Lockrack system = Broken surfski

6 months 1 week ago #30724 by Gaspar
Hi, Guys!

Be careful with the lockrack system.

I was testing the surfski model for the first time and my surfski broke under the action of lateral wind.

That happened to me on the motorway driving very calmly but it's true there was a strong wind.

The general opinion between my fellars and me is that the system is not conceived for carrying composite crafts cause it is too
rigid but the manufacturer sells it for this application.

Has anybody tested this system? What's your experience? Positive or negative?

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6 months 1 week ago #30728 by robin.mousley
A lot of guys use them here in South Africa.

I have heard of skis folding in very strong lateral winds - and it's sometimes caused by the ski not being held rigidly enough.

I really don't think that it's logical to blame the lockrack system. In most circumstances it's far better to have the ski held rigidly so that it's aligned with the direction of travel of the vehicle than to have it sliding backwards and forwards.

Rob

Currently Fenn Swordfish S, Epic V10 Double.
Previously: Think Evo II, Carbonology Zest, Fenn Swordfish, Epic V10, Fenn Elite, Red7 Surf70 Pro, Epic V10 Sport, Genius Blu, Kayak Centre Zeplin, Fenn Mako6, Custom Kayaks ICON, Brian's Kayaks Molokai, Brian's Kayaks Wedge and several others!

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6 months 1 week ago - 6 months 1 week ago #30731 by Kiwi Dave
For my last 3 boats I've made custom 'cradle liners' to ensure there are no 'hot spots' where the roof rack cradles meet the boat. Can't get a better fit than this ... I just slip them between the boat and roof rack cradles then strap down as per usual.

Edit: Thought this was the old bow strap = broken surfski thread but I see its not :P Will leave the reply as it may still be useful to some thinking about transportation.
Attachments:

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6 months 1 week ago #30732 by Gaspar
Tks Rob for your response!

As you know, the system is really easy to use and there is no room for error.

On the other hand, I drove about 200 km before the incident and I verified that it was well tighten two or three times before the incident

I find this system really ingenious and practical but the fact of having various cases as you mention, event if the craft is not well tighten, introduces a reasonable doubt about the product.

Thanks one more time

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6 months 1 week ago #30734 by kwolfe
The other question is, how far apart are your strap/clap points. I have the Goodboy vbars and my points are 8ft apart which means I only have maybe 6ft hanging out front and out back. If your mounting points are 3-4ft apart, that leaves a lot of leverage for the wind to act on.

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6 months 1 week ago #30735 by Wombat661
From an aerodynamic and loads point of view, I see no reason why tightening the ski on the rack makes any difference in the load on the boat. A force is a force, the surfski is going to see bending force no matter how you cinch it down. The LockRack has way too small a spread.

Assume cross section area on the surfski facing the cross wind is constant, and strength does not vary, the ideal spread on the bar should be 1/2 the length of the surfski. So for a 18' surfski, it should be 9'.
The 8' spread is about right on the Goodboy Kayaks bar.

Just for reference, on a 20’ boat about 11” high, the aero force on the each of the bar would be about 68lbs at 40mph side wind. 50mph is 107lbs and 60mph is 154 lbs.
The generous padding on the Goodboy V-bar is also a good thing.

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6 months 1 week ago #30736 by nwsurfskier
In addition to the security of the Goodboy rack, it takes about 1 min to load and secure the boat with its bungee strap system

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6 months 6 days ago #30740 by Gaspar
A normal car distance but it's true that in strong wind conditions is better too reduce the leverage.

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6 months 6 days ago #30741 by robin.mousley
The forces can be huge... I have Thule cradles on my car - also the standard "car length" apart which is only about 1.5m I think.

In my case it was the cradles that broke, not the ski.

So I always use a T-bar at the back of the car now if there's any wind blowing.

But I suspect that this wouldn't help with the risks of the ski breaking - it just helps to keep it more stable on the roof of the car and reduces the twisting forces on the cradles.

Rob

Currently Fenn Swordfish S, Epic V10 Double.
Previously: Think Evo II, Carbonology Zest, Fenn Swordfish, Epic V10, Fenn Elite, Red7 Surf70 Pro, Epic V10 Sport, Genius Blu, Kayak Centre Zeplin, Fenn Mako6, Custom Kayaks ICON, Brian's Kayaks Molokai, Brian's Kayaks Wedge and several others!

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6 months 6 days ago #30742 by Gaspar
Hi, Wombat.

Your calculus correct. The reaction in each support was about 70lbs at 40mph side wind (simplified calculus) and less "cantilever" would have reduced the moment and the tensions introduceds by the flection but the fact is that my surfski broke under a lateral compression what means the result would have been the same with a superior distance between the racks.

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6 months 6 days ago #30745 by kwolfe
OK, we need to see pics!

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6 months 5 days ago #30751 by Wombat661
Gaspar,
Yes, lateral loads would be the same regardless of spread of the bar.
If lateral load is the problem then the only way to solve it would be wider and thicker padding to spread the load out.
Hopefull the Goodboy rack is wide enough with enough padding.

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