No doubt about it; since flogging my much-used Sunny in 2011, followed by a flawed experiment with a Feathecraft Java, I’ve become spoiled by high-pressure IKs like my fast Incept K40 (based on the Forelle’s design), the brick-hard but slower Grabner Amigo and my current lightly modified Seawave. Just 25-60% more pressure makes all the difference, especially once the boat gets usefully long.
I only had my K-Pump Mini to inflate the Forelle after its repair and mods. I’d hand-pumped it up as hard as I dared but was probably a bit too cautious to not over-stress the old trout. Getting in I was reminded of that uninspiring slackrafty squidginess. I should have topped it up after putting in the cold water, but anyway there’s no easy way to accurately check the pressure off lilo plugs (I tried jury-rigging my manometer). Presumably in the 70s the idea of using tough, one-way rafting valves on IKs hadn’t been thought of yet.
In this under-inflated state and with a slight breeze, tracking away from a headwind was tricky, though I knew that new boats require a quickly acquired knack. As expected, the crumpled keel strip didn’t really do much, perhaps that’s why the Forelle 2 came with a rudder mount. As you can see there’s some taco-ing (folding) going on below me – and this was before lunch! Without a skeg or a rudder such sagging won’t help good tracking either.
My over-pressure caution was understandable, but thinking it over, I decided the Semp was under-inflated. What this boat needed was a better pump. A couple of days later a £10 Sevylor stirrup pump turned up (I left my super-duper Bravo kite pump down south) and I whacked in what felt like Sunny pressures. With the position of the lilo tubes tucked under the stern cover, and the need to yank off the hose adaptor while pinching the tube to stop air escaping, and jam in the lilo plug, it’s a bit awkward. These plugs really do grip/seal well.
That’s another great thing with running calibrated PRVs on all chambers: you just pump away until they hiss and the boat is correctly inflated while being protected from over-pressure. No need for manometer faffing.
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 as fitted to white water rafts and pictured left. 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. Brands include Halkey Roberts, Leafield or whoever makes your boat. In America they’re also called ‘military’ valves.
You either push and twist the button clockwise to lock open (deflating). 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 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. Post-2010 Gumotex valves are ‘push-push’ valves (graphic left) which are even easier to use. 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 also useful 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 Gumotex (as well as drop-stitch boats) , you’re better off using a bayonet fitting (below right) so it 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 toy valves and airbed plugs (below) which are still found on cheap IKs.
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.
Boston-type valves are 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.
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 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.
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. 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 is a bit soggy. A quick top up is all you need to so. 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 and 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. 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.
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 Gumotes 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.
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.