The day I bought my first kayak, I had to make several stops on the way home and I realized there was nothing to stop a miscreant from taking it off the roof of my Explorer. After my first paddle, I immediately set out to make it theft resistant.
I had an idea was that a vinyl clad steel clad cable would be ideal for securing the kayak. This left me with two questions to answer: How do I connect the cable to the kayak, and how to I secure the cable to something?
I looked my kayak over, and then took a look at other models and decided that all kayaks are divided into two groups: those with something permanent to connect the cable to and those without.
My first kayak was a Perception Swifty; the seat was molded out of the same piece of plastic that the hull was. A cable wrapped around the seat support in that type vessel (or through the hull, as would be the case with a sit-on-top) cannot be removed without tearing up the boat or cutting the cable. If you have ever tried it, you know how hard that is.
The other kind of kayak or canoe is manufactured with no way to connect the cable permanently. I later purchased a second kayak, an Old Town Loon, and in that vessel the seat mounts to an aluminum rail that is bolted through the plastic hull. Anyone with pliers and a screwdriver can easily unbolt the seat and remove the security cable, so that is not the way we want to approach that situation.
Forget cabling the kayak for a moment. What can we connect the cable to that will hold the kayak securely and keep if from being stolen? Very simply, your vehicle. And we will do it by closing the two ends of the cable in one of the vehicle's doors. Provided there is something that keeps the cable from being pulled through the door opening, the only way the thief will get the cable out is to break the glass and unlock the door. A thief is most likely not planning on making a lot of noise or attracting attention, and as an opportunist, may not be equipped with anything to break the glass with.
Let's begin our Instructable and I will tell you why we do what we do as we go.
First, buy some vinyl clad aircraft cable. You can get this at your neighborhood hardware store. I would get the 1/8" size; it has a working load of about 340 pounds, so nobody's going to break it. With the vinyl coating, it is about 3/16" in diameter, and will easily close in a car door without hurting anything. You will need about fifteen feet; if you buy more of it, you can get a firsthand illustration of just how hard it is to cut.
Second, get two 3/4" PVC pipecaps and some JB Weld. Drill two holes near the sides of the end of each cap, just slightly bigger than the cable. Take one end of the cable and run in in to the open end of a cap, make a loop, and run it back through the second hole. Adjust the cable end so it is not protruding past the end of the cap. Do the same for the other cap, fill them both with JB Weld and let them cure. What you then have is a piece of cable with a knob on each end that will keep somebody from pulling it through the door opening.
Actually, you are done with the cable part of the Instructable unless you want to dip the ends in Plasti Dip rubber tool handle coating to make it look more professional.
Say for the sake of argument that you have a craft like my Swifty. Make it fast to the roof of your vehicle, or throw it in the bed of your pickup, then run one end of the security cable through the seat mount and out. Close both loose ends in the vehicles door and lock it. Your Swifty will be right there when you come back. Couldn't be any simpler.
If you have the other type of kayak, there is a chance you already have a metal security connector on your craft. This may take the shape of a U with both ends connected to the deck, or else a flat plate connected over a depression in the deck. If you don't have one like that, you need to visit your local boating supply store and buy a stainless steel pad eye, a couple of stainless Phillips-head bolts and nylon insert nuts, and a pair of stainless washers. Mount the pad eye on the rear deck near the cockpit, tighten the bolts, and strip the bolt head by drilling it out. ( We don't want somebody with a screwdriver and a pair of pliers removing the nuts.)
Using the pad eye involves a slight trick, since obviously you won't be able to get the PVC cap through it. All you have to do is make a hairpin in the cable about a foot from the end and pass that through the pad eye. Then, pass the other end through the hairpin, pull it tight, and close it in the door.
Now you can take your kayak on vacation with you, or on a weekend paddle, and worry less about it going home with somebody else.
NOTE: I have had comments that perhaps someone could cut the cable and steal the boat. True, they could. But I assume that every potential thief isn't walking down the street with bolt cutters, or even wire cutters. Even if they are, cutting aircraft cable is tough as a rule and it takes time, which is something they will likely shy away from. Try it yourself with a pair of wire cutters and see how hard it is. Lastly, you can make the cable size a little larger to make it harder to cut, if you want.
I can't guarantee it is a perfect solution but so far, nobody has ever told me they made one and had their kayak stolen.