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Stuffing box
Posted by: paulmcnicholas (IP Logged)
Date: July 6, 2011 08:05PM
Category:

My stuffing box hose is about 10 inches long and is totally inaccessible once the engine is in (engine muffler covers it completely). Was thinking of lengthening the hose to about 24 inches to bring the business end to a point where I can adjust packing nuts with engine in place. I will leave enough room to back off the nuts and repack as required. Any reason why I should NOT increase the length of the hose? Given that prop shaft comes in at a shallow angle the whole thing should remain below the water line and therefore should get the requisite 3-4 drops/min.
Also, given the difficulty in reaching stuffing box as thinking of using graphite packing - ay comments
Thanks for your feedback.
Paul

Re: Stuffing box
Posted by: Bil (IP Logged)
Date: July 8, 2011 02:22AM
Category:

Use of graphite packing depends a little on:

1. the nature of your prop shaft; and

2. whether the boat sits for long periods in seawater with no movement of the prop shaft.

The crux of the matter is that the graphite and passivated stainless steel 316 combination is not ideal in stagnant (ie low oxygen) seawater.

Theoretically, graphite will act as the cathode and ss as the sacrificial anode, with a potential difference of as much as 0.4 - 0.6 volts.

In practice, I've run a MV with an ss shaft and graphite packing. And did not notice any electrolysis of the ss. I've heard of other vessels with the same combination.

In my case, I did change back to traditional packing after realising the potential for electrolytic corrosion. The real situation is more complex than the theory - most seawater contains enough organic matter that, when captured within the shaft log (or anywhere else), decays to form hydrogen sulfide H2S. That changes the theory considerably.

Cheers

Bil

BCC 116 Zygote,
Scarborough Marina, Moreton Bay, Queensland, Australia



Edited 1 times. Last edit at 07/08/11 10:37PM by Bil.

Re: Stuffing box
Posted by: paulmcnicholas (IP Logged)
Date: July 15, 2011 04:04PM
Category:

Very useful, thank you Bil. any comment on extending stuffing box hose?
Paul



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