Rope-Cutters on Prop-Shaft

[Babylon]

Looking to fit a rope-cutter on the the prop-shaft this winter. Seem to recall a recent YM or PBO group test on rope-cutters, but cannot find it anywhere in my collections of these mags.

Tried a ybw.com search, but without a result.

Any pointers?

 

[Tranona]

The most recent one is in MotorBoats. The most often quoted one is in Sailing Today about 7 or 8 years ago. Very little has changed since then. At least one of the manufacturers has a link to it on their website. Suggest you get on the websites of all the manufacturers and start your comparisons from there.

 

[Skyva_2]

IIRC the best at the time was Ambassador Stripper, might be worth starting there.

We bought one at the time and found it easy to fit and durable.

 

[jimi]

Also got the Ambassador, excellent kit, been on the boat 8 years now and chopped a couple of things, would reccomend

 

[TigaWave]

You can read the test here, link below, however the quicKutter was not included in the test, or we declined to participate for reasons as detailed on our website where you can also find a link to the full test.
MBM rope cutter test

The shaver type of cutter was first used in 2003, after the sailing today test/report.

There are now three types of cutting system.
Disc - prop protector + others, Scissor - spurs, stripper, gator and shaver - quicKutter.

 

[misterg]

There was a big test in Sailing Today a few years ago. It's reproduced on the Ambassador Marine web site - pdf file.

Ambassador's stripper came out very well. (Just fitted one).

Andy

 

[Refueler]

The stripper is good and I know it worked on mine with something real serious. But in doing it's job it ripped the fixed mount of the stern tube. I'm just left with the 3 blade job behind the prop now. I don't want to drill and tap the tube again. The blades on their own I reckon have done their job as well !! without the fixed part.

But if you fit one - please don't do as the previous owner of my boat did .... he ignored it and the plastic bearing discs wore out, the blades then moved and wore slots into them. They were totalled by time I got to boat. The rattle when engine running !

So each lift out - check that float and plastic rings ... it's an expensive piece of kit that is worth looking after !

Here's it's replacement ....

Sadly as above - I now don't have the fixed blade and mount parts on the stern tube anymore - having had mount ripped off.

 

[Roberto]

this video is interesting


http://uk.youtube.com/watch?v=JImiuemabIY

 

[vyv_cox]

Same here. I have lost the fixed part twice now, and they are not very cheap to replace. First time was on polypropylene, about 14 mm, and the second time was on one of our double braid 14 or 16 mm stern warps. The second time it didn't even cut the rope, just stripped the three bolts out of the P-bracket. If I was going to fit one again I would be drilling and tapping right through into the cutless bearing as well. P-brackets are now so thin that I question whether this type of cutter is ever going to be reliable.

I have more or less decided to go for a disc type instead.

 

[TigaWave]

This makes painfull reading, I'll have to restrain myself and take a back seat. Maybe its time to leave the computer and office and sort the fittings on my shiny new mast!

 

[[10753]]

Happy with my Spurs Cutter. Service from Spurs based Yarmouth IOW has always been superb. Have to replace little anode every 2 years and the plastic washers every 5 years. Not sure what goes on under the water but whatever it does or doesn't do it does give me reassurance.

 

[stevebirch2002]

Ive had the AmbassadorStripper on for nearly 8 years, cut through many a rope (Inclusing my stern lines, three times!

They must be fitted on something that will bear the strain, not some thin bit of platic. Ambassador made a lovely adaptor plate for my Vega.

As with all equipment, periodic checks and maintenance is needed.

SB

 

[JerryHawkins]

I fitted a QuicKutter from www.H4Marine.com to the current boat (had Ambassador on last boat - wouldn't fit current boat in any case). QuicKutters are fitted to the RNLIs all weather lifeboats so that has to say something about them.

 

[Sy-Revolution]

I have a proprotector, When I had the boat out last winter there was evidence that it had done it's job admirably.

Cheaper option too.

 

[Refueler]

[ QUOTE ]
They must be fitted on something that will bear the strain, not some thin bit of platic.

[/ QUOTE ]

Steve ... the ambassador is a magic bit of kit - but if you see the damage to the stern tube where it tore out - I mean tore out, not just pulled out. The tapped holes are elongated into ovals where the fixed part bolts must have been forced round and finally just gave way.

I've left the 3 blade cutter on the shaft and it seems to keep my prop clear of stuff. As you know, I had a diver down last year because of a rope on the prop. The rope wasn't stopping use of engine etc. - but I knew a short piece was missing from the end I had in hand. It didn't surface in my canal. So had to be on the prop. Diver came up with it and remarked that cutter on it's own appeared to have done it's job. That was 12mm 3 strand polyprop. It was basically a short length curled onto blades.

