Folding kayaks

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kayakski
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Folding kayaks

Post by kayakski »

Hi, Out of interest does anyone transport folding kayaks such as Feathercrafts, Klepper etc., on the roof of their vehicle assembled ready to use. If so what kind of stresses are involved? I know of two kayakers who transport these kayaks
othe roof for short journeys only with V cradles. Has anyone else done this? I reckon motorways would be a no no!
Many thanks and look forward to some answers.

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Douglas Wilcox
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Re: Folding kayaks

Post by Douglas Wilcox »

Hi Ronnie, David C has used his assembled Tyne folding double on V bars on the roofrack about 800m from his house to the beach. A lot of boing in the system!

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Re: Folding kayaks

Post by flat earth sails »

I often transport Nortik folders both singals and doubels on the car, singals in j bars just like a hard shell and the doubel flat on the cross bars. Even long distance at 120kph I treat them the same as hard shell boats

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MikeB
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Re: Folding kayaks

Post by MikeB »

I have a pal with the big F/craft double which is kept assembled all season, and transported on a specially extended horizontal bar system - 4 cradles. It's fine. I once moved one of the F/craft singles the length of the Outer Hebs, in my J cradles. It flexed alarmingly, and I doubt I ever got over 50.

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Grian
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Re: Folding kayaks

Post by Grian »

Mike, do you remember which model / how many cross-ribs the single had? Some models have fewer and that could make quite a difference.

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MikeB
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Re: Folding kayaks

Post by MikeB »

Grian wrote:Mike, do you remember which model / how many cross-ribs the single had? Some models have fewer and that could make quite a difference.
The fast, sleek one - - - might be the Khatsalano or a K1? I paddled the Farnes years ago in the company of someone else with one. It flexed with the waves, so quite possibly the same. I ended up tying bow and stern lines on, even with that it still flexed alarmingly. The double I noted earlier is the K2.

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Grian
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Re: Folding kayaks

Post by Grian »

Khatsalano is the fast one, its 17'10, so might flex a bit more than a Wisper at under 16' which has the same number of ribs, or a nortik which is 16' something.

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Re: Folding kayaks

Post by Irish Sea »

I've transported my FC Wisper more than once on regular roofbars and also on kayak trailers where the boat is only supported at 2 points. There's a bit of flex but nothing to be concerned about. I wouldn't do it with a loaded boat though. Also don't inflate the sponsons too much on a sunny day. It's also a good idea to put some foam or similar between your straps and the deck to prevent rub marks.

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Re: Folding kayaks

Post by kayakski »

Hi All,

All sorted we have made wider V Cradles, and got special shoulder pads for the straps. We do not advise on bow and stern lines as these cause extra strain on glass and other types of kayaks however we are looking at bow/ stern line of bunge cord to absorb some of the flexing.
Thanks to all who replied.

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Re: Folding kayaks

Post by MikeB »

kayakski wrote:Hi All,

All sorted we have made wider V Cradles, and got special shoulder pads for the straps. We do not advise on bow and stern lines as these cause extra strain on glass and other types of kayaks however we are looking at bow/ stern line of bunge cord to absorb some of the flexing.
Thanks to all who replied.
They shouldn't be tight. The boat will move in the cradle, they are just there to control excessive movement and (hopefully) control the thing from becoming airborne if a strap or the rack fails. I generally don't bother - but on one journey in appalling weather with strong side winds, adding lines gave far more stability to the load. And that was just two singles. This said, I know one well-known paddler who found that lines didn't help when his boat took off.

Having once had two singles and an NDK double on the rack, I'd say that lines were essential with that sort of load. There was a scary amount of movement, vertically and laterally. In fact, had the guy who'd borrowed the double used them, then maybe the entire rack wouldn't have ripped off the car on the M74 - in calm conditions too. Which is why I ended up with his boat on my car.

I'd be interested to hear how the bungee bow / stern lines idea works out.

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Re: Folding kayaks

Post by Douglas Wilcox »

I was crossing a windy Rannoch moor with three sea kayaks on J bars on the roof. We had separate bow lines for each kayak. I was doing about 40mph but heavy gusts were shaking the car. A sudden gust much worse than the rest broke the mounting for the front right J bar and the bow of the kayak swept out to the side. The 5mm dyneema bow line snapped and as the bow swung round it then snapped the strap holding the kayak to the rear J bar and the kayak went flying never to be whole again.

