Monday 15 May 2023

Exploding Propeller Rope Cutter

An expensive day out. Just how did a plastic shopping bag cause the destruction of $800.00 rope cutter designed to chop through large ropes.

While all the advertising lets you know how good these are at chopping large rope, it was the $0.001 plastic bag that brought it undone. 

We seem to have a very good idea how it was destroyed, and it could happen to any choppy choppy spinney spinney moving blade style rope cutter. When we pulled the boat out of the water for annual maintenance we found the blade broken off our very expensive rope cutter. On further examination something blue was in the bearing area and could be seen in the hole left where the blade had broken free from. As it turned out, this blue material was what we now believe was the remains of a shopping bag. There was a couple of metres of it and it took some time unwinding to get it free of the shaft, we could have cut it but where’s the fun in that. We and others we have talked to all seem to come to the same conclusion. The bag material was fine enough to fit between the blades as they rotated and one blade caught the bag and it was drawn into the fine gap between the rotating blades and filled the bearing area until enough plastic was wound in and not being able to compress any more caused the case to break off.

The old rope cutter in happier days almost ready to go back in the water

Before returning the boat to the water we changed style of rope cutter, while we believe the choppy choppy spinney blade rope cutter unit was OK for rope, we had seen enough plastic in the water to feel we would likely be throwing good money away if we replaced it with the same type. Besides it was a bit too expensive for our budget if we had to pay postage then get it through customs.

The new type rope cutter we fitted, simple shaft driven rope cutter, no choppy choppy moving parts, and no bearings to replace annually, and as long as you sharpen it when out of the water it can cut through thick ropes in the blink of the eye. 

All ready to go, if using this type of rope cutter you need to make sure that the diameter of the propeller hub isn't so big that it stops the blade from being able to get purchase to cut through the tangled rope. 

I don't know if it was fate or not but our maiden voyage after we went back into the water after fitting the new rope cutter we ran over a partly submerged fishing float and line. The 25 mm (1”) rope cut through so quickly we didn’t even notice a change in the pitch of the engine. We do know it was 25mm because we heard the float bounce under the boat and we turned around and went back to pick it up.

Rope we picked up after the rope cutter did its job.

We travelled through Asia for a couple of years and found it was a very important safety device, but I don't think all submerged, or floating ropes and plastic bags are only found in Asia, where ever you are it could be worthwhile getting a rope cutter put on.

Our friends boat prop, this was picked up when at anchor and got wrapped up on the prop when they tried to pick up the anchor in the middle of the night when a storm was rolling in. They didn't have any type of rope cutter fitted, and this mess didn't allow them to get under way.

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