View Single Post
Old 10-13-2022, 10:18 AM   #18
rslifkin
Guru
 
City: Rochester, NY
Vessel Name: Hour Glass
Vessel Model: Chris Craft 381 Catalina
Join Date: Aug 2019
Posts: 7,552
Quote:
Originally Posted by Shrew View Post
I agree no short lines. It's about the lines ability to stretch. Typical double-braided nylon line can stretch up to 20% before it's tensile strength is impacted. So this is really only about 1.2" per foot.

But the other side of the coin is reducing slack. Too much slack and the line gets shock-loaded each time the boat accelerates, then reaches the limit of the line stretch.

This puts us into another paradox. On a fixed dock, how do I keep the boat from hitting the dock or pilings during high tide with storm surge, but also keep the boat from hanging on the lines at extreme lows or when storm surge blows the water out instead of in?
Long lines help with that last scenario as well. If everything is a long spring line at a shallow angle, they can absorb more height change while still keeping the boat held in place (as the height change causes less angle change on a longer line, so less slack is needed).

Stretch-wise, you don't want to load a line above about 20% of breaking strength. At 20% load, most 3 strand, 8, or 12 plait nylon lines will stretch 10 - 12%. Double braid nylon will typically stretch about 5 - 6% at the same load. The longer the line, the more stretch you get, so the "no short lines" rule is more important if using double braid.
rslifkin is online now   Reply With Quote