Rope Stripper Clearances

[Laysula]

Looking at the blades, surely the design would force the blades together when put under the pressure of cutting anything>

 

[pawl]

Whatever the vernier tells you, the practical approach to the Ambassador Stripper is to check if the plates touch when assembled and rotating freely. This will obviously generate wear to both blades. If your gear passes this test all is well. However, wear is not confined to the nylon bearings but the SS parts take a hit too from particles in the water. You will see they have been ground and a lip has formed. You will therefore find that a new set of bearings will not compensate for the lost metal and the cutters will still strike - ie if the gouged metal is that deep. That costs a new cutter - try and negotiate with Ambassador. Otherwise it's several hundred £. Think of it as a cost over 7-10 years, so bearable for the job it does.

You can grind the edges of the cutting blades to ensure the teeth do not jam together when they rotate. It gives another 2-3 seasons, if you are adept at these things.
Ambassador is the best mechanism, I have to say and yes, I have paid up for a complete new cutter in the past when wear has required it and no machining can sensibly rescue the gear.

PWG

hi, thanks for the response, my problem isn't that the blades are too close, Ambassador state a minimum of .004" with the blades squeezed together, I'm well above that. The problem is that, imho, there is too much gap, particularly since I fitted the new bearings. I have twice recently been brought to a standstill with a fouled prop which the stripper wasn't able to deal with. In my view a rope cutter that doesn't cut is worse than not having one at all, as it is sure to jam. A new stripper is about £600 and I doubt that I have 7-10 years of sailing left, plus there's a shed load of other kit I would prefer to spend my money on.

 

[pawl]

Mine has a lot of the wear as desribed by Peter Gibbs in the post above. The stainless on the fixed blades has worn so that the tolerance between the cutting blades on new bearings is only .005" which does not give enough scope for wear. My solution was to make a thicker plastic bearing and fit that. What I did was to take an old worn plastic bearing , remove the locating lip with a stanley knife , bond the old bearing to a new one and the lap the new thicker bearing down to make the assembly just free to rotate when assembled. This has saved me buying a new stripper.

If anyone is interested I will do a post with the details of how I did this.

hi, interesting, my problem is not with the blades being too close, quite the reverse. However, I think that a thicker plastic bearing is the answer. I can easily turn one from solid but would like to be sure of the clearances. Do you know what clearance you ended up with and has it worked?

 

[pawl]

Looking at the blades, surely the design would force the blades together when put under the pressure of cutting anything>

hi, I have assumed the opposite thinking that the blades would act like scissors. However, if you are correct then I may need to rethink this. Have you got any information supporting this view please?

 

[Refueler]

I apologise - but I cannot help but think too much thought is going into this .............

 

[Halo]

Mine is a saildrive type but I dont think that makes a difference.
The thrust does not go through the plastic bearings or the blades.
The centre "tube" is slighly longer fore and aft than the cutting parts and carrries the load (thrust ) forewards
The moving cutter "floats" in the assembly and no matter how much you tighten the assembly this should not make the assembly tight in terms of turning .
The reason the manufacturer is only interested in the minimum clearance between the blades is that the only real issue is if the two cutters come into contact
Look at the cutters - they are designed to cut through the fouling rope like one of those line cutters in an expensive life jacket - these line cutters work like blades not scissors
If you have a bigger clearance between the cutters (when you push the two together post assembly) then rejoice! -your static cutter plate is not worn and you dont have a problem.

 

[Laysula]

hi, I have assumed the opposite thinking that the blades would act like scissors. However, if you are correct then I may need to rethink this. Have you got any information supporting this view please?

No info as such but you only have to look at the assembly and imagine where the forces would be acting when cutting through a rope.

 

[Refueler]

I can tell you that when the V mount sheered from the shaft housing and I had to lift boat to remove the now loose cutter. I was left with just the fixed shaft half ...

It does NOT cut on its own ! I had to have a guy under the boat to cut away a length of garden cheap 8mm ...... this surprised me because the edges of the castellations are SHARP !!

 

[pawl]

Mine is a saildrive type but I dont think that makes a difference.
The thrust does not go through the plastic bearings or the blades.
The centre "tube" is slighly longer fore and aft than the cutting parts and carrries the load (thrust ) forewards
The moving cutter "floats" in the assembly and no matter how much you tighten the assembly this should not make the assembly tight in terms of turning .
The reason the manufacturer is only interested in the minimum clearance between the blades is that the only real issue is if the two cutters come into contact
Look at the cutters - they are designed to cut through the fouling rope like one of those line cutters in an expensive life jacket - these line cutters work like blades not scissors
If you have a bigger clearance between the cutters (when you push the two together post assembly) then rejoice! -your static cutter plate is not worn and you dont have a problem.

hi, thanks for the response, I think that saildrive model must be different as I don't recognize mine from your description.

 

[pawl]

I apologise - but I cannot help but think too much thought is going into this .............

hi, no need to apologize, it seemed such a simple question, at least to me. Ambassador say that when the clearance reaches .004" its time to change the bearings. What I would like to know is what the clearance started at, i.e. from the factory, just thought someone might know.

 

[Halo]

It is a fair question ! The governing factor is the thickness of the bearing which you can measure with a micrometer or vernier calliper. If the clearance is more than the thickness of the flat part of the bearing something is not sitting right

Cutting is a complex process. Scissors have a complex shape to give rolling shear and compression and the blades touch. Knives cut differently.
Practice has shown the stripper works with a clearance between the blades. It’s not scissors, it’s not knives it’s some hooligan flat spikes that rip rope apart.

 

[Refueler]

hi, no need to apologize, it seemed such a simple question, at least to me. Ambassador say that when the clearance reaches .004" its time to change the bearings. What I would like to know is what the clearance started at, i.e. from the factory, just thought someone might know.

I appreciate your question ... and was not trying to be rude.

I fitted one and never occurred to me about what 'new' gap is ... I just accepted they knew what they were doing !!

The fact that it ripped away from my shaft housing is another matter !

 

[Refueler]

It is a fair question ! The governing factor is the thickness of the bearing which you can measure with a micrometer or vernier calliper. If the clearance is more than the thickness of the flat part of the bearing something is not sitting right

Cutting is a complex process. Scissors have a complex shape to give rolling shear and compression and the blades touch. Knives cut differently.
Practice has shown the stripper works with a clearance between the blades. It’s not scissors, it’s not knives it’s some hooligan flat spikes that rip rope apart.

That's how I understood it and posted earlier ... that the serrations are basically tearing the rope .. and the gap allows strands etc. to not jam the two blades.