Q&A: Propeller Shaft Rope Cutters

Question: Do you have a rope cutter? I ask because we are thinking of fitting an Ambassador Stripper (stainless) to a new build alloy [aluminum] yacht with an alloy sterntube, and we wonder if it is possible to get the two to live happily together.

Answer: Some twenty years ago we picked up a ball of netting at sea on a passage from Bermuda. When we got to Nova Scotia, unaware of our new underwater decoration, we started the engine and put it in gear. The result was a bent shaft and strut that required having the boat hauled twice before we finally got things sorted out. As I recall, the total cost was in excess of US$5000, making the price of the cutters we installed the next year look like a very good deal.

That was on a previous boat. One of the first things we did in 1992 when we bought this Morgan’s Cloud was to install a set of Spurs cutters. Since then they have saved us from being disabled by a rope around the propeller at least a dozen times. Although even the Spurs could not clear the running gear when we picked up the whole cod-end of a net, some years ago .

Bottom line, there is a lot of rope and netting floating around the ocean and so we strongly recommend line cutters, particularly since getting disabled at the wrong moment, say entering a harbour situated on a lee shore, could even cost you your boat.

We have no experience with the Ambassador Stripper but we can tell you that any cutter you install on an aluminum boat should not compromise the isolation of the stainless steel shaft from the hull. The Spurs cutters are great in this regard since they have small plastic bumpers and plastic bearings that isolate the spinning part on the shaft from the fixed part that attaches to the strut or stern tube.

Does anyone have any experience with the Ambassador Stripper or any other thoughts on line cutters? If so, please leave a comment.

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Meet the Author


John was born and brought up in Bermuda and started sailing as a child, racing locally and offshore before turning to cruising. He has sailed over 100,000 miles, most of it on his McCurdy & Rhodes 56, Morgan's Cloud, including eight ocean races to Bermuda, culminating in winning his class twice in the Newport Bermuda Race. He has skippered a series of voyages in the North Atlantic, the majority of which have been to the high latitudes. John has been helping others go voyaging by sharing his experience for twenty years, first in yachting magazines and, for the last 12 years, as co-editor/publisher of AAC.

16 comments… add one
  • richard Jul 7, 2010, 7:42 am

    I put Spurs on my Jeanneau 34 and upon mounting them I was surprised to find they were complete with their own set of tiny anodes that I made a mental note to inspect periodically…not something I had foreseen, but the apparatus looked so good and seemed so sturdy that I wasn’t unhappy…Unfortunately the anodes lasted only a few months but I wasn’t about to haul out just to replace them…then about a year later when I did haul out I was disappointed to see that half of the apparatus was totally missing rendering the apparatus totally useless. I don’t know how long this had been the case although I did succeed in replacing the missing part(s) after communicating with the mfr…So at the end of the day I found Spurs is one more regular maintenance item to schedule when my original perception was this would not be necessary…bummer!

  • Colin Speedie Jul 8, 2010, 8:58 am

    We bought one of the simple French disc types with a serrated edge this spring, but sadly didn’t have time to fit it due to a chaotic haul out/relaunch schedule that we found ourselves stuck with. We had one on our previous boat for nearly ten years, and on the two occasions we needed it (that we know of) it did its job perfectly.

    These are very basic, but have the advantage that they are easy to fit, relatively inexpensive and shouldn’t interfere with the isolation of the shaft.

  • Alan Teale Jul 8, 2010, 10:13 am

    I comment as the person posing the original question to John.

    Having discussed this with a number of folk, to whom I am very grateful for advice, I am inclined to go the way Colin suggests, i.e., to fit a simple disc cutter. In addition to the fact that this type does not introduce another stainless to alloy fitting problem, it also avoids the potential for damage to the sterntube due to the torsional loads that could be exerted on the fixed part of a scissor type (e.g., Spurs and Stripper) when faced with something very tough to cut.

    For those who may be interested there is a reasonable overview of a selection of cutters in Yachting Monthly, April 2009.

    • Neil Young Jan 17, 2011, 12:21 pm

      In response to mounting on an Al bearing carrier we have one image here http://www.h4marine.com/Images/Al%20strut%20and%20cutter.jpg

      This cutter (quicKutter) is very different in the way it operates from the disc or scissor types. It is also the one used by the UK RNLI and the Royal Navy.

      We were asked to participate in the YM trial you mentioned but had to decline for two reasons. Their test rig was the one made for the gator cutter, a scissor cutter. This requires a large gap between the prop and the bearing carrier and the test methodology was designed to show how the cutters could cut and not what happens if debris is caught by a prop blade. I was there at the test.

      To get these to cut rope they fixed one end of the rope to the P bracket so it would be dragged along the shaft close to the cutter, this also meant the debris was fixed relative to the rotating shaft. This could be the reason why the discs seemd to work so well.

      The quicKutter cuts debris that is caught by the prop and hence rotating and winding on the shaft, this is after all what happens in practice if you look at the result of catching a line or rope. It winds in the gap until it welds into a solid lump or in worst case pulls the gearbox off the engine. The shaver cutter (quicKutter) is a fixed blade angled so that it shaves into the debris as a lathe tool would.

      We have many fixed to al carriers and to date no damaged fixings, partly as there no shock loads when debris is cut.
      You can see how it works better here.

