The real problem is that you never know when wind shear can grab your boat. I used to travel Florida on a racing circuit. I have had shear from storms try to dismount my boats often. Worse, sometimes, is the jerk in the tractor-trailer blowing by you at eighty and creating suction enough to move your car. Think what that does to your boat. Always, at least, use a bow tie down. The stern is a bit closer to optional, but not much.
I have two Thule Hullavators on my Santa Fe and of course I use the Thule tie-downs. Why wouldn’t I as it only takes 5 minutes max to clip them to under hood loops and captive loops under the rear door?
M kayaks “blowing off” or my racks doesn’t concern me as much as if I get hit by another vehicle. In that case I want all the protection I can get. So far I’ve driven with my boats at highway speeds between Maine and Florida several times without incident.
I too wear my seatbelts - and value my airbags - for the same reasons.
I use bow lines or not, it depends on the situation and the vehicle.
Driving to the PNW two years ago in a Jeep Commander with a factory rack, I used a bow line because of winds - and the factory rack. Trying to cross the bridge to Folly Beach, SC last fall, I stopped and added a bow line because the post hurricane crosswind was so bad.
My 1992 full size Blazer however had longer aftermarket side rails installed during her restoration last winter. That means, as others have mentioned, there’s a wide spread between the crossbars. My 17’ 10" Necky and 17’ Pygmy are secured 1/3 of the way from each end and barely even vibrate when I pass a semi. A compact car with a 17’ kayak on top isn’t going to have that kind of stability so a bow line is a good idea. It is the movement that creates issues. That’s the reason manufacturers downgrade rack load limits for off road use.
When loading, I pass the straps under the crossbar, over the 'yak and then through the side rail, attaching it to the car on that side. I add a third transverse strap from the back crossbar over the cockpit and through the side rail at the front as a alternative to a bow line. If a strap fails - there’s two others to take the strain until I can pull over (and I drive in the right hand lane except to pass). If a crossbar fails, the straps around the side rail will offer as much reaction time and attachment to the car as a bow line would.
Three people I know have lost 'yaks off their cars. Two forgot to tighten the straps (well…) and one had a rain gutter clamp-type rack peel off the roof even with a bow line. I had one of those racks on the Blazer years ago and was so paranoid that I put a strap over the RACK and through the cab doors!
I have been paddling for over 40 years and I always used bow and stern tie downs, except once couple of years ago and guess what? I lost my boat.
I was driving a VW Jetta with a Thule rack and we finished paddling early that day and were happy to go home. We tied down the canoe on the rack for the shuttle and forgot to install the bow and stern tie downs (it was only a short shuttle after all !!!). It was a short shuttle on a highway and it was a bit windy but nothing excessive. I was driving about 50 MPH and suddenly noticed that the boat was moving on the roof. I took a quick look at my mirrors to make sure I could safely pull off and noticed a motorcycle at a good distance behind me and figured out I could safely pull off. By the time I put my eyes back on the road, I saw the boat coming off and flying over my car. My first thought was about the motorcycle following me. He was now closer and didn’t manage to avoid the canoe and got hit.
We were both lucky that the motorcyclist only got minor injuries but both the canoe and the motorcycle were scrap. When taking a closer look at the scene, I found out that the rack completely came off the car (it was still attached to the canoe). I regularly inspect my rack to make sure nothing is loose but it looks like it loosen enough to come off this time. Trust me, bow and stern tie downs would have prevented that type of situation.
I’m a whitewater canoe instructor and trust me I now tell all my students to never take the road (what ever the distance is) without bow and stern tie downs when carrying a boat on their roof.
So the take away is bow and stern tie downs aren’t important until they are and you need them (but you didn’t put them). whatever the type of boat you carry (canoe or kayak).
I also had another situation where this time I had bow and stern tie downs. I was coming back from a paddling weekend on a major highway and the wind picked up. I never drove in such a wind. I said to myself “Am I lucky that I put the bow and stern tie downs”. I was driving a Pathfinder with a factory rack. When at home, I noticed that rack was loose. A very meticulous inspection reveled that more than half (8 out of 12) of the rivets holding the rack failed. My truck was less than 2 years hold. I had to go back to the dealer to have them replaced. Was I lucky that I had bow and stern tie downs. Without them, I would have certainly lost my canoe once again.
