JohnDean

I wouldn't bother with anything other than the bog standard Nitrile seals. You don't need the extended temperature range and the seal will fail through lack of lubrication in the end. With all the will in the world, it's almost impossible to adequately lubricate these and I don't think water is that great a lubricant. They last pretty well so long as you periodically grease them, and now you know how to swap the seals for next to nothing it's really not a problem if you end up doing it every few years. Just have a spare set of seals and an 'O' ring in the spares kit.

You're most welcome. You did get some of the right grease from Vetus to squirt in between the two seals though? Don't panic if you didn't just get plenty in there as soon as you can. I think the instructions say to fill it at least half full of grease. I don't think the one on mine ever had any grease so that's why I'm saying don't panic. I'm sure it won't hurt it to run for a little while without. I just had alarm bells going off in my head because you didn't mention the grease. They do say that it's important to only use their grease by the way. You can get it from their web site.

The ones on the original unit didn't have garter springs, but the type I bought did. I don't think there's an issue with either type. I think the ones without the garter just use more rubber to provide the grip on the shaft, that's all. You're most welcome. I think it's only fair to give something back when people have been so helpful. This repair has saved a lot of money and I'd like to think that someone else will now have everything they need to do the same without any major headaches. Without all your help, I wouldn't even know what stern tube make is was, let alone get it all fixed. These places are gold dust if we all feed back what we discover.

If you go to this page, you can enter the dimensions of any seal you like and you'll get all the options. The originals are standard Nitrile ones, but Vetus must be a pretty large outfit because they've had their name added to the moulding. I expect they would tell you that they're special, but I'm certain that they aren't. Just bear in mind that mine has a 35mm shaft, yours may be different. They go up in increments of 5mm, so just wrap a piece of paper round yours and mark off the circumference, divide by 3.14 and that will tell you what yours is. http://simplybearings.co.uk/shop/index.php?cPath=19_4463 I think someone from here said it was an R&D coupling. It's pretty flexible. You need have no worries about these stern tubes, in my opinion they are very sound in principle and less maintenance than most. I suppose the Vetus fitter ought to know what the tube is for, and that's what I would call it. There's no continuous flow through it, as some suggested. It just ensures that the gland is always full of water. It's nothing more complicated than that.

Gosh, that's a lot of feedback.... I'll try to address all the issues as well as I can from what I discovered. Firstly, there's only a flat plate covering the top of the weed hatch, no extension and a flat plate above the propeller. The outlet of the small pipe is a very long way indeed above the water level, there's no way you would put something in that position if it was supposed to be taking in water. This is clearly a vent. Without it, I suppose it's possible that water could be prevented from reaching the first seal and it needs that for lubrication. There are a key couple of words in the instructions that call the large rubber hose connecting the fixed part to the seal the 'Water Feed Pipe', that's a big clue. Presumably the function of the vent is to allow the water to rise up it until it's level with the water outside. This will mean that as the pressure varies due to the action of the propeller, the level will change but the area around the seal will remain full. This all makes sense to me. Cooling is irrelevant in these terms, there's no significant heating on the bearing or the seal that would not instantly be conducted away by the water and metal parts. The engine mount is very flexible, and the coupling is fairly compliant too. I don't think the alignment is that bad else I wouldn't have been able to get the propeller shaft out while the four bolts to the flexible piece were still tight. I think it's probably not far enough out to warrant any further attention. As far as I can see, the only way to check the alignment properly would be to remove the flexible piece from the centre of the drive coupling and then use a dial clock attached first to one coupling flange and then the other. It would be possible to determine not only the height difference in the middle of where the flexible coupling would be, but also the relative distances between the flanges at four points of the compass. With a little ingenuity you could figure out what angle and offset the engine had to the stern tube. Do bear in mind though that the propeller shaft will only be in the nominal centre of the stern tube, wherever it naturally sits due to the pressure of the seals. You can very easily displace it some distance in either direction so going overboard about accuracy is a bit meaningless. You'd have to force the shaft in each direction and measure those positions from some reference point before you could be sure of where the true centreline is. Even then, would you be aligning it with where it's worn already? I think that if the coupling goes together easily, and the shaft doesn't have to be forced to one side or there's an alarming amount of slack to be taken up when you tighten the bolts to the centre part of the coupling, then I'd leave well alone. For your information, here's the repair procedure I've noted for the cartridge itself.... Repairing the seal cartridge... The lip seal used in the cartridge is a rotary shaft seal 35x52x7, these being the dimensions in mm. The 'O' ring is 2mm section with an inside diameter of 56mm. Both of which can be obtained from SimplyBearings.co.uk The seals are not a tight fit and can easily be pushed from their housing with a screwdriver from the back. Make sure to fit both of them the same way round ie with the open end of the seal facing the inside of the cartridge. Bear in mind that this is for a 35mm propeller shaft. Yours may be different. The seals are very cheap, less than £4 each, so knowing what I know now, I'd just measure the shaft with a pair of vernier calipers and do the same where you can see the outside of the black seal. Those two dimensions will probably determine what thickness the seal is going to be, and for that price it's worth a punt and just buying them. The seals need to be pressed in flush with something flat but it takes very little force. All this can be done while the seal is off the boat, it only takes a matter of minutes. Take out one seal at a time, then you could always put it back if you ran into difficulty. Now I've got the spare, I've replaced the seals, bought new 'O' rings, and that can sit in the spares box in case there's ever a 'next time'. I hope that's useful

