Pros and Cons of Steel/Aluminum/Aluminium Allow hulls

Discussion in 'Metal Boat Building' started by GumbyTheBorg, Jan 3, 2007.

  1. GumbyTheBorg
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    GumbyTheBorg Junior Member

    Hi all,

    I am trying to get some feedback on the pros and cons of varying hull/superstructure materials. Specifically, I'd like to know the pros and cons of Steel vs. Aluminium vs. Aluminium/Magnesium vs. Composite hulls. Stuff like strength, cost, weight, rust resistance, etc.... Just wondering.

    GumbyTheBorg
     
  2. GumbyTheBorg
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    GumbyTheBorg Junior Member

    :confused: Wow, not a single response... You'd think that people would have an opinion on this subject, but apparently, it's either a very taboo subject or no one cares... <sniff>
     
  3. M&M Ovenden
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    M&M Ovenden Senior Member

    Hi,
    I think you're not getting much answer for a few reasons. The subject of pros and cons of different materials is already covered in other threads and because a whole essay could be written just to talk of pros and cons of one material so to try to cover four of them in one shot appears overwhelming. It is also tricky to discuss intelligently the pros and cons without narrowing down the discussion on certain boat type. What can be a pro for a certain boat can well be a con for the other. Did you have a more precise idea in mind when bringing up the subject?

    Cheers ,
    Murielle
     
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  4. GumbyTheBorg
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    GumbyTheBorg Junior Member

    I see your point. Ok, well let me rephrase my query then. The target is a 140 foot long cruising yatch (exploration type), full displacement hull. The goal is to build the ship to be as "green" as possible (this includes fuel efficiency and drastically reduced noise pollution that is harmful to sea life), so we will be designing in a diesel electric system that uses HTS electric generators and electric engines (HTS = High Temperature Superconducting, Siemens is gearing to produce such engines in the short term) as well as podded drives. We will also be using micro-bubble emitters for the hull (i.e. drag reduction). That being said, the ship must be designed to take a licking and keep on ticking. So it's not one of those fancy luxury yatch that has to run for cover once the seas reach 4 feet... The hull and superstructure material must be quite strong, yet light... (lofty goals?).

    So it terms of strength, maintainability, durability, cost of manufacturing, cost of goods, how does steel vs. aluminium vs. aluminium composite (i.e. magnesium) vs. composite fair out?

    cheers,
    GumbyTheBorg
     
  5. korvello
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    korvello Senior Member

    HI: I'm not an expert in any way about boat building[ in buildings yes] and plannig to start building a catamaran sometime this year i've found that building a large boat in anything than metal makes no sense and even if steel has better properties than aluminum ,the maintenance and extra weight makes it hard to digest when compared to aluminum specially if you leave the boat unpainted. another thing that i,ve found is that everybody underdesigns and underbuilds so they are always worried what if i hit a submerged container or a rock or will the hull flex to much, ridiculous one should build a boat to be able to ride a hurricane hit a rock or anything else in between or stay close enough to shore or maybe only go out in mild seas at the first sign of bad weather here they go running to shore.ther are plenty of sites that advocate aluminum versus other materials but almost everybody with common sense will tell you if they could chose the boat same size and same price they will go aluminum.i've got mixed info about the grade because in the u.s. almost everybody sells and uses 5086 but in australia they prefer 5083 that suposely has better numbers.as far has how tick most people uses 5mm for below water up to 80 ft long DASHEW used 6 mm in his 83 ft even if the book said he could use 5mm if the seas where not more than 12 ft ,something like that ridiculous............up to yor size i've seen 8mm that i think is not enough,at least below water.somebody in this forum mentioned that at10mm you don't have heat deformation but i'm not sure if that's the case because the extra thicness requires more heat...there are very experienced people in this forum that would know better ..how and where do you plan to build ...korvelo
     
  6. MikeJohns
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    MikeJohns Senior Member


    Hello do you have a first name we can use?

