This time of year, you see a lot of canoes and kayaks going down the road tied to the top of cars. Some of them not as smartly anchored as others.
One of the configurations that I see a lot is the "It's not going off the back" method. A quick look at google finds these two examples:
Is this method to transport your canoe safe or will it be likely to be lost while driving? What is wrong with this tie down method?
To answer your underlying idea, mounting a canoe on the roof of a regular car can easily be done safely - however you've chosen two poor examples.
First photo: not safe
There's no proper roof-bars. The type of foam pads used aren't suitable for anything bigger than a surf-board. Used like this they will also damage the car roof. I wouldn't ever consider the type of tail mount used.
Second photo: better - right idea but poorly executed.
Here we see the boat on proper roof-bars with good straps. However, the boat should be centred on these, even if this means sticking out more at the back.
Correct: Solid roof-bars (available for all normal cars), with the bars spaced out as much as possible and the boat centred on these - with good quality straps used to secure the boat to the bars. A rear light should be added where necessary.
Note: when the boat is centred, this prevents forward/back movement because the straps are either side of the middle/widest point.
Note2: both photos place a heavy emphasis on nose/tail strapping. In reality they add very little and should never be relied upon. They can help reduce bouncing but if the boat isn't secure without them, it won't be secure with them.
There is absolutely nothing wrong with it.
In a perfect world, the rear strop would be tided further midships to prevent the Kayak moving forward, however, in a pragmatic world, this is not needed.
The forward strop prevents the kayak lifting the roof rack off the car and wind forcing the kayak backwards. The forward and rear strop and prevents side winds twisting the kayak on the rack. Should the Kayak start to move, the driver can easily see and fix it, however this is not normally a problem as the correct attachment to the racks is not hard to achieve.
In an accident involving a sudden stop, the kayak might move forward until the rear strop comes tight - possible 2 or more meters. This is less than ideal, but the forces required before this happened would almost certainly render the car undriveable.
In both cases it would be better if the racks were further apart.
The auto in the top photo has a rack that is in the hitch receiver to support the rear of the canoe. With the strap holding the boat on the rack it appears very secure. The front looks to have only one strap, on the centerline of the car. I'd certainly prefer straps going to the sides of the front to assure the boat doesn't start to wobble on the roof from wind pressure. But this looks reasonable and the driver may well have used this setup enough to be secure with it.
The SUV, with the canoe tied front, back and to the rack and looks very secure. The main problem with both the front and back straps slanting to the back is that the boat may slip forward in an emergency stop. Proper tieing to the rack should prevent that.
