stuffing box choices for aluminum inboard boat

Discussion in 'Metal Boat Building' started by Northeaster, Oct 28, 2015.

  1. Northeaster
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    Northeaster Senior Member

    Hi Folks,

    Back at the (amateur) boatbuilding. Roughing in engine placement, shaft and strut locations, etc.

    My plans show a home made (aluminum materials and packing) rudder stuffing box / packing gland but yet spec a synthetic stuffing box for the prop shaft (i.e. made out of synthetic materials and not made from aluminum, bronze, etc, and not only referring simply to synthetic packing material!)

    I am using a non-electrical conducting drive-saver flexible coupler
    insert between the gear coupler and the shaft coupler and plan on using a SS shaft, although not purchased yet.

    I would like input into what is recommended or at least typically done for stuffing boxes in aluminum boats.

    My concerns are mostly wear on materials, and electrical issues if I do not choose correct or acceptable materials. If synthetic stuffing boxes are the norm, any reference to brand/ suppliers would be appreciated!
     
    Last edited: Oct 28, 2015
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  2. gonzo
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    gonzo Senior Member

  3. Northeaster
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    Northeaster Senior Member

    Thanks Gonzo! When I searched for synthetic stuffing box - all I came up with were hits for the packing itself.

    I looked on-line for the Sierra Marine stuffing box ( for 1 1/4" shaft) and found it - part 49411 , but it does not come with full specs like O/D - so I know the I.D. size of hose I require, or more importantly to see if it matches the O.D of the shaft tube I will be using (either 1.75" or 1.9" depending on pipe schedule or tube thickness.)

    I looked at the Sierra Marine on-line catalog, but it does not even show the stuffing boxes as available - only packing.

    Failing other options, I could order it and just see what the OD is when it arrives and pick my shaft tube accordingly.

    I read one article about this type of stuffing box melting, but i looked like they perhaps used a wrong type packing, so it did not cool.
    I have had good luck with Gore-tex packing on my low power sailboat - the bronze box is never hot to touch and it only drips when running a bit.

    Are these synthetic boxes very common and reliable?- Sierra Marine or other brands?
     
  4. gonzo
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    gonzo Senior Member

    I use the teflon impregnated packing. It barely gets moist and stays cooler than the traditional flax.
     
  5. Northeaster
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    Northeaster Senior Member

    The Sierra marine synthetic stuffing box (for 1 1/4" shafts) does not seem to be available any longer.
    I can't find it in the Sierra catalog, nor in West Marine's website.

    I come up with a few hits on the net, but nothing current or in stock.

    Does anyone know of other brands?

    Or, should consider a lastdrop or similar dripless seal, as I think at least some are synthetic? I really liked the idea of a simple one, and one that could not fail quickly.

    I have read not to use a bronze stuffing box - Is it really an issue as it would connect via a hose to the aluminum shaft tube, and I will be using a drivesaver synthetic coupler to isolate the prop shaft from gearbox?
     
  6. gonzo
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    gonzo Senior Member

  7. Northeaster
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    Northeaster Senior Member

    that is a great site -
    Unfortunately, I don't see a prop shaft stuffing box for 1 1/4" shafts.....


    I like the aluminum rudder stuffing boxes. A bit pricey, but very nice. I could weld in one of those, instead of making my own, for the rudder... Or, the 1" prop shaft stuffing box kits are less expensive...Any issue with using a prop shaft stuffing box for a rudder installation? - I would also have a pipe welded through hull with a cutlass bearing for the rudder shaft. But, those parts would start to add up and the first choice may be best.
     
  8. gonzo
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    gonzo Senior Member

    I don't think there is any difference on the packing part. They usually have a flange to be bolted to a shelf instead of clamped to a hose, but it could be cut off.
     
  9. Northeaster
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    Northeaster Senior Member

    Thanks - any recommendations of specific brands of (synthetic) dripless prop shafts seals? i have no experience with any of them, Lastdrop, PSS Shaftseal, PYI, etc with regards to reputation, performance and/or value!
     
  10. sdowney717
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    sdowney717 Senior Member

  11. Northeaster
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    Northeaster Senior Member

    If that's similar to Gore-tex type packing - yes, have used it on my sailboat - almost no drip and stays cool....

    But, the problem I have is not trying to find the packing material....It is trying to find a stuffing box that is NOT made out of bronze or similar.. They recommend a synthetic (or aluminum I suppose) stuffing box itself with aluminum hulls, not just synthetic packing material!!!!
     
