nb-Dusk Till Dawn

[bottle]

I see the lubrcation system but no flexible coupling is this still needed, or as mentioned before, the engine is solidly mounted so no flexibility is required.

Sorry to be a pain but am trying to learn.

[Amicus]

In this case no flexible coupling is fitted nor is it desirable. It's difficult to explain this

Try this, imagine the engine and shaft as a unit (which they are here) the unit waggles about an arc centered on the bearing, the bearing is right aft, just in front of the prop' the bearing is made of a resilent synthetic rubber and can accomodate the waggling.

The gland is some way forward of the bearing so has to accomodate some radial movement, so is mounted on a short lenth of rubber tube. Hope this helps, if not praps we should go to PM.

ps. another way to see it, the engine hanging from the shaft, like a pendulim and the bearing is the pivot

Edited February 9, 2005 by Amicus

[bottle]

Thanks Amicus

 

I think I understand, There is a small amount of movement allowed by the design of the bearing (Not solid i.e. brass) and the gland is also flexible (rubber tube).

 

Thanks again

[Amicus]

Correct, If a flex coupling were to be introduced the whole system would be too wobbly.

Edited February 10, 2005 by Amicus

[Amicus]

As an aside for those interested/curious, a Cutlass Bearing; a brass tube, say 150mm long filled with a synthetic material, looks the same stuff as Doc Martin boot soles, this has a hole up the centre to take the shaft. The hole is not circular but octagonal, the dimension across the flats is slightly less than the shaft diameter. This bearing slides into the outboard part of the stern tube and held with a couple of grub-screws. It should be considered a “consumable” to be checked for wear regularly, cop ‘old of the prop and give it a good shake, if any play is felt replace the Cutlass, they aint big dollar.

[ChrisPy]

Amicus, what you are saying makes a lot of sense and is indeed what I have experienced on salty boats.

 

I suppose if you decide to fit a flex coupling, then you should use a fixed stern gland (that does not incorporate the hose section).

 

I guess it is also very important that the engine runs smoothly (which modern high speed diesels should do, compared with their elder brethren) and the mounts are in good condition. The limited flexibility in the system supplied would not tolerate a badly knocking engine or very soft mounts. We should really talk about 'resilient' engine mountings, not 'flexible', because flexible gives the wrong impression.

 

The beauty of such a simple system is that engine alignment is simplified. Because the stern tube centreline is only defined at one point, the only requirement is that the gearbox output shaft has to point in the right direction (at the centre of the cutless bearing).

 

I hope that Stuart and I can now relax.

[ChrisPy]

interested to see the bilge pump is fitted under the gland.

Is the compartment under the gland sealed off from the rest of the bilge?

Is there a separate bilge pump?

[Gary Stacey]

Its the first time I have come across this arrangement in a narrowboat. Coming form a power station engineering background i am used to the fixed bearing flexible coupling arrangement so often seen in motor pump combinations.

 

In view of Amicus's explantation and his greater knowledge opf this area I do belive you can rest easy. I would suggestthough that the alignment has to be 'reasonable'

 

 

Gary

[stuart]

interested to see the bilge pump is fitted under the gland. 

Is the compartment under the gland sealed off from the rest of the bilge?

Is there a separate bilge pump?

<{POST_SNAPBACK}>

 

The gland bilge compartment is sealed from the rest of the engine bilge. At present there isnt a bilge pump in the engine compartment. I presume this is so that engine oil/grease cannot be sucked up and spat into the canal.

 

However saying that, theres also no water in the engine bilge at all. Bone dry I assume the self draining deck and boards are working as they should.

 

The existing bilge pump is as supplied by Liv. Boats.

 

I did think that it was a little strange that they purposely cut a square "tray" out of the base just to locate the pump. I expect it may foul on the prop shaft if they didnt do this.

 

If you look at the gear box picture in the earlier posts you can see the steel wall seperating the two. Theres no "drip" from the stern gear at all. The water in the bilge is what I've put in there (to test the pump) and since removed!!

Edited February 10, 2005 by stuart

[nigel carton]

Hi Stuart,

 

I delivered a new LP boat from Hanbury wharf last year to Sawley marina, all went well apart from 'breaking down'! Here's what happened. Going along the canal, I noticed a drop in power, it got worse to the point that I had to pull over. First line of action, weed hatch, there was some crap in there, so cleared it, and on my way again, for about 5 minutes! Same problem occured. This time I susspected a fuel problem. After a couple of hours of investagative work, I managed to remove bleed screw on water separater and 'blow back' after going a purple in the face I felt a 'glup' in the tank. This sorted the problem. Told the owner and we decided it could have been some ptfe tape come adrift from the isolation valve and acting as a diaphram. The owner after a couple of weeks was not happy that his brand new boat could have nastys floating around in the tank, got lp out to investigate further. What had happened, when the two feed and return holes where cut at the top of the tank, one of the discs had fallen inside and had blocked the fuel feed pipe. I'm sure this was an isolated insident ( nice boat ). One last thing, don't forget to turn the red valve on stern tube on, your picture shows it in the off position.

