Pumping the pump, the pressure built up and PRV ‘burped’ suddenly at an indicated 0.4 bar. But as my manometer needle zeros at 0.1 bar and not zero, we can probably subtract that 0.1 and call that 0.3 bar which is 4.34psi. Close enough to 4psi. Now I can fit these PRVs with confidence.
The hole which must be cut in the boat to fit this valve is 24mm ø, but to get the back nut inside the hull you’ll need to go in via the larger inflation valve aperture. So cut the PRV hole close to the inflation valve. Once loosely screwed together, the knurled outer housing can be tightened with some wrench or another.
Accounting for manometer error, the PRV burped at 10% more than claimed, which is pretty good.
Not for the first time I will boldly speculate that the Austrian-made Semperit Forelle (‘trout’) or maybe the Dolphin before it, was the first serious modern IK, designed in the 1960s from tough hypalon ‘rafting’ fabric. Around the same time Sevylor released the PVC Tahiti watersofa in North America and maybe worldwide. I bet the Tahiti has outsold any Semperit 1000:1. I know which one I’d rather own.
Semperit Dolphin II, Alaska, 1970s. Pic: Micheal K.
According to my measurements the Forelle 2 is 3.56m long, 70cm wide and weighs 10.5kg + seat. This guy says Semperit were last made in 1983 at which point (or soon after) Grabner (also Austrian) bought the rights.
Grabner Fun kayak
Grabner then got Gumotex, in Braclav just over the border (and behind the Iron Curtain, back then) to produce a cloned Forelle called the Grabner Fun (left), but made from Gumotex’s hypalon-like fabric called Nitrilon. Back in the 1980s I’m sure Commie Nitrilon would have been cheaper and probably as good as DuPont hypalon made in western Europe. The Fun was discontinued (or stock ran out) a few years ago.
Not being one of their boats, the Fun was undersold by Grabner (notice the table, above). Instead, the similar but longer Holiday range got the fanfare and is still made today with few changes. Grabner boats are made from a hypalon-like fabric called EPDM which, combined with Grabner’s hot vulcanising method, explains how their boats managed to run 50% more pressure (0.3 bar) than the Fun and other Gumotex IKs at the time. Gael A. paddled an aged Grabner H2 along the Scottish Sea Kayak Trail a couple of years ago. Among others, Incept also used the twin-side beam design to produce a 70-cm wide K40 which is also 70cm longer than the Forelle II, and one of the fastest IKs around.
I would say the obscure and expensive K40 and the more popular but also expensive Austrian Holiday 2 and 3 IKs are modern iterations of the twin side tube Forelle design, with the Holidays (below) right down to the wooden bow clamp (right).
You can occasionally find aged Forelle IIs for around €300 in Germany; a new H2 goes for €1900, while Funs were being discounted for as little as €400 new, but seem much rarer now. I was curious about tracking down a Forelle recently (I succeeded) and below are a few shots I picked up off the web and from some sellers. Apart from the odd repair, the indestructible hypalon fabric stands up well (or does it?) and the seats may well have been improved (Grabner’s still use crude and bend-prone alloy bars).
Some boats come with a huge wooden rudder which might be replaced by a skeg, but one off-putting aspect are the basic inflation ‘lilo plugs’ (left); no better than an old Gumotex seat. These could easily be cut out and replaced with proper Gumotex valves (right), maybe in a more accessible position, too. It seems older versions (grey and orange, below) have a half-inch deep keep strip right along the bottom (as well as a rudder fitting) while later ones like the yellow one, do not. One thing that can’t get avoided is that a Forelle (and a Fun) still run only 0.2 bar pressure. Same as most ordinary Gumos, like the Solar 3 though the stiffer twin side beam hull helps. Modern Grabners run 0.3 bar which makes a big difference. Some newer Gumotex IKs now run 0.25, though that can be pushed to 0.3 bar with care.
Thanks to Gael and OP for extra details. Most pics lifted from ebay sellers.