  12. sdowney717
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    sdowney717 Senior Member

    You already have a SS shaft, so can you get a SS stuffing box?
    Mount it to the hull with a rubber hose, which prevents direct electrical connection.
    Maybe even coat inside the stuffing box with thin layer of epoxy to cut down on exposed metal.
    A bronze stuffing box isolated from the aluminum with all the metals coated underwater in close proximity with each other to prevent galvanic current flow should be ok.

    How about sleeving a glued in liner of plastic pipe the shaft runs up the boat to stuffing box.
    Or use fiberglass tube as the liner and bolt rubber hose to it then bronze stuffing box.
    If I used a plastic or fiberglass tube, I would want to use a polyurethane glue maybe 5200, etc..., it will not crack like an epoxy might, so the underwater metals will stay dry. Metal stays dry, no galvanic corrosion. I have seen fiberglass tubes on McMaster Carr. http://www.mcmaster.com/#fiberglass-(frp)-tubing/=10okyws
    Or make your own fiberglass tube. Or use a piece of SS pipe glued into hull. A glued in section of SS pipe using a 5200 type adhesive will be electrically isolated from hull and offer an attachment point for a standard stuffing box. It will never come loose. Coat some epoxy on top of the SS so the black carbon rubber tube will not corrode the SS.

    I suppose you have an aluminum strut with a shaft bushing? Or is it coming out from the keel?
    Anyway, just thinking a little about this.

    [​IMG]
     
  13. Northeaster
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    Northeaster Senior Member

    I appreciate you thinking about it, and outlining any options I may not have thought of.

    Frankly, I am not sure why I can't use a bronze stuffing box, as the shaft is isolated from the gearbox/engine with a flexible drivesaver insert.

    And yes. the strut is aluminum, welded up through the hull and I have a lower strut leg which will likely connect ahead to the small skeg / keel and aft to support the rudder bottom. ** I had conssidered a full bo keel, and could still do that, but more likley what \i said above...
    I did use a cutlass bearing with a synthetic housing and where the shaft runs against rubber, so would this and the drivesaver not isolate the shaft?

    I haven't seen SS stuffing boxes...yet anyway..

    Plans/ build notes also call for an aluminum or SS prop, but they are hard to find outside of smaller ones common on ski boats I think... Again, is this really necessary, with the cutlass and drivesaver??? If experts say it is, fine..I juts don't see why..
     
  14. sdowney717
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    sdowney717 Senior Member

    The biggest galvanic problem with an aluminum hull is when your plugged into shore power, the entire hull would be anodic to other boats underwater bronze parts through the copper ground wire directly connecting all the underwater metals into a circuit. So best idea is an isolation transformer or a galvanic isolator.

    For just your own boat, keeping metals separated electrically by coatings keep them from forming a galvanic circuit and corroding your own underwater metals, the less exposed underwater metals the better. I would simply use the bronze prop and bronze stuffing box and make sure neither electrically connects or say make sure they have a very high resistance between them.

    I have used the plastic vesconite shaft bushings for my SS shaft in my wood boat. They work very well unless a rope gets wrapped around the shaft. If left there, it can wear away the plastic bushing. http://www.vesconite.com/

    And use magnesium anodes on the hull?
    http://www.performancemetals.com/anodes/AnodeFAQs.shtml
     

  15. Northeaster
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    Northeaster Senior Member

    sdowney -thanks for the additional info.

    Yes, I am familiar with the general issue of galvanic corrosion, specifically, as you mention - when connected to shore power, especially in a marina with other boats, many suffering from unknown electrical conditions...

    This 25' power boat will not have any AC / shore power hookup, so I should be safe there. It will sit at my own docks on a tidal (brackish) river about 1/4 mile upstream from the mouth of the bay / ocean.. I swim there a lot - can taste a bit of salt some days /tides more than others, but in much less concentration that the ocean - the river has a good fresh water flow rate.

    It would be great to be able to use more commonly available used bronze props and easily found stuffing boxes - I certainly can look at coating some common surfaces with epoxy or other barrier materials - whatever is recommends.
    I am on a budget for this home-build and I would like to try a used prop or two to see how it performs, before either searching for / trying other different pitched props or possibly buying new once I am in the ballpark.
    I would much prefer a traditional stuffing box (with good Gore material) over a dripless seal for price and simplicity.
     
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