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Old 17-05-2011, 19:10   #1
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Prop Protector ?

I ran a search but could not find what I was looking for.

Has anyone used a Prop Protector or Shaft Shark? Good? Bad? Comments?

PROP PROTECTOR USA
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Old 17-05-2011, 19:21   #2
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Re: Prop Protector?

Not seen it before but seems like a sound idea. Can't see the advantage over conventional rope cutters though and I would have thought it would add drag too.
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Old 17-05-2011, 19:26   #3
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Re: Prop Protector?

It is just a single sharp disc which IMHO will not cut a fouling line or net quickly or sufficiently. I have the "Spurrs" system on my boat and more than a few times it has saved by butt by cutting loose drift nets and lines and fish pots. See: Spurs Marine Line & Net Cutter Systems
- - It is based on the "scissors" principle that absolute cuts any fouling lines, etc.
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Old 17-05-2011, 19:33   #4
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Re: Prop Protector?

Another thought that occurs to me is this would only be effective with the prop spinning at high rpm. In many cases, a prop can be stopped dead within a couple of seconds and then it would be useless. A more conventional cutter would at least have hacked through part of the rope in a couple of turns as would the above system.
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Old 17-05-2011, 23:10   #5
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Re: Prop Protector?

Quote:
Originally Posted by simonmd View Post
Another thought that occurs to me is this would only be effective with the prop spinning at high rpm. In many cases, a prop can be stopped dead within a couple of seconds and then it would be useless. A more conventional cutter would at least have hacked through part of the rope in a couple of turns as would the above system.
If you are referring to the razor disk, yes maybe, but stopping a prop that quickly would require a major sized line. With the Spurrs system I have chopped 3/4" nylon anchor rode with total ease.
- - However, chopping the fouling line only allows the propeller to remain rotating. You still have the problem of line or net wrapped around the blades of the propeller itself. So the cutter protect the prop/engine from sudden stoppage but you must usually go over the side to clean the rest of the line, net off the blades of the propeller.
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Old 18-05-2011, 05:45   #6
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Re: Prop Protector ?

I'll try and give a balanced reply here as we do work with one rope cutter.
I'll give you the choice and how they work and let you research and make up your own minds.

What happens with a prop fouling.
Debris rope/net/line is caught by a blade of the spinning prop.
It will wind on the shaft between prop and bearing with no cutter, it will be turning with the shaft as it winds on. This debris will be very tight, so tight it can weld itself in to one solid lump of plastic if it is pp rope

There are three types of cutter available
Disc (prop protector/shaft shark) do effect water flow/performance
Easy to fit.
Scissor (Spurs/gator/stripper) do effect water flow/performance
quite easy to fit.
Shaver (quicKutter) need a machine shop to machine and fit spool so harder to fit.

With disc the debris will not be moving relative to the blade as the debris will also be spinning, so they only cut once debris has wrapped over the disc and then pulls tight.

With scissor they will cut debris before it winds onto the shaft as it drifts past but I believe if debris is caught by the prop and is winding on to the shaft aft of the cutter they may be overwelmed or pushed /bent when debris reaches the rotatiting blade, they can also be easily broken if something they can't cut gets between the blades such as a fish hook or swivel. Like scissors if you try and cut something too big or too tough you break the scissors. There are many stories of mooring lines being chopped up by scissor cutters if you drive over them but this chopping may not be chopping rope that has been caught by the rotating prop.

With shaver, the shaver blades cut debris that has been caught and is winding on the spool which sits over the shaft. Very dificult to break even when swamped with masses of net or thick rope. Used by the UK RNLI (they removed spurs cutters) the RN and fitted as standard on Christensen yachts as well as many commercial builders boats.
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Old 18-05-2011, 07:52   #7
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Re: Prop Protector ?

another device upon which barnacles can flourish.
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Old 18-05-2011, 08:11   #8
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Re: Prop Protector ?


barnacles but still working
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