On 12/16/20 8:11 PM, Kenn Sebesta wrote:
On Wednesday, December 16, 2020 at 12:31:34 PM UTC-5, Bob Hills wrote:
What is the consensus of opinion of using steel thimbles on aero tow ropes?
Sailors care lots about long-term rope survival, so this is a subject of keen interest and experience. https://www.practical-sailor.com/sai...plice-thimbles goes into great detail on the various thimbles and ropes. Drew Frye, the author, is one of the most rigorous testers out there, writing for Practical Sailor, one of the most rigorous general sailing publications.

Note that the lowest D:d ratio is 1:1, and that's only for certain types of rope. However, I know of no rope used which is as small as the Tost tow ring so a thimble is almost certainly a very good idea if you want the rope to perform as rated.


The back end of a tow rope is a strange use case. There is a lot of
dynamic loading, a maximum acceptable rope strength, and flailing seems
more of a wear contributer than loading. Also a flailing rope end can
hurt things. I only have experience on grass, but a hard runway should
bring another set of issues?


The thing that looks safest to my eye is what is usually done. Hollow
braid Polyprop chinese finger grip eye splice, chafe protection with a
piece of clear tubing, and a bit of electrical tape to keep it in place.
A possible improvement is to taper the clear plastic tubing in the
inside of the Vee where it usually wears first, but checking the splice
and freshening the nip when it gets frizzy seems more important.

The practical sailor says hollow braid lays flat in the load bearing
point and that would make the diameter of the big ring look really big
compared to the rope already. A metal thimble has a lot of relatively
sharp edges and these can cut the rope unless you can keep the splice
tight enough to keep the thimble in just the right spot. The article
suggests this is difficult and using a webbing chafe guard which might
be better in a situation where there is no inspection?

With occasional inspection has anybody seen a splice loop fail? It
doesn't happen often, but I've seen the rope fail just ahead of the
splice where the single rope goes into the finger grip. Things usually
look fresh at the tow plane end which leads me to think that flailing is
the major issue.