Is there a certain pound strength a bow/stern tie down rope needs to be? If not, is 550 pound (mil spec) paracord stupid to rely on? Those would be in addition to two heavy duty utility straps over a 12’ kayak on a saris rack.
No hard facts
from me, but imagine if your rack failed and your boats and rack were flapping in the breeze at 80mph.
How strong would that bow line need to be?
Into the valley of death rode Jsaults
This is going to be a long and argumentative thread.
Personally I use 5/16" braided polyester. Do not know the breaking strength, but most folks seem to believe that 1/4" is the minimum size. Restraining a loose kayak requires less working strength than a flying canoe would.
most folks use a slightly heavier line just because it's easier to work with. Nylon will shrink and stretch with water exposure.
It's probably more important that whatever line you use that you get proficient in tying and untying and that it can NEVER get lose and catch under the tire. And that goes for webbing straps.
I've heard of more than one light weight racer broken in half, roof/rack crushed from a caught bow line under the tire. My experience was tieing lumber on a roof rack and driving 3' with a loose strap in the lumber yard. It got under the rear tire and pulled the Yakima tower back 6" on the gutter. All at .5mph.
500 pounds is plenty strong, but…
your tie-downs probably aren’t nearly that strong.
What knots are you using? Even a good knot will cut the breaking strength of a rope by 40 to 50%. Age, UV exposure and abrasion all cut the strength further.
So, your down to maybe 200 pounds. Which is still probably pleanty strong.
Nylon has some properties that are less than desireable for rope. It is slippery, so many knots don’t hold well. It tends to get longer when wet, so if you tie dry, and hid a rain storm, it will loosen, or of you tie wet and it dries out, it tightens.
Also, as pointed out earlier, small diameter cord is more difficult to untie than larger rope.
Webbing Strap tiedown kits rock
Easily worth the money.
* edit *
I'm on the road in 5 minutes easy. No knots to fuddle with, oh these arthritic fingers. Re-tightening is fast and easy. Never have to loop and through and pull and play.
I have used para cord
and it is a PIA to use. get some webstraps, with buckles, fast, easy, secure.
Dosen’t really matter
IMHO bow and stern lines are a bckup system and in all likelyhood will never actually come into play.
I’m such a rebel, I don’t use any
My vote is one of confidence. If Thule sells them, you can be sure that their risk management people asked many questions before they started marketing them.
I have been using these for several years as bow/stern tie-downs on a 17’-10" touring kayak. I bought mine at Lowes, and replaced the open “S” hooks with small marine SS snaplinks. They are the same as Thules, but I didn’t like the open design of the OEM hooks.
I am comfortable with the strength (rated at 250# WORKING LOAD) and the convenience of easily loostening and re-tightening the rear rope when I have to access my car’s rear hatch.
I will replace the ropes this year (getting fuzzy) but other than that, the mechanism still works flawlessly.