Tag Archives: prv

Semperit Forelle – the original IK

forelleIn 2017 I bought an old Forelle 2. Read more about the…
…afternoon refurb
Semperit at Sea
Semperit at Sea 2
Semperit Mori
Semperit autopsy

sempNot for the first time I will boldly speculate that the Austrian-made Semperit Forelle (‘trout’, left) was the first serious modern IK, designed in the 1960s from tough hypalon ‘rafting’ fabric. According to my measurements a 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.

funfunGrabner then got Gumotex, in Braclav just over the border (and maybe the Iron Curtain, back then) to produce a cloned Forelle called the Grabner Fun (right), 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.

Grabner Fun: length and width 365 x 75 cm; weight 12 kg; payload 170 kg; pressure 0.2 bar; fabric 1100 dtex Nitrilon

grabcomp2011funnyNot being one of their boats, the Fun was undersold by Grabner (notice the table, right). Instead, the similar but longer Holiday range got the fanfare and is still made today with few changes. Grabner boats were made from another 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.
You can occasionally find aged Forelle IIs for around €300 in Germany; a new H2 goes for €1600, 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 and the seats may well have been improved (Grabner’s still use the crude ‘backrest bar’ design).

gumvalveSome boats come semperit forellewith 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 below, do not. A long keel is a bad idea, I suspect. Some modern Sevys or Sea Eagles have them; good for tracking but makes the boat harder to turn.
One thing that can’t get avoided is that a Forelle (and a Fun) still run only 0.2 bar pressure. Same as most Gumoteii, though helped by the stiffer twin side beam hull. Modern Grabners run .03 bar which I feel 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. Pics not mine lifted from ebay sellers.

Inflatable kayak valves and PRVs

Pumps are here
Installing high-pressure PRVs
Updated Summer 2020

The best inflation valves for an inflatable packboat aren’t the simple bungs you find on an airbed or an old Semperit. Nor the twist valves off a Feathercraft Java or an old Alpacka.
What you want are one-way valves like the high-pressure ones on white water rafts, pictured right and copied by many. Like a car-tyre valve, one-way operation as well as a secure seal are the key, so what pumps in doesn’t push back or escape when you remove the inflation hose.


With proper IKs valves, pushing the button down and turning clockwise locks the valve open to release air. For pumping up, push lightly and turn anticlockwise so it springs back up to seal. This closed ‘button up’ position is the best way to transport an IK as the valve mechanism is less vulnerable to damage. 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.
Post-2010 Gumotex valves use ‘push-push’ valves (left). I always make sure I refit the cap seal straight away to keep grit or water out.


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 useful too for removing the valve (or a PRV; see below) should it play up.

When it comes to inserting the inflation hose, one-way IK valves can take simple push-fit adaptors as shown below left; just shove the adaptor in and it sort of 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 Gumotii, you’re better off using a bayonet fitting (below right) so it won’t pop off as pressure builds.

Low-pressure valves for packrafts

Screw-cap Boston valves  are used on cheaper IKs as well as slackrafts and packrafts. They have two caps: the main one unscrewed (below left) to dump the air, and a square cap to access the one-way valve to top off a boat (middle). These are low-pressure valves using a simple soft rubber ‘mushroom’ on a stem (below right) which is fine on a boat you top off by mouth, not a pump – ie: packrafts not proper IKs. With a packraft, the one-way valve eliminates the need for a separate top-up valve which means one less thing to leak or malfunction. Most packrafts use these now.

Pressure release valves (PRV) for IKs

I’ve learned to be careful not let an IK get too hot out of the water. On a warm day you can feel the side tubes tighten like a drum. This of course happens to be good for paddling efficiency but isn’t good for the seams or an I-beam floor.


The floor tube on my old Sunny had a pressure release valve – oddly it’s something never mentioned in the specs, even now. It’s there to protect the I-beam floor which could separate under pressure (I-beam floors explained here).
The valve is set at a certain pressure to purge when the air inside heats up and expands. It means an IK can feel a bit soft in the cool morning following a hot day; don’t worry, it’s unlikely you have a leak.
The handy thing with a PRV is that it makes a good guide to how hard you ought to pump up the rest of the boat without a pressure gauge. At whatever pump effort the valve starts hissing, that’s the same or a-bit-more pressure to put in the side tubes which may not have PRVs.

The air in an IK can also get cooled, for example when pumping up on a hot day and then putting in a cool river. Because you want the boat to be as rigid as possible, after inflation it’s worth topping up once the boat is in the water; splashing helps cool the sides. Topping up or tempering optimises rigidity and with low, 2psi boats you need all you can get. In the same way, pumping up your boat in way sub-freezing temps and then putting it on water which actually ‘heat’ it up, though this is a much less likely scenario.

A PRV purging
K40 PRV leaking from the sides not through the valve.
Needs tightening with special tool.

My higher pressure Incept K40 had PRVs on all chambers which meant you could confidently leave it in the baking sun 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 their tightness after buying the boat, as recommended by the manufacturer. My Gumotii never needed such tightening or checking in years ownership.
I ended up also fitting side tube PRVs to my Gumotex Seawave to run higher pressures.


Oddly, my Grabner Amigo didn’t have any PRVs at all, even though it ran potentially damaging high pressures. One presumes Grabner are confident in their vulcanised construction to think they’re not needed. If your pump has no gauge Grabner do PRVs to fit on the hose (left) and purge at 0.3 bar, so dispensing with faffing about with a handheld pressure gauge.