Rope cutter advice

[Tribute]

Someone I know has a rope cutter as he should on the prop shaft of his yacht, when she was lifted out I had a look at the rope cutter and was surprised to see about a 5mm gap between the cutting blades. Surely that can never work? He is adamant that is how it should be. What do you all think?

 

[vyv_cox]

Not if it's a Stripper. Should be a very small clearance.

 

[Tranona]

Depends on the design. There should be a gap as the blades should not touch - they are kept apart by a composite bearing. 5mm is however, excessive and suggests the bearings are worn and probably the blades have been touching so wearing the faces. It could well be "rattly" as well.

Suggest your mate checks in accordance with the maker's instructions.

 

[sailorman]

Someone I know has a rope cutter as he should on the prop shaft of his yacht, when she was lifted out I had a look at the rope cutter and was surprised to see about a 5mm gap between the cutting blades. Surely that can never work? He is adamant that is how it should be. What do you all think?

check-out the manufacturers site for installation download.
my Ambassador is close-fitting but i cant remember the actual tolerances

 

[Tribute]

You can also wobble the blades back and forth, no wear on the blades though. Will try and find out what model it is.

 

[emandvee44]

Rope Cutter

I have just had a look at the service instructions for our Ambassador Rope Cutter - if the gap is LESS THAN 0.1 mm when the moving and fixed parts are squeezed together, it is time for a bearing change.

Michael.

 

[vyv_cox]

I have just had a look at the service instructions for our Ambassador Rope Cutter - if the gap is LESS THAN 0.1 mm when the moving and fixed parts are squeezed together, it is time for a bearing change.

Michael.

The clearance is determined by the thickness of the bearing. When new it is somewhat less than 1 mm I would estimate, which reduces as bearing wear takes place. If you do not carry out the squeeze test eventually you will hear the rotating blades striking the fixed ones.

 

[prv]

How's the non-rotating part mounted? On some boats the engine pushes forwards a few mm on its mounts when put in gear - this can only mean that the shaft and prop are doing the same (of course, they're the cause not the effect). Perhaps this closes the gap on your mate's cutter?

Pete

 

[Tranona]

How's the non-rotating part mounted? On some boats the engine pushes forwards a few mm on its mounts when put in gear - this can only mean that the shaft and prop are doing the same (of course, they're the cause not the effect). Perhaps this closes the gap on your mate's cutter?

Pete

No. The blade clearance is determined by the bearing and wear - independent of the shaft. when the shaft moves backwards and forwards, the whole cutter moves with it.

 

[Stork_III]

No. The blade clearance is determined by the bearing and wear - independent of the shaft. when the shaft moves backwards and forwards, the whole cutter moves with it.

Are you sure about that? Isn't the fixed blade fastened to the P bracket or cutlass bearing tube?

 

[sailorman]

Are you sure about that? Isn't the fixed blade fastened to the P bracket or cutlass bearing tube?

No only the spring device to stop the fixed/stationary part spinning

 

[prv]

No. The blade clearance is determined by the bearing and wear - independent of the shaft. when the shaft moves backwards and forwards, the whole cutter moves with it.

With a Stripper, which is what I also have, you're quite correct. Nobody here knows what the OP's mate has.

Pete

 

[Tranona]

With a Stripper, which is what I also have, you're quite correct. Nobody here knows what the OP's mate has.

Pete

All types (although there are only two sold in any volume) with moving blades are the same in this respect.

Whichever type it is, the gap is almost certainly the result of worn bearings allowing the two faces to contact and wear. Even without the bearings there would not be 5mm between the blades on a new one.

 

[moody lady]

Tribute

If the engine had moved back for some reason the gap would be that much larger, however if the engine moves foward under load the gap may close to the required distance, there always should be a gap which closes when the prop is working if the gap is too small when the prop is working the two blades will rub together possibly causing excess wear.

 

[mjcoon]

No only the spring device to stop the fixed/stationary part spinning

And presumably to provide the reaction force if a rope actually has to be cut?

MIke.

 

[pvb]

If the engine had moved back for some reason the gap would be that much larger, however if the engine moves foward under load the gap may close to the required distance, there always should be a gap which closes when the prop is working if the gap is too small when the prop is working the two blades will rub together possibly causing excess wear.

I'm not sure which ropecutter you're referring to, but all the ones I've ever seen maintain a constant gap regardless of the load on the engine.

 

[Tranona]

I'm not sure which ropecutter you're referring to, but all the ones I've ever seen maintain a constant gap regardless of the load on the engine.

Think there may be some comfusion as to which "gap" is being discussed. My understanding is that the OP was referring to the gap between the blades, which as you say is constant except that it widens if the bearings wear and then the faces wear.

The other gap is between the cutter and the stern gear, which does indeed change when you go in and out of gear - that is why there is a gap. If the gap is insufficient or more likely the striker block is in the wrong place, the fixed cutter will bottom - which wears the bearings and the faces. This is what I suspect has happened to the OPs mate's cutter.

 

[pvb]

Think there may be some comfusion as to which "gap" is being discussed. My understanding is that the OP was referring to the gap between the blades, which as you say is constant except that it widens if the bearings wear and then the faces wear.

The other gap is between the cutter and the stern gear, which does indeed change when you go in and out of gear - that is why there is a gap. If the gap is insufficient or more likely the striker block is in the wrong place, the fixed cutter will bottom - which wears the bearings and the faces. This is what I suspect has happened to the OPs mate's cutter.

Even allowing for some people's inability to write down what they mean, I think the OP's post was clear - "...I had a look at the rope cutter and was surprised to see about a 5mm gap between the cutting blades. Surely that can never work?"

 

[Tranona]

Even allowing for some people's inability to write down what they mean, I think the OP's post was clear - "...I had a look at the rope cutter and was surprised to see about a 5mm gap between the cutting blades. Surely that can never work?"

Yes, I know it was clear, but others started talking about "the other gap" and confusing the issue.

 

[Neil_Y]

As a supplier, it's best to get hold of the latest set of instructions from the manufacturer.

We have recomended clearances for correct operation and I'm sure Spurs, Gator and Stripper will have the same, these are the three types of scissor cutter currently available. They all have one fixed blade and multiple blades that rotate with the shaft.