Shaft Seal

Tranona said:
Radice, which is a version of the Volvo type seal but with a vent that removes the need for burping. Also a port for greasing which avoids the need to go to McDonalds to get a straw (the recommended tool for greasing the standard type. Of you have problems fitting the Radice because of the external diameter of of the stern tube then a Tides Marine is also a vented lip seal, although a different design, but has a greater choice of bore size for attachment to the tube.
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McDonalds have stopped doing the straws.
Cardboard tubes now, and I've never yet managed to nurse one to the end of a milkshake without it disintegrating
 
Does the Radice seal need a water feed - seems to be varying info on the web re this

Does the PSS need a water feed
 
No. The pipe is intended as a vent to go above the waterline. Water feed is optional usually for higher power/speed craft ot as in my installation because the stern tube is long and there is an inboard bearing. Even then it is not strictly necessary but might as well connect it during the initial installation.
 
Tranona said:
Quite common for the shaft to float in the stern tube. You need to centre when you lone the engine up without the seal, then disconnect the shaft put the seal on and reconnect.

If that were my boat I would remove that inner rube housing, have a bearing (length of cutless or you could have one made in a composite like Vescomite or Maritex) inserted and the outside machined to take a Radice seal. you would have to use a good flexible coupling like a Bullflex or a Centaflex as the shaft will be fixed. New shaft needed with that amount of wear IF it is where the Radice seals will run.

This exactly what I am having done with my new Beta installation in my GH. My shaft length is on the limit for having no intermediate bearing. I like this arrangement as that is what I eventually ended up with when I re-engined my old Eventide and it worked very well - I am using a Bullflex coupling, again the same as I used before.

Hope this helps.

BTW where are you located? Lake Engineering in Poole are doing the machining on mine.
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Will a PSS seal provide some form of bearing/support for the shaft - difficult to ascertain this from the data sheets
One supplier advises that no modern seals provide shaft support so its a bit confusing when trying to decide which seal

Many thanks
 
gavin400 said:
Will a PSS seal provide some form of bearing/support for the shaft - difficult to ascertain this from the data sheets
One supplier advises that no modern seals provide shaft support so its a bit confusing when trying to decide which seal

Many thanks
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No, it doesn't provide support. The carbon piece with the vent pipe is attached to the bellows which in turn is mounted on the stern tube and floating around the shaft, the stainless rotor is fixed to the shaft and bears against the carbon. I'm lucky in having room to spare for fitting.

I got through two Radice moulded seals in the space of three years, each one eventually leaking unacceptably despite the engine alignment being as near perfect as possible. These seals eventually wore rings in the shaft, which was also new when the first Radice seal was fitted. The PSS seal as pictured leaves tha boat perfectly dry now

PSS.jpg
 
Does the shaft then just rely on the coupling to the gearbox for support to keep it centred in the stern tube

My shaft is just over 1m long (the stern tube is approx. 700mm long) and as far as I can tell there is no support anywhere along the length - it looks as though the packing in the old stuffing box kept the shaft centred


Lightwave395 said:
No, it doesn't provide support. The carbon piece with the vent pipe is attached to the bellows which in turn is mounted on the stern tube and floating around the shaft, the stainless rotor is fixed to the shaft and bears against the carbon. I'm lucky in having room to spare for fitting.

I got through two Radice moulded seals in the space of three years, each one eventually leaking unacceptably despite the engine alignment being as near perfect as possible. These seals eventually wore rings in the shaft, which was also new when the first Radice seal was fitted. The PSS seal as pictured leaves tha boat perfectly dry now

View attachment 138564
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gavin400 said:
Does the shaft then just rely on the coupling to the gearbox for support to keep it centred in the stern tube

My shaft is just over 1m long (the stern tube is approx. 700mm long) and as far as I can tell there is no support anywhere along the length - it looks as though the packing in the old stuffing box kept the shaft centred
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Yes, it does with mine, gearbox at one end and cutlass bearing at the other
 
gavin400 said:
Does the shaft then just rely on the coupling to the gearbox for support to keep it centred in the stern tube

My shaft is just over 1m long (the stern tube is approx. 700mm long) and as far as I can tell there is no support anywhere along the length - it looks as though the packing in the old stuffing box kept the shaft centred
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It all depends on the design of the flexible coupling. Some are designed to allow the engine to move while the shaft is restrained by an aft bearing (alowing for both radial and angular misalignment) and some designed to keep the shaft centred in the coupling when there is no aft shaft bearing (only providing angular misalignment) . The Vetus Bullflex couplings have a centering ring that can be removed or left in depending on what is required. You certainly do not want the wrong combination.

www.solocoastalsailing.co.uk
 
gavin400 said:
Will a PSS seal provide some form of bearing/support for the shaft - difficult to ascertain this from the data sheets
One supplier advises that no modern seals provide shaft support so its a bit confusing when trying to decide which seal

Many thanks
Click to expand...
Not specifically, only in the sense that the bellows have a degree of rigidity. The Volvo/Radice does as the round part that attaches to the tube is effectively a cutless bearing approx 50mm long. In most cases this is all that is needed and is really no different from an conventional stuffing box on a short hose in that it supports the shaft while offering a degree of flexibility.

Whether you need a fixed intermediate bearing depends on the length and diameter of the shaft. The maximum unsupported length of a 1"/25mmn shaft is approx 1.5m. Over that and you can get shaft whip. If your shaft is shorter than that you can go with a solid or just flexible coupling, a Radice and cutless, provided you centre the shaft in the tube and the tube has enough clearance - 30mm+ ID for a 25mm shaft. If you don't have that clearance then you run the risk of the shaft touching the tube if you have a bouncy engine. I found this out the first re-engine I did with a 1GM and a Stuart Turner tube that had 1 1/4" ID and a 1" shaft This was not shaft whip - the shaft was less than 1m long but simply engine movement with a solid coupling.

The solution was to fit a short piece of cutless in the inboard end of the tube (originally there was a white metal bearing which we had removed) so the shaft was supported at both ends, a Volvo seal (later a Radice) and a Vetus Bullflex coupling Worked perfectly.

My project Golden Hind has a long shaft 1.6m and currently has (I think - have not taken it apart yet) a bearing at the inboard end and a flexible hose to a stuffing box. The engine is 35 hp with an R&D coupling to a shaft 1 3/8" and a 17" prop. It will be replaced with a Beta 30 and 2.6:1 reduction Bullflex coupling a 30mm shaft, Radice seal, bearing in the inboard end if there is not one already and a cutless outboard to a 17" Featherstream prop. This is essentially the same as above except the larger shaft because of the extra power and length of shaft.

Personally I don't like face seals based on both principles of how they work and experience when they were first available for boat shafts. I appreciate that the PSS is far better engineered to overcome the basic problems (face seals do not like any shaft movement either fore and aft or particularly side to side), nor do they like being left for long periods without rotating with a water flow. They were originally designed for things like pump shafts that were fixed and in constant use. However the engineering to make them work in boats means they are now very bulky and 3 times the price of simple lip seals like the Radice and require careful setting up and monitoring. Their big advantage is that the don't run on the shaft so are great if you have a worn shaft. However you are doing a new installation so you won't gain anything from this.
 
I tried a PSS for 8 years always had a bit of spray I put this down to shaft length. Also stopped a friends boat from sinking when his bellows ripped on a PSS type seal. Probably lack of maintenance . I just never slept calmly with the idea a piece of rubber is the difference between submarine or boat then again same goes for sail drives. Its whatever you are ok with . Stuffing box and greaser for me.
 
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