Rope Stripper Clearances

[pawl]

Hi, I'm hoping someone might help me with some information. I have a "rope stripper" fitted to my boat, 1" shaft, 3 blade AM10 model. I'm just in the process of renewing the plastic bearings etc. Although the unit is quite old and has obviously been through the "wars", the plastic bearings seem not to have worn very much. However, one had broken into two pieces so I have to change them. Problem is that with the new bearings in place I have a lot more "play" between the stationary and rotating blades and the clearance has increased from .008" with the old bearings to .018" with the new ones. To my mind this is too much "slop" but I may be wrong, does anyone have any experience of how much clearance there should be for the cutter to work effectively? I have been in contact with Ambassador Marine but, so far, have not been able to get any useful information.

 

[pvb]

You can download the instructions from Ambassador's website - https://www.ropestripper.com/documents/servicing-am5-10-15.pdf

Minimum clearance is .004" so you were getting close. If you've installed new plastic bearings from Ambassador, the clearance will be correct.

 

[pawl]

hi, thanks for the response, the Ambassador instructions only give the minimum clearance, as you say .004" I can't see where they give any maximum values. The clearances might be "correct" if I replaced all the parts, but if there is wear in the rest of the unit they may not.

 

[pvb]

hi, thanks for the response, the Ambassador instructions only give the minimum clearance, as you say .004" I can't see where they give any maximum values. The clearances might be "correct" if I replaced all the parts, but if there is wear in the rest of the unit they may not.

Surely wear in the rest of the unit would reduce the clearance? The clearance is provided by the plastic bearings, which are replaceable. If you've used the correct bearings, the clearance will be correct.

 

[pawl]

hi pvb, perhaps I didn't word my post very clearly. What I'm concerned about is the maximum amount that the stationary and rotating cutters could separate. There are a series of mating faces on this unit some of which if they wear will allow the cutters to get closer together and some which will allow the cutters to separate. At the moment, with the new bearings in place, the cutters can separate to the extent of .018" which is .010" more than they could with the old bearings. What I'm thinking is that if a rope gets round the prop it will be forcing the blades apart and not together. With a larger gap I would have thought that there is more chance of the thing jamming rather than cutting, rather like trying to cut something with a wonky pair of scissors. But I may be wrong. I would be very surprised if the amount of play I have on this thing is what was intended at the factory.

 

[pvb]

What I'm concerned about is the maximum amount that the stationary and rotating cutters could separate. There are a series of mating faces on this unit some of which if they wear will allow the cutters to get closer together and some which will allow the cutters to separate.

As far as my memory allows, I thought that the rotating cutters are fixed on the shaft, and that the stationary cutter floats on plastic bearings. Which mating faces do you think will allow the cutters to separate? And, as the interface is stainless steel vs plastic, which side is more likely to wear?

 

[pawl]

You're quite correct the 3 blade section is clamped onto the shaft and obviously rotates with it. Mounted onto this assembly are the two plastic bearings, the stationary cutter blade and the clamping ring. The two bearings sit either side of the stationary blade, which is "floating", on the forward side of this blade and the plastic bearing is the clamping ring. I would have thought that any wear on the forward face of the stationary blade, either side of the plastic bearing or the aft face of the clamping ring would allow the cutting blades to move apart. What I know from over 30 years in the plastics industry, is that moving plastic materials will wear away stainless steel albeit slowly, this stripper must be at least 20 years old. What I don't know and can't seem to find out is what the original dimensions of the parts were, therefore I don't know what, if any, wear has taken place.

 

[pvb]

Is it possible that you're over-thinking this?

 

[duncan99210]

The cutter is designed to have a gap between the blades. That’s set by the plastic bearings, which are designed to wear: as they wear, you tighten the screws which holds the assembly together. That brings the blades closer together until they reach the wear limit laid down in the instructions. You then replace the plastic bearings, which opens the gap between the two blades to something over the specified minimum. And that’s it, you repeat the annual process of gradually reducing the gap until yet another set of bearings is required. Takes years of even pretty hard use.
Mines been fitted for at least 14 years and the bearing haven’t needed replacing yet. There’s no sign of wear in the blades and the biggest problem I had was removing scale from both the blades and the bearings.