    For a start read the following threads:

    http://www.boatdesign.net/forums/showthread.php?t=5785&highlight=aluminium

    http://www.boatdesign.net/forums/showthread.php?t=13174&highlight=fatigue

    http://www.boatdesign.net/forums/showthread.php?t=11455

    And perhaps
    http://www.boatdesign.net/forums/showthread.php?t=5963

    Most of us work and will answer specific queries, Your post as Murielle said is a little too broad to attract a professional response.

    Hope this helps.
    Cheers
     
  7. korvello
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    korvello Senior Member

    HI: ...I've reading and listen to as many opinions,facts,tests etc...about the advantages and disadvantages of aluminum versus steel and and for my money i don't see how steel is better ,,and why people with limitedless funds such as the u.s. navy,coast guard will want to build with it maybe they don't get it too...please anyone explain to me where i'm wrong?????????/ steel has better properties ,suports fatigue better but it's close,,, but when you use the same weight of aluminum versus steel ...aluminum has the advantage ,being maintenance free oh yeah you can have some problems in some marinas and others but compared to the ongoing painting of steel rust fighting after 20 years ther is no comparison.let's see a strong hull on a 80 ft plus hull of 1/4 inch steel versus a 1/2 inch hull on the same boat maybe the steel will have an advantage in a direct impact with a sharp rock i would like to see numbers on that ..but the aluminum hull would be stiffer and so less afected by bending and torsion ,able to ride heavy seas has easy as steel.or better ..unfortunately boat builders suffer from the same disease that the car makers or house builders suffer they don't build for the existing conditions ,like the car makers that test their cars to survive a 30 mph impact when we all drive 70mph i find that criminal... i can say the same for the houses in the u.s. all disposable ,i don't understand the sense behind it... you leave your home inthe morning never knowing if you'll came home to a pile of ashes or ruble ...boat builders on the other hand don't build their boats to take a 20 ft drop ,ride a hurricane, hit a reef or container even the idiots at lloyds give out building references based on mild, lake like conditions ...no wonder that most boaters when faced with a big storm either run away or latch down and pray,maybe god designed it that way.. they know that is not built for those conditions just like in the houses ,cars the tecnology is available nobody does it... i don't know about you but it insultes me ,i'm a house designer,engeneer,builder and i i'm quitting building junk you want a disposable house build it yourself ,i would never build one for myself either..i see the same mentality in boat building how can you put your sweat and tears into a floating house and not build to survive whatever the seas throw at you...the tecnology is there .....i've looked at the framing used by most builders and it's a joke ..not more than a skeleton to hold the skin that itself is too thin no wonder cracking develops in aluminum boats they are underbuilt..any common sense engeneer can design a rigid frame that can aided by the skin be completely rigid or maybe they need uncommon sense...i intend to build a catamaran not as big has i would like but if you would see my drawings some would laugh just think that 0n a 60 ft i'll use 1/2 inch aluminum below water line and 1/4 everywhere else on the shell ,i cannot even find channel strong enough for what i need...i would like to hear ideas on how to make a boat stronger,safer not excuses why everyone doesn't do it ..some of you guys know a lot about hull design ,weight distributing,and all the other involved factors but little or no input on strenght and safe hulls to ANY condition......sorry too long ...GUMBYTHEBORG if i may why 140 ft if you are worried about fuel use ..the bigger the more you'll use i would like to build 80 ft but cost will be twice that of a 60 ..... korvelo
     
  8. MikeJohns
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    MikeJohns Senior Member

    Korvelo

    If any one material was head and shoulders above the rest we would use it exclusively. All materials have their pros and cons. The longevity and durability of any material is effected more by design and construction than by material choice. Unfortunately there is a lot of ill informed and very prejdiced opinion on the subject of hull material.

    When it comes to alloy remember that the design UTS is the weld strength not the stock material strength, UTS of alloys suffers considerably when welded well and catastrophically when welded poorly. Alloy also suffers severely from corrosion if not properly designed and maintained. Another problem with shipping is that it burns very well once ignited.

    You ask ...why steel?
    Steel is the strongest most forgiving and longest lasting of all the materials when coated properly and reasonably maintained modern coating systems last many decades.
    Steel is the easiest of all hull materials to repair to full strength, achieved simply by replacing existing material.

