Rather like sails where I MYO’d, lost interest, then returned to the idea (with a proper WindPaddle), after five years I’ve come back to the idea of fitting a rudder on Seawave 2. Mostly, this was inspired by a much simpler pivoting footrest tube idea of fellow Seawaver Jules, instead of cumbersome foot pedals I made. It could make the Seawave more useable in a slightly greater range of weathers, which includes sailing which I tried again recently.
I could have bought the Gumotex rudder kit for £219, but as always it’s more fun to piss about on the pretext of saving money. I coughed up 25 quid on the longest rudder mechanism I could see on eBay, at 510mm. The stern-mounted rudder plate is another slab of LDPE chopping board, but clamped down only via the drain hole and with stick-on velcro, as Jules and Gumotex use. I found secure clamping of the rudder mounting plate to be important to stop it turning on its axis. Two points of fixture will eliminate any deflection, and hopefully the stick-on velcro will do that.
Another smart idea idea Jules had was running the rudder lines forward under the deck velcro inside long, thin tubing. That largely eliminates any exposed lines which can get caught up in a puffin’s waders. Finally, I will use his idea of controlling the rudder by pivoting my footrest ‘drainpipe’ tube pivot from the centre, eliminating the need for cumbersome foot pedals, whichever way you do it.
A couple of fellow Seawave owners got in touch recently to share their ideas and modifications.
Jules showed me his very nicely milled MYO rudder similar to my Mk2 design of 2016 made from HDPE chopping board. I doubt the alloy one is any heavier. He also uses a deck, but replaced the four bulky welded alloy bars fit for a Zeppelin with a much lighter arrangement in heat-bent plastic pipe with alloy end slots. Were I to get a deck again (solo decks only go for around £145 – over half price of the full kit), I’d definitely make something similar, maybe with tent poles or even thick garden hose. It would pack much more compactly. Jules adds: … I’ve made a very efficient rudder for the Seawave using a tube that pivots on tape as a pedal bar or locks off to form footpegs, with cables running in PTFE tubes under the velcro for the deck. It means no exposed lines and works very smoothly.
I take that to mean a hard drainpipe tube (like I use) which pivots from the centre like handlebars with the rudder lines attached at each end. In an IK that’s a much neater way of doing it than any pedal system. Tucking the lines under the deck velcro in tube sleeves is also much better. It’s about time that deck velcro did something useful! The photos below may help clarify Jules’ system
Meanwhile Gavin adds: On my most recent trip I experimented with looping a couple of straps across from one side to the other around some of the attachment points, one strap near the bow and one near the stern. I then tightened the straps so that it pulled the side tubes closer together. It makes the kayak narrower, gives a slightly more pronounced keel from the floor being squeezed together, and seems to stiffen the kayak along its length as well as across its width. Obviously it takes away some stability, but I can live with that as a trade-off for being more efficient.
I usually paddle single-blade and sit on a bench seat held under the velcro on the side tubes. The Seawave is faster than the Palava paddled like that, although it lacks the width and stability… I’ve got a rudder steered with a tiller held in place by friction under the fixings for the deck support bars, so I can do straight strokes instead of having to J-stroke to keep a straight course.
I like the tiller idea too, though of course it works best for canoeing. Anything to dodge the clutter of foot pedals and rigging, though Jules’ idea improves on that.
Thinking over the mods and ideas I applied to my original Seawave over the years, on Seawave 2 I believe the best or most essential ones are:
Replacing the stock footrest cushion with a solid drainpipe footrest tube. Proper support, lighter. Replacing the stock inflatable seat/s with with a stiffened foam backrest and light packraft seat base. Better support, lighter, less bulky. Adding a Gorilla tape strake under the bow; simpler than gluing on a strip of hypalon. My skeg-wheel trolley is great too.
Other old Seawave mods I tried am not in a hurry to reimplement. Rudder: too much faff for the fair-weather day paddling I do, but were I doing an overnighter at sea (with or without sailing) where you can’t always pick you winds, a rudder would be a very handy and I’d apply Jules’ ideas, starting with a 20-quid rudder mechanism off ebay.
PRVs in the sidetubes: worked great but as explained here, after a recent paddle in Seawave 2, where I paddle heat is not a big problem and the extra care required and time saved is minimal. I still run 0.32 bar or so, not 0.25 but better to make use of an accurate pressure gauge.
