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installation diagram

The diagram on the right illustrates the components associated with the selection and installation of all types of Prop Protector. Although the diagram shows one type of stern shaft bearing, the following notes apply equally to craft fitted with either P or A struts or brackets.


In most installations, the gap between the propeller hub and the shaft bearing is wide enough to allow the installation of a Prop Protector. This gap must be sufficiently wide to accomodate the cutter plus an additional gap of 6mm (1/4 inch) between the Protector and the bearing. Extra Large cutters need a gap of approximately 12mm (1/2 inch).


This extra gap is necessary to allow water to circulate to the shaft bearing for cooling and lubrication. It also allows for any end float on the prop shaft. If there is excessive end float due to gearbox end play or over-flexible engine mounts, this extra movement has to be provided for. The recommended gaps for all types of Prop Protector are shown in the specifications. If the gap on your shaft is inadequate, it can be increased by any of the following methods:


1. For adjustments of between 2mm (0.08 inch) and 5mm (0.2 inch), it may be possible to disconnect the prop shaft from the prop shaft coupling, move the shaft aft by the required amount and re-tighten the connection. If this method is used it is important to ensure that there is still suficient engagement between the shaft and coupling to maintain a secure connection under full power.


2. For larger adjustments, a coupling spacer or a flexible coupling may be fitted between the coupling and the gearbox flange.


We can now supply coupling spacers for most of the popular gearboxes 'off the shelf'. See order page for further details. We can also arrange for the supply of spacers for gearboxes not listed. Please allow three weeks for delivery and supply full details of your engine and gearbox.


Underwater Installation

One of the unique features of the Prop Protectors is that they can be installed with the vessel afloat.


However, the thread-locking compound supplied with each cutter to secure the fastenings is intended for use only with the vessel out of the water; the compound will not cure underwater.


Owners wishing to carry out underwater installation should not use the fastenings or the thread-locking compound supplied, but should order the special self-locking fastenings we supply for this purpose and which are described below:


For all Slide-On cutters from 19mm (3/4 inch) to 50mm (2 inch) diameter shafts a single set screw is required per cutter.

For all Clamp-On standard, medium and large cutters for shafts 19mm (3/4inch) to 62mm (2 1/2inch) diameter, one set screw and two cap screws are required per cutter.

For all Clamp-On extra large cutters for shafts 37mm (1 1/2 inches) to 100mm (4 inches) diameter, a similar but larger set of fastenings is required per cutter.

These fastenings have been fitted with a plastic insert which serves as a self-locking mechanism and can be re-used up to five times.



Other factors to consider when selecting the correct Prop Protector for your vessel

1. The diameter of the cutter blade must be larger than the diameter of the propeller hub and of the bearing housing in the strut of stern tube. If the blade is shielded by either of these, it cannot cut entangled line. The overlap of the blade should be at least 6mm (1/4 inch).

cutter kit


2. The minimum gap specified for each type and size of cutter should be of UNTAPERED shaft. If all or part of the gap consists of tapered shaft, a cutter for a slightly smaller shaft diameter should be selected so that it can then be machined to match the taper of the shaft.


3. Prop Protectors may be installed with the vessel afloat. Owners wishing to carry out underwater installation should not use the standard fastenings normally supplied but should order the special, self-locking fastenings available for this purpose.


All Prop Protectors are supplied with A4 Stainless steel fastenings, allen keys, thread locking fluid and installation instructions. Both types are easy to install. For instance, the Clamp-On cutters can be installed in ten minutes


Typical Prop Protector Kit

Shown on the right is a typical Prop Protector kit. Kit includes Prop Protector, allen screws, allen keys, locking fluid, safety warning labels and full fitting instructions.