So for my own safety and the safety of other drivers, I now always use bow and stern tied downs because you never know when you will need them. Better be safer than sorry…
I have the Thule hullivator system for both sides of my Jeep. The fit can be adjusted so the boats really nestle in the cradles. I would NEVER travel any distance going over 40 MPH without bow and stern tie downs. First, I don’t want damage to my boats, and second there was an incident where the cradle of my rack became loose after hitting a nice pothole on the freeway… Without the tie downs, I would have watched my favorite boat hit the interstate and shatter instantly. Not safe for anyone. Our local kayak outfitter would never sell a boat to someone without stressing the importance of using proper tie downs.
Sucked it up and bought the Rhino T Loader for our 21’ Seda Tango on our Subaru Outback. Did a few trips w/o it and used every strap, cam and hook that I own, representing nearly every maker! With the T Loader that Viking battleship is going nowhere but to sea!
Being the cause of a “sig alert” (…kayak in the HOV lane of the 15 southbound, two lanes closed while Caltrans mucks up the debris,…) and dealing w/ a tangled pile of plastic, fiberglass or Kevlar, while people driving past laugh at me for not properly securing my load - I’ll goat rope my boats!
@string said:
There has to be a boredom component.
Yup. Lots of heavy rain or late snowstorms over the US.
Interesting stories here, especially marctibo’s.
If they lead to one boat more securely attached, all the better.
Also, I don’t have the years and years of experience as so many here do, so reading about paddling is always fun for me.
I will always use bow lines, as they probably saved the life of the car behind me. I had three kayaks on top of my Chevy Tahoe. Two were in kayak holders attached to Thule crossbars, and the third was tight in the middle to the crossbar. All had bowlines connected to my front bumper. I also had stern lines connnected to my trailer hitch. I was driving on the highway about 70 mph (legal speed in FL) when the wind on the three kaysks ripped my GM factory rails off the Tahoe. The front bolts of each side rail simply pulled through the sheet metal on the roof. The front of the three kayaks lifted slightly and shifted wildly from left to right, but were held in place by the bow lines. The three kayaks were securely fastened to the cross bars, but the who set up would have would have blown off my car and landed on the car behind me if the bow lines were not present. Why take the risk? Use bowlines!!
If I were using vehicle factory racks I would be doing the same, but I use racks installed by me and know what they are attached to.
No risk ! Plain and simple, they are part of my vehicle.
Your post brings attention to a very common problem with factory racks - not knowing the weight limits. Putting great aftermarket crossbars on a factory rack doesn’t change the manufacturers’ specs.
I don’t think Chevy rates any of their racks for more than 150 - 165 pounds. Three 60 pound kayaks on that rack and you’re over the weight limit even before you add in the weight of the crossbars and saddles.
The result is that the roof flexes with the weight (and when you hit bumps) weakening the metal roof at the attachment points. This is why the bolts pulled through - metal fatigue.
Anyone who wants to know the weight limits of their factory rack should check the owners manual or ask your mechanic to check the service manual, which are available on line.
@JackL said:
If I were using vehicle factory racks I would be doing the same, but I use racks installed by me and know what they are attached to.
No risk ! Plain and simple, they are part of my vehicle.
That is good to do, but I would make that clear before suggesting that bow and stern tie downs aren’t necessary. Most folks don’t do what you did with your rack.
@KayakerBee said:
Your post brings attention to a very common problem with factory racks - not knowing the weight limits. Putting great aftermarket crossbars on a factory rack doesn’t change the manufacturers’ specs.I don’t think Chevy rates any of their racks for more than 150 - 165 pounds. Three 60 pound kayaks on that rack and you’re over the weight limit even before you add in the weight of the crossbars and saddles.
The result is that the roof flexes with the weight (and when you hit bumps) weakening the metal roof at the attachment points. This is why the bolts pulled through - metal fatigue.
