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That Sinking Feeling (story In Pictures)


TeamElla

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which sits in the right position at rest”

At least I hope so. That’s in the hands of the yard fitters.

We can’t do anything about the shaft sitting high in the shaft log without taking it out and refitting it and THAT’S NOT GOING TO HAPPEN. (I’m done with removing it, refitting it and glassing it back in again).

Re using the meter to check continuity:-

You’re right Simon but resistance through the water will be very high. Using the buzzer is your best option to check for actual contact. Apart from the actual resistance readout, it needs a little extra current to flow (albeit very small) to sound the buzzer.

 

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19 minutes ago, SimonA said:

I'm watching with interest! Perhaps you could make a few pounds selling them to other Madeira owners, I'm sure lots of us will have the same problem. 

I don’t think that the “waggle” would be a problem if our prop shaft was sitting bang in the centre of the shaft log, but the PSS Shaft Seal will certainly appreciate not being waggled about.

Another revelation:-

During the waggle, water comes pouring out the end of the tube on the PSS Seal’s air vent (It seems to act like a pump!)

This seems to happen on all PSS Seals when you’re going astern and I’ve wondered for months where the small amount of water in my engine compartment bilge was coming from.

PYI have now produced a special valve to put on the end of your vent tube that shuts when water reaches it. It’s called something like “hy vent”

Link will follow when I find it....

 

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55 minutes ago, TeamElla said:

Another revelation:-

During the waggle, water comes pouring out the end of the tube on the PSS Seal’s air vent (It seems to act like a pump!).

 

I should clarify that.

Water only comes out when the waggle is causing the prop shaft to hit the shaft log. Directly on cue it comes pouring out during the banging (and I do mean pour, it’s no trickle).

Astern it always happens.

 

 

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probably the seals are designed to work in compression, when you go astern the boat is being pulled along by the prop shaft, so the seals are no longer compressed, this may be curable by lessening the amount of play fore and aft in the prop shaft, when you have a wiggle going the seals will be struggling to seal the shaft.

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Again to clarify:-

Our PSS Seal never leaks (even during the prop shaft waggle). These seals always have river water within their vent tube up to the boat’s water line. Both our’s and Simon’s vent tube run right up to the top of the engine compartment and that’s where the water has been emerging. Weirdest thing to watch and I have the video to prove it.

On a fast boat (at above 12 knots) it is necessary to pump water down this tube to lubricate the PSS seal as the water drains outs of the shaft log / stern tube at greater speeds.

On displacement boats like ours there’s no need for all that malarkey.

 Re our prop shaft:-

I am not aware of it moving  fore and aft at all under way (forward or astern)  

For those that are not familiar with PSS Seals:-

The rubber gaiter clamps onto the shaft log / stern tube and has a mobile graphite sealing block on the other (forward) end of the gaiter which bears against a machined stainless steel mating ring that is clamped onto the prop shaft. This ring has an “o” ring seal to the prop shaft and it is slid backwards to compress the rubber gaiter a set amount to maintain the graphite/metal rotating seal. When it’s first fitted, the graphite/metal seal needs to be run in for about an hour to stop it dripping and leave you with a bone dry bilge from then on (unless water’s coming in from somewhere else).

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  • 3 weeks later...
22 minutes ago, BroadAmbition said:

Wow, Nice one, well done :default_beerchug:

Griff

Thanks Griff

It’s thanks all round really with Vaughan posting the original introduction to plummer blocks, followed by your pic (which set the seed of an idea) and finally to Horning Pleasurecraft for carrying out the actual fabrication and fitting of the custom bracket.

I’m just glad that I got the measurements right!

p.s. if Simon is reading this, I will give the bracket drawings and details of the plummer block (as used) to any centre cockpit JGM Madeira owners that ask for them.

Rgds,  Steve

 

 

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That looks great. I've now got new rear mounts fitted to my boat. The bolts through them still look off centre so I'm not sure how long they will last. The mechanic that fitted them reckons they are OK and I don't have any vibration under way or at idle. One mount was totally scrap but the other wasn't too bad, so I have a spare for the future. 

I think (hope) there wasn't any damage to my shaft log but it's impossible to tell for sure as it can't be inspected. 

My mechanic said it is very difficult to align the shaft on these as it doesn't have a natural central position. 

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