Prop Shaft Stern Glands

graysonlad
8th June 2009, 19:42
50 years ago, when a ship was dry docked and the stern gland and shaft bushing was to be replaced, in our yard, the wooden bushing, removal and refitting, was carried out by the shipwrights. When the lignum vitae had been duly fitted by the shipwrights, a boring machine was assembled in the dock and the timber machined to the correct tolerances for the refitting of the prop shaft.

Accepting that ship design, materials and practices have changed is the above method still used, and if it is, which trade carries out the work? If more modern systems and materials are used what are they?

Thank you.

Satanic Mechanic
8th June 2009, 20:36
I think it is fair to say that things have changed somewhat!!!!!!!

Although in saying that I encountered a retro fitted Lignum stern tube only a couple of years ago.

Anyhoo - Most modern systems are oil lubricated white metal bearings with various types and systems of lip seals fore and aft. The stern boss is usually bored vertically with a degree of slope on it to compensate for the shaft sagging. The method of fixing the the stern section is actually a very closely guarded secret but it involves welding sequences and the use of 3 dimensional theodolites. Due to the quality of Finite element Analysis now available all the dimensions and alignment data is carried out before construction!!!!!!! So once the stern tube is in place and the block erected they can then put all the other blocks on top with all deformation already accounted for.

I have checked the quality of this work and found the real stern tube centre line position at the end of construction to be within 0.4 mm of the calculated - which is frankly spectacular

steamer659
9th June 2009, 02:07
Stern Tube Bearings and Strut bearings have evolved significantly since then. The old Lignum stern tubes were first replaced with "live" rubber type stave bearings which were actually shipped a lot like Lignum- in water filled casks- then the neoprene proprietary bearing rubbers and polymers came- (I still "soak" these on my vessels for 24 hours prior to turning over the shafts for the first time after renewal) then the metal backed so called " white metal bearings" ( not to be confused with the simplex type seal runners) which ran in oil luibricated stern tubes...All of them have a common enemy- misalignment and improper installation- especially in pre-torqued loading....

GeeM
9th June 2009, 03:59
I sailed on a Turnbull Scott bulker called the Trongate in the early eighties which had a Glacier Herbert split sterntube bearing which was bolted to the sternframe from shaft alleyway side. It was possible to inflate a rubber doughnut which sealed the shaft against the prop boss, unbolt the stern frame attachment and then slide the bearing forward on the tailshaft.

The bearing was split horizontally. The top half could be raised with chainfalls attached to eyebolts and the lower half could be lowered In the same manner. This enabled Inspection and renewal of the inboard and outboard lip seals and also Inspection of the bearing and the shaft journal. I dont believe this system Is on the market any more. Has anybody experience with this design and Is It still marketed?

Satanic Mechanic
9th June 2009, 13:25
There were/ are a number of systems which have fallen out of favour with a number of companies. These have largely been self lubricating polymers, as yet they have never quite lived up to their potential.

To be honest a well installed and aligned oil lubricated metal bearing works fine.

Billieboy
9th June 2009, 15:09
It was a long time ago in Lisbon (Ante Revolution), I was getting into the last taxi on the rank at the airport headed for Lisnave yard for a Denholms managed vessel with a few problems. Two guys behind me asked to share the cab, OK; off we went. Got to the gates and we have to get out and walk, it seems that these two guys were engineer supers for Mobil and were visiting the Mobil Pegasus, which had been repaired after suffering an 'M' class bang. We were just walking past the stern and the prop was at an unusual angle, the shaft had over heated and fractured on trials! Coming around the corner of the dock approaching the gangway, we saw two guys with suit cases waiting, "That's the Chief Engineer and The Mate", The super said, "They're on the next flight out"! (Cloud)

It seems that all tanks had been drained in dry dock but the Aft peak, which was the stern tube cooling tank, had not been refilled. Later, chatting to the Yard Manager, who had been on board, I was told that the Master had asked if it was OK to go back to the yard, yes said the Yard manager, but it's a new job number! (Wave)

Philthechill
9th June 2009, 17:17
I think it is fair to say that things have changed somewhat!!!!!!!