Last summer the owner of that kayak was driving down to SW Ireland in very windy weather with three kayaks on a Karitek easy load roofrack mounted on a Subaru Impreza roof rack (made by Mont Blanc). He had one 6mm dyneema line tied to the bows of the three kayaks. A sudden gust caused complete failure of the mounts between the mont blanc bars and the mont blanc feet. The feet stayed bolted to the car roof. The three kayaks and the easy load roof rack went down the road as the bow line snapped. The three kayaks were still mounted in the J bars on the roof rack. They suffered extensive damage but were repaired.

We no longer carry three sea kayaks on the roof and drive much much slower when it is windy. I am glad that manufacturers like KCS and Karitek advise against bow lines. They do SFA except encourage drivers to overload their roof racks and drive too fast because they have a "safety line". The windage and leverage of a load like a sea kayak generate enormous forces.

Douglas

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Re: Folding kayaks

Post by Grian »

Does tying down bow (and stern?), or not doing so, have any impact on insurance/liability in the event of an accident?

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Re: Folding kayaks

Post by Douglas Wilcox »

Grian, since two of the manufacturers of sea kayak carrying gear advise against bow lines I think not. More relevant is the load limit of the car roof. I have a big car and it is 75kg. By the time you add roof bars perhaps an ELRR and two composite kayaks you would be pretty close to that. Also the car manufacturer's idea of load is a compact thing like a roof box that does not have the windage/leverage of a sea kayak.

The breaking strain of 5mm dyneema is 1200kg and 6mm is 1900kg (though the knots lessen that). That shows the enormous force that can act on a sea kayak at speed or in a wind and how futile bow lines are. The breaking strain of the ropes we used were about 20 times the recommended roof load of the car. So that just shows the force of the wind is much more significant than the force of gravity in terms of sea kayaks coming off the roof. Mike and I now both have trailers though we still do use roof racks. It was very windy on my recent trip up to the Sound of Arisaig. Even with just one sea kayak on the roof I slowed down to 30mph on the exposed bits of the Mallaig road and yes the car was still shaking.

Douglas

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GrahamC
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Re: Folding kayaks

Post by GrahamC »

I had not considered bow and stern lines before for my sea kayaks but do use them for my sailing canoe. I generally carry my sea kayaks on a strong racing kayak V bar, however, although this distributes the forces more evenly to the hull, it subjects that roof bars to similar forces to J-bars. I am probably going to change my car soon for Honda Jazz and the stated roof loading there is only 55kg. However, this has had me looking at lots of roofrack dealers, most of whom suggest bow and stern lines to prevent the lifting / dipping of long loads due to wind. One dealer states that they have seen all makes of rack fail but never with bow and stern lines.

Being a physicist I started looking at the forces involved and also my fuel economy. Firstly, best fuel economy (to which I attribute least forces on the car) was with the boat in V bars with a cockpit cover fitted. Worst has been J bar without cockpit cover. For bow and stern lines to be effective in reducing stress on the roof fittings they must be tight, actually very tight or completely non-elastic. To prevent failure they need to immediately provide a force equivalent to that trying ti rip off the rack. Bearing in mind that the bow and stern lines are not perpendicular to the kayak the actual force in the line is even higher and this is transferred to the boat as a horrible bending and compression. In a J-bar situation this is a very high force because of the long leverage (a lot less with a J-bar). It does not surprise me that 6mm dyneema gets broken, I would also expect the toggle line to break if tied to that. It also does not surprise me that roofracks break. Many are coupled with only an M6 bolt in each strut and you can snap an M6 quite easily just by overtightening. Also, those sturdy looking roof rails on some cars are often only connected by a few M6 bolts.

After all the consideration I think that we are often complacent about loading our racks. How often do we actually check them? We overload them with static weight, then massively overload them with lateral wind, especially in the case of J bars; we also drive fast (remember the force increases at the square of the speed). When we set up a tow on the water we are careful to consider what happens if a deck fitting breaks, but on the rack or J-bar, what happens if that bolt breaks or the welded loop fractures? Bow and stern lines may help to stabilise the load and lessen the effects of a rack failure, but they are unlikely to prevent a rack failure (unless so tight the boat fails first!). The main thing is to check the rack, not overload it and drive accordingly.

Going back to the original post, I have seen built up Kleppers transported but usually in a cradle, the right way up, and with a cockpit cover and at sensible speeds. Remember that the forces on the water are very high too, but distributed over a greater area.

