Stuffing box seal

[Tamar]

I'm about to replace the packing in my traditional stuffing box. The stuff I bought is 1/4 inch for a inch shaft, it contains PTFE and silicone. So just looking on the web if how to tackle this job and most people say to use graphite impregnated packing. No I'm confused..the boat is only being lifted out for an hour to complete this job and I want to get it right, any advice on both packing material would be welcome. The boat does lots of hours. The last lot has lasted five years without problems.

 

[Deleted member 36384]

Do not use graphite according to this article (also contains descriptions of packing material options) https://marinehowto.com/re-packing-a-traditional-stuffing-box/

The down side to graphite impregnated packing’s is that graphite is the most noble element on the galvanic scale. In other words graphite packing materials can cause localized damage to shafting and can increase anode erosion rates. The ABYC and Western Branch Metals (The largest prop shafting manufacturer in the US) specifically disallow the use of graphite packing materials.

A YBW thread which may help http://www.ybw.com/forums/showthread.php?390080-Gland-packing-Graphite-or-PTFE

Cox Engineering, which is very useful http://coxeng.co.uk/stern-gear/stern-glands/

I used the traditional flax stuff now, with grease lubrication.

 

[Tamar]

Thanks, I've read lots this windy afternoon. There seems to be +s and -s for both. I have both types in my boat locker, I'll see what comes out. I have motored 1000s of miles in the last 5 years with no problems.

 

[vyv_cox]

I realise that NormanS will tell me that PTFE packing is perfectly OK but my experience is different. I repacked the gland on my motorsailer, 1.25 inch shaft using PTFE, went for a short motor and it overheated severely. Thinking I had cocked it up somehow I returned to my berth and repacked it with new braid, this time very carefully. Same result and we were forced to pour seawater over the gland to keep it cool. I then repacked with flax and graphite, perfectly good.

There is a theoretical galvanic issue with graphite and stainless steel but I know of no cases where it has been a problem. I fitted my PSS seal to replace traditional packing when the boat was about 20 years old and do not remember any shaft corrosion.

 

[Tamar]

I realise that NormanS will tell me that PTFE packing is perfectly OK but my experience is different. I repacked the gland on my motorsailer, 1.25 inch shaft using PTFE, went for a short motor and it overheated severely. Thinking I had cocked it up somehow I returned to my berth and repacked it with new braid, this time very carefully. Same result and we were forced to pour seawater over the gland to keep it cool. I then repacked with flax and graphite, perfectly good.

There is a theoretical galvanic issue with graphite and stainless steel but I know of no cases where it has been a problem. I fitted my PSS seal to replace traditional packing when the boat was about 20 years old and do not remember any shaft corrosion.

Hi vyv, hi looked at you excellent website earlier. I think I'm leaning towards the graphite stuff. The roll I have has been in the stern locker for the 5 years I have owned this boat, will it be ok to use? It's pretty stiff but playable .

 

[vyv_cox]

Hi vyv, hi looked at you excellent website earlier. I think I'm leaning towards the graphite stuff. The roll I have has been in the stern locker for the 5 years I have owned this boat, will it be ok to use? It's pretty stiff but playable .

I cannot think of any component of it that would go off, so should be fine to use.

 

[NormanS]

Someone mentioned my name.
On my previous boat, with a 3.5" bronze shaft rotating at a max of 300rpm, "Teflon" packing lasted for years and years without a problem. I have also used it extensively on large turbine water pumps.
On my present boat with a 1.5" stainless shaft rotating at a max of 1500rpm, I have always used graphite packing, without any problems.
Take your pick, and pack it properly, and you won't have any problems. Remember that the packing for a boat's prop shaft has to withstand only a very modest pressure of water, so don't pack too tightly, or you will get heat.

 

[vyv_cox]

Someone mentioned my name.
On my previous boat, with a 3.5" bronze shaft rotating at a max of 300rpm, "Teflon" packing lasted for years and years without a problem. I have also used it extensively on large turbine water pumps.
On my present boat with a 1.5" stainless shaft rotating at a max of 1500rpm, I have always used graphite packing, without any problems.
Take your pick, and pack it properly, and you won't have any problems. Remember that the packing for a boat's prop shaft has to withstand only a very modest pressure of water, so don't pack too tightly, or you will get heat.

I see that the thermal conductivity of bronze is more than four times that of 300 series stainless steel. I wonder if that might be an explanation? In the past I have had studies carried out at Cranfield seals unit on the subject of substituting PTFE for other seal materials. It was always the very low conductivity of PTFE that killed off the idea.

In both attempts with my motor sailer the yoke plate nuts were loose and the shaft rotated freely by hand. Within half a mile up Milford Haven the gland was too hot to touch.