Although in saying that I encountered a retro fitted Lignum stern tube only a couple of years ago.

Anyhoo - Most modern systems are oil lubricated white metal bearings with various types and systems of lip seals fore and aft. The stern boss is usually bored vertically with a degree of slope on it to compensate for the shaft sagging. The method of fixing the the stern section is actually a very closely guarded secret but it involves welding sequences and the use of 3 dimensional theodolites. Due to the quality of Finite element Analysis now available all the dimensions and alignment data is carried out before construction!!!!!!! So once the stern tube is in place and the block erected they can then put all the other blocks on top with all deformation already accounted for.

I have checked the quality of this work and found the real stern tube centre line position at the end of construction to be within 0.4 mm of the calculated - which is frankly spectacularSM, your comments on the precision that alignments can be carried-out, with various high-tech bits of equipment these days, reminds me of how I used to have to do compressor/motor alignments when I was working for an Industrial Refrigeration company called UDEC.

When I first started with them all alignments were done using clock-gauges and, on some of the bigger units (Sellafield had 3kva motors on their screw-compressors weighing two tons), it could take forever and a day getting the alignments within tolerance. (Vertical and angular had to be less than .002").

Then one day I was working at Shell Chemicals Plant at Carrington, where we were installing a new fridge system on their Polypropylene Plant, and I was doing the alignments on one of the compressors, cutting bits of shim, effing and blinding at having to jack the motor up, put the bits of shim under the motor feet, hardening the holding-down bolts down, turning the coupling and watching the deflection on the clock-gauge, realising I was still too high/too low, slackening the holding-down bolts off, cutting bits of shim etc. etc.

Then this Shell bloke appeared and, asking me if I wanted a hand with the alignment, opened the smallish "suitcase" he was holding which was full of fascinating little bits and bobs which he attached to the motor/compressor coupling and then turned the whole assembly through one rev.

"Right!", he said, after consulting the screen of the instrument his sensors were plugged into, "You want .002" under the front feet and .005" under the rear feet and that'll do it".

Sure enough, after doing as he said, the alignment, up and down and angularly was within .0015" which was ok for me.

What was this amazing bit of gear achieved such accuracy, so rapidly?

A laser alignment tool.

"Brilliant bit of kit!", said I, "I'll have to see if our outfit will get us one of those-----------how much are they?".

"Around 2000", said my saviour.

Needless to say, and exactly as when I started with UDEC, I was still using a clock-gauge right up to retirement!!! Salaams, Phil (Hippy)

Satanic Mechanic
9th June 2009, 17:37
Phil

I know where you are coming from. The old way of doing shaft alignments and boring etc is still actually more accurate than the modern gizmo's BUT if most of the work can be done outside the building dock then the less time the vessel is in the actual dock (I believe the saving to be up to 7 days) - which means they can get another vessel in, the downside is a hit in quality, but not such a hit that it is outwith tolerance. What I find amazing is the fact they can be accurate to 0.4mm of their calculated prediction (because that is what it is) of any individual spot on the stern frame when they are finished - now that is very very impressive

Bill Davies
9th June 2009, 21:11
Always found repair to the Simplex Stern Seal interesting. Have had the seals replaced in situ ( well down by the head) and on other occasions the grooves on the chrome liner would be spiral welded and then machined.
Can understand the former. Always thought the latter was false economy. After going to all the trouble a new chrome liner could have been fitted in half the time.

eriskay
10th June 2009, 10:57
Brings back memories of the difficulties experienced shoreside in trying to achieve acceptable alignments on all sorts of pumpsets associated with Middle East Desalination Plants. Typically, a site installation might have up to two hundred pieces of rotating equipment, ranging from minor fractional horepower equipment up to some fairly heavy kit, e.g. large vertical borehole-type brine recirculation pumps with 11 KV 2,000 Kw drive motors. Manufacturing tolerances, especially on the major equipment, were tight but not impossible. What made the whole exercise frustrating was the effect of temperature variables.

