I just bought a stacker kayak rack that will be carrying 2 kayaks. I understand that a bow and stern tie-down is a good idea. My question is, do I tie down each boat separately to the bumpers (two spots per bumper), or do I form a “y” connection which would mean only one tie connection on each bumper, which is attached to the Y?
either
Many folks don’t use front tie downs on very short boats like most of today’s whitewater kayaks, because there is relatively little lifting force on the front when traveling at highway speeds.
With longer boats, front tie downs resist the lifting force and also help reduce the tendency of the stem of the boat to yaw in reaction to crosswinds and wind blast when passing, or being passed, by large trucks.
If you have long kayaks the most effective way to reduce the yaw tendency is to have two independent lines running from the sides of your bumper, or the sides of your hood, to the stem of each boat. This fixes the stem more effectively than a single line.
The front tie down also serves as a backup in case the strap or rope across the belly of the boat at the front rack fails, for some reason.
If you are carrying very short kayaks and choose not to use front tie downs I would consider using two independent straps across the boat at the front rack. Also, and particularly if your rack crossbars are positioned relatively close together, I would do something to make sure that the boat cannot move forward or back on the rack if your straps or lines loosen slightly. It is possible for the entire boat to go shooting off the rack onto the hood of the vehicle during a panic stop if that happens.
One way to do this is to use a strap or line a bit longer than needed to go around the boat. After securing the line to the rack, take the excess and bring it under and around the front rack and secure it to the front toggle or grab loop of the kayak. You can do the same with the line or strap securing the boat to the rear rack to prevent the kayak from working its way rearward.
two separate lines
Rather than rigging some y-shaped harness, I’d just use a separate bow and stern line for each boat. A V-shape to the same central tie-down, or an X-shape diagonally to opposite ends of the bumper is best with a stacker because it will keep the boats tight against the stacker.
bow tie down
We use bowlines even when carrying ww boats. Besides the added security, they offer the reassurance to visual confirmation that the boats aren’t moving around.