Propeller Shaft Seals

[BillD]

Question of the week (for me anyway) ?

I "borrowed" this picture from the General Marine 26 cc build.

The shaft seal in this boat?

Would you call it a "traditional" dripless shaft seal?

Also, the water inlet nipple appears to be "downhill" of the packing material.

How do these seals work? Do these seals "leak" ?

How does the packing material stay cool? Engine water?

Also, with a shaft tube design, does the engine water cool the stern bearing?

Or is the stern bearing lubricated/cooled from sea water same as an "open" cutlass bearing?

As always.

Appreciated, Bill D

 

[Blitzen]

Would you call it a "traditional" dripless shaft seal?
No it is not a dripless seal, you still have packing in the packing nut that needs some water for lubrication and cooling.

Also, the water inlet nipple appears to be "downhill" of the packing material.

How do these seals work? Do these seals "leak" ?
They should drip.

How does the packing material stay cool? Engine water?
Water from the raw water side of the cooling system.
I also like the Dura-Max packing in this system.

Also, with a shaft tube design, does the engine water cool the stern bearing?
Yes upper and lower..

Or is the stern bearing lubricated/cooled from sea water same as an "open" cutlass bearing?

 

[BillD]

Would you call it a "traditional" dripless shaft seal?
No it is not a dripless seal, you still have packing in the packing nut that needs some water for lubrication and cooling.

Also, the water inlet nipple appears to be "downhill" of the packing material.

How do these seals work? Do these seals "leak" ?
They should drip.

How does the packing material stay cool? Engine water?
Water from the raw water side of the cooling system.
I also like the Dura-Max packing in this system.

Also, with a shaft tube design, does the engine water cool the stern bearing?
Yes upper and lower..

Or is the stern bearing lubricated/cooled from sea water same as an "open" cutlass bearing?

John,

"If" the water flow from the engine was "interrupted" (broken hose clamp or whatever) what is the "maximum" that would happen ?

 

[captainlarry84]

John,

"If" the water flow from the engine was "interrupted" (broken hose clamp or whatever) what is the "maximum" that would happen ?

This is a conventional flax packing stuffing box. The water feed is downhill of the packing, However with the amount of water pressure from the raw water feed the water flows in both directions. Once the first ring a flax packing gets wet the water starts to capsulate until each ring is wet. The rest of the water is pushed down the shaft where it meets the cutlass bearing and the water is forced out the back of the bearing. In doing so the shaft is always riding on a film of water.
Should the water feed be interrupted the flax packing becomes hot, dyers and it will mare the shaft. On a dripless box with water the damage can be much worse. In addition the lack of water will also make quick work of the cutlass bearing.
It is always a good idea at the start of every trip to make sure the water flow is not blocked. I always like to grab the water feed hose and hold it for a minute or so. It is feels cool you have flow.
When tapping in for your water feed never remove a zinc pencil to access water for the feed. Always find a plug nice and high in the heat exchanger. The higher the better, this way no debris can settle in the feed and stop the water flow. On some raw water pumps there are taps for water before the heat exchanger. These taps are always safe because no debris such as a broken zinc pencil can get in the way.
Back to the stuffing box in the picture, which is of high quality. The best way to tighten the stuffing box is to:
Start the motor
Loosen the stuffing box until water starts to enter the boat.
Next tighten the stuffing box by hand until you get a drip every few seconds.
Tighten up the jam nut & seatest
On seatest the bronze housing should be slightly warm to cool when you touch it.
If it is getting warm you will need to loosen it up some.
Lastly when we install wet tubes we also like to drill to holes facing forward in the wet tube outside of the boat. Should you lose water flow these two holes will always some water in to cool the cutlass bearing.