STEEL HULLS with Composite Superstructure / Topsides

Discussion in 'Boatbuilding' started by brian eiland, Jun 16, 2013.

  1. MikeJohns
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    MikeJohns Senior Member

    Not a bad article.
    A couple of comments: Steel medium to heavy displacement boats can be lighter in hull construction than all other sensible forms of construction (except alloy) once the length gets over around 50 feet.

    Steel boats are stiffer globally than other construction methods.

    The reason for the massive reserve strength of metal boats in a grounding or collision is the difference between brittle fracture ( wood, Composites, ferro cement) and a metals yield point. Metal still has a long way to go after yield before it reaches fracture, that means that a metal boat has a damage tolerance to failure significantly higher than a material with brittle failure.

    I've been involved in salvaging boats that have run up on reefs and rocky beaches and been worked by the waves. Often the metal boats and particularly smaller steel craft are often pulled off with only very minor damage, sometimes no damage at all except to the coatings. Composites and wooden hulls are usually constructive write offs and are broken up on site with an excavator after stripping and they don't take well to being dragged back over rocks to get back into the water.

    Metal boats are the most popular in the Pacific for remote cruising, I ran onto a coral head at 7 knots once in a 45 foot steel boat and put a hand sized dent in the boat. The impact was terrifying, the damage required a little filler ! It's not just financial insurance.

    But I keep reiterating that steels boats must be designed by someone who understands the maintenance issues. No inaccessible areas inside around bilges ports, stern tubes rudder ports, hull fittings and deck hatches. All linings in these areas should be easily removable. The factory build European production boats were a disaster in steel. They were built to last 20 years and you can find them rusting away in many areas of the world. They really gave steel a bad name and fortunately for the consumer they have moved to alloy now.

    Oh and steel doesn't rust due to oxygen, oxygen is a requirement but not the cause of rust, bare steel in pure oxygen is completely inert.
     
  2. Yobarnacle
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    Yobarnacle Senior Member

    formula Fe2O3. It is one of the three main oxides of iron, the other two being iron(I) oxide (FeO), which is rare, and iron(II) oxide (Fe3O4), which also occurs naturally as the mineral magnetite. As the mineral known as hematite, Fe2O3 is the main source of the iron for the steel industry. Fe2O3 is ferromagnetic, dark red, and readily attacked by acids. Iron(III) oxide is often called rust

    http://en.wikipedia.org/wiki/Iron(III)_oxide

    But inert in pure oxygen?

    Not that I doubt you, but hard to get my mind around. :)

    Can you cite this information?
     
  3. pdwiley
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    pdwiley Senior Member

    Many years ago we put a big steel power cat onto a coral head in the Wessel Islands on a falling tide. It was the wet season, no visibility and poor charts.

    Anyway, the tide went out, boat heeled, hung up on one hull. Lots of nasty noises and a bloody big list. Couldn't run generators etc so the beer was getting warm. Tide came in, we floated off, no damage other than scraped paint and a need for the skipper & deckie to put on a load of washing after the underwear change. Cold beer resumed. All good.

    I like steel boats. They make Braille navigation more survivable.

    PDW
     
  4. MikeJohns
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    MikeJohns Senior Member

    Have a look inside a steel O2 tank and you should find it clean so long as the gas was 'dry'.

    It's pretty basic material science which is why I mentioned it, to form rust from Iron you need some ion exchange AND available oxygen the lattice doesn't give it's electrons up that easily. Oxygenated water will do.
    If steel simply oxidised in the presence of O2 the material wouldn't exist outside of a lab curiosity since the oxide is porous.

    Of interest; In a range of alkaline conditions steel is passivated, that's why steam ships engineers had to descale boiler tubes when the ship was in port and the rest of the crew was seeking the delights of the city. A property of steel they must have cursed ! It's also why lime-cement wash protects bare steel very well and why reinforcing doesn't corrode in concrete while it's alkaline.

    Aluminium is at a much higher energy state and reacts instantly with oxygen to form what is bascially a ceramic coating. Aluminium will burn in a pure oxygen environment once ignited, just as magnesium burns in atmospheric O2 levels. Aluminium can be ignited in a pure O2 environment simply by scratching it with a piece of steel.
     
  5. Yobarnacle
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    Yobarnacle Senior Member

    I understand and have seen the phenomenon you describe.
    also why ancient auto bodies last longer in our desert states, a boon to restorers.
    Iron WILL burn, though. Even in air. Light off some steel wool! :D
    And iron and aluminum burn excellently together. Thermite. :)

    Entering closed tanks is entering a death chamber if its been closed for a long time, all the oxygen combined into rust, even in dry climates.
     
  6. MikeJohns
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    MikeJohns Senior Member

    Collisions are common for cruising boats. I've never yet met a long term cruisier that didn't have a potentially dangerous encounter at some stage, dragging anchor is a very common cause.

    Boats over a few tons built of steel ground better than alloy. Alloy spalls and the 'cutting tool' can get a bite and does a lot more damage in bending as well. If you intend to explore the uncharted shallows ( many suitable anchorages ) you either need good local knowledge, or a boat that doesn't mind the odd clonk. That's where catamarans often come unstuck, we see total constructive losses from groundings that a well build monohull gets no more than cosmetic damage from. Not just ULDB's either.
    But there are disasterous monohull materials for collision too and for example my old ferro ketch is on the bottom near Cygnet (a subsequent owner) after encountering a rock.

    I dragged down onto a submerged wreck once, that was a bit concerning. Another time a series of combined waves once gave us unexpectedly high waves with their associated unexpectedly low troughs and 2 m of water below the normal troughs disappeared, the boat was dropped quite hard on a rock shelf 3 times before normality resumed and we got out of there.
     