Whereas a near-perfect alignment might be achieved at 08:00 hours, ready for inpection at, say, 09:00 hrs, even in that short space of time, one hour, the effect of the rising sun could already render the earlier alignment results borderline, and by mid-morning well out of specification. Of course, Clients and their Consultants were reluctant to take cognisance of the thermal influences, just as equipment Manufacturers were equally loathe to grant any form of concession to their demanding alignment tolerances. With most of the pumpset below ground, straddled by a 7 tonne motor mass that is being exposed to ambients reaching 45 degrees C, and significantly greater surface temperatures from solar gain, the entire exercise became one of trying to get final alignment and inspection integrated one joint exercise within a maximum of a one hour duration!

Under these circumstances it was best to keep on the right side of the inspectorate or they might take it into their furtive minds to deliberately turn up a hour or two later than planned - knowing well that the alignment figures necessary to earn a pass mark were by then unlikely to be achieved. Grrrr .....

The original thread reference to lignum vitae bushing for 'tail ends' evoked some memories from an apprenticeship - over half a century ago. It was a privilege to watch these being fitted out by the Yard shipwrights, and quite something really to align long shafts over such a distance right through to the propeller to such exacting standards, in an age when the benefits of laser equipment were unheard of. My other memory of lignum material was half-inching the scrap bits and cuts for the home fires - took forever to burn but had a reasonable calorific value!

As the song goes .... "Thanks for the memories, ..... " !

Gareth Jones
10th June 2009, 11:57
Wish I knew what this thread was about ! sounds very technical - Whatever happened to the graphite impregnated rope that I saw once replaced with the aid of a frogman and plasticine ?

spongebob
10th June 2009, 12:21
Eriskay, my memories of lignum vitae propeller shaft bearings dates back to the 50's when the Royal NZ Navy received a gift? of Bathurst class mine sweepers from the Royal Australian Navy. They were little twin screw triple expansion steamers and with lignum vitae slats fitted in caged bearing halves that slid into the outboard "A" brackets.
I worked in the dry dock on one ship fitting new lignum bearings before the vessel was laid along side in reserve for 12 months. During this period a fitter and an apprentice were sent on board to turn the engines over with hand ratchet gear after a few months or so to rotate the prop shaft in the lignum bearings and counter marine growth but little did they realise that the warm weather had allowed the barnacle and mussel spat growth to rapidly build up on the shaft surface in the bearing slots to the extent that one revolution of the engine saw the shaft seized solid and the new bearings badly damaged.
A fine bit of woodwork by the shipwrights stuffed up by lack of thought.
Next time in dock for a hull clean we fitted new rubber type cutlass bearings and a new timetable for frequent shaft turning was drawn up for idle vessels.

Bob

eriskay
10th June 2009, 12:48
Yes, Bob, you may be sure your problems are just starting as soon as you 'lay up' anything, whether it is a ship, an engine, or just about any item of moving machinery or equipment, and that even takes into consideration planned and preventative maintenance programmes.

The introduction of the cutless rubber bearing for numerous applications, marine, water turbines, centrifugal pumpsets, etc., was a revolution. In my own particular business, seawater distillation, the ingress of sand and other fine particulate matter, even with excellent prefiltration, was always a hazard, but cutless rubber bearing designs were an excellent solution, the fluting serving well to divert any foreign matter away from the close clearance bearing surfaces which were in any event very resistant to that kind of abrasive damage. Running them dry (a possibility on vertical borehole style cannister pumps) was the only real risk with cutless bearings, and that was readily overcome by intoducing a piped water preflush to each of the cutless bearings and giving them a 2-3 minute pre-start flush to wet all the surface and avoid dry friction wear or tear.

Thanks for your anecdotal recall - most interesting. Somehow, although convenient and efficient, it was perhaps not just as interesting unpacking a nice brand new cutless bearing ready for installation as watching these shipwrights demonstrating their great skills shaving the lignum vitae to the desired dimensions and shapes - akin to watching a boatbuilder wielding an adze.

Angus

spongebob
10th June 2009, 12:58
Angus, that trade of shipwright must be almost a lost art these days but during my apprenticeship with a dockyard's collection of both steel, and wooden craft these tradesmen were considered elite.
A civilian shipwright apprentice used to have to build a clinker or ship lap naval dingy as a final trade test and I always used to envy that skill.