It’s Midsummer’s Day up here in the MidSummer Islands, but it’s barely over ten degrees and blowing from the northwest. Now my Seawave PRV saga has been resolved, there’s enough (but not too much) wind to sail the four miles over to Achininver for a visit. It’s the last day of paddleable weather before we pack up and head back south with the geese.
It’s also my first chance to try out my trolley with wrapped-round inner tube tyres. It’s less than a mile down to the beach and the racket of solid plastic wheels is gone. This trolley really is one of my better ideas for the Seawave. It ditches the need for a car for short hops, and elsewhere means you can paddle somewhere and wheel back if there’s a road or decent track.
As it’s chilly and will get splashy on the paddle back, I slip into my Anfibio dry suit. If the sailing goes awry and I fall in, I have an impression of being protected, even if its insulation effects will be marginal. Best of all, I can dip myself into the brackish loch behind Badentarbet beach for a salt rinse and be dry by the time I wheel home.
My WindPaddle is the 1.2m Adventure II model, big enough to haul the 4.5-m Seawave with me in it. I flip it out and off we go, trying to steer SW for Rubha Dunan point. Only it’s not really working so well. Apart from the usual sail swaying on bigger gusts and flopping back on lulls, whitecaps are rolling in from the right, pushing me onto the Achlochan peninsula. Later I realise this drift is probably because the Seawave’s skeg (no bigger than my hand) is too small to stop the light Seawave drifting across the wind which across the bay may be turn WNW. This is why sail boats need keels and dagger boards. If I had a third hand or a passenger, the paddle could’ve been used as a rudder, but as it was my hands were full managing the sail and trying to take the odd photo. You don’t want to risk losing the paddle.
I’m pushed into the rocky shore where the refracted waves and added fetch make things a bit lively, but the ever-stable Seawave is reassuring. So with a quick cross-fold, the sail is stashed between my knees and I paddle on to Rubha Dunan. Once round the corner the sea is smoother but the wind remains so I cruise past the sandstone cliffs towards Badenscallie Beach, an alighting point for Horse Island. Out of the lee the waves build up and with the odd gust the Seawave races on. When you’re not trying to control the sail, it is a marvel to sit back and look round as the water tinkles past the bow.
It took me an hour-fifteen to cover the four miles to Achininver Beach, at times lazily sailing slower than I could paddle. It took only another 15 minutes to hack back non-stop into the wind at 2.4mph, but by the time I got in I was just about pooped. It was a fun excursion, but to make it worthwhile you need more wind than you’d want to paddle back against. A better use of the sail would be going somewhere and not having to crawl back.
Time to head back up the hill, dry out the boat and roll it up for this season in the Summers.
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.
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.
Sea Eagle’s Fast Track 465 (4.65m) is a high-end PVC IK has been around for several years, one of the earliest ‘hybrid’ IKs combining a removable dropstitch (DS) floor and conventional side tubes. It sits alongside their dumpy, all-tube SE cheapies, more whitewatery Explorers, and the all-DS, fixed-floor Razorlites. They even make a full-DS canoe. From the side the 465FT is a sleek looking IK with slender 24cm side tubes and the distinctive frontal keel under the bow to keep it on track (and which Gumotex have vaguely copied on the Rush models). Quoted weights vary as usual: from 17kg to a ‘hull weight’ of 20kg on the official US website. For a 15.25-foot PVC IK, 44lbs sounds about right.
Sea Eagles only sell these boats in ready-to-paddle packages which include a paddle/s and a pump as well as the usual wrap-around carry bag and repair kit. They start at $1600 or £1299, though in the US are regularly discounted by nearly 30%. When you read scathing ‘reviews’ of otherwise perfectly good IKs panned for not coming with a pump or paddles (even if that was clear at purchase), you can see why SE do this. Just don’t expect a stiff and light paddle. Upgrades include seats with proper backrests, as well as better paddles, three-seat combos and even rowing and motor rigs. And one thing that sets SE apart is the phenomenal 180-day return period and three-year warranty – at least for US customers.