 

[Anonymous]

[ QUOTE ]

I have more or less decided to go for a disc type instead.

[/ QUOTE ]I have had a disc type since 2004 and I am sure that it must have cut up plenty given all the miles we've done! However, when leaving a harbour last year I caught a lazy line and while is seemed OK I had poor consumption. I have a hookah diving kit and inspected it in the Mar Menor to find that the rope was heavily wrapped round the disc and in gap between the prop and the cutlass bearing. I had to tug with my feet wedged against the hull to free it, as well as cut with a sharp knife.

In 1972 we got a 50mm (sic) rope round both props on a TSDY, 12 nm out of Fiumicino and had to get a tug in. Funnily enough the same tug is still here all those years later! It took TWO strong workmen to free that. Amazingly, there was no damage to the props, P Brackets or shafts!

Talking to other cruisers, I have heard very bad stories about the stripper type -- they always seem to get bits knocked off or hammer themselves to pieces. I think that the problem is they can never be strong enough.

I think that on balance the disc is best and then reckon to dive down to clear it if the disc hasn't worked.

 

[Tranona]

I think you may be passing on old wives tales. Scissors type cutters have been on the market for 25 years - long before discs appeared - and as you see from the majority of posts on threads such as these they are effective. They do not get "knocked off" or "hammer themselves to pieces". They are fitted by just about all major boat builders and are standard equipment on Oysters, for example.

On the rare occasion that the striker block comes off, it is because this is the "fail safe" feature of the design. If you pick up something that is imposssible to cut, the holding bolts may pull out - which is, I suggest better than pulling the stern gear out!

By all means fit a disc cutter - it is better than nothing, but just think about how effective a swinging sword is in cutting a floating or swinging rope compared with cutting it with a pair of pinking shears.

As for diving to clear a prop - except in benign conditions that is a mugs game - I could recount the real life example of somebody losing his life doing just that - but I won't because it was not a pretty sight, particularly for his wife who watched it happen and had to call the coastguard to recover his body. All this less than a mile from one of the most popular beaches on the south coast.

 

[TigaWave]

As far as information is concerned on marine components, to get an accurate picture talk, if you can, to commercial vessel owners and operators. Boats that are doing 2000-3000 hours a year will give an accurate view of the ralative robustness and failure rates of systems and components.

Come to Seaworks in June and talk to the boat owners there.

 

[Refueler]

Dear Tranona ... please with deepest respect take a look at this :

This is the stern tube and prop of my present boat. As you can see the 3 bolts that held the block have failed. The two to left have just pulled out destroying any chance of retapping the holes - they are oval'd and thread has completely gone. The last one to right has actually sheered.

We don't know what caused this but believe it to have been a submerged branch or maybe cable. We have a good idea where it happened - exiting my canal when water level was reduced and boat was ploughing her way out. Shortly after we had a grating noise when throttle was opened. Later we lifted the boat to find the fixed cutter part twisted and loose with fixed block torn away. The grating noise most likely being that two blade portions interfering with each other at certain revs.
I am glad that the block gave way - because if it had been the stern tube - results could have been catastrophic. I am reluctant to buy and fit a new block, I have spare shaft parts of cutter, as I am not willing to have another incident of strain on the tube.
I believe that the cutter has worked even as now - judging by the findings of the diver and lack of material on shaft / prop at lift out.

One point that many have missed is that biggest problem is not so much material caught on prop, but that most material found in water now is synthetic and once it winds onto shaft irrespective of cutter - it welds itself in place. Even big ships have a problem with small lines etc. for that very reason. In extreme cases the line can wind on tighter and tighter, heat generated, welds and forces then get applied to shaft ..... look at the video posted above and you'll see that no matter what cutter - some materials have that property of wrapping on the shaft.

 

[Tranona]

Thanks for the picture. That is precisely what it is supposed to do if you pick up something that the cuttter can't deal with - very rare in any case. Just imagine what damage it might do if you did not have a cutter. There are loads of examples around of P brackets bent, shafts bent, engines pulled off their mountings - there was one of these posted here a couple of months ago.

There is no problem tapping another set of holes at either 90 or 180 degrees to the old ones. That bronze casting is a very substantial bit of kit and takes no load normally - and as you see is "protected" by the screws failing if any undue load goes on it through the cutter. On very thin stern gear such as on early Westerlys and boats that use GRP or stainless tubes a clamp fitting is usually used.

As to using it without the fixed cutter, it may deal with some things rather like the disc cutters, but is not an effective cutting instrument just as using only one blade of a pair of scissors is not effective.