Rogan,
In general, I would always recommend getting your spring
lines out first. In fact, I'll go so far as to say that you should have at least one spring
line on the dock before you run any breast or head/stern
lines-always. A spring
line can, quite easily, become a breast
line, or even end up a stern
line. But a head
line or a breast
line will little serve you when you really need a spring
line to work against. The reason I say always is that nature is fickle. If your engine control is going to fail in the ahead position, is it going to fail during the hour trip up river, or is it going to fail in the five seconds before you need to move it to astern to prevent ramming M/V Legal Beagle? There is nothing like a spring
line for controlling the vessel alongside. And, as Val says, you should leave them rigged at all times when alongside. In a situation where excessive strain is placed on your
lines, ie...collision, large surge, tide/current, the breast
lines will always part first. Your springs and head/stern will part last, and prevent you fro doing the severe damage more likely to result from running ahead or astern. The suggestion on polypropylene is a good one as it floats in salt water, but will not take the strain of other synthetics.