Bob

Klaatu83
10th June 2009, 14:40
Part of my job on my first ship was to inspect all the fire fighting stations, including the one in the shaft alley. I clearly remember being more then a little perturbed by the sight of huge quantities of water pouring in through the stern gland. She was a World War II-vintage Victory Ship, operated by the Military Sealift Command. She was already more than thirty years old at that time, and clearly not in the best shape. When I mentioned the state of the stern gland to the engineer on watch he shrugged it off, saying "don't worry, it's always like that". I had no seagoing experience at that time, so I figured he must have known what he was talking about. However, I have never seen anything even approaching that state of affairs since!

Philthechill
10th June 2009, 14:49
Yes, Bob, you may be sure your problems are just starting as soon as you 'lay up' anything, whether it is a ship, an engine, or just about any item of moving machinery or equipment, and that even takes into consideration planned and preventative maintenance programmes.

The introduction of the cutless rubber bearing for numerous applications, marine, water turbines, centrifugal pumpsets, etc., was a revolution. In my own particular business, seawater distillation, the ingress of sand and other fine particulate matter, even with excellent prefiltration, was always a hazard, but cutless rubber bearing designs were an excellent solution, the fluting serving well to divert any foreign matter away from the close clearance bearing surfaces which were in any event very resistant to that kind of abrasive damage. Running them dry (a possibility on vertical borehole style cannister pumps) was the only real risk with cutless bearings, and that was readily overcome by intoducing a piped water preflush to each of the cutless bearings and giving them a 2-3 minute pre-start flush to wet all the surface and avoid dry friction wear or tear.

Thanks for your anecdotal recall - most interesting. Somehow, although convenient and efficient, it was perhaps not just as interesting unpacking a nice brand new cutless bearing ready for installation as watching these shipwrights demonstrating their great skills shaving the lignum vitae to the desired dimensions and shapes - akin to watching a boatbuilder wielding an adze.

Angus Re. your "lay-up" remark, Angus, I've often wondered what state some of the electric-motor bearings must get into on ships which get "laid-up" for considerable lengths of time.

I suppose if they don't have any machinery running i.e. gennies or fridge compressors then there won't be any real problems but if they DO have running machinery (with its attendant vibrations) then, unless the motors are turned regularly by hand, the motor-bearings must suffer considerably from "false-brinelling" and must cause many a scratched head for the engineers, who have to fire-up a ship that's been laying dormant for some considerable time (and don't know of this phenomena), when they experience the numbers of (apparently) knackered bearings as evidenced by the vibrations they will be feeling and the noises they will be hearing!! Salaams, Phil(Hippy)

Satanic Mechanic
10th June 2009, 14:55
Re. your "lay-up" remark, Angus, I've often wondered what state some of the electric-motor bearings must get into on ships which get "laid-up" for considerable lengths of time.

I suppose if they don't have any machinery running i.e. gennies or fridge compressors then there won't be any real problems but if they DO have running machinery (with its attendant vibrations) then, unless the motors are turned regularly by hand, the motor-bearings must suffer considerably from "false-brinelling" and must cause many a scratched head for the engineers, who have to fire-up a ship that's been laying dormant for some considerable time (and don't know of this phenomena), when they experience the numbers of (apparently) knackered bearings as evidenced by the vibrations they will be feeling and the noises they will be hearing!! Salaams, Phil(Hippy)

On a similar note Phil, I am of the habit of storing non running purifiers bowls outside the purifier as they are not a weekly change over and giving the shafts a manual rotation as part of Saturday routines

eriskay
10th June 2009, 15:34
For Klaatus83 :
That situation was by no means abnormal on certain ships, especially as they got on in years. Even after being newly repacked, the stern-gland often allowed the briny inboard in copious quantities. Not particularly dangerous as long as it was not an indication of greater problem 'round the corner', and it was more a nuisance value than anything, slowly filling the bilges and if splashing around the place causing unsightly corrosion of anything in its path.