Though you’ll struggle to see any evidence of this, the DS floor is removable, so it should be easy to clean and dry the boat. Assuming the floor comes out easily, the hull still has somewhat redundant closeable floor drains. Some outlets claim these to be self-bailing ports. There’s a big difference between the two: the former helps drain inaccessible cavities to help dry the boat without removing the floor; the latter allows waves that pour over the sides to drain away via holes in the floor – ideal for whitewater or surf. Such boats need thick floors to sit you high above the drain ports so the kayak doesn’t have water sloshing across the floor and soaking your butt. The 465 (and similar Aquaglide Chelan) doesn’t have a thick floor, though if you’re light you can give it a go. As it is, any 15-foot IK will be a handful in whitewater or surf conditions.
Oddly, the 2014 manual still online suggests you put the same 3.2 psi (0.2 bar) in the DS floor as the tubeless side tubes. Later models have ‘max 8-10 psi labels at the valves, but there is no way you’ll reach that pressure with the archaic foot pump supplied in some base packages. Then again, the couple in the video below inflated their 465 by foot pump. They represent perhaps the recreational core of SE’s customers: prepared to spend four figures but not that bothered about performance or equipment.
One thing that seems to be missing from online images are footrests. For all but the most undemanding recreational paddlers (which may be most of SE owners) a solid footrest to brace off makes a huge difference to paddling efficiency, while also stopping you sliding down the seat. It can have benefits to stability too, although at 91cm wide (36″) that won’t be a problem on the FT as some might find with the FDS Razorlites. Some D-rings could easily be glued on, but for what you pay, it’s odd to not see them included. They’re not even an accessory part. the drainpipe/strap idea I use on my IKs would work fine here.
What they call Deluxe seats are comfy looking vinyl blobs which sit you 5 inches up and clip to the hull sides (as well as the seat base). But because the backs are inflated (via Boston valves), they’ll have little support to lean on because low-psi inflatable backrests tend to crumple under pressure. Non-inflatable foam-board‘tall back’ seats (found on most other Chinese-made IKs) are supplied in pricier packages will have better back support, except the base is thinner. A slab of foam underneath will see to that, but without footrests you may not notice the benefits.
The innovative Needleknife frontal keel is inflated via a raft valve accessed by a hole in the front floor. Flat, DS-floored boats need some help here, and it does appear to greatly improve tracking, especially while not adversely affecting turning. If that’s the case you do wonder if a long, low slip-on plastic skeg, or just a keel strake as of the Chelan 155, might not work as well with less assembly complication. Perhaps the Needleknife’s softer profile works better, especially in sidewinds where the keel (and low sides) is said to deflect the boat less. There is a large slip-on skeg which is now more swept back, but could still be a bit on the long side. Luckily it’s easily replaced or shortened, but the boat will need some sort of skeg to track well.
Another forecast of calm winds in the Summers. Or is it? The BBC and YR reports are contradictory: the former has too-strong-for-IK winds from the south; the latter shows light winds from the north. Others show light winds from the south. How can they all be so different? Maybe I should just look out across the water? All looks serene so let’s make paddle while the sun shines. I wheel back down to False Man’s Harbour and set off with two hours before high water.
No side PRVs? Am I missing not having added pressure release valves in my side tubes, as I did to my original Seawave? Not really. I am running 0.3+ bar in the sides (official: 0.25) but temperatures up here in NW Scotland are hardly tropical. I try and leave the boat in the shade at the house and de-air the side tubes for a couple of seconds after a paddle, effectively manually depressurising the sides to about 0.2 bar, rather than having fitted PRVs do it for me automatically. The more vulnerable stock PRV in the floor purges automatically at 0.25. On my next paddle I have to top up all three chambers with the K-Pump as I would have to do with all-round PRVs anyway. About 30 kpumps brings the sides back up to over 0.3 bar. The difference now is I use a manometer to check I the sides about right. Before I would just pump until the side PRVs purge. It’s about a minute’s more faffing. As with a lot of things I do to my IKs: sails, rudders, decks and now, trolleys and headwind weight transfer – it’s fun to experiment. But in the end they’re all largely over-shadowed by the simple enjoyment of paddling. With sides pumped to >0.3 bar I find I can cruise easily in the near-still conditions at 6kph.
After a fortnight of chilly north winds and a diminishing woodpile, today was one of those rare days in the Summer Isles (far northwest Scotland) where you could paddle pretty much where you liked in an IK. It was also a chance for me to try out my new skeg-wheel trolley which Jon, who was staying down the road, had made for me. With no boat of his own this time, we set off in mine to see what we might see.