Anyone who wants to know the weight limits of their factory rack should check the owners manual or ask your mechanic to check the service manual, which are available on line.
Good point. We rooftopped two sea kayaks on a Tahoe on several long road trips, including one from CO to AK and back again. All in states where high wind gusts and semis are common. We have Yakima hardware attached to the standard factory rack and use bow and stern tiedowns when rooftopping. That old Tahoe now has more than 157k miles on it.
@castoff said:
@JackL said:
If I were using vehicle factory racks I would be doing the same, but I use racks installed by me and know what they are attached to.
No risk ! Plain and simple, they are part of my vehicle.That is good to do, but I would make that clear before suggesting that bow and stern tie downs aren’t necessary. Most folks don’t do that.
I don’t believe that I ever said they are not necessary. If you read some of my past posts, I said I use bow lines on my long skinny ultralight canoe and my Carbon Epic 18, but that is not to keep them from flying off. It is to prevent damage to the bows from cross wind shear.
If I had a vehicle and was relying on factory racks, I would absolutely use front and rear tie downs.
When you go out for a drive the next time take note of all the painters vans and construction pick-ups with their ladders on their roofs- See any front or rear tie downs?
@JackL said:
When you go out for a drive the next time take note of all the painters vans and construction pick-ups with their ladders on their roofs- See any front or rear tie downs?
No, but then again ladders are mostly empty space, not a hydrodynamic hull shape capable of generating significant drag at a right angle to the direction of travel.
Jack I enjoy reading your many post.
Construction vehicles generally have truck toppers with bolted or welded racks, or all metal racks mounted to the bed. Work Vans also generally have after market rack systems. Very different from factory car racks. I worked in construction we didn’t use front and back tie downs either, but a ladder has a much different profile than a kayak or canoe. I have seen stuff come off the top of a work truck before it was plywood and lumber. I have also seen a work truck after a wreck with stuff on the ground that had been on the top.
The implication I take away from your past posts is they aren’t necessary. Just stating that when you say you don’t use them it would be helpful to make it clear that you bolted your rack to the top of you vehicle, and have confidence in it’s stoutness and security.
@wade@lippman.us said:
I have carried 26’ shells on a Subaru Impreza for 500 miles. You can’t use bow/stern straps on a shell because if you get it tight enough to do anything it is likely to snap them.
Wade I have a 2014 Impreza that didn’t come with a rack so I added the Yakima landing pads that use one bolt at each of the roof top rack attachment points. The spread between the cross bars is 32.5". I am curious as to the rack you use and the spread between the the front and back cradles? Recently I had to re tighten the drivers side front landing pad as the bolt had backed part way out.
If I over tighten the bow lines on the front of my 17’ 4" Buccaneer sea kayak it will deform the fiberglass hull as the cross bar in front of the cockpit isn’t near the bulkhead. I don’t over tighten the lines I snug them down just enough. I don’t use a single bow line, but use two lines in an inverted V arrangement, and the same at the stern. The bow and stern lines are in opposition to each other, and in this arrangement they prevent both side to side and front to back movement. They don’t have to be very tight just take the slack out to hold the boats in place,
I would suggest you check your rack for play from time to time if you use the Yakima landing pads on the roof. I do wonder if snugging the bow or stern line would break your shell what driving into a strong headwind at 70 miles an hour is doing to the shell.
@castoff said:
…I do wonder if snugging the bow or stern line would break your shell what driving into a strong headwind at 70 miles an hour is doing to the shell.
Based on a similarity analysis, driving at 70 mph through air would create the same forces on the wetted surface of a kayak hull as paddling from 4 mph up to 7 mph (depends on temperature of the water and air). The analysis is based on equating Reynolds numbers of a given hull traveling in air and in water. This is the analysis used to determine testing conditions for aero/hydro dynamic model testing, either in the same or different fluid as the actual vehicle.
There would be additional air drag on the part of the hull normally above the waterline, so the friction drag on the hull on the top of the car would be approximately doubled. On the other hand, there is no wave-making drag while transporting a hull on top of the car (since there is no air-water interface). Since wave drag can be around 50% of the total drag at ‘high’ speed, the drag on top of the car should be approximately the same.