Philthechill :
You have identified a problem that is more widespread than you might think. Have seen a lot of this in my time and the only solution is good lubrication, frequent rotation, exclusion of humidity, and good cleaning, inspection and fresh lubrication regime immediately prior to return the equipment into service. I also hold the view that current designs of ball and roller bearings are not just as tolerant as their predecessors, or at least I cannot recall the relatively high incidence of bearing problems nowadays with that of years ago for fairly similar conditions. Precautions and good practices, such as the one illustrated above by Satanic Mechanic, are the answer to many of these ills - in my opinion.

Angus.

Satanic Mechanic
10th June 2009, 15:54
Eriskay

whilst on the subject - which incidently I can see rapidly becoming the meandering Engineering discourse that we just can't stop ourselves from doing (Jester) - LNG vessels make their own nitrogen, high purity and very low dew point which is very usefull for blowing through equipment, pipes and spare gear etc for dehumidifying reasons and for lay up purposes.

I spent a good while experimenting with the plastic bag machine and spare gear to seal some essential spares in a bag with nitrogen - seemed to work ok, but possibly a bit of overkill - still it is these wee things that make life interesting, you never know what you may discover.

eriskay
10th June 2009, 19:07
Evening, SM :

Aye - it's hard to stop once you get started ..... !

Anyway, back in the 'bad old days', Desalination Plant shells were manufactured in carbon steel which was 'protected' by up to 400 microns thickness of expensive paint systems that invariably failed early in life due to the nigh-impossible task of successfully priming and multi-coating complex box structures with countless stiffeners, baffles, weirs, framing, etc., unhelped by the high humidity and condensation levels. When operational, the ensuing damage was relatively light, but under shutdown or mothballing conditions, the onset of severe corrosion was significant where punitive evergreen warranties and penalties were prevalent.

The solution for Plant in shutdown and boxed-in mode, was either to raise and maintain full vacuum (28-29" Hg in old money) within the shell, or, alternatively, introduce a nitrogen 'blanket'. Due to the large volume of nitrogen required for these large Plants, the former solution was generally opted for.

In later years, as the implication and associated costs of corrosion became evident to Clients and Consultants in this emerging field, specifications were brought out for clad or solid stainless steel platework, or cupro-nickel bonded plates. Nowadays, even that has been surpassed in the hot stages of Plants where titanium is widely used ....... ouch, oooh the cost, the cost ..... !

Old Desalter Fogie

Satanic Mechanic
10th June 2009, 19:19
Eriskay

I dig your jive(Hippy)

I have recetly been working on dual Fuel diesel electrics and have been actively pursing the idea of the dry lay up of a steam seperator on them using nitrogen. It goes without saying that the chemical manufacturers heard about this and immediately told dire stories of terrible and horrible accidents that befell anyone who has ever tried this in the past - I still think it was the better idea though.

Titanium - no matter what the cost is a god sent gift from heaven. It does have one potential problem though - it is so cathodic it can turn a whole system into an anode, seen this a few times

A Bernera boy

Duncan112
10th June 2009, 20:01
Eriskay


I have recetly been working on dual Fuel diesel electrics and have been actively pursing the idea of the dry lay up of a steam seperator on them using nitrogen. It goes without saying that the chemical manufacturers heard about this and immediately told dire stories of terrible and horrible accidents that befell anyone who has ever tried this in the past - I still think it was the better idea though.




Be interested to know what the accidents were - I have visited a couple of Lycra plants that manufacture under a nitrogen atmosphere - the problem there has been people using the nitrogen lines to supply air line breathing apparatus as the fittings are (or were) interchangable with a bit of force - as we breath an atmosphere of around 80% nitrogen there was no smell or warning just nearly immediate unconciousness followed by, in most cases death.

eriskay
10th June 2009, 21:49
SM - A Bernera boy? Small world indeed. Och, your wee island is only marginally bigger than my wee island, so there ..... !