 

[pawl]

Well, quite possibly, however, as I have the boat out of the water and have spent some £35 on the new bearings I would like to make sure I've done the best that I can before relaunch. Particularly as I have had two situations recently where the stripper has failed to prevent the loss of propulsion, where the clearances were tighter than they are now. At the moment it would be hardly any trouble and no cost to true up the faces and machine a thicker plastic bearing to take up the slack, if I knew how much slack to take up that is! I can't do it once it's back in the water.

 

[pawl]

The cutter is designed to have a gap between the blades. That’s set by the plastic bearings, which are designed to wear: as they wear, you tighten the screws which holds the assembly together. That brings the blades closer together until they reach the wear limit laid down in the instructions. You then replace the plastic bearings, which opens the gap between the two blades to something over the specified minimum. And that’s it, you repeat the annual process of gradually reducing the gap until yet another set of bearings is required. Takes years of even pretty hard use.
Mines been fitted for at least 14 years and the bearing haven’t needed replacing yet. There’s no sign of wear in the blades and the biggest problem I had was removing scale from both the blades and the bearings.

hi, thanks for that, but there is no provision on mine to make any adjustments and as I have said I have installed new bearings and I believe there is way too much slack in the assembly.

 

[Refueler]

I cannot answer the 'gap' question as I just was given the bits in hand when I bought the boat .. had new parts and fitted it all correctly.

Few months later - I had the most awful clattering sound under the cockpit ... lifted sole ... everything fine .. started motoring again and BANG BANG BANG ...

Finally we lifted the boat and found that the stripper had sheered the holding bolts for the clamp letting the fixed part run loose and clattering ...

The damage to the shaft housing was severe ... I have photos but bloody Photobucket is not letting me at them .. but once I find them - I will post. The damages was such - I dare not drill and tap for new bolts.
I now just have the shaft part remaining and its failed to prevent rope from being tangled ... maybe I should move it fwd more .... this is the only photo I can show till I get the rest :



If you get it zoomed in ... you will see that one of the bolts actually sheered .. the others ripped out destroying the tapped holes.

I can only assume that what ever got picked up was too much for the cutter ...

I believe the gap they advise is to allow when cutting that strands etc. will not jam in between the jaws ... because it does not cut in one motion like scissors but cuts progressively by repeat revolutions. That's my theory anyway.

Will I refit it ? No. Only if I renew the shaft housing. ... then only maybe.

 

[duncan99210]

hi, thanks for that, but there is no provision on mine to make any adjustments and as I have said I have installed new bearings and I believe there is way too much slack in the assembly.

There’s no provision in mine to make adjustment either..... You simply fit the bearing material, tighten the screws up and that‘s it. If there’s too much play, you haven’t tightened the screws up enough. Or is there something I’m missing in your description?

 

[pawl]

There’s no provision in mine to make adjustment either..... You simply fit the bearing material, tighten the screws up and that‘s it. If there’s too much play, you haven’t tightened the screws up enough. Or is there something I’m missing in your description?

hi, I don't quite understand your point either, unless the screws move the parts closer I don't see how the screw tension could reduce the gap between the blades. In any case I have tightened the screws as tight as they would reasonably go. The problem I have is that there is more play in the unit now than there was before I put in the new bearings. The old bearings were somewhat thicker than the new ones, hence the additional slack. This could be due to either; a) the new bearings are actually thinner than the old ones, a point I took up with ambassador marine. They suggested that the old bearings might have a build up of calcium deposits, which may be correct although it is hard to tell from looking at them. Or b) that the bearings do have a layer of deposits on them which is masking wear in the stainless steel parts. Either way I could overcome the problem but would just like to know what the original clearance should be rather than me just guessing it.

