H4 Marine Limited innovation in technology

Technical generic name: Shearing action cutter

Cutting action: rotating blades shear against fixed blade.

Common generic name: scissor cutter.

Brand names: Spurs - Gator - Stripper

Blades continuously shear against each other.

Fitting is relatively straight forwards.

Stripper is available for sail drives.

The cutting action is complex and the cutter will require replacement of bearings and moving parts as routine maintenance, these will also be prematurely worn by sand and silt.

A larger gap is required than other types.

If they encounter debris that can not be cut the loads exerted on the scissor blades will induce a shock load and can damage the cutter or cause the striker plate to shear off.

They will effect the water flow to the prop, this is of particular concern on faster vessels.

They can give rise to noise and vibration.

They can present a hazard if you do need to dive to clear debris should you encounter a large net.

Metal used is in most cases 316l which is effected by crevice corrossion, so not ideal for long term salt water emmersion.

Technical generic name: circular knife cutter

Rotating knife cuts debris that is fixed relative to the shaft and is drawn across blade.

Common generic name: disc cutter

Brands: Prop protector - R&D - PLastimo - Shaft shark

Easy to install

takes very little space

no moving parts = little maintenance

Blade rotates with the shaft, so debris caught by and rotating with the prop will not see a moving blade.

Causes disruption to clean water flow, which can be an issue on faster vessels

Metal used is in most cases 316l which is effected by crevice corrossion, so not ideal for long term salt water emmersion.

Not suitablle for legs or saildrives

Technical generic name: shaver cutter

Cutting action: shaves or peels away debris that is pressed against the fixed blade, similar to a machining tool.

Common generic name: (UK) H4 cutter!

Brands: quicKutter

No moving parts = very little maintenance

Almost zero effect on water flow. In five years no reported loss of performance.

Proven on commercial craft

Extremely robust, even a damaged blade will still cut.

Unique blade and blade holder alloy is resistant to crevice corrossion so is suitable for long term salt water immersion.

Requires removal of prop to fit.

Requires accurate measurements and machining of spool and hence fitting process is more involved than other types.

Not suitablle for legs or saildrives

Maritex advanced composites