Graham
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Re: Folding kayaks

Post by Douglas Wilcox »

Thanks for those informed comments Graham. The 6mm dyneema was threaded through the three end toggles. The 5mm dyneema was threaded through the hole where the end toggle goes (it had previously worn through). Peugeot 406 estate owners need to be particularly careful, a friend's roof rack failed because the roof rail mountings rusted through at the front and the roofrack came off. He used a green canoe strap to tie down the front but it also broke.

If you ever need to replace roof rack bolts make sure you get the right high tensile ones. Just because they fit does not mean they are strong enough. My car comes with a torque wrench to tighten the roof rack bolts.

Breaking strain of ropes is tested statically. In both my own case and in Mike's the angle of the front tie down was such that the boat moved back a fair distance before the rope tightened. The tie down was only stopping the end of the kayak moving up, not back because it was just about vertical when seen from the side. This resulted in a shock load on the line which is more likely to break it than a static load.

Douglas

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Re: Folding kayaks

Post by Grian »

I really did perceive them as a useful 'safety line'. Good to know.

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Re: Folding kayaks

Post by Douglas Wilcox »

Graham,
One dealer states that they have seen all makes of rack fail but never with bow and stern lines.
Ahhh.. the confidence of ignorance.

Douglas :o)

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Re: Folding kayaks

Post by sunstreaker »

Just out of interest, I am guessing it's the difficulty and time it takes to assemble a foldable that prompts the OP and all those who have experience of car topping a foldable kayak?
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Re: Folding kayaks

Post by Douglas Wilcox »

Yes David's folding Tyne double from the early 60's takes a long time to assemble and disassemble. I am sure more modern designs are quicker though.

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Re: Folding kayaks

Post by kayakski »

Hi all, Bow and stern lines when used with sea kayaks will or can cause damage as when going over a bump on the road the kayak will move taking up the shock, the bows line will go tight then the stern will buck back up and go tight. In this situation they the bow and stern lines will create a shock through the kayak ( composite or folding ). The idea when we designed the first J & V cradles was for them to take the vibration caused while travelling with sea kayaks on the roof. Bow and stern lines will never keep a kayak on the roof if the bars fail, at the best if they do not break the kayak will be beside your car and not splattered behind! Bow and stern lines will also stop the cradles from working as they should.
As one has stated many roof bar suppliers state you must always use bow and stern lines as a safety item, they are not involved in the sea kayaking industry and are therefore unaware of the damage they cause and that they will not stop the load from staying on the roof, the forces involved would see to that.
My idea of using bunge cord heavy duty is to help stop the bounding or flutter being created with the much lighter construction of a Feathercraft on the roof, yes empty, anyway you could never get a loaded kayak onto a roof! ( one comment, make sure it's not loaded! ). The V cradles I have made are wider than normal, however the kayak must be supported on the ribs and not the stringers, plus I have padded shoulder pads for the straps which will spread the load.
Thanks to all for all the comments, great feed back.

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Re: Folding kayaks

Post by MikeB »

Douglas Wilcox wrote:Grian, since two of the manufacturers of sea kayak carrying gear advise against bow lines I think not.
But Thule do advise lines - - -

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Re: Folding kayaks

Post by Douglas Wilcox »

Hi Mike since at least two specialist companies do not recommend them there is hardly a consensus. Also in the three cases where I and two friends lost 1, 3, and two kayaks from the roof bow lines were used. The bowlines not not prevent the racks failing nor did they stop the kayaks flying off as all three broke. If an insurance company did try to wriggle out of paying for third party damage then just refer them here!

Neither Mike, Jim nor myself attempted to claim for the loss/damage of the kayaks and fortunately there was no third party damage. Interestingly Mike's Subaru/Mont blank roof bars failed where the bar joins the rack foot. Amazingly there was no metal to metal contact. The joining piece was plastic! Thule and BMW bars are both more substantial with metal to metal joins. I understand that Karitek are now developing a new ELRR bar that rack feet attach directly, to thus eliminating the existing crossbar.

By sheer coincidence I drove down to the Solway from Glasgow early yesterday afternoon. I had one kayak on my roof rack. It was very windy on the long high straight road past Loch Doon. I was doing 45-50 when I was overtaken by a black Audi A6 with three sea kayaks on the roof. It was doing at least twice my speed in a 60 limit. That is how kayaks come off car roofs, not whether there is a bow line or not.

Douglas

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