The best inflationvalves for an inflatable packboat aren’t the bungs you find on an airbed or an old Semperit. Nor the thin, twist cap stems off a Feathercraft Java or an old Alpacka. What you want are one-way valves. Like a car-tyre valve, one-way operation as well as a secureseal are the key, so what pumps in doesn’t push back or escape when you remove the inflation hose. Found on cheaper IKs and packrafts Boston valves are simple and effective for lower pressures. More below.
What I call raft valves (left) like Halkey Roberts, Leafield suit higher pressures and are needed for dropstitch panels. In America they’re called ‘military’ valves. With raft valves you either push and twist the button clockwise to lock open (deflating). For pumping up, push lightly and turn anticlockwise so the button springs back up to seal. This closed ‘button up’ position is the best way to transport an IK too. To lose a little pressure (say, the boat is getting hot in the sun) just jab the valve core button, same as on a car tyre.
Many raft valves are now ‘push-push’ (graphic left) which work like a clicking biro so are even easier to use. I always refit the cap seal straight away to keep water and grit out of the mechanism.
Two raft valves. On the left the collar goes inside the hull, the valve body screws into it tightly and the dust cap goes on top.
I’ve found these valves reliable on all my IKs, although this Gumotex 410C owner didn’t. Once in a while – or after the boat is new – you may want to check the valve is screwed tight against the fabric with the valve spanner, right. They’re also useful for removing the valve (or a PRV; see below) should it play up.
When it comes to inserting the inflation hose, a simple push-fit plug as shown below left can work; just jam the adaptor into the valve body and it usually stays in place while pumping. It looks cheap but on a Gumotex at least, works fine. With higher-pressure boats like Grabners and Incepts and some Gumotex (as well as dropstitch boats), the jam-fit can blow off so you’re better off using a bayonet fitting (below right) which won’t pop off as pressure builds.
Low-pressure valves for packrafts
Alpackas and even Feathercraft used to use crappy, soft plastic twist-lock oral stem valves (below left) which you could never be sure were done up just right and which didn’t take well to pump nozzles.I suppose they were a step up from blow-up airbed plugs (below) which are still found on cheap IKs.
Retractable one-way flap valve. Annoying to delateLilo plugs: Ok for seats, crap on a hull
Now best used on inflatable seats and the like, they’ve been superseded by similar one-way stem valves (below right) with a light spring closure easily openable by lung pressure. They’re a bit trickier to deflate: you have to depress the ‘X’ with a finger while squeezing out the air. The one below right is actually on a buoyancy vest.
Twist-Lok: OK for seats and old packraftsSpring valve one-way for higher pressure
Boston valves is a generic name for a one-way valve long used on cheap IKs as well as slackrafts and have now become common on packraft hulls. Note they’re widely copied and not all may be identical, like well-known branded IK valves. The square top cap screws onto the round valve body which itself has a knurled edge to easily unscrew from the hull port (below right). Here you attach your air inflation bag or open to quickly dump the air when rolling up.
Inflation: top cap removedRubber ‘mushroom’ valveDeflation: unscrew valve body
Ideally suited to low-pressure boats like packrafts, they use a simple rubber ‘mushroom’ valve on a stem (above middle). Once the main valve body has been screwed back into the hull, unscrew the square cap to finish the inflation process by either topping off by mouth or with a hand pump.
A one-way Boston-type valve eliminates the need for the old separate stem valve and the whole assembly has swivelling plastic lanyards so nothing drops away when unscrewed.
Pressure release valves (PRV) for some IKs
I’ve learned the hard way to be careful and not let an IK get too hot when out of the water. On a hot day you can feel the more exposed sidetubes tighten like a drum. This of course happens to be good for rigidity and paddling efficiency but isn’t good for the seams or an I-beam floor or the sewn seams of a cheap shell&bladder IK.
Oddly, not all Grabner IKs have PRVs which means…… faffing about with pressures on hot days.
