Tag Archives: Semperit Forelle

IK autopsy

Performing my cutting-a-kayak-in-half trick gave me a long overdue chance to see exactly how they’re put together, as well as other stuff, like why it was failing and how well certain glues stuck.

hypalon fabric
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The neoprene inside
I used to assume it was the same coloured coating inside the boat as out; it’s just simpler. But of course the diagram right is clear: what’s outside and what’s inside an IK hull is not the same stuff. There’s no need to waste UV-resistant hypalon coating (or colouring or that matter) inside the boat’s benighted chambers. All it needs to be is the same durable and airtight coating, and neoprene – the brown rubber-like coating left – does that fine.
I bet I’m not the only one to mistake ‘neoprene‘ as simply that closed-cell sponge used in wet-suits or laptop sleeves. In its solid form it’s a durable synthetic rubber, but I presume lacks the full-on UV resistance of hypalon which DuPont invented shortly after.

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I-beam floor
As mentioned here, an inflated vessel will seek equilibrium by attaining a rotund form, be it tube or sphere. A flat inflated plane such as an airbed or an IK floor needs to be a series of parallel tubes – or just a non-inflated sheet, like packraft and white-water raft floors. It also works the other way with bed mattresses. The springs and foam must be constrained by straps or whatever to keep the spring mattress flat.
So this is an IK I-beam floor (left): probably the same tough core of nylon or polyester scrim, but without the impermeable hypalon and neoprene coatings of the exterior panels.
Note the pre-folds or creases to help the Semperit pack flat. I imagine modern IKs do the same, but it all explains the necessary attention to detail which makes ‘tubeless’ IKs like this so labour intensive, compared to ‘bladder’ designs like Aire.

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Twin side-tube IKs like this Forelle, the Incept and Grabner Holidays, have two smaller tubes one on top of the other, rather than one fat side tube like my Seawave (left, red) or Amigo. It gives the same buoyancy, more freeboard (above water height), a slimmer profile (more speed) or make more volume inside (easier packing). The red Seawave on the left is 82cm wide; the Semperit is 72. It makes the boat look a whole lot better too and overall because it’s also no less stable, I’d say it’s the best design for an IK, but it also needs I-beam sections to constrain the two side tubes.
I can’t say I could suck air through the scrim easily, but I’m pretty sure it’s porous – I didn’t find any transfer holes to allow air to flow between adjacent tubes – they might be a weak point.
When an IK like this is over-inflated (or left in the sun) and is unable to purge through PRVs (none on the Semperit), you imagine it’s this scrim which either tears apart, most probably at the T-join where it’s glued to the neoprene (left). I tried tearing sections of scrim by hand;  impossible where it was uncut, but as soon as you nick it with a knife it would tear quite easily. This fabric was at least 40-years-old and had one or two patches of mildew, but was still tough and the whole assembly of the boat has held together amazingly well over the years.

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Where mine failed
Inspecting the fatal second leak alongside the earlier repair, it seemed air was pushing through where two sections of I-beam scrim butted against each other. Perhaps the old coatings stretched differentially here or were just worn out.  It did look like the hypalon was simply flaking away – as you’d expect after four decades.
I could have fixed that leak but, as mentioned, another would probably pop up somewhere else, quite possible while at sea in either my- or a new owner’s hands.

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Glue test
I repaired the big original ‘L’ tear with a 5″ round patch of hypalon and two-part glue (above and left).
I then patched a down-to-the-scrim scratch under the hull with one-part Bostik 1782 (left). I used the same glue to repair the initial new leak inside (bubbling water, above).

Although I’m pretty sure they’d have lasted, I could easily pull off the Bostik patches by hand. Pulling off the big round Polymarined patch was another matter. It just so happened I’d sawn through the round patch but, only once I got some pliers under a lip (left) was I able to separate it from the hull. As you can see in the big image below, either the ancient orange hypalon coating of the IK, or the newer red hypalon of the patch separated from their respective nylon cores – the glue’s bond was stronger than the actual hypalon coatings.