Indeed you did! That's why I listen to those with actual experience and don't get spooked by those who haven't. It's really easy to be put off doing anything like this when your first contact with the supplier is a very negative one and there are dire warnings from people who've not had one of these apart in the water. It also doesn't help that the boatyard didn't even recognise the type, said they couldn't repair it and it would be better to fit a completely new unit of a different more common type! Still, a bit of research, help from people like your good self and a healthy dose of common sense and here we are with it sorted out without difficulty. It doesn't say much for the boatyard, does it.

Ok, after much thought and all your good advice I can now report that the job has been done and it was very easy indeed and not at all alarming. The 'Cassette' with the two seals in it was bought from Vetus for just over £100 delivered which wasn't too expensive. It's the 35mm size for this boat, that's the size they normally fit to wide boats by all accounts. It was out of stock but took less than a week to arrive. The flexible engine coupling is of a type that doesn't use a key, it relies on friction alone on the plain shaft. The four bolts were slackened and I managed to twist the propeller shaft out of it with a bit of effort. I was expecting that to be much more difficult. With hindsight, I should have slackened the four bolts that go to the flexible cross element of the coupling too, it would have made life easier. I only discovered this when I couldn't easily re-insert the shaft. It started easily enough, but there's obviously a slight misalignment else it would have gone on as easily as it did with those up tight. The propeller shaft have clearly been cut to length with some kind of disc grinder, and the edges were razor sharp. I rounded them off with a file and emery paper until they were nice and smooth. A trial of the new seal on the shaft showed how easy it was to get on so there was nothing for it but to have a go. The instructions mentioned an assembly sleeve, but that hasn't been included in the kits of this size at least for some time. I've fed this back to Vetus. Since there's no key on this installation, it wouldn't have been needed anyway. After taking off the three Allen Cap screws on the old seal and breaking the seal, there was very little water indeed escaping. You could have left if for an hour and it wouldn't have been a problem. A cup full every minute at the most. I'd already greased the shaft with the grease supplied and put the bulk of the tube in between the two seals. They say fill it to about 50%, and that's about all the grease you get anyway, it's not a big tube. I kept a little back to add later but I need to get another tube really. Slipping the old one off and putting the new one on was very quick and easy. There's an 'O' ring instead of a gasket on this size, but the 'O' rings is about the same diameter as half way down the taper of the mating face. It wasn't clear how to line that up really. I greased it and inserted it into the fixed part of the stern tube and it seemed to stay in the middle. Whether there's a proper register for it is hard to tell, I couldn't get close enough to get a look. Anyway, offering up the cartridge with just a gentle pressure was enough to completely stop the water so I presumed the 'O' ring was located correctly. That all tightened up with the three Allen Cap screws and now there's no sign of a leak. Now I've got the old one home, I can see that it hasn't got the slightest hint of grease on it, so I can only assume that it was installed without any. It's no wonder it failed! Anyway, all's well that ends well, and I thought it only fair to report back and to pass on what I learned. This isn't a scary job at all, and you shouldn't be spooked by any of the doom and gloom merchants who think there's going to be a Tsunami when you remove the seal. (other stern tube designs may differ!)

Many thanks, that's most reassuring.

Thanks for that.

I'm struggling to find any technical data on this alternator fitted to my Big Fish wide boat. I've searched the internet and HMI don't seem to exist and entering the part number on the plate draws a blank too. Does anyone have any idea who makes and supports this type?

