knots, splices, braids and plaits
This is a complex, challenging thread which forced me to do a fair amount of research in order to verify that my understanding of this important problem was not based on poorly remembered facts or preconceived notions. Here is a brief summary of my newly updated understanding of some of the key issues involved. Non-constrictor type knots such as the figure eight and the bowline, especially when tied "on a bight" as mentioned by the original poster, indeed appear to be the best knot choices to preserve dock line or anchor rode strength. These rather bulky knots keep the bending radius of the rope as large as possible (compared to the rope's own radius) and avoid severe pinching. The fact that this becomes easier to achieve a better ratio between rope diameter and bending radius if the line is relatively would seem to provide one of the main arguments for using "double braid" nylon (i.e. a nylon braid mantle over a nylon braid core). Since double braid has about 25 % higher breaking strength than 3-strand of the same diameter it may allow one to size down one or two steps. On top of that, double braid has higher chafe resistance and far less tendency to kink and form spontaneous knots when being paid out than 3-strand. Multi-plait nylon (8-strand) rope shares some of these desirable characteristics but provides only marginally higher strength compared with 3-strand. However, it is much easier to splice than double braid. The "solid braid" mentioned by the original poster falls into the same category with regard to handling and breaking strength as "multi-plait" but has lower stretch and is hard or impossible to splice according to several sources. The "low stretch" reputation of some nylon kernmantle braids derives from the fact that they have straight fiber instead of braided kerns (cores). Moreover, these types of braids are said to be very sensitive to bending and pinching. A special version of that type of braid, viz. with relatively short core fibers, is still being used in "dynamic" climbing ropes which are built to be discarded after one or more hard falls and are totally unsuitable as docklines or anchor rodes. Although a proper splice around a comparatively large thimble is generally recognized to produce less strength loss than a knot, this advantage can only be maintained if the other end of the dockline or anchor rode is tied off around a relatively large diameter bollard, cleat or samson post without any sharp bending or severe pinching. Moreover, any chocks, fairleads or toerails the line touches in between need to meet the same requirements. If this cannot be realized one might as well save oneself the trouble or cost of splicing docklines and just use proper knots and hitches on both ends. Have fun! Flying Dutchman