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.
In a line Lightweight, compact ‘day’ or back-up stove using ethanol wax blocks.
Cost ‘Shoe polish’ tin (from £1) + optional band + cross-stand (from £5) + FireDragon blocks (from £1.14 a filled tin). Total: around £8.
Weight Tin (25g) packed with fuel: 133g. Cross-stand 28g, 10cm wind shield 7g. All up: 168g + lighter.
Where used River Wye and Knoydart, Scotland.
Light, simple, compact Fast set-up, easy to light Sits low (stable and out of the wind) Tin makes a large burning area and is refillable Tin fits inside a 400ml Tatonka folding-handle mug No noise, no smoke, no smell, no residue on the pot Fuel cools and resolidifies quickly and will relight later Presumably can be carried on a plane, especially if you label it ‘hand sanitiser’ (which it also is). So light and compact it can be used alongside or to back-up a gas stove or a woodburner
Expensive at around 37p to boil a big mug Fuel may be harder to find than gas cans at outdoors stores, but sold in ‘home & garden’ stores like B&Q
Review: This Gimp Stove (a military acronym, apparently) isn’t something you can buy off the shelf. My bush-crafty mate put it together once he learned FireDragon ethanol firelighter blocks could be packed into a ‘shoe polish’ tin and easily refilled and re-lit. He identified a small, screw-top tin (multi-buys off eBay or amazon) with the right diameter to fit the notches of the CNC-cut stainless steel cross-stand also widely sold online from around a fiver. For a stable set-up, finding a tin to fit this cross-stand’s notches is the key. Or you can as easily make your own stand to suit any tin you like, but the tin’s lid needs to be airtight so the fuel doesn’t dry up. My mate even added a silicon wrist band round the base so you can seal it good and tight.
I managed to cram about four blocks (108g) into my ‘100ml’ tin (actually more like 130ml). From this I got three 360-ml (big mug) boils in the field. To extinguish blow it out, or smother with the lid. The liquified gel quickly cools and resolidifies and will readily re-ignite next time. Timings were 4 minutes tested indoors, and about 7 mins outdoors, using a thick tinfoil windshield from the base of a fruit pie or a take-away curry. There is no noise, no smoke, no smell and unlike toxic hexamine tabs, no residue on your cup or toxic smoke. On the first freezing morning of our Wye trip, even though I’d slept with a 45% full gas can inside my sleeping bag, it failed to boil my water once out in the freezing morning air. The Gimp would have lit up readily and done the job. And the fact that you’re easily able to place a windshield on the ground, and need clever, faster but totteringly unstable, bulky and pricey JetBoils is another tick for the Gimp. All in all, the Gimp is a handy, cheap and foolproof pocket stove. I used the Gimp again on a four-day Scottish trip to heat up water for lunch soup. Light and compact enough to carry in your day pack, it made the whole business effortless, while saving gas for other meals.
FireDragon Fuel Made by BCB International from waste vegetable matter, the blocks come in individual sealed 27g (1oz) pods, bought 6 or 12 at a time. It’s the same (and can be used) as hand sanitiser. Once the packet is opened, the block (a mashable wax of ethanol or denatured alcohol, left) will evaporate and shrivel, but sealing in the screw tin works fine, at least for a few days. Long term you may want to verify this. The good thing with a full tin or two is you have no packaging to get rid of responsibly; you just come home with empty tins to refill. Apparently you can ignite with a flint (BCB’s stove kit, right). I tried but couldn’t do it on used fuel, even with some magnesium shavings (the fuel lit right up with a lighter). I may try again with a fresh block, but honestly Bushcrafters, a lighter takes one second. The best price in the UK works out about 28.5p a block by the dozen, so a penny a gram with a big mug boil at 37p – quite expensive. And you’ll struggle to find it at that price; very often it’s nearly double, or gets that way with postage. Your best bet seems to be larger Go Outdoors stores. I would guess you could get at least 30 same-sized boils from a typical 220g can of gas costing around £4 which is more than half price.
I skimmed through an online review (one guy was even wearing camo gloves!) and apparently the FireDragon boiled loads faster than hexamine (which I’ve never considered trying). I’m told the Brit army now use FireDragon instead of hexamine.