Propeller Rope Cutter Test – Yacht Monthly
Back in 2015 the Yachting Monthly Magazine carried out a detailed test to compare propeller rope cutters on the market at the time. Despite several new entrants to the rope cutter space (including our very own HydroAxe rope cutter), the article is still one of the “go-to” propeller rope cutter test reports.
The testers at Yachting Monthly evaluated seven different propeller rope cutters including:-
- Spurs Marine Rope Cutter
- Ambassador Stripper
- Gator rope cutter
- Plastimo rope cutter
- R&D Marine cutter
- Prop Protector
- TW Norris Shaft Knife
They set up a test rig with an electric motor and a 40cm by 30cm (16in by 12in) fixed three-blade bronze prop to simulate a real life sailing situation, and then filmed the outcome through a clear window.
The testers tried several different types of rope to simulate the most common material encountered whilst out sailing. Three-strand polypropylene rope – 6mm, 12mm and 25mm diameter; three-strand and braided polyester – 15mm and 25mm; and three-strand 15mm nylon rope.
Several types of netting were also tested, from the finest monofilament, through 3mm nylon and up to 4mm polypropylene. The net was cut into 1m x 2m rectangles and fed into the prop.
Heavy-duty polytarp sheeting was next on the rig – being cut into 1m x 2m rectangles. 10mm2 copper cable was also put through the test rig, and the final test involved 1.5mm-diameter galvanised steel wire, both single strand and cable.
Different types of Rope Cutters on the test
There were several different types of rope cutter put through their paces on this propeller rope cutter test and it is useful to understand how they work when comparing the results.
Scissor Rope Cutters
A scissor rope cutter is a type of propeller rope cutter that uses two opposing blades that come together like scissors to cut through ropes and other debris that may become tangled around a boat’s propeller. They were the first type of rope cutter to hit the market and have been popular because they have such a positive cutting action.
Scissors are the only option for saildrives and the cutter consists of a rotating cutter clamped to the shaft (with two or more blades), plus a fixed cutter bolted to the P-bracket. As the prop rotates, any obstructions are drawn down into the scissor blades and shredded or cut.
Installation can be a little more complex than other rope cutters and will require periodic maintenance – every couple of years or so. Our HydroAxe Rope Cutter is a scissor rope cutter.
Disc Rope Cutters
A disc rope cutter consists of a thin stainless steel disc that has a sharp cerated edge. The disc is either split and clamped round the shaft or it is installed as one solid disc, which means the prop will need to be removed beforehand. Once the disc is set up it is held in place with a small grub screw.
A disc rope cutter operates in a very simple way – as the shaft spins, so does the disc. So as any rope or debris is pulled in towards the prop it passes over the the knife-edge of the disc which will gradually cut through it.
This rope cutter system is simple to install, offer minimal drag and generally a low cost solution. They can can be fitted to any type of shaft-drive boat. The big disadvantage however, is the lack of a positive cutting action – so discs can struggle to cut through weed and plastic sheeting.
Shaver Rope Cutters
Shaver rope cutter – used by US Navy and UK lifeboats
When the test was carried out, shaver rope cutters were fairly new to the market. They comprise of fixed blades that are mounted on a block that is attached to the P-bracket. A plastic spool or cylinder is then slid over the shaft and attached to the front boss of the prop, running under the cutter blades. Any rope or debris that come close is forced into the gap between the blades and the prop – and as the blade spins, the rope is gradually shaved.
The main advantage of the shaver rope cutter is the reduced load that is put on the yacht structure and transmission when the disc is cutting.
Outcomes from the 2015 Propeller Rope Cutter Test
The 2015 Rope Cutter Test highlighted that having a rope cutter installed on your yacht clearly brings safety benefits. And the testers were surprised how quickly the rope cutters cut through most of the debris when set up on the test rig.
The scissor type of rope cutters performed the best – and coped with the majority of the rope, netting and poly tarpaulins. During the test, the disc cutters sliced through the rope and netting, but struggled a little with the polytarps and weed.
HydroAxe Rope Cutter
The HydroAxe Rope Cutter has been designed and developed by Darglow and is a scissor slicing type cutter for Saildrive applications.
We make them here in the UK, and they are simple to fit. The advanced locking system used on the HydroAxe ensures that no modifications are needed to your propeller no matter what propeller type fitted! We spent significant time in development to ensure that the HydroAxe is compatible with as many low-drag and fixed props as possible.
HydroAxe compatible props:-
- FeatherStream propellers
- Flexofold propellers
- Kiwi propellers
- Bruntons Autoprop propellers
- Bruntons Varifold propellers
- Gori propellers
- Volvo folding propellers
- Fixed propellers and Max-Prop Classic models.
The HydroAxe is currently available for
- Yanmar SD20 / SD25 / SD31 / SD40 / SD50 / SD60 Saildrive
- Volvo Penta 120S / MS25 /130S /150S Saildrive models and
- Beta Seaprop 60 Saildrive models.
Don’t forget fitment is simple with no specialist tools needed for installation
Have we got a rope cutter for your yacht model?
We have supplied rope cutters for lots of different yachts. We keep a database of technical information on many of our installations along with feedback from our customers.
Check our full list of yachts we have supplied rope cutters for here.