    When it comes to rigidity, as you may know materials exhibit strain in response to stress, just how this strain is accomodated and what it loads in turn is an important consideration, we need to determine just how the stresses will flow through the structure.
    If you make one part masively strong it will simply pass the stress onto adjacent structure rather than absorbing it in elastic strain. If such stresses are passed through weld zones in alloy you will accelarate failure in the weld.

    A good mix if you want strength and lower maintenance is a steel hull and alloy deck and superstructure.

    Remember that weight and strength are the two faces of the coin. Its all compromises, cost, durability, performance ease of repair .... Generally we use alloy when we want lightweight structures where the expense and lower fatigue resistance (and subsequent maintenance) is offset by performance gains. If you want heavy strong scantlings steel is a very good option.

    Cheers
     
  9. korvello
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    korvello Senior Member

    HI: Thank you Mike i understand that steel has better properties my only problem with it is no matter what coatings you use you will always be carrying a paint can and a brush for the rest of your life they do it in the navy ,on cruise ships i guess they don't know of the coatings you're talking about.....about stress and fatigue i understand your point that it will break in the weakest point i just disagree with you because on an aluminum boat you have to make the all boat strong so it reacts as one piece flexing as you point out doesn't go with aluminum and that 's the biguest flaw i see on most aluminum builders.they treat it as steel...as an example in motorcycle racing the aluminum frames have to be gussed and so over built that they weight almost the same as the steel ones but they are much stiffer ...i don't know the exact number but maybe you do aluminum for the same weight is much stiffer/rigid than steel...trust me it makes you think and i wish there was an alternative maybe same day titanium will be afordable ..i've been on a steel boat on very heavy seas and flexing noises are scary at times and if an aluminum boat would flex like that it would fall apart ...
     
  10. korvello
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    korvello Senior Member

    HI: sorry Mikejohns ,i forgot to mention i did like your idea of building hulls in steel and the rest in aluminum ............and what kind of steel would you use.. cor-ten ? and do you or any one know anything about hardox and weldox steel they look to be 3 times or more, stronger than aluminum and at least twice the strenght of cor-ten and have the advantage of been available in coil what makes for a nice continuos panel onthe hulls..
     
    Last edited: Jan 20, 2007
  11. alaskatrawler

    alaskatrawler Previous Member

    Steel/Aluminum/Aluminium Alloy hulls

    Hi All

    Ive been reading this thread with interest and agree with Mike Johns. With due respect to Korvello I feel that if you have a painted hull either out of aluminum or steel a chip in the paint will cause rusting on steel and oxidization on aluminum. Both that if left unteated can cause extensive paint damage. So you better have a can of paint on hand for alumium as well.

    I have seen painted aluminum hulls that look worse than rusty steel as that powdery oxide spreads very agressivly when exposed to air. The paint comes off in large sheets. Steel will rust but with the modern zinc rich coatings the rust movement is really quite slow. I have chipped Balto in a couple places and the exposed steel remains bright until I touch it up sometimes after several weeks.

    It seems that with aluminum it is much less forgiving during the painting process to get the root adhesion that freshly blasted steel provides. Aluminum left unpainted is the way I would go if I were to build with aluminum. I believe in steel for strength especially for hull material. Aluminum is what I would use for radar arches etc. Also for vessels that need speed to plane etc.

    When you use aluminum for your superstructure you have to be careful that you don't make the vessel to light otherwise you will have one uncomfortable boat due to the snappy roll that to light a topside structure will give you.

    Thats the way I see it

    Regards
    Dan Walsh
     
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  12. alaskatrawler

    alaskatrawler Previous Member

    Pros and Cons of steel/Aluminum Hulls

    Hi again

    I read Korvellos post wondering why the Coast Guard and Navy does not build vessels out of aluminum but mostly out of steel. I feel it is because navy ships are built to a strength class rating that cannot be achieved by aluminum.
    During the Falkland Islands war the British ships were made of aluminum and when hit with a missle burned as if the were a flamable chemical.
    Also many of military ships are rated for Ice as they must be prepared to go anywhere in the world they are called upon. Coastal patrol boats are the exception and these are usually made out of aluminum or composite material.