All noted and taken on board. Good point about protecting the seal by covering any keyway and also doing a trial fit before removing the old one. I imagine that a sea going boat is likely to have the stern tube a lot further below the waterline. If that's the case, the pressure would go up in proportion to the depth so on a big boat that could be significantly more than on a canal boat. I sent Vetus the pictures and indicated that I'm an Engineer and that prompted a more positive response as follows.... That is definitely one our ZWB bearings – looks bigger than a 25mm shaft. Most wide beams use 35mm. With the boat standing still – there shouldn’t be any water coming in through the water feed tube. If you open the hatch; you should (if it’s been installed correctly) see the water level below the skin fitting. The cassette slides off once the three Allen headed cap screws are removed (not the top greasing one): http://www.vetus-shop.com/replacement-dual-lip-seal-for-vetus-zwb35-p-2549.html You have an R&D ‘half split’ shaft coupling – which will be easy to slacken off. The shaft will need to slide back enough to slip the old seal out and the new one in with its gasket. I would clean and grease the shaft with some silicone grease first. Once the front cassette is removed – there is no seal between the shaft and the stern tube – so water will gush in through the flutes in the bronze housing. A combination of a rag stuffed in and your Rulemate 750 switched to manual should cope. Please note; I am not encouraging/advising you to do this yourself with the boat in. It’s really a job for a marine engineer. Out of the water you’ll have no problems. That's a lot more encouraging, and is more in line with what I was thinking. It's clear that the bearing is designed to pass water so their comment about stuffing rag into the gap makes sense while it's off. It certainly sounds like it's going to be more than a trickle though. Can I ask Bizzard if the ones you've done have been of this type and while in the water?

I had this reply back from Vetus... It is possible – but not advisable. You would need to separate the shaft from the gearbox coupling and have enough room behind the prop to give you a 2” gap. If you are quick – then you can slide the old cartridge off and get the new one on. Not a job for the faint hearted. I'm inclined to think that they're just covering their backs really. From the replies here, the amount of water coming in with the seal removed isn't that alarming. I'm inclined to just be prepared with an extra pump and just get on with it. It can't take more than a couple of minutes to swap the seal over. Is that the conclusion that anyone else comes to?

I'm not sure how much flex there is in that coupling. It's not a simple matter to confirm the alignment to an accuracy of a few thou. I could take the coupling off completely and then clock round the engine shaft with a dial gauge on the propeller shaft I suppose. I have that sort of kit, being an engineer. That wouldn't tell if the axis of the engine was true to the shaft but it would give an indication as to whether it's miles out. I guess the most telling piece of evidence will be how much play there is in the propeller shaft bearing when it's detached. If there's precious little then I'll leave it as it is. I think some rag wound round the shaft on the exposed end of the stern tube ought to stem the flow while the seal is being replaced. Hopefully that won't take long and it won't be necessary.

What a helpful and knowledgeable and friendly bunch you are! I can't thank you all enough, this information is exactly what I need to know. I guess it will be obvious how out of line anything is when the coupling is undone and the propeller shaft is slid forward. From what you say it doesn't sound as if there will be an alarming amount of water coming out of the tube unless the bearing is badly worn. Even if it is, the new seal ought to keep the water out until such times as it can be taken out of the water. There's no sign of any tube of grease in the bits and pieces I've inherited from the previous lady owner. It's entirely possible that she didn't appreciate that this needed regular if infrequent greasing, so it may just be that just the seal has been destroyed. Looking at the Vetus web site, they sell the seal with gasket and grease for just under £100 delivered which sounds reasonable to me. I just need to measure the shaft diameter and then it's decision time.They only seem to make the one style and in 5mm shaft increments so it ought to be easy enough to get the right part. Once again, a big thank you to you all, it's very much appreciated.

Thanks for that Kevin, there are a couple of suggestions there. I'll ask Vetus as well if they have a preference. That thread seems to suggest that it's possible to replace the packing on stern tubes in situ but the Vetus one isn't an adjustable type. Does anyone know if it's possible to be done on the type I've shown in the picture? Since it's a water lubricated type, maybe you can't? I was surprised to see that there wasn't a permanent way of inserting grease into that type of seal, I have no idea what the thread size is or where I can get an adaptor for a grease gun. How is it normally done, and does water erupt from the hole when the bolt is removed?

Thank you so much, that's a huge help. So are you of the opinion that it's just short of grease then? As you can see from the closeup picture, there's a steady stream of water coming in. Is there a particular silicone grease that you know the grade of?

I've recently purchased a wide steel hulled canal boat that was manufactured by Big Fish Boats who I understand have gone out of business. The stern gland has a significant leak that needs attention but I'm having difficulty in identifying what make and model has been fitted. From what I can see, It would appear that it's a job that could potentially be tackled while the boat is still in the water because it looks like the propeller shaft could be detached from the coupling and slid towards the stern. That would allow the seal to be replaced, albeit with water escaping while the seal is being swapped. So the key questions are these.... Does anyone recognise this stern gland from the picture and where a replacement seal can be bought? Is there any way of contacting someone associated with Big Fish who would know what they used to fit to their boats? And finally,,,,,, has anyone been brave/stupid enough to affect the replacement of a seal while the boat is still in the water? Any help would be much appreciated. Hopefully these photos will show enough detail to identify the stern tube.