The floor tube on my old Sunny had a pressure release valve – oddly it’s something rarely mentioned in the specs, even on current Gumboats. It’s there to protect the I-beam floor which could rupture inside under pressure (I-beam floors explained here). The valve is set to purge (open) at a certain pressure when the air inside heats up, expands and pressures rise. With Gumotex it is 3psi or 0.21 bar. It means an IK can feel a bit soft on a cool morning following a hot day; don’t worry, you don’t have a leak, it just purged some air when hot yesterday and in the cool air make sit a bit soggy. A quick top up is all you need to do. The handy thing with a PRV is that it makes a good guide to how hard you ought to pump up the other chambers of the boat without PRVs when you don’t have a pressure gauge. At whatever pump effort the floor PRV starts hissing, that’s the same or a bit more pressure to put in the side tubes which usually don’t have PRVs.
As mentioned, the air in an IK can also get cooled, for example when pumping up on a hot day and then putting the boat in a cool river: a normal scenario. Cold air contracts (loses volume/pressure). Because you want the boat to be as rigid as possible, after initial inflation it’s worth topping up again once the boat is in the water; splashing helps cool the sides. Topping up, or tempering as it’s called, optimises rigidity and with long, 2psi boats you need all the rigidity you can get. Conversely, pumping up your boat in sub-freezing temperatures then putting it on water which actually ‘heat’ it up, though this is a much less likely scenario.
A PRV purging correctly
PRV leaking from the sides not through the valve. Needs tightening with a special tool; a common necessity with hastily assembled new IKs.
My higher pressure Incept K40 had PRVs on all chambers which meant you could confidently leave it in the Sahara and it would safely purge then feel a bit soft once cooled down back in the water. Picture above: Incept PRV test with the protective cap removed and purging correctly through the centre. Below: a PRV being resealed after leaking from the edges (left). This was because I failed to check tightness after buying the new boat, as recommended by the manufacturer. (My Gumotex IKs never needed such tightening or checking in years ownership.) I ended up also fitting sidetube PRVs to my Gumotex Seawave to run higher pressures and the be able to leave it pumped up and out of the water for months at a time. Like any valve, PRVs can leak due to grit on the seal or a weak or sticking spring. Grit is not so unlikely when you think they can’t have a cap and have to sit on the floor of an IK, with water and sand occasionally swilling in and down into the body. Try removing the cap and blasting it out with air and maybe give the spring a squirt with 303 (UV protectorant). The best thing is to remove the PRV with the same valve tool, inspect and clean the sealing surfaces and reinstall.
Oddly, my Grabner Amigohad no PRVs at all and neither do the latest Holiday models and a few other Grabners, even though all run higher than normal 0.3-bar pressures. One presumes Grabner are so confident in their construction they’re not needed, despite the warnings above. It should be included with the boats, but if your pump has no gauge, Grabner do pressure relief adaptors to fit on the hose (left) which purge at 0.3 bar, so dispensing with faffing about with a handheld pressure gauge. It’s a good idea.
Another good idea are TRIB airCap live pressure monitors so your boat doesn’t end up like the Seawave left (actually an unexplained internal rupture while in the water). These TRIB solar-powered gadgets replace the valve cap on bayonet-type inflation valves like Halkey Roberts or Gumotex. One fitted securely an LCD display displays your pressures in psi, kPa or bar, a bit like TPMS for cars and motos. And like TPMS, you can even set a bleeping alarm at anything up to 20psi / 1.37bar. You need to make sure the seal is good and air is not slowly leaking out, but you can also use them as simple digital pressure gauges: twist on, measure and remove. Once fitted, you can watch as pressure drops after you put the boat in the water, and then seeing it rise out on a hot river bank. If I kayaked in a hot country (ie: not the UK) they’d be a simple alternative to the faff of installing PRVs. TRIB airCaps cost $40 in the US and the same in £s in the UK. The ribstore sells them.
Inflatable Kayaks & Packrafts 