    Regards
    Dan
     
  13. MikeJohns
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    MikeJohns Senior Member

    Higher carbon steels are not really necessary unless you are trying to save weight. So more compromises, they are also more prone to fatigue failure and less forgiving in welding.
    .

    As Alaskatrawler says alloy is less durable than steel .

    Aluminium must be epoxied below the waterline , in the bilges and tankage. As you may have found paint systems fail rapidly with alloy, the corrosive products lift the paint very well for great distances and the alloy corrodes quickly underneath. Steels corrosion is much more localised and considerably slower, cavities in steel can be filled with a cement grout to both strengthen and stop corrosion even bare steel can be protected this way. Alloy is a lot fussier and when it corrodes (which it often does) it does so quickly.
     
  14. Crag Cay
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    Crag Cay Senior Member

    This urban (maritime ?) myth keeps doing the rounds, but is based entirely on a misinformed newspaper report that was later retracted. Why these things are still quoted I don't know.

    No Royal Navy ships with aluminium superstructures were hit by missles. HMS Sheffield and the Atlantic Conveyor were both all steel.

    The frigates were hit by bombs and there was no evidence that the aluminium contributed to their loss in any way what so ever. There is no ship of that size that could withstand the detonation of five bombs, whatever the construction material.

    The only significant change made to RN policy directly as a result of the fires on board these ships was that man made fibres were no longer used in manufacture of sailors uniforms.


    ********
    "Because of the widespread use of aluminium alloys in building, transport, home appliances and offshore structures, it is necessary to address the issue of aluminium and fire and to answer the question, 'does aluminium burn?'.

    The answer is, of course, "No". Each year hundreds of thousands of tonnes of aluminium scrap are fed into remelt furnaces and heated up to and beyond the melting point. The aluminium melts when the temperature exceeds the melting point, it does not burn. If it did, the recycling of aluminium would not be possible.

    During and following the Falklands conflict between Great Britain and Argentina, several misleading statements appeared in the press, suggesting that aluminium alloys, used in the superstructure of some of the ships that were sunk, had burned and contributed to the loss of these ships. Of the nine ships sunk in this conflict, only three had aluminium superstructures. All three vessels had steel hulls and in each case the damage inflicted suggested that these vessels would have sunk regardless of the materials of the superstructure. In no case did aluminium burn. HMS Sheffield, the first British destroyer to be sunk, was widely reported to have an aluminium superstructure. This was, in fact, an all-steel ship with a steel hull and a steel superstructure. The Defence White Paper published on 14 December 1982 concluded, 'there is no evidence that aluminium has contributed to the loss of any vessel'. Similar conclusions were reached by the Ministry of Defence Working Party convened to review ship design. The Chairman of that Working Party was reported in the Financial Times, 24 December 1982, 'I am not aware of any evidence to suggest that any ship was lost because of the use of aluminium in its construction, nor was there any evidence that aluminium or aluminium alloys had burned or suffered from a series of small explosions. Aluminium, like any other material, has advantages and disadvantages in any given set of circumstances. Where the balance is in favour, aluminium should be used in warships or elsewhere.'

    In fire tests on aluminium materials, when the temperature exceeds the melting point, in the range 600-660oC, the aluminium surface exposed to the fire can be seen to melt, but it does not burn. At the end of the fire test, the metal remains as a resolidified pool.

    Aluminium in the form of finely divided powder or flake oxidises exothermically, but this is a very special case because of the very large surface-area-to-weight ratio. Aluminium then behaves in a similar way to other finely divided materials such as iron and titanium, tea, flour and coal, all of which will also readily oxidise exothermically in the powder form.
     

  15. MikeJohns
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    MikeJohns Senior Member

    Thanks for that Crag
    Another myth expounded, I even read this in a journal recently I'll try and contact the author. Even if Aluminium did show some tendency to burn from a warhead it certainly has no chance of burning in a normal vessel fire but it does melt and perhaps this is where the myth tends to get fuel :)
     
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