I'm noticing a lot of interesting ideas on this thread. Let me tie some of them together. The knot on your winch hook is not likely to be your most likely point of failure with your winch due to loading if tied right. With a synthetic line, it's more likely the point of failure due to friction at that point is from induced heat. The ratchet gear is actually your most likely point of failure provided your line is in good condition. Alternatively, the field windings on your electric winch motor is where you're going to see your failure when your winch is on. When it's off, it's the ratchet gear again. Nylon lines are less susceptible to uV damage than polyester lines or mixed blend polyester lines are, but they will still suffer from uV damage, a little bit. Keep them out of the sun as much as possible anyway. The stiffness of your line determines whether a bowline will spring loose on you, or not. For most marine grade lines this won't be a problem. For ropes used in logging work it is. Double figure eights do have better protection against loosening. Their biggest advantage, however, is that they hold more of their strength than other knots when under extreme load.
But none of this tells you your real problem when you're attaching your winch hook to your winch line. In addition to damage from extreme loading, synthetic lines are also damaged from heat due to friction. Continued loading will cause the line to become damaged from the heat of friction if there's play against the eye of the winch. That heat will cause the line to melt and weaken. Whenever a dynamic load is placed onto your hook and line, if there is any play between the hook and the line, that play will translate into friction and heat. That heat will damage your line. The most important thing you can do is to take all of the play out of the knot between your winch line and your hook. To do this, neither a bowline nor a double figure eight is all that helpful. A double lashing is better. Run two loops through the eye in your hook. Take the free end and bring it through both loops. Then to finish off the knot pull the hook through one of the loops to tighten the loop down down around the running end of the knot. The other thing this does is that it has two windings holding your hook in place. Normally, with a line through a pulley, you're not increasing the holding strength of your line by increasing the loops. You're reducing the amount of work involved in moving the line, but the tension on the line is uniform throughout. However, when you have a line over a bight, that friction holding the line in place means that you are also increasing the amount of load that can be handled for the total number of loops on the bight. This is why lashings work, and so in this instance multiple windings are better.
You should never rely on your winch line to hold your boat in place while trailering. Again, the single most common point of failure is the ratchet gear. They're only rated for about 300 lbs. That's what a good marine line is rated for. A climbing line might be rated for static loads of over 500 lbs, but they're generally too stiff for marine applications. Using a steel cable comes with some serious drawbacks. Having a cable with a static load rating of 800 - 1,200 lbs does you no good if your ratchet gear is only rated for 300 lbs. Plus, there are some other safety concerns with using a steel cable. If you do have a cable failure or cable separation, that cable is going to whip back and really hurt someone, and that someone is probably not going to be wearing any protective clothing when it happens, either. I wouldn't recommend using a steel cable for that very reason. And once again, your winch cable is not what is supposed to be holding your boat on the trailer when you're road bound. It's only there to get your boat onto the trailer. You want your safety line at the bow roller to be under tension when you're trailering, and you want to take the tension out of your winch line to prevent damage to both your ratchet gear and your winch line. This is where having multiple loops of your safety line through your bow eye is really important. But that is still not the single thing that should be holding your boat onto your trailer. Your boat may very well weigh more than 2,500 lbs, but these lines are not handling that load, unless you're rappelling your boat straight down the side of a cliff. Also, for most recreational boats, the fiberglass holding your bow eye in place can't take much of a load, so steel cable is overkill. What you're really concerned about is the load on your safety line at the bow eye. The load on your lines is the friction load for moving the boat forwards and backwards on its bunks or rollers while your road bound. This is why tie down straps at the stern are so important. When pulled down tight, they are increasing the friction of those contacts. They're not actually holding anything in place. They're just there to increase friction - and to prevent movement up off the contact points from bouncing. Similarly, a bow bridle that goes over the deck and around the bow cleats and then under the trailer tongue is also a good idea for increasing the friction of the boat against its contact points on the trailer. All these things increase the friction of your boat on its trailer, to reduce the movement and the dynamic loading of your boat against its bow nose secure point. There should be no means for movement at that point. That is what will keep your boat safe when you're trailering it, and that is the job of your safety line - not your winch line.
Tim Whitmore, former LT USCG
Alumni, U.S. Naval Academy
https://www.facebook.com/tim.whitmore.399
