Durable Steel Hulls

Discussion in 'Metal Boat Building' started by Wynand N, Nov 20, 2004.

  1. Wynand N
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    Wynand N Retired Steelboatbuilder

    In these forums I came across various statements where steel is described as "problematic".
    The silliest remarks of the lot is that the "rust factor" is build into the hull plating, hence the heavy weight of steel hulled vessels.
    The most popular criticisms are rust and weight. :mad:

    With modern steel designs & building teqniques plus epoxy paint systems, a steel hull displacement can be very comparable with similar GRP and would probably outlasts it with the same or less maintenance if build correctly.

    For starters, paint is only as good as it's preparation.
    I have seen to many builders using pre-primed plates, touching up welded areas later. This is to invite disaster. Let me explain.

    1. Paints have overcoat times. Piants don't like to be mixed. You have to keep to a paint system of the same manufacturer within the overcoat times.

    Usually with pre-primed plates the overcoat times have expired and the builder uses a different paint of his choice for top coats. The results visible after a few months or a year or two for all to see.

    2. Steel has to be shotblasted to spec SA2.5 (grey metal) before an epoxy primer is to be applied.
    I had the case where a worker touched a shortblasted area with his barehand, and this "oily handprint" showed up in the primecoat causing all sorts of covering problems and had to re-blast the area.

    3. The under & top coats of the same paint system have to be applied within the manufactures recommendations.

    I had seen some builders using rust converters, rust removers to clean a hull before painting and of this people I would rather say nothing......ever wondered where all that rust streaked hulls came from. :?:

    OK, you GRP people will say that a steel hull rust from the inside out.
    If all the frames and longitudinal stringers in a steel hull have drain holes where it should be, the hull properly shotblasted, and a good epoxy primer (ie. Coaltar) applied thichly - about 150 microns - with an airless spray unit, it should be more durable than a plastic boat.

    :!: It goes without saying that should you accidentally damage your paintwork, it should be repaired properly soonest. The same applies to GRP boats.

    The only drawback of a steel hull is that damn sacrificial anodes... but then again, ever tried to fix an exotic laminated fibre damaged hull at far away islands, thats to say if it survives.

    Wynand Nortje
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  2. Thunderhead19
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    Thunderhead19 Senior Member

    Can they be attached (and function) without breaching the epoxy below the waterline?

    I also think that steel is a fantastic building material. There is a lot said about how aluminium has a higher strength to weight ratio than steel, but for a member of a given size steel is still stronger, stiffer, more abraison resistan, more fatigue resistant (often overlooked by people building aluminium boats) and a lot cheaper. The epoxy paint systems they have now make the rust issue nearly a one sided arguement. I'm kind of curious about what goes on with the fasteners that hold the sacrificial anodes in place. Can they be attached (and function) without breaching the epoxy below the waterline?
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    FAST FRED Senior Member

    Steel is OK IF the suporting/reinforcing structure is flat bar.

    The use of L angle or T bar makes it almost impossable to blast to clean up under the angles.

    The cost of aluminum is probably LOWER if the maint and "round turn " cost is considered.

    Aluminum has far less maint , and does not even need to be painted above the waterline. And will always have a higher resale value.

    The total cost of ownership , from first dollar to resale is more important than cheap inital cost.The hull is only a small (15%?)cost of the boat.


  4. MikeJohns
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    MikeJohns Senior Member

    The longitudinals should be normal to the plate unless specified otherwise and they will trap water even with notches. We recommend filling the trap, used to use morter but lately have used polyurethane such as the building grade Sika products to good effect.
    We have also experimented with the same sealant applied in a 2-3 mm coating over epoxied steel in the interior of chain lockers. It provides a rubbery very tough coating that stops the epoxy being chipped. One vessel is now in its 4th year with this and we hauled the chain out just recently to find no breach in the coating, its holding up really well.

    Larger vessels should have T frames and bar longitudinals otherwise the equiv section modulus flat bar frames get too heavy. The larger T frames can be got at ok. I agree smaller vessels should have flat bar frames.