  7. MikeJohns
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    MikeJohns Senior Member

    Yes good point everything needs qualifying and all metals burn under the right conditions.
    Steel wool burns well, but it's a bit different as the high temp to sustain the oxidation reaction is maintained because there is no effective heat sink. But even as a foil it's a different scenario. It's a bit like the difference in igniting fine crushed rock suspended in air or trying to burn rocks. But you can ignite a large block of Aluminium very easily with no more than scratching it with steel ( in high concentraitions of O2)!

    Thermite is a mix of Iron oxide, (not Iron) and Aluminium but it needs to be finely ground. We used a themite lance once ( or rather the welder did) to shrink a large shaft of the crown wheel of a bucket dredge so it could be disassembled. It just bored straight through, great tool. You can cast steel with a thermite furnace and weld assemblies like railway tracks.
     
  8. pdwiley
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    pdwiley Senior Member

    Yeah - that's why, when the opportunity presented itself, I increased the thickness of the keel shoe from 200 x 25 to 200 x 40. Saved me quite a bit of money as well both in not buying new steel as opposed to the used stuff, and the extra mass meant I need less lead. I did ask the designer's consent first.

    So, provided the keel hits and not a corner of a rock etc into the hull plate, I'm not too worried about doing more than scraping the paint off. Bernie Harberts hit a submerged wreck all standing in a Witch off of East London IIRC. He skidded right over the top of it, no damage except to the keel paint. His keel shoe was a lot thinner than mine.

    PDW
     
  9. brian eiland
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    brian eiland Senior Member

    Building a Steel 41-plus DUCK in Turkey

    Interesting building discussion and photo presentaton
    http://dieselducks.com/41-plus%20construction%20Page%201.html

    Note mention of 'floating-longs system' on page 2 & 5

    And how about his simple reasoning for steel boat construction,
     
  10. pdwiley
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    pdwiley Senior Member

    The plate on my hull is fair and the longs weren't allowed to 'float' out to the steel hull plate as it was applied. In fact the plate was pushed against the longs and frames as it was tack welded.

    The difference as I see it is, the designer of my hull knew steel and drew a boat that could be plated as designed, plus I took a lot of time to actually build to the design by lofting out on a 1:1 scale and making all the frames etc before I tore up the full scale set of lines.

    I've seen it done both ways and I prefer to do it properly, which is not allowing the longs to float off the frames when the designer specifies that they don't.

    I definitely would not trust *anything* George Buehler said about steel boat building; at best he's repeating second hand information as he doesn't weld and has never built a steel boat himself.

    Besides there's a dangerous implicit assumption in allowing the longs to float, that being that the steel sheets you're working with don't have any curvature themselves as delivered or as cut, before being fitted to the hull. This is a very risky assumption to make IME. I pushed quite a bit out of my plate, some inherent and some generated by heat distortion when the plate was cut. And yes, I did use a plasma cutter.

    Whatever - I'm happily if slowly fitting out and that's a right annoying process regardless of hull construction etc. Damn sight easier to fit transverse bulkheads to frames if you don't need to worry about gaps around the longs though.

    PDW
     
  11. brian eiland
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    brian eiland Senior Member

    Steel Protective cleaners & coatings (Hull, etc)

    ....from a recent Designfax newsletter

    Henkel Corporation has introduced a new, water-based reactive autodeposition coating, Bonderite M-PP 930C, formulated specifically to deliver a uniform, defect-free surface coating on raw cast components and ferrous metals. This paintable epoxy-acrylic urethane coating easily coats both the inside and outside of complex components and delivers enhanced corrosion and abrasion resistance, excellent thermal stability, and superior edge protection, abrasion resistance, and flexibility. The coating covers the entire inner diameter of cylindrical parts, controlling warranty exposure.


    http://henkeladhesivesna.com/henkelna/10400_LT6267_SurfTreat_eBrochure_Final251798.pdf

    ...excerpt
    HENKEL BRANDS

    ALODINE: Registered as a trademark in 1946 as the conversion coating for aluminum substrates, Alodine® is a series of conversion coatings
    that improve paint adhesion and provide corrosion protection for light metal substrates. These coatings include metal pretreatments
    and post rinses for light metal pretreatments.

    BONDERITE: Since the early 1930s, Bonderite® has been well established in the automotive and metalworking industries as a brand for
    conversion coating processes and chemistries to improve paint adhesion, corrosion protection and wear resistance to ferrous-based
    alloys, mixed metal alloys and plastic surfaces. The products that make up the Bonderite® brand include process line chemistries,
    cleaners, pretreatment chemistries including activators and conditioners, conversion coating chemistries, post treatment chemistries
    (including rinses and passivation), as well as auxiliary products including toner, additives, accelerators and neutralizer.

    P3: Registered in 1894, the P3® brand didn’t begin to represent cleaners until the late 1920s. These cleaners are for metallic and
    nonmetallic surfaces, fouling prevention and corrosion protection, together with disinfection of water and use with wastewater treatments.
    These products are liquid/powdery products designed for use in low- and high-temperature applications at different pH ranges (acid,
    neutral and alkaline), and in high-pressure applications, depending on customer conditions.
     

  12. brian eiland
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    brian eiland Senior Member

    CNC-cut Metal kits

    There is an interesting affirmation article concerning CNC-cut metal kits in the latest issue (Apr/May) of Professional Boatbuilder:
    http://www.proboat.com/table-of-contents-148

    Precisely engineered CNC-cut metal kits simplify custom and production projects at aluminum sailing-yacht builder K&M and steel-motoryacht builder Jetten, ..both in the Netherlands

    In case you are unable to access this article on-line, I will just hi-lite a few of the notable observations.

     
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