 

Nigel

[Richard Bustens]

Hi all

I have just looked ar the vetus page on the shaft, and it still shows it used with a flex coupling.

[Amicus]

Yes it does, and I am adamant this is incorrect. Having said that, at the power levels we are talking here I don’t think it is critical. You pays yer money etc.

I have been involved with some high power planing boats where the flex coupling type set-up has caused sever problems, bloody frightening it where.

[ChrisPy]

I s'pose we should think realistically.

 

When an engine is rocking on its resilient flexible mountings (the normal mode of movement), it is moving rotationally about a centre of rotation close to centreline of the final drive shaft. That type of movement represents next to nothing in terms of lateral or angular displacement with reference to the prop shaft.

If the engine is correctly aligned and the mountings are in good condition, there is no other opportunity for movement. If it is shaking in any other sense there is something seriously wrong with the engine.

 

On a steel boat we should not have to worry about the engine not being fixed relative to the sternpost or wherever the shaft leaves the hull. That would be a concern in a more flexible hull (timber or GRP).

 

 

........... all a storm in Richard's teacup? (sorry, couldn't resist).

[Amicus]

The beauty of such a simple system is that engine alignment is simplified.  Because the stern tube centreline is only defined at one point, the only requirement is that the gearbox output shaft has to point in the right direction (at the centre of the cutless bearing).

<{POST_SNAPBACK}>

Care needed here, when aligning the engine the shaft must be in the centre of the forward end of the tube, if doing it ashore loosing the gland and slide it forward out of the way then move the engine so that the shaft is centred in the tube.

To do this afloat is a whole new ball game and involves a lot of water where it oughtn’t be. Alright in the summer but a bummer when it’s freezing

[Guest]

One last thing, don't forget to turn the red valve on stern tube on, your picture shows it in the off position. (Quote from other post.)

 

I will stand corrected if I am wrong, but I am nearly certain the valve handle should point upwards for "on" in this instance-I will check ours at weekend!

Edited February 10, 2005 by stan hesketh

[bottle]

I agree about the valve position being open in the picture.

 

I have always believed a valve of this design to be "open" when the lever is in line

with the pipe/hose etc.

[Amicus]

Hi all

I have just looked ar the vetus page on the shaft, and it still shows it used with a flex coupling.

<{POST_SNAPBACK}>

Just had anuver shuffty, the gland shown is new to me. It appears not to use a stuffing box but a lipped seal, I think this is the same as what in my motor cycle days was called a "Payen Seal", common or garden oil-seal type gizzmo.

If this is the case all my ramblings about PTFE etc. are redundant.

I did admit to being not up to speed

[Guest]

It does have a double lip seal (Vetus seal in our case) and is lubricated by silicon grease only. About one c.c. of (silicon) grease is added per year. The pipe up to the weedhatch is a breather pipe, and the valve should be open. Sometimes we get a couple of tiny spots of water thru seal when in reverse, but otherwise nothing. How long will it last? Who knows!

[Amicus]

"The pipe up to the weedhatch is a breather pipe"

 

Aha! now the light is dawning, that make a lot of sense.

I was worried about water getting thru that pipe from the weed-hatch. Learn something new every day

[John Orentas]

Looking at the more detailed photo's the stern tube may well be the rubber mounted flexible type which was quite common some years ago. But there does not appear to have a flexible coupling at the gearbox end which is still required, though a single Hurth type would be ok.

[Guest]

Ours is almost the same as photos enclosed (which all appears to be vetus) with the addition of a nylon r and d coupling detween gearbox and shaft. I have seen others with the same set up but minus the r and d. I am not knowledgable enough to know what is right or wrong, save to say that our last elderly boat had an r and d and seemed to have lasted ok. That had a more traditional stuffing box though. I have seen pictures of sea going vessels many of which appear not to use flexible couplings.

I would have thought that L'pool boats have got their installation correct after the amount of boats they have produced!

[John Orentas]

Stan.

 

I don't know the percentages but Liverpool Boats don't fit engines as a matter of course, they build shells, that's what they are good at. The problem is that the narrowboat business has always been plagued by a significant minority of 'Engineers' who are here one day and gone the next, many of them have only the vaguest idea about engines, boats and engineering generally.

 

Sea boats traditionally had their engines rigidly mounted and had long slim prop-shaft which would flex a little to allow for small inaccuracies.

[stuart]

Heres the latest photos and progress reports. Only 4 building days left until I have to return to work to pay for this damn boat! so progress may slow a little bit now.

 

 

Work done since last update. Continuing panelling the shell. Built some steps from the stern into the cabin (really should have done this on day 1 as it would have saved a lot of hassle). Sorted out the centre roof channel to hold the lights and cabling etc. Real pain to get a good centre line down the length of the boat. Time to start putting in the electric cables now.

 

My wood work skills are improving, if only my angles were better!

 

 

 

[nigel carton]

Annoying when that old work thing gets in the way!

[Big COL]

Hi Stuart

 

Its looking good. How many of you working on the boat? you seem to have done a lot of work in a short space of time. I hope there weren't too many mistakes,we have all been there, remember the old saying. Measure TWICE and cut ONCE. Good luck it will all be worth it.