There are many designs of cutters designed to sever ropes that may be picked up while motoring. These can be roughly categorised as those that cut the rope using a scissor type action, having a rotating and fixed blade, or those that rely only on a single, very sharp blade that extends circumferentially around the shaft. We have experience of both types.
Our original cutter was a Stripper that has a single blade attached to the shaft, astern of the P-bracket, and a fixed blade bolted to the P-bracket. The first time this was called into service was on a town quay in France, when one of our 14 mm warps fell into the water as I was manoeuvring to leave the quay. The warp was cut, fortunately only about 30 cm off the end, but the fixed part was ripped out of the P-bracket. Despite a search with mask and snorkel I could not find it. The fixing bolts supplied have quite coarse threads and the P-bracket bearing housing is thin, plus the P-bracket was elderly and showed signs of dezincification.
Not very long after this I replaced the P-bracket and took the opportunity to replace the failed fixed part of the stripper. This time I drilled and tapped through the P-bracket into the brass sleeve of the cutless bearing, before fitting the P-bracket to the boat, hopefully to increase the strength of the bolting and avoiding any possibility of damaging the shaft when doing the job in-situ.
However, within a very short time we picked up a 12 mm polypropylene rope in a bay in Corsica. Once again the rope was cut, leaving a short length wrapped around the prop that was easily cut off using that time-honoured tool, a bread knife. Unfortunately though, once again we had lost the fixed part of the cutter. Since those times it is now possible to buy a sleeve for attachment outside the P-bracket that apparently provides far greater strength and should avoid this costly replacement.
Having twice bought replacement fixed parts for the Stripper we decided that enough was enough and replaced it with a Proprotector. a simple device that consists of a single sharp blade extending right around the shaft astern of the P-bracket. This simple device performed quite well in the Yachting Monthly tests, only failing to cut copper wire.
In the 10 years or so that this was fitted we never suffered any problems with rope entanglement, although we are not aware that the device was ever asked to perform. Then on a calm, sunny day in Greece we were motoring south along the east side of Leros. I realised that although the engine revs had not changed in the slightest, our speed was declining rapidly. I put the gear into neutral, upon which the boat stopped and even appeared to be moving astern. Finding nothing wrong inside the boat I put on mask and snorkel to investigate in the water, finding that a length of 8 mm polypropylene rope, fixed to the seabed about 100 metres below us, was now wrapped around the propeller. I assume that there was at one time a buoy on the end of this rope, now long gone. The rope had wound itself around the shaft and the boss of our propeller, aft of the cutter which was rendered helpless.
It might have been possible to unwind the rope by running the engine in reverse but I was not very happy to do this while swimming alongside it. Fortunately conditions were not too bad with warm water, light wind and a swell of about half a metre. It was not difficult to cut the line, enabling us to motor to a nearby anchorage in Alinda, where I was able to cut and unwind the rope in perfect shelter. I was amazed to find that having removed it all its length was 10 metres!
