Right up front let me say that the foam cradles that slip on the Yakima or Tule bars are inexpensive, easy, and effective. What I describe here is a relatively big effort, but custom cradles do provide the ability to get a bigger surface contact on the hull, mount it at whatever angle you desire, and allows for cantilever of the boat out over the front of the vehicle when you’re towing a trailer and don’t have any space at the rear end. In my particular case, my topper already had Thule mounts in place, so I did not take the option to put mounts forward on the roof of the cab. This puts my forward cradles very near the middle of the kayaks.
I elected to mount my kayaks on their sides. This will allow for an eventual third boat in the middle. It also allows one to use the coaming as a lifting/grip area that is balanced for a one-person load and unload. Once you establish the orientation of the boats and the location of the bars (which establishes where the cradles will grip the hulls), you can begin taking measurements for the cradle parts.
The first thing you discover is that there are no level surfaces or 90 degree angles. This requires some mock up and trial fits to get a good fit. The most important first step is to anchor the hull in the attitude you want, using temporary braces, tape, and foam blocks. I wanted the hull to be level in order to reduce the potential aerodynamic lift across it (the cross section of the hull on its side is very much shaped like a wing) in order to keep it from wanting to pitch up at 75 mph.
Here’s a couple of photos that show the complexity of the measurements and fit for these Pygmy kayaks. One interesting thing to note is that the Tern and Coho turned out to have almost identical angles at the outer panel, e.g., between the bottom and top hull panel (on the Tern there’s just two hull panels, of course).
The final cradles are ready to fiberglass. They don’t sit flat due the stainless steel bolts that project down and provide a way to secure the attaching plates that go under the rack bars. The bolts are glued into the bottom block using the same resin that is used to apply the glass. The insides of the cradles are also coated with resin for waterproofing. The access hole in the one rear cradle is to allow access to the top of the bolts, in case the resin fails. It turns out that wasn’t necessary.
Note that because the kayaks are cradled on their sides, the Tern cradles always go on the driver’s side and the Coho cradles are always on the passenger side. This is basically because the aft cradles have a lot of slope in their bottom surface.
This view of the front cradle for the Coho shows the attachment plate and the strap the goes around the cradle and kayak. The straps go under the cradle and above the bar. The front strap is restrained by a friction pawl latch. The rear strap uses a locking ratchet, which is physically bigger, but fits nicely on the back side of the cradle. You can get to this easily from the back bumper, but wouldn’t work on the front cradles, since the latch keeper has to be mounted on the smaller face of the outside arm–you can’t easily get to the back of the front cradles. Note that the strap is screwed to the cradle, both on the face and on the back support.
The resin was colored using the same technique as the comings. Old wetsuit material was glued to the inside faces to protect the kayak varnish. There’s also a long rectangle of neoprene in the underside of the cradle and on top of the Thule bar to allow some compressive friction to hold the cradle in place.
It would have been helpful if I had designed the bottom of the cradles to more easily fit over the Thule upright supports, which would allow the kayaks to be loaded further outboard. Lifting them up and then a foot in over the topper is a bit harder than necessary.