Cutting dyneema

[lowviz]

...//... if you can hold the line against something like a table. ...

Yeah, I think I now understand the problem: "Wrapped around the shaft."

I use a Dyneema blend for depth sounding, see pic. I just found out that it takes on a life of its own when wrapped around something and seized. Just tried it.

Spinning the tool so that the blade cuts in,
or spinning the tool like a lever around the prop axis?

IMHO, both.
Try to cut strategic pieces free if you can get the tool around them or just keep taking the fight out of the mess by spinning the tool around the prop axis.

 

[lowviz]

OK, one more implement of destruction. Have your client buy you both tools, the cutter and an Irwin 12LC locking pliers. See pic. Don't ask why mine is rusted. Grab the knot with the pliers and wrench it back and forth while favoring the reverse direction to loosen the mess.

 

[mrfixitchapman]

I have all Dyneema lines on my sailboat. The best thing that I have found is a ceramic blade knife. I bought a set from Amazon,
Amazon.com: Bamboo Handle Ceramic Knife Set - Premium Ceramic Kitchen Knives - Ultra Durable High Quality - Blades of 6" Chef's 5" Cleaver 4" Utility 3" Paring - With Covers: Kitchen & Dining

I place the rope on a plastic cutting board and swipe across while keeping pressure on the rope. Usually one slow, steady cut does the job, but I have had to saw the blade back and forth some times.

DC