Hot dip zinc gaalvanized steel boat

Discussion in 'Metal Boat Building' started by tojeres, Dec 14, 2019.

  1. tojeres
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    tojeres New Member

    Hi

    Does anybody have experience with hot dip galvanized steel whole boat ?

    regards
     
  2. jehardiman
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    jehardiman Senior Member

    That would be a huge and very expensive dip tank (remembering that the tank must be heated to the melting temperature of zinc). I'm sure you could probably find someone with a tank that could possibly fit a 2-2.5m hull (check the guys making cattle watering troughs), but nothing larger. Also remember that HDG results in a significant lowering of the strength of the steel. Plasma/thermal sprayed zinc has been around for more than 30 years and is the way it is normally done. Note that making repairs to thermal sprayed steel as its own issues.
     
  3. tojeres
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    tojeres New Member

    Thank you for the opinion. Yes, HDG has to be done professionally in a factory. Regarding lower strength, I think it is negligible. I assume boat would be more sensitive to corrosion on scratches outside of a hull and less sensitive to corrosion inside a hull.
    I was not aware of thermal sprayed zinc. From other threads I see it is sucessfully used. I assume it is similar to HDG and therfore HDG seems good option.
     
  4. gonzo
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    gonzo Senior Member

    You could use Thermal Spray. It uses a flame to melt the metal to be deposited and heats the base metal.
     
  5. Wynand N
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    Wynand N Retired Steelboatbuilder

    Actually, a steel hull usually rusts from the inside out...think condensation.
    If possible, a hot dip hull plates would distort badly. I used to get some large tanks dipped and plates warps from the heat and it is safe to say a boat hull would act the same way.
    HDG like "jehardiman" suggests is the best way to go and I used it on a few hulls with great success.
     
  6. pauloman
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    pauloman Epoxy Vendor

    aluthane - an alumium filled MCU coating is commonly used to 'replace' failing galvanized surfaces in the field (like stock tanks, metal roofs, fences, farm equipment etc.) It would be as close as you can come with a brush on coating. Uses a lot on aluminum boats too. see epoxyproducts.com/aluthane.html


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  7. Barry
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    Barry Senior Member

    At the low temperatures of HDG 850 F and the first major phase change in the carbon steel alloy probably found in steel hulls occurring at around 1400 degrees F, there should not be a reduction in the strength of the steel

    As the hull would not be in the tank very long, at this low temperature and the hull may be thicker than the large tanks that you had dipped, there should not be too much distortion BUT as Ad Hoc has presented the preferred/proper/meeting
    various standards construction method for steel/aluminum boats is to roll the plating to the precise shape before welding. This is so the plating is not under an induced load/stress during the construction and after the construction.
    Often small boat and perhaps even larger boats builders will take a flat plate and bend it manually to conform to slight curves, ie building in stress and then do a weld up. If this type of constructed hull is then heated for a period of time
    there may be a chance that the pre stressed condition allows the curvature to change/distort.

    Welding by itself introduces stresses due to localized heat at the weldment. On some type of structural components, these stressors can be relieved by bringing the steel up to around 650 F for several hours.
    So with HDG, there may be a slight reduction in these stresses, but due to the short dip time, it is probably insignicant

    But as Jehardiman stated, it would be difficult to find a tank large enough to dip a complete hull.

    As an aside, you have to be extremely careful when welding zinc'd? steel. With an arc a particular gas is given off which will make you extremely ill so proper ventilation is required, free air respirator preferred
     
  8. Mr Efficiency
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    Mr Efficiency Senior Member

    That's something I was unaware of.
     
  9. Barry
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    Barry Senior Member

    I need to amend my comment above to include gas welding as well as arc welding. The vapor that is given off is ZnO, Zinc Oxide and can give symptoms similar to the flu in a short interval but longer serious health
    risks when exposed for a long time I had only mentioned arc welding originally
     
  10. Mr Efficiency
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    Mr Efficiency Senior Member

    Zinc oxide is toxic ? It is the ingredient in zinc creams, but inhalation may be another matter.
     

  11. Barry
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    Barry Senior Member

    Evidently,
    I had an experience with this brazing on a hot dipped fuel tank. That is why I included it in the post, and then googled Health Risks Welding Zinc coated metal, lots of papers on this
    And of course people working over tanks doing the work are also impacted
     
    Last edited: Mar 7, 2020
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