  • Richard Elder Jul 9, 2010, 12:04 am

    How much are spurs worth?
    A couple of years ago an 82′ Italian Azimet motoryacht came into our shop. One V 12 CAT engine had started smoking badly & the factory mechanic changed the fuel injection system and put the engine back together with the boat still afloat. Before he completed the fuel system control re-connection the “professional” skipper helpfully tried to start the engine and it ran away uncontrollably to self destruction- connecting rods sticking through cylinder heads, oil all over the engine room etc. When we hauled the vessel we found a rope wrapped around the prop, the real cause of the performance problem. So at this point the bill for the spurs was at $235,000. But there is more! The boat was a wiring and design nightmare and leaked like a sieve through the decks and bulwarks. Having spent all his money on a new engine, the owner refused our suggestions to rewire the boat to proper standards and stop the water leaks. The day after we finished the engine rebuild the boat caught fire and burned to the ground. So how much are spurs worth? $2,000,000!

  • Ed Seling Jul 22, 2010, 11:51 am

    I have tried both the Spurs and one I cannot name that was a plain SS disc ground to a razor edge. The Spurs worked but had lots of small parts difficult for a diver to work with and bearings and zincs that needed to be replaced. After losing 2 of the shaft connected bits ($80 ea.) I got rid of the things. The plain SS disc on the other hand was simplicity it self. The first time it was called into use (poly prop line) the edge simply folded over.

    I now have a Shaft Razor made by Evolution Marine in Rockland ME. (Who would know better about this problem than a “Mainer”?:-)

    So far it has been called into use only once but it did its job well and without stress to shaft or strut. I like the serrations on the front face in addition to the rim. They also machined a special shaft hole size for me at no additional charge. Good customer service.

  • John Jul 22, 2010, 2:32 pm

    Hi Ed,

    The Shaft razor looks like a very nice product. As you say, the Spurs, while functional, have a substantial maintenance burden attached to them.

  • Petter Jan 15, 2012, 8:01 pm

    So John, I am qurious to know what you installed in the end – if anything.

    Motor Boats Monthly did a test of various types and a nice video is located here: http://www.youtube.com/watch?v=JImiuemabIY

    Having looked into the various ropecutters the disc type appears the easiest ones to attach and maintain, but the knife like cutters the most efficient. However, I really dislike the idea of drilling into an aluminium the stern tube to attach a stainless item with stainless screws. Views and/or comments on this objection or related issues are as always appreicated.

    • John Jan 16, 2012, 6:59 pm

      Hi Petter,

      As the post above says, we installed the Spurs and have been using them now for about 25 years on two different boats.

      We have never had any problems with the SS screws into our aluminum shaft strut. Although it is important to read the note on isolation in the post above.

      • Petter Jan 17, 2012, 10:29 am

        Thanks, John.
        I must confess that I, at a reasonably late point of the day, misread the question above as you were considering fitting an Ambasador type to Morgans Cloud. Thanks for clearing that up. If you find time it, would be great if you would you care to quickly walk me through the steps and materials you use in installing the Spurs cutter to avoid corrosion issue. (Mostly thinking about the fixed part attached to the stern tube)
        – petter

        • John Jan 18, 2012, 10:25 am

          Hi Petter,

          We just installed the block, which is made of aluminum, on the strut with SS screws beaded in Tefgel, no problems as yet and they have been there for 19 years.

          • Petter Jan 18, 2012, 12:29 pm

            Thanks John, that was nice and simple as well as pointing me to tefgel as an alternative to Duralac

    • Neil Young Jan 16, 2012, 7:28 pm

      So why would the Royal Navy and the RNLI remove spurs cutters to fit shaver cutters if the knife type are the most efficient? Christensen, Aqua Star, Alicats, baltic work boats and Austal also use shaver cutters.

      • John Jan 16, 2012, 7:48 pm

        Hi Neil,

        Just to clarify, I did not say that Spurs were the best, but simply that we have used them for a long time with good success. At the time we installed them, that was all there was. Things may have changed, but we have not done any sort of evaluation.

  • Neil Jan 18, 2012, 6:30 am

    Sorry John it was more in response to Petter “knife cutter smost efficient” but this was only in a test that compared disc and scissor types.

    Withe regards to isolation we frequently attach stainless to Al P brackets, they are protected in the same way.
    I have an article about cathodic protection I can e-mail if anyone is interested this is the part about quicKutters.
    Isolating is not always the answer as they are all in a conducting electrolyte.
    quicKutters are constructed of 316L stainless steel and therefore may be
    regarded as cathodic, in much the same way that a stainless steel
    propeller shaft is cathodic to a bronze propeller. The entire submerged
    metal componentry of a vessel should in any event always be electrically
    connected to sacricial zinc (or, in some cases magnesium) anodes which
    should be strategically located, constantly monitored and replaced
    quicKutters are cathodic to marine structural and propulsive metals that
    comprise a vessel such as steel, aluminium, and bronze. Should a
    quicKutter be fitted to a vessel, the additional mass of cathodic metal
    componentry compared to pre-existing componentry such as stainless
    rudder and prop shafts, bronze or stainless propellers, or brackets, is
    relatively insignificant.

    • Petter Jan 18, 2012, 12:33 pm

      Neil, it would be great to receive a copy of the document you mentioned. You may use petterms – at – gmail – dot – com.

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