Philthechill
10th June 2009, 22:10
Be interested to know what the accidents were - I have visited a couple of Lycra plants that manufacture under a nitrogen atmosphere - the problem there has been people using the nitrogen lines to supply air line breathing apparatus as the fittings are (or were) interchangable with a bit of force - as we breath an atmosphere of around 80% nitrogen there was no smell or warning just nearly immediate unconciousness followed by, in most cases death. Two things about the Ethylene Plant I worked at in Ras Lanuf, Libya. (I was converting one of their fridge Plants from working on R.22 to propylene. Why? Because of the fact that R.22 was a Du Pont product [American] and Libya at the time was under strict sanctions it was very difficult for them to obtain the large amounts of R.22 they needed to keep their many fridge-plants workable and as they manufactured propylene, on site, and it has a similar b.p. at -47C to R.22 it made sense to convert).

I arrived there to be told that there had been an accident involving a labourer who had been doing some work using an air-driven chipping tool to clean old paint off some pipes which needed painting. He'd put one of those "helmets" on (not unlike an old-fashioned diving-suit helmet), plugged the air-supply hose for the helmet into the nearest "air-line" and dropped down dead, asphyxiated by the Nitrogen he'd plugged into. So they were in the process of changing the fittings on the air-lines/nitrogen-lines (as you said Duncan, they were very-near identical) to make sure it never happened again. A bit late for the poor sod who was dead!!!

The other item, concerning Ras Lanuf, was a huge "field" of plate-coolers there.

I was told (maybe apocryphal, I wouldn't know) that when the Russian supplier made these plate-coolers it caused a world-wide shortage of titanium. Salaams, Phil (Hippy)

Satanic Mechanic
10th June 2009, 22:30
Absolutely essential to have different size connections. It happened again last year in DSME Korea. Painter plugged himself into the argon line - it should not have been possible.

Phil

I have been trying to get people to see the advantages of Ammonia plant for a while now, including using it indirectly for air con - whats your take on it?

Philthechill
11th June 2009, 09:27
SM! Morning! (08.25hrs.) Terminal 5 at Heathrow has got 4 off, 6.6mw water-chillers for the a/c system using NH3 as primary refrigerant. Ammunition there for you to use methinks!!!!!

Yes there are certain safety issues, regarding the use of NH3, but in this day-and-age of acute safety awareness and, of course, the vast experience gained by people like York, Sabroe, Frick etc., in the use of ammonia as a refrigerant, means there are very few safety problems these days.

I have, personally, been in some very fraught situations, with ammonia leaks, but they were, invariably, on pumped-liquid systems. This fact will come as no surprise to someone, like yourself, who has a more than passing knowledge of engineering principles and will understand what the pit-falls of a fully-pumped system will be.

I have no doubt that fully-pumped (ammonia) liquid systems are still being built but they have so many Achilles heels, in-built, I wouldn't be at all surprised if they weren't eventually outlawed in favour of using a secondary (thermal-fluid) refrigerant. I was involved in just such a system at the Glaxo plant at Stevenage. Ammonia was the primary refrigerant and a thermal-fluid (the name escapes me at the moment but, at 22.17, I just remembered! It was called Dowtherm!!)) was used as secondary. This thermal-fluid, chilled down to -25C, was pumped round the complex to be used in the various processes. The NH3 plant was in its own area which could be isolated and water-drenched if a sufficiently serious leak ever manifested itself. (Which I believe is "the norm" for NH3 systems these days where there may be members of the public close by).

There are several factors, about using ammonia as a refrigerant, which are attractive the most important, of course, is that NH3 is entirely natural being composed of Nitrogen and Hydrogen so, if there is a leak, it causes no harm to the environment. Another useful point about it too is its pungency which means that even the smallest leak soon lets itself known about! It's COP (Coefficient of Performance) is very high too which is another plus-point.

Not unsurprisingly CO2 is also experiencing a resurgency of interest but, because of the high-operating pressures (over 1000 p.s.i. on the high-side) compressors etc. have to be built on the "substantial" side, ergo, they are very costly!!!

We mustn't forget the good old absorption fridges either!

Refrigerant? NH3, Hydrogen and water all working happily together under the guidance of Daltons Law of Partial Pressures!!

