Why A Stuffing Box?

[TFU]

I've been reading the posts about stuffing boxes and since I've have previously only sailed boats with an outboard motor my new (used) boat has an inboard so it will be all new to me.
My question is why is it necessary to use the current method of "stuffing" the connection? I have a drain pump that needs to transfer water through a 1" water pipe up 2 floors to a waste tank via an electric motor and it uses rubber sealing rings with no back leak in the system (head pressure is about 25'). The pump speed is fast; water pressure is high; and there is no stuffing box and no leaks.
Just want to know since my stuffing box is all will have.

 

[Steve Dion]

Re: Why a stffing box

What happens when that pump quits?

 

[Stu Jackson]

Re: Why a stffing box

The issue is basically an engineering one: the type of seal that is used to keep the water out on a relatively slowly spinning shaft, no different than pumps.

The Traditional stuffing box is a simple way to do. There are others.

 

[Rick D]

Option

Basically, the shaft seal is a tried and proven arrangement for watercraft. Boaters tend to be conservative when it comes to keeping water outside the hull. But, there are plenty of alternatives. Here's a popular one: http://shop.hunterowners.com/pss/detail-pss.htm

 

[Ed Schenck]

Re: Why a stffing box

Is the answer that the shaft is not fixed, that it gets out of alignment and vibrates? His pump seal analogy is good, high speed shaft running in rubber o-rings. Why not the same thing built into the stern tube?

 

[Bill Roosa]

Re: Why a stffing box

Consider for a moment how you would install an O-ring on the shaft and you will see that is is much easier to us a stuffing. You would have to disconnect the tranny from the shaft, move the shaft back, slip on the O-ring, futz it into the gland proper then put the thing back together. this assumes that the prop shaft does not slide out once you disconnect it.
there are several alternatives to a packing gland also. But at $300 for the solution and $5 for new packing I'm thinking I'd never recover my investment in the life of the boat. At $5 every 4 years it would take 120 years to add up to $300. so it is also cheaper.
Cheaper and easier, a no brainer.

 

[Ed Schenck]

Re: Why a stffing box

Except Bill that high speed pumps run for years without leaking. For me sliding the shaft back every ten years to slide on new seals would be an improvement. Has to be another reason than just cost. Even the expensive dripless solutions like PSS don't rely on o-rings. I agree that the standard stuffing box is a good alternative, cheap and easy. But I don't like the related liabilities of the hose, the clamps, and the stern tube.

 

[Bill Roosa]

Re: Why a stffing box

I believe that if you check all the solutions have hoses, clamps and stern tubes to contend with. the ONLY difference is the way the seal is accomplished. You still have to connect the non moving side to the hull somehow and that looks like a stern tube in all cases.
You have never taken a prop shaft off the coupler after 10 years have you? Not a task for the faint of heart or light of pocket (the coupler usually breaks in the process)

 

[TFU]

Gentlemen, I had no idea my question would generate so much information. This was my first post. What a great site.
Thanks to all, even "what if the motor quits" guy.
Bill

 

[Ed Schenck]

Re: Why a stffing box

Actually Bill mine was almost thirty years old when I pulled it to replace the motor. Took maybe fifteen minutes. Maybe an advantage of fresh water. I am only suggesting that if we could guarantee the alignment between the engine and strut there might be better options. Like a heavy duty stern tube with built-in bearings and seals.

 

[captainpat]

Re: Why a stffing box

True; there are options from a "what's possible" viewpoint, however, there are some other issues. What's possible is not always what's best, a concept that is all too often driven home with technological advances. Too often a technology is embraced for its own sake when the tried and true may often be a better solution.

This subject is one which will cause endless discussion as it is opinion and individual taste that will fuel the dialogue. However, at the risk of adding fuel here are some of my thoughts

It's always a good idea, on any boat, to prepare for the worst case scenario. I think the best argument for the stuffing box is that you want to be able to make the easiest repair in the worst possible imagined conditions. It's a relatively scary but simple matter to change out the flax from a leaking stuffing box when offshore, while just about impossible to change o-rings. Another factor; the shaft does not stay in the center of the opening. It tends to "wander" around a bit due to a number of factors such as boat motion, sea conditions, engine alignment, underbody design, engine vibration at different rpm's, etc. An O-ring is ineffective and sensitive to misalignment and would wear much faster than the O-ring in a water pump, where it is most effective. The flax, on the other hand, is very forgiving in such conditions and, even if the gland does leak a bit too much, can usually be tightened until more favorable conditions are present to change out the flax. Also, the new graphite/Teflon flax that's on the market will last a long time; maybe as long as that 0-ring!

I have misgivings about the "dripless" solutions also, which I had on a previous boat. My feeling is that if it fails, you have a pretty large opening to let the sea inside the boat. Not true with the more traditional packing gland. That packing gland is time tested, safer, cheaper, and easier to maintain with the simplest of tools.

 

[TFU]

I think the last post may have answered (for me) why stuffing boxes are still around. In boating, like SCUBA diving, the way to a safe and enjoyable sail/dive is to be prepared and anticipate problems before they happen. That way the shock affect is reduced and your past experience is more at the forefront to solve the problem. To think nothing is going to happen with your through hull fittings is false hope. The current stuffing box allows, as per the last post, a simple doable fix in case of the unthinkable. Again thank you all for the info and it looks like I'll have to get proficient in learning how to repair this area of a sailboat.
Bill