 

[pawl]

I cannot answer the 'gap' question as I just was given the bits in hand when I bought the boat .. had new parts and fitted it all correctly.

Few months later - I had the most awful clattering sound under the cockpit ... lifted sole ... everything fine .. started motoring again and BANG BANG BANG ...

Finally we lifted the boat and found that the stripper had sheered the holding bolts for the clamp letting the fixed part run loose and clattering ...

The damage to the shaft housing was severe ... I have photos but bloody Photobucket is not letting me at them .. but once I find them - I will post. The damages was such - I dare not drill and tap for new bolts.
I now just have the shaft part remaining and its failed to prevent rope from being tangled ... maybe I should move it fwd more .... this is the only photo I can show till I get the rest :

View attachment 94158

If you get it zoomed in ... you will see that one of the bolts actually sheered .. the others ripped out destroying the tapped holes.

I can only assume that what ever got picked up was too much for the cutter ...

I believe the gap they advise is to allow when cutting that strands etc. will not jam in between the jaws ... because it does not cut in one motion like scissors but cuts progressively by repeat revolutions. That's my theory anyway.

Will I refit it ? No. Only if I renew the shaft housing. ... then only maybe.

hi, your arrangement is similar to mine, however, whoever fitted mine made or had made a sort of stainless steel clam shell arrangement to fit round the cutlass bearing housing. To this they welded the "striker plate". This fitting is clamped onto the bearing housing with six 8mm bolts, three each side. Therefore, unless the thing is ridiculously over tightened it would turn on the bearing housing rather than destroy it.

 

[vyv_cox]

hi, your arrangement is similar to mine, however, whoever fitted mine made or had made a sort of stainless steel clam shell arrangement to fit round the cutlass bearing housing. To this they welded the "striker plate". This fitting is clamped onto the bearing housing with six 8mm bolts, three each side. Therefore, unless the thing is ridiculously over tightened it would turn on the bearing housing rather than destroy it.

I have twice suffered having the static part ripped out of the P-bracket. Ambassador now make a clamp that is supoosed to prevent this. I don't think it is necessary to weld any parts together but I gave up after my second experience and went for a Proprotector instead.

 

[Refueler]

And I only ever met once person who had similar happen as I ...

I feel more 'relieved' now to know I am not only one !!

The idea to clamp round the shaft housing occurred to me - but I'm wary as that could be a serious stress on that deadwood area ...

If I can find the close-up photos I took - I'll post them up.

 

[pawl]

I have twice suffered having the static part ripped out of the P-bracket. Ambassador now make a clamp that is supoosed to prevent this. I don't think it is necessary to weld any parts together but I gave up after my second experience and went for a Proprotector instead.

hi, I think the stripper clamp I have long predates the Ambassador one which I think I have seen on another Vancouver similar to mine. The one I have looks more "home made" but seems to do the job and avoids any necessity to drill and tap any part of the hull. I don't think that I can justify the expense of changing to another make. However, we seem to be getting away from the original point of my post. What I would like to find out is what is a reasonable clearance between the cutting blades. Ambassador have said that as the parts wear the efficiency of the cutters declines, but fail to give any guidance on actual values.

 

[peter gibbs]

hi pvb, perhaps I didn't word my post very clearly. What I'm concerned about is the maximum amount that the stationary and rotating cutters could separate. There are a series of mating faces on this unit some of which if they wear will allow the cutters to get closer together and some which will allow the cutters to separate. At the moment, with the new bearings in place, the cutters can separate to the extent of .018" which is .010" more than they could with the old bearings. What I'm thinking is that if a rope gets round the prop it will be forcing the blades apart and not together. With a larger gap I would have thought that there is more chance of the thing jamming rather than cutting, rather like trying to cut something with a wonky pair of scissors. But I may be wrong. I would be very surprised if the amount of play I have on this thing is what was intended at the factory.

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

 

[Halo]

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.