PROP PROTECTOR® 
A simple shaft driven rope and weed cutter which is easy to install and maintain. It is a circular, razor sharp knife fixed to he propeller shaft. It revolves with the shaft and instantly cuts any rope or weed picked up by the propeller

The width is 0.67" (17mm). A gap of 0.9" (23mm) is sufficient; this includes 1/4" (6mm) of space for water to circulate to the shaft bearing. It is clamped onto the shaft by two Allen screws and is also fixed by a set screw that locates into a small drill dimple made in the shaft. This type is available for shafts of 3/4" dia. up to 1 5/8" and 20mm to 40mm.

The Clamp-On Medium
Manufactured and fitted as the Standard, the width is the same, the only difference is the blade diameter that is 4.13" (105mm). This type is available for shafts of 1 3/4" dia. & 2" and 45mm & 50mm.

The Clamp-On Large
Manufactured and fitted as above, these large cutters have a width of 0.87" (22mm). A gap of 1.26" (32mm) is sufficient; this includes 0.39" (10mm) of space for water to circulate to the shaft bearing. See chart for size range.

The Clamp-On Extra Large
For vessels that are built with large struts or stern bearings. They are fitted in the same way as other Clamp-On units and have a width of 1.18" (30mm). A gap of 1.65" (42 mm) is sufficient; this includes 0.47" (12mm) of space for water to circulate to the shaft bearing.

Cutters in the range 2 3/4" to 4" & 65mm to 100mm are for use on large vessels such as trawlers, fishing boats, harbor patrol boats, luxury yachts and cruisers. These cutters have a width of 1.3" (33mm). Not all cutters in this range are held in stock.

Diagrams

The diagrams illustrate the two basic designs in which Prop Protectors are available, the Slide-On and the Clamp-On.

   

Test Results

          

What We Tested

In the May 1, 1992 issue, we examined two propeller protectors called Spurs and The Stripper. Both of those worked like shears, with a rotary and a stationary blade that will quickly cut any line that gets between them. Spurs is still around, and doing well; the Stripper, as far as we can tell, is no longer being imported. The Prop Protector, a much more recent import from England, is an even simpler device. It consists simply of a circular blade that is fitted around the propeller shaft between the propeller and the support strut or bearing and rotates with the shaft. It's all-stainless, of course.

We received a clamp-on version of the Prop Protector to test; there are also a couple of slide-on versions that can be installed only with the prop off. It came with three pages of instructions which were quite clear and easy to follow.

What We Found

The Prop Protector went on easily and fit quite well. The manufacturer even furnishes the Allen wrenches needed to tighten all screws and a small vial of thread locking compound - a nice touch. We set the prop at 450 rpm and tossed lengths of line into it.

We started with 1/4" polypropylene and worked up to 1/2" nylon. Once the line got wrapped around the Prop and the simulated strut, the Prop Protector cut it quite easily. There was no noticeable stall or stress in the operation of the motor as the line wound up. Even when we turned the set-up by hand, we could cut 1/2" line with very little effort…once it was firmly caught.

Although the Prop Protector doesn't look nearly as vicious about cutting up line as the Spurs, it still works quite well. While the rotary cutter of the Spurs will cut line as soon as it gets within reach, the Prop Protector requires the line to get a wrap on the prop and on the strut (or around the shaft) so that it is pulled tight over the sharp edge of the blade. In our tests, the Prop Protector worked well both in set-ups where an outboard cutlass bearing is present, and in those that use only an inboard bearing and a short shaft.

familiar American ("grub" screws, for example, are what we call set screws). The Clamp-On version is convenient in that you don't have to pull the propeller to install it, a considerable savings in time, effort and expense.

Conclusions

The Prop Protector should do a good job protecting your prop and drive shaft from damage from stray line. The version we tested installed easily and fit well. It's no-moving-parts, no-contacting-parts design should let it last indefinitely and not require any maintenance. It won't cut wire as will the Spurs product, but we don't think that's a major concern for most boat owners.

It has the disadvantage that installation leaves you with what's essentially a 3" diameter circular razor blade situated just forward of your propeller - divers beware! The Prop Protector comes with a protective rubber "tyre" (English, you know) around the sharp edge. The instructions direct you to leave it in place until the installation is complete. This is a good idea because the blade is very sharp. We also would recommend saving the tyre in case you have to work on the prop or cutter.

With simplicity comes economy: The Prop Protector costs significantly less than the Spurs product. For a prop on a 1" shaft, for example, Spurs would cost about $275-$325, depending on the specific configuration. A Slide-On Slim-Fit Prop Protector (try saying that fast three times) in that size lists for $165, with the Slide-On Standard and Clamp-On Standard listing for $187 and $199 respectively. Prop Protectors are available for shafts from 3/4" to 2-1/2". (Prop Protector, Yachting Services, 1-800-618-6748.)

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These comments are extracted from the evaluation carried out jointly by "PRACTICAL SAILOR" and "POWERBOAT REPORTS" and published in Vol. 22, Number 10 dated May 15th, 1996 of the former and in Vol. 9, number 4 dated April 1996 of the latter.