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wakeparadise

Shaft Packing Question

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wakeparadise

Hi,

Can someone explain to me in detail how the packing works (and cooling) on the prop shaft? Why are some water cooled and "drip" and some are "dripless"? Furthermore, why does the shaft heat up in this one spot?


Thanks!

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nuttyskier2002

Mounted to the inside hull of your boat is the shaft log. It is moreless a "pipe like" structure with a mounting flange to bolt it to the bottom of the hull. At the forward end of the shaft log is a threaded portion that looks pretty much like a threaded piece of pipe. This is where the packing gland screws onto. The packing gland looks like a large nut. One end of the packing gland is open and threaded. The other is almost closed in except for a hole large enough for the prop shaft to go thru. Inside the packing gland is what is called flax. Flax is what seals the water out. But actually it is a controlled leak. There are a few different types of flax. The original and most common is the wax impregnated rope type. There's also the "gore" type which is replacing the wax type more and more.

Usually there are two rings of flax stuffed inside the packing gland and wrapping around the prop shaft. As the packing gland is tightened the flax is squeezed between the inside wall of the packing gland and shaft. The wax seals and lubricates as the shaft spins inside the gland. It is allowed to leak (drip about 1 drop every 15 - 30 seconds) to cool the flax. This keeps the flax from burning up. Wax type flax will usually last 2 - 3 years or so before it needs replacing. Of course this depends on usage. The gore type flax uses graphite mixed with something else (not sure what). But the gore type will last longer and seal better than the wax type.

When replacing the flax dig out all the old stuff with a pick or dental tool. Then wrap the new flax around the shaft and cut it with a razor blade so that you have a single ring that wraps completely around the shaft with the ends butted up squarely. Do this twice (two pieces). When sfuffing the two flax rings into the packing gland....stagger the butted ends. Stuff the two flax rings all the way into the gland. Then thread the gland back onto the shaft log. To seal the new flax you won't have the tighten the gland more than about hand tight. Then tighten the gamm nut against the gland. When you get to the water....make you final adjustment. If you use the gore type it will not leak as much. 1 drop every 30 seconds or so is good for the gore.

The dripless is a totally different animal. It uses a rubber or plastic seal and requires plumbing from the cooling system to keep it cool. I can not vouch for the dripless system as I have never used it on any of my boats. I can however vouch for the gore type flax. When I replaced the original wax stuff with the gore in mt last boat.....I did not have to adjust the packing nut for over 3 years. It never leaked afterward. Your mileage will very of course.

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Woodski

The contact of the seal (any type) to a spinning shaft creates friction which is where the heat comes from. The water is used as a lubricant to reduce friction and provide a cooling medium. The rope type seals have a fairly wide contact surface and no real seal so water migrates across the seal to provide the lubrication and due to water pressure on the backside, then drips in to the bilge. The rubber lip seal is exactly that, and the water cooling effect is against the vertical surface of the seal itself. The main key is to keep the temperature low.

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