This is all approximation, of course, but should be correct to say, plus or minus 20%. In the end, aerodynamic drag forces (in the direction of motion) on a hull during car transport are not as dire as one might imagine. However, crosswinds can easily create fairly large lateral forces on a hull that may not happen while paddling in normal conditions, which is what tie downs are really needed to counteract.
For a shell, it seems like the lateral forces would be very problematic, but maybe those hulls are OK with side to side forces, while a tie-down exerts a primarily vertical force. I did speak with a crew coach from West Point years ago, and he told some tales of 8-man shells breaking in pieces while going through large wakes from barges on the Hudson during practice - it seems the vertical stresses caused local buckling that led to the failure.
Thanks! I have wondered in the past about this. A 70 mph vehicle driving against a 20 mph head wind with gust to 40 I suspect would have a bit more force on the hull, but perhaps not be too extreme. I play with my sea kayak in the surf, and bet that is a lot more force involved. I saw a sheet of 1/2" plywood on a rack break from wind catching the front over hanging a car once, but that isn’t very aerodynamic.
@castoff said:
Thanks! I have wonder in the past about this. A 70 mph vehicle driving against a 20 mph head wind with gust to 40 I suspect would have a bit more force on the hull, but perhaps not be too extreme. I play with my sea kayak in the surf, and bet that is a lot more force involved. I saw a sheet of 1/2" plywood on a rack break from wind catching the front over hanging a car once, but that isn’t very aerodynamic.
Yes, the comparison has to be for geometrically similar shapes. Head winds and gusts can certainly increase the velocity appreciably. If you consider trying to drag a sheet of 1/2" ply through the water at 5 mph, it seems obvious that would create some high forces, so it’s not surprising that plywood, drywall, mattresses, etc. are subject to high forces on car roofs.
The similarity calculation is fairly easy - forces will be the same on similar hulls with equal Reynolds number. To get equal forces in an air-water comparison of the same length hull, equating Re number gives a velocity ratio equal to the kinematic viscosity ratio. Since kinematic viscosity of air is about 15 times greater than water, the velocity in air that gives the same force will be 15 times greater than in water.
It’s an interesting coincidence that normal (non-insane) highway travel speed happens to be about 15 times greater than kayak travel speed. It means that the drag force on a kayak on your roof is approximately equal to the force required to propel the kayak, generally in the 3 to 10 pound range. Actual air/water temps can vary the ratio from perhaps 10 up to maybe 17 or so, kayak deck shape plays a part, the rack components will add drag, etc. But overall, forces from aerodynamic drag while transporting kayaks are not particularly high and will be comparable to paddle forces. I did this calculation (OK, estimate) years ago while sizing bolts to hold V-bars on crossbars. The calculation gave a bolt size smaller than I liked, so opted to go several sizes larger, and used 5/16". I noted at the time that bolts in commercial towers I looked at were size 10 or 12 or perhaps 1/4". Wimping out like I did is called ‘factor of safety’ in engineering.
It may seem counter-intuitive that air is more viscous than water, but kinematic viscosity is absolute viscosity divided by density. Absolute viscosity governs velocity gradients, whereas kinematic viscosity is what governs the magnitude of the drag force created by the gradient. A good exercise is imagining out how fast you would have to wave your hand through air to feel the same drag force as when waving it through water (or vice versa).
In contrast to the aerodynamic drag, crosswinds are problematic for two reasons: (i) the transverse force created by air impinging on the side of the kayak bow is going to be large, since the hull is not streamlined in that direction, and (ii) the moment arm for the bow can be pretty long, so the torque created can be large. V-shaped bow lines are used to counteract the torque. V-bars are helpful in effectively reducing the length of the moment arm by placing the forward cradle close to the bow, so will reduce the torque.
Sorry to go on so long, I am desperately trying to avoid a mundane task I really don’t want to do, talking fluids is much more enjoyable…
I learned something new…Thanks for the explanations. I did have a grasp of some of this already, I suspect the aerodynamics of the front of the vehicle, and how the air is directed may also have an influence.