    Anode mounting is no problem, the epoxy sticks so well it doesn't peel off around the anode mounting studs.

    Many vessels are over protected with anodes and this is another issue.
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    D'ARTOIS Senior Member

    Steel as Shipbuilding Material

    Mr Wynand Nortje is in all aspects correct. For any boat over 45 ' steel will be an excellent construction material. Save for the carbon-racers that are built for one-time purposes.
    I have a 100 ' schooner, steel built and stilla as strong as of the day of her launching in 1956.
    It is as Mr Nortje says: even if you use pre-primered steel sheets, shotblast it and use a two-components epoxy underground paint ( i.e. Ameron) and cover it with a top coat of the same brand, also two components. Do it inside out and that boat will be protected for a very long time.

    In Holland and Germany, where the best steel yachts are built, the experience and knowledge about the
    treatment of steel is plenty available, which is not so the case with other countries that concentrate on FRP and hybrid mixtures of woven- and non woven fabrics in combination with vinylester/epoxy resins.
    France, for example. It's a matter of culture and tradition, not that this material is better then that one. But if you are looking for the best there is, take Titanium. No corrosion to speak of in 1250 years (TiV6 Alloy), a bit more expensive than stainless steel and equal difficult to weld.
    In 1998 I was very close to build a motoryacht of 180 ' out of this material that was at abundant quantities in stock in the ex USSR.
  6. webbwash
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    webbwash Junior Member

    Interesting -

    Got to remember that a well preserved steel hull can last a lifetime and them some -- gets to be like the person who sold the "original" hand axe that George Washington chopped down his cherry tree with. 5 handles and 3 heads later it is still the "original" --

    When plate gets thin, because of poor preservation, cut it out and replace it, when stray current fields exist on any dock, be aware and properly protect yourself. Case in point, although with aluminum, a Palmer Johnson built aluminum luxury yacht sitting at the floating dock in Mexico. Somebody dropped some electrical leads long term in the water and the boat started getting pinholes in the coating leading to pinholes through the hull. Replated the hull because the boat was still worth more than not having the boat.

    Anodes are EASY -- weld a stud on a hull, clean up around it and represerve the coating, then attach the anode, with it's proper stand-off distance. Too many is expensive, not enough is extremely expensive.

    Have a good day.
  7. mabelsgift
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    mabelsgift Junior Member

    One of my friends in Cape Town has a 25 year old steel boat that has almost no signs of corrosion anywhere because it was done properly in the first place. He used a good marine paint (Dulux) and did a proper job.The few places that we found recently he fixed immediately and properly. In his diary we could find only 2 other occasions in the 25 years when he found any corrosion at all. If you are not going to do things properly don't build a boat, it's that simple. A badly built boat in any material is not a good idea.
  8. Mynhardt Coertz
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    Mynhardt Coertz Junior Member