I get a bit lazy about having to faff about with two-part glue, and I also wonder if I ever guestimating the 25:1 ratio (or whatever it is) correctly. But as you can see, this stuff sticks. If you absolutely, positively want it to stay stuck, use two-part adhesives.
I still don’t know if the second part curing agent merely speeds up the drying process, or is actually chemically integral to creating the very strong bond. I’d think it’s the latter, otherwise why bother.

There’s more about glues and repairs here.

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Other stuff
Well, the distinctive marine plywood bow has lasted fine – no warping at all and the rivets still intact.
It may have been an early design solution to easily joining the three sections of the hull in a nice sharp point, though they managed that join easily enough at the back. Maybe it was as much for protection and a frontal tracking aid.
I now have enough hypalon patches and D-rings to see me out. Other images from the autopsy below.

Semperit at sea – 2

aziWith an inexpensive Sevylor barrel pump I was able to get the sevypumprepaired Semperit up to a good pressure. Ten days passed while i finished my current project, during which time the boat lost no air that I could feel. Over the same period the Seawave was a little soggy all round, as you’d expect with PRVs purging with changing temps. I keep the boats alongside the shadiest north side of the house, but this far north the early morning- and late evening sun still lights it up. In fact, looking at the graphic, above, it’s amazing just how far north the sun comes and goes at this time of year, a month from the solstice. Work out your own angles and azimuths.

sevy4-2Back to the Sev. With the desk finally cleared, conditions were as good as they ever get up here: hot, sunny and virtually windless – a triple meteorological miracle.
I decided to nip over to Horse Island from Badenscallie (bottom of the map, above right), still assuming the boat might still track poorly and feel saggy. As it was, the Forelle felt much better – as good as you can expect of a 3-psi IK. With just the slight 2 o’clock head-breeze, I was reminded of the technique for skeg-free paddling: simply pull gently to stay straight. You go a bit slower but in the near-calm conditions it worked, with the odd double pull to bring things back on line.

sevy4-7With spring tides peaking, I was too late to pass through the channel between Horse and Meall nan Gabhar, so I clambered up a hill. Looking south to Eilean Dubh and the outer Summers (below), had I moved quicker I could have done the full tour in the Seawave. You only get a couple of days a year like this.



Back at the boat, it seemed a shame just to paddle the mile back to Badenscallie now that it had proven itself. So I set off north around Rubha Dunan. With the ring of mountains from the Torridans (below) up to the Assynt, what an amazing day to be out in a kayak.


sevy4-8On the way back I managed a quick selfie to assess the sag (left) and have to say that’s pretty good considering I’m nine times the weight of the 3.5-m boat.
In a ruined croft on Horse I’d spotted a plank bench and thought about pinching it to level out the boat (by sitting on the plank),  but in calm waters the fully pumped up Semperit was holding up fine.

It wasn’t all rosy: my old packraft seatpad was leaking from the stem base, and with my reluctance to lean back on the basic rope backrest, I couldn’t relax fully. I ended up sitting on my water shoes (a new pair of Teva Omniums) which gave me nearly enough butt-over-heel elevation for good paddling efficiency. The rope could work well enough, but I don’t want to stress the ageing Forelle’s rather puny seat-mounts. sevy4-3What the boat really needs are a couple of bomb-sai14proof D-rings on top of the sides to take the backrest strain in line (like I did on my old Amigo – right), but as I’ll be selling the boat, I’ll let the new owner decide what sort of seats they want. Like all IKs, with a higher seat or a small crate, the Forelle could easily be used as a canoe. I know a lot of people like them.

According to the map, Port Mhaire is where I landed. From here a new track led inland to the Piping cafe at Polglass where I dumped the boat under some shady trees and walked back to Badenscallie.

With proper seat support and perhaps an articulated skeg pivoting off the existing rudder mounts, the Semperit would make a nifty boat for calm inshore and lochs, and rivers. But in the Seawave and my Alpacka Yak, I’ve got all the boats I need. It was fun to do up and try out the Semperit, probably the first serious IK from which twin side-tubers like most Grabners, the Incept and Gumotex Seaker can all trace their roots.


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

Not 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.


Grabner 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

Not 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.

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 €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).

semperit forelle

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 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. Most pics lifted from ebay sellers.