Novel sterntube and seals?

Discussion in 'Boatbuilding' started by ongolo, Jul 26, 2003.

  1. ongolo
    Joined: Jul 2003
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    Location: namibia

    ongolo Junior Member

    Hi all,

    I am building a 55ft steel schooner (gaff) and it is virtually al coming to an end.

    From the beginning I was not happy with stuffing box/cutlass idea. The boat has been designed to look at an iceberg in the southern atlantic one day (hopefully NOT TOO closely) and all systems on board must be serviceable at remote locations. So I have been podering and over the years have drawn various designs. I even obtained the out dated drawings of South Africa Navy/ French built Submarines to what they do. I have worked on a japanese built research vessel which used a German system colled SIMPLEX seals. These are best imagined as overgrown oil seals as used in cars wheels, gear boxes andengines etc.
    Then I was given plans of what some french yachts use, they use a series of roller bearings with three oil seas on bothe ends of the sterntube, the sahft running in an oil bath with a header tank. The French using even mild steel shafts at times. Using more than one bearing (unless they are matched pairs) is sensless and even if they are matched, the potential slight misalignement makes (in my opinion) the use of deep grove ball bearings a disadvantage.

    So, I have designd and turned all parts ready for assembly and welding the last bits together.

    I use self-aligning roller bearings with a taper adaptor

    Three oil seals either end with lantern rings to facilitate lubrication of the outer seals until these get over time lubricated by seepage from within.

    The system is designed that seals and bearings could be replaced under water, but this would require extensive flushing out afterwards. The inner seals could be changed without much effort, except the mess of draining the oil.

    If the system should fail, a vesconite or teflon cutlass bearing is carried anyway and can be inserted in place of bearings and oil seals.

    A stuffing box and packing can replace the inner assembly.

    I could have made all parts smaller and more streamlined, but using needle bearings would have given problems with alignment I believe.

    Does anybody here have an opinion on that system as such? The advantages of all this is a dry bilge.

    :confused: :confused:
     
  2. CuleBreeze
    Joined: Aug 2003
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    Location: South Carolina

    CuleBreeze New Member

    I work in the Petrochemical industry. There are many functional split mechanical seals that could bolt on the (stuffing box) stern tube in the place of a packing gland. I have toyed with the idea of a loosely packed normal stuffing tub as a back up then make the primary seal a split seal or split double seal. Flowserve makes these seals. The are used to keep toxic chemicals or hydro carbons in the process. Lives depend on the reliabilty as well. Talk to a Mechanical Seal Engineer not a Salesman. Kind regards Culebreez
     
  3. ongolo
    Joined: Jul 2003
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    Location: namibia

    ongolo Junior Member

    Thank you for your well meaning reply, but I doubt that I could find a "mechanical seal engineer" on the whole of the african continent where I live. It would be nice to have split seals, but I have to use what is anywhere any time available.

    I shall serch the net for "split seals" although all parts are made already.

    Thank you again.

    ongolo
     
  4. BVI Jon
    Joined: Sep 2003
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    Location: British Virgin Islands

    BVI Jon Junior Member

    Just a couple of thoughts:

    You say that your multiple-seal water-intrusion-prevention device is able to have the seals replaced from in the water (or while the boat is in the water - same thing). But first you say something about icebergs.

    If you hit a peice of ice large enough to damage the stuffing box, the prop will also likely be damaged (out of balance) and the shaft possibly bent. And the water will be too cold for a person to enter for the period of time necessary (weather permitting) without being seriously affected by hypothermia.

    Now, while I will compliment you on the apparent worthiness of your stern-tube ideas, I think that the level of serviceability needed on a cruising yacht precludes its use.

    I don't know the shape of your hull or how long the shaft is, etc, but for serviceability away from home port, a "P" bracket with cutlass bearing (if a "P" bracket is needed) and a traditional flax-packed stuffing-box is very difficult to beat. Cutlass bearings are quite durable, usually replaceable in the water, don't require much room as a spare, and have no moving parts.
    Compression-nut stuffing boxes are very forgiving. Very few moving parts. They can withstand quite a lot of wobble in the shaft, and still keep the majority of the ocean on the outside.

    I hope I didn't miss the idea of your post.

    Best of luck,
    Jon.
     
  5. ongolo
    Joined: Jul 2003
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    Location: namibia

    ongolo Junior Member

    Hi Jon,

    No we have crossed wires here, when my stuffing box or sterntube is damaged by an iceberg, I will go down for sure.

    The idea is that I have zero water in the boat if I can help it. The prop will run in an oil bath with a header tank, so first if there is a leakage, oil will leak out.

    That should get me where is warmer water. Stuffing box is great, but some of us have to experiment, otherwise we would still be using stone tools. Would'nt we?

    Some French Yachts are using a similar system and so do all Blohm & and Voss built large ship by the looks of it. Large ships almost never use stuffing boxes anymore.

    I will try and do an article in PBO when I get around to it. It sounds more complicated than it is, but I can anytime in an emergency replace the inboard assembly with a stuffing box (already at hand and the nut required) and once the inboard end is sealed, I can just replace the outboard end by removing the seals, lantern ring and bearing and replace it with a piece of already manufactured Vesconite.

    I have confidence it should work, but so was Ikarus. :)))

    No actually I have designed my own boat and have considerable design expertise in mechanical and electronics.

    I did not make the diesel, the gearbox, the Radar and some instruments, everything else I had to make in this desert of ours.

    regards ongolo
     
  6. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    Dripless shaft seals are cheap and have been in service for many years. They look like an oil seal and have a small hose to the engine raw water pump. The trickle of water lubricates and cools the seal. They directly replace a stuffing box. Tubes with lubricant that can leak are a problem. Servicing them in the water is a violation of environmental laws anywhere in the world.
     
  7. Palmer
    Joined: Nov 2002
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    Location: Tacoma, Wa

    Palmer Junior Member

  8. Guest

    Guest Guest

    Gonzo,

    No, if it has to be serviced, the inner seal would be done first and all oil is out, then the outer seal would be done, then the tube would be flushed with oil to get the water out, maybe repeatedly.

    The finally oil would be filled again into the header tank.

    No environmental problem that I can see. Or am I missing something?

    ongolo
     

  9. gonzo
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    gonzo Senior Member

    If you flush the tube with oil, what happens to the contaminated oil and water? Also, when the seals come out, so will the oil. Dripless seals lubricate and cool with water. They are durable and clean. I don't understand the advantages of an expensive complicated system in an oil bath.
     
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