I'm taking the liberty of posting prop shaft rope cutter test results from a comparison test conducted by Motor Boat Monthly, a UK magazine. The results I've copied were posted to the T&T list by Roger Bingham, but I thought people on this forum who don't get T&T might be interested. The results do not recommend brands so much as cutter types and configurations. However the video shows which brands were used.
Another T&T poster who is a diver pointed out that all of the test materials were fed into the prop from the direction of what would have been the bow of the boat. He stated that in his experience diving on boats to disentangle stuff from props, line cutters rarely work if a boat backs into a line because the line encounters the prop and wraps around it before it gets to the cutter.
Here is the bulk of Roger's post:
The testing rig was a reversible electric motor driving a standard shaft &
prop with standard P bracket.
Too see which brands were tested and the visual results of the tests see the
<pre>Three strand polypropylene in 8mm, 12mm & 25mm dia
Three strand and braided polyester in 15mm & 25mm dia
Three strand nylon in 15mm dia
Netting in monofilament, 3mm nylon and 4mm polypropylene (1m x 2m rectangle)
Heavy duty polytarp sheeting in 1m x 2m rectangles
Copper cable 10sq mm
Galvanised steel wire 1.5mm dia
The testers concluded that any rope cutter will bring a definite safety
All the cutters tested quickly cut through most of the debris ie ropes, nets
and copper & steel wire.
The scissor types had the edge coping with everything including polytarp and
The disc cutters were good but were sometimes defeated by the polytarp and
cable. These cutters could potentially have the same problem with weed on a
The clamp-on disc cutters are much easier to fit.
The R&D cutter benefits from its tapered leading edge which shrouds the
Scissor types are more expensive.</pre>Roger Bingham
-- Edited by Marin at 18:21, 2009-01-17