When I was working in Botswana for a couple of years (1975-77) I would have to go out in the bush installing/servicing diesel gen-sets in remote hospitals, border-crossings, schools, etc. and every village I would come across would invariably have a bottle store with a vast chest-type beer-cooler full of Castle and Lion ale. All of these coolers would, of course, be cooled by an absorption-system using a kerosene-burner as the heat-source.

Absorption-system fridges are used by caravanners too so many, many, people rely on NH3 to keep their butter, milk, ale etc. cool, unbeknownst to them, of course!!!

So, after all this long-winded diatribe, SM, I guess you've worked-out that I am an enthusiastic supporter of NH3 just as I am of nuclear-power----------but that's ANOTHER pet hobby-horse of mine I won't go into just yet!!! Salaams, Phil(Hippy) P.S. I forgot to mention, too, there is a lot of interest being shown in NH3/CO2 cascade systems with NH3 used as the condensing medium for the CO2.

eriskay
11th June 2009, 10:58
Philthechill and SM :

Jings .... and there was me thinking I knew a wee bit about the science of refrigeration ..... ! (Slinks off in disgrace, head down, a wee bit wiser and certainly more informed .....)

Thanks for this thread !

Satanic Mechanic
11th June 2009, 14:26
Phil

Your on my wavelength on this one. I am a great fan of ammonia, it is pretty safe , probably the most efficient refrigerant, ecologically friendly, not very flammable, you always know when you have a leak and as you say it is easily knocked down with water.

My idea is to have a separate refrigeration plant room in the engine room and to use a straight forward vapour compression cycle with ammonia as the primary refrigerant and probably brine as a secondary either two systems for provisions and AC or a single brine system covering both. - so a relatively small primary charge of cheap and eco friendly refrigerant. HCFCs are so expensive as to be worth more than gold - why not just use the easy solution. Ammonia of course has a reputation amongst those who don't know it well - shame really.

CO2 as with nitrogen (which I have also used as a refrigerant in reverse Joule (Brayton) plant!) makes me nervous - no smell = nasty gas

sbkenn
20th September 2014, 22:28
Hi. Can anyone offer advice on replacing the V bracket bearing on my little ship, Portisham. I believe the original to be Lignum Vitae, but this, apart from being a CITES CatII protected species, would seem to be nearly impossible to find. I don't have a lot of cash available, but the shaft has dropped nearly an inch, so the job needs to be done.

surfaceblow
21st September 2014, 00:11
The following company supplies replacement for Lignum Viate Bearings.

http://www.pacificmarine.net/information/distributor/lignum-vitae-bearing.htm

Joe

sbkenn
21st September 2014, 15:29
Thanks Joe, I have sent them an email. Hopefully I won't need a mortgage to get one.

baileysan
21st September 2014, 20:41
Lignum Vitae

Early days at sea as junior, remember being in Panama News Year Eve, could see the fireworks from the local yacht club. loaded ship, we were down the tunnel with the 2/E trying to top up the excessive leaking stern gland. Split gland, With long studs, remove upper half force half turn greasy packing in the gland , pull up the the upper half and then try to do the same on the lower half. Nearly drowned in the aft tunnel bilge.

Sailed and drydocked many ships with LV tubes, if you docked at the right yard with the old time shipwrights they fitted and bored out the tube to about 1-1.5 mm clearance, however the secret was in the first few hours running, bring the shaft up to full revs over a few hours, stand over the gland and ease back to allow trickle of leakage never allow the gland to get hot or you could lose it, with big leakage or even more serious tube problems. I have have seen a few ships having to redock due to overheating and burning out the gland Fun and games however we never had to worry about leaky oil glands, but thats another story.

chadburn
21st September 2014, 20:56
Greasy Hemp packing will bring back memories for most Engineers along with a couple of turns of Serpent C.

Farmer John
21st September 2014, 21:47
Hi. Can anyone offer advice on replacing the V bracket bearing on my little ship, Portisham. I believe the original to be Lignum Vitae, but this, apart from being a CITES CatII protected species, would seem to be nearly impossible to find.

