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?

Currently we use some clear tubing in the loop to protect the rope from wear of the Tost tow ring. Not only does this allow the rope to bend sharply causing a weak point but it also seems to fill with dirt. This then manages to find its way to the sharp bend in the rope where it grinds away at the rope (poly) and precipitates a breaking point.
A steel (or other hard material) thimble in the loop would seem to eliminate this problem and look a lot more professional too.

Anyone out there do anything different or profess not use thimbles?

Bob 7U

If you wish to keep the rope at full strength, then appropriate thimble use is required (unless the object spliced to itself is suitable larg in radius.

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. Please get an appropriately rated thimble so that it doesn't flatten under the load, depriving the rope of the needed bend radius.

Also, when selecting thimbles note that there are sailmaker thimbles and open-ended thimbles. The sailmakers resist the crushing load far better, but they are closed and so can only to on something which is open-ended. So you'd need a shackle-- I'd recommend a soft shackle-- to go from a sailmakers thimble to a Tost ring.