Stainless Steel Karabiner

[thinwater]

• Main Axis Load: 60kN

That's a bit over 6 tons. You could pick up three of your boats without overloading it. I'm no expert on climbing gear, but I'd expect the breaking strain to be several (10?) times that. If that lets go, your backup line won't stand a chance!

The rated load is the breaking strength. The working load of climbing gear is not defined as such.

 

[thinwater]

... 2000kg boat can jerk an anchor chain and generate 60kN force. Normally catenary on chain acts as snubber, but in very high wind the chain is taut so no catenary thus rope snubbers needed or chain and cleats may fail. ...

Nope, seriously doubt that. More than the wind load, which is less than 500 pounds in the worst storm.

ABYC says 1500-pound WLL for 25 feet (the OP is 23 trailer boat) for a perminant mooring, or about 7500-pound BS. That's 33 KN, and there is a healthy safety factor in the standard.

 

[davidpbo]

Unfortunately the first link I posted which was 60KN was to a non stainless Karabiner. The stainless one I bought is 20KN I will take care when it used.