Sneak down to you local bowling green and conceal yourself near to the green. When play is towards you, judge your time and then leap out and steal the woods. Run off, giggling, with what may be a great harvest of Lignum vitae. ;>]

sbkenn
21st September 2014, 22:22
Lignum Vitae

Early days at sea as junior, remember being in Panama News Year Eve, could see the fireworks from the local yacht club. loaded ship, we were down the tunnel with the 2/E trying to top up the excessive leaking stern gland. Split gland, With long studs, remove upper half force half turn greasy packing in the gland , pull up the the upper half and then try to do the same on the lower half. Nearly drowned in the aft tunnel bilge.

Sailed and drydocked many ships with LV tubes, if you docked at the right yard with the old time shipwrights they fitted and bored out the tube to about 1-1.5 mm clearance, however the secret was in the first few hours running, bring the shaft up to full revs over a few hours, stand over the gland and ease back to allow trickle of leakage never allow the gland to get hot or you could lose it, with big leakage or even more serious tube problems. I have have seen a few ships having to redock due to overheating and burning out the gland Fun and games however we never had to worry about leaky oil glands, but thats another story.
Nearly drowning in the tunnel sounds like fun. The nasty spaces in my ship were down the fuel hold. 8 ft deep, 4ft wide, and just space for my hips to turn in. The other was inside the fuel tanks (2 x 850, 1 x 1000gallon), albeit on the quay. I had to suppress the panic until I got myself out again otherwise the tank would have to be cut open.
The bearings I need are outside in the V brackets. No access for greasing, so just water, and then just surrounded, not force fed.

chadburn
22nd September 2014, 13:27
[QUOTE=sbkenn;1064233]Nearly drowning in the tunnel sounds like fun. The nasty spaces in my ship were down the fuel hold. 8 ft deep, 4ft wide, and just space for my hips to turn in. The other was inside the fuel tanks (2 x 850, 1 x 1000gallon), albeit on the quay. I had to suppress the panic until I got myself out again otherwise the tank would have to be cut open.
The bearings I need are outside in the V brackets. No access for greasing, so just water, and then just surrounded, not force fed.[/QUOTE

Cutlass Bearings?

Duncan112
22nd September 2014, 13:41
Plenty here - should be well seasoned!! http://www.ebay.co.uk/itm/lignum-vitae-/141393040704?pt=UK_Crafts_Other_Crafts_EH&hash=item20ebae9540

sbkenn
22nd September 2014, 14:01
Plenty here - should be well seasoned!! http://www.ebay.co.uk/itm/lignum-vitae-/141393040704?pt=UK_Crafts_Other_Crafts_EH&hash=item20ebae9540

I had been checking eBay fairly frequently, but hadn't seen that one. Thanks
Can anyone describe how the bearings are made ? 1/4 sawn wedges, turned and split(or vice versa) ? I hope I don't have to pull the shaft ... not impossible, but a lot of heavy work, including removing rudders.

vickentallen
22nd September 2014, 15:04
Try Tufnol, can't remember what grade ( Bear ?? ) , but was used with success when Lignum Vitae became scarce..

chadburn
22nd September 2014, 18:54
You will have to remove the Props, then remove the intermediate shaft, thoroughly clean the Propshaft outside of the Hull and pull the shaft back out of the bracket but not out of the Stern Gland. Clean off the bracket so you can see the o/d of the bush and have a steel half inch thick washer made which can be used to pull the bush out using a strong back, threaded bar and distant pieces the length of the bush the washer should be just below the o/d of the bush. I hesitate to suggest knocking the bush out with a hammer and mandrel as the Hull area where the bracket is held may be a bit ripe. Look for grub screws which hold the bush in place and remove them one way or another. Other than that it could mean removing the bracket from the Hull to remove/replace the bush and then realigning refitting the bracket. Why are you not considering Cutlass Bearings?

Basil
22nd September 2014, 20:28
Thank you to the OP and contributors for a fascinating and informative read (Thumb)

chadburn
22nd September 2014, 20:54
If the prop shaft is worn where the bracket bush is located check that the prop shaft is reversible, usually they are. The taper, keyway and thread size are the same at both ends.