  9. Brent Swain
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    Brent Swain Member

    Durable steel huls

    My current boat used wheelabraded and pre primed steel , primed with cold galv primer. The paint job is as good as the day I put it on, 25 years ago.. I washed the zinc primer with TSP to make sure there was no grease on it, then with vinegar to get a slight etch and remove any zinc oxide and welding smoke, then with water, let her dry in the hot dry weather, then epoxy tar, five coats. All my designs, using epoxy over pre primed plate , wheelabraded and primed with cold galv primer, have had no problems , as long as they cleaned the primer before puting anything over it . This also eliminates the problem of cleaning behind angle stringers. It eliminates the need to sandblast, and gets the plate clean at a fraction the time ,work and expense of sandblasting.
    One huge advantage of steel over fibreglas is that cleats , handrails and other hardware , welded down , simply never work loose and never leak. There is no bedding compound as reliable as welding .
    Anodes can be bolted on with ss bolts, welded to the hull. A bit of stainless weld around the bolt hole reduces the chance of a bit of corrosion around the bolt hole insulating the anode from the hull, altho I prefer to guarantee the connection with a tack on the end of the strap. Too many zincs tends to cause your paint to bubble.
    Angles are far more rigid than flatbar, and as long as the steel is wheelabraded and primed, and you force enough epoxy tar behind them, and foam over them to make limber holes redundant, they are a far better option. I found flat bar not structurally rigid enough.
    Steel is a far better material down to 26 ft, as long as you don't let dinosaur age framing make it uneccesarily heavy.
    Electrical cords are an ever present danger , if you tie up in marinas. On my last boat the steel on the bottom of the keel was bare for the 11 years I owned her, and looked as good as the day I built her. The surveyor said that was because I never tied up to docks with their huge electrical fields around all electric wires.
    A friend ran a fishing and icemaking barge in BC. When he took over the job, he was told "This barge eats zincs like candy. He checked the shore power supply, and found a 440 volt line hanging in the water. He tied it up out of the water, and when they hauled the following year ,the zincs looked almost new. "What did you do?" they all asked.
    People in the fishing fleet say "Aluminium welds often break, steel welds rarely do. . It's hard to find an effective antifouling for aluminium that won't eat it."
    Aluminium however can be an excellent material for a cabin on a steel boat.
    The percentage of the total price that the steelwork represents can be huge or small depending on how resourceful the builder is. For my boat it was at least 75% the cost of getting her sailing and liveable, At any rate , it is a much larger portion in a steel boat than a fibreglas boat. A cleat costs under a dollar if it is fabricated of scrap stainless and welded on, up to $40 for a fibreglass boat. Ditto handrails, hatches ,hatch hinges, mooring bits, anchors, anchor winch,woodstove , engine mounts,self steering etc, etc ,things that are fabricated in place on a steel boat , but bought and bolted down on a fibreglass boat.
    Cement , being a strong alkali, inhibits corrosion on steel when it is used to fill hollows,and doesn't lose it's alkalinity much while being protected from the elements, inside a hull.
    I believe if many fibreglass boat owners had any idea of the punishment a steel boat can survive without sinking , there would be a lot more of them out cruising.
  10. Ad Hoc
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    Ad Hoc Naval Architect

    Fast Fred.
    You make the most obvious points which are often overlooked when comparing steel versus aluminium.

    I have twice designed vessel for UK MoD where their initial stance was for a steel vessel. However, the through-life-maintenance costs were an important factor. The 20~25 year study clearly showed that initially, yes steel is better, but once time progresses, aluminium is the clear winner in terms of life time costs.

    The "Stoic" MoD eventually changed their minds and order an aluminium design...still took some convincing though, despite "the numbers"...
  11. Brent Swain
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    Brent Swain Member

    The life time costs of my 31 footer are less that $100 a year and she cost me $6,000 to get sailing. Aluminium would have cost me four times that just to get sailing. I'd worry a lot more if I were tied to a dock with electricity, in an aluminium boat ,than in a steel boat. Had I gone aluminium, it would have taken me a decade of hard work on just to pay for everything and get out cruising. I'd rather spend that time cruising, and cough up the huge sum of $100 year.
    Believing the line" You better pay a fortune that you don't have now to save money later " is a suckers gam, or just plain elitist. Thank god I was never that gullible, or I would have done very little cruising, let alone 11 months a year since my mid 20's.
    Your year to year study, clearly ,is grossly inaccurate ,based on false figures, and predetermined biases.

  12. Guest62110524

    Guest62110524 Previous Member

    it would be good if this thread was left ON STEEL,
    keeping alloy out of it
    here is my very first build,, the bottom plates are one run as are the topsides plates, why? cos nobody told me that was wrong:)) started with no money, bought an old compressor 6 pots 4 on low stage 2 high, and with 10mm venturi nozzle could blast48 sq feet in 10 mins, altex 310 ZN primer 75microns dry film, then 250 microns altex devoe 230 pressure pot in one hit, close framed at 400mm, photo in 1976
    Last edited: Jun 21, 2010
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