steel hull vs other materials

Discussion in 'Boat Design' started by ajflick, Sep 19, 2006.

  1. ajflick
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    ajflick Junior Member

    We're considering buying a steel yacht for bluewater cruising and have been thinking pretty strngly about steel for a variety of some info on another site though that seemed a bit negative and thought we'd check these points out for some responses here...

    "The problem with steel is the weight of the material that is necessary to achieve the necessary stiffness of the other materials. There are designers who have done a lot to mitigate this problem, but in the end you have a lot of weight just where you don't want it in the hull and deck structure. While many steel boats are built with wood decks for this reason, an all steel boat has a tough time making sense as a distance cruiser. You may think that we are talking about a cruising boat. Who cares about weight ? Weight is almost more important in a cruising boat. Every pound of weight in the hull is a pound that can not be used as ballast or in gear and supplies. Steel boats have notoriously low angles of recovery and tend to be rolly. I consider motion is a seaway and important issue to crew well-being and of course angle of recovery is critical to safety."


    "Metal boats are seen as being very durable, but again in the weights of materials used in yachts I seriously question that idea. All boats flex; it is only a mater of degrees. Over time this flexing work hardens and fatigues the steel especially the skins at frames and other hard spots. Rust, mostly from the interior makes the skin thinner."

    "My biggest gripe comes down to sailing ability and how this affects deck and cabin materials. More weight means that you need to have more sail area for a given speed and a given sailing ability. More sail area means that a boat needs more stability to be able to stand to this bigger rig which means more ballast which means more weight which means more sail area. The problem gets worse because steel boats often have steel topsides, steel decks and steel deckhouses. This is weight high above the center of buoyancy and as such reduces stability further making it hard to carry a decent sail area to weight ratio. In the ultimate bad sailing day, it also means that once inverted you are more likely to remain inverted longer."

  2. Crag Cay
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    Crag Cay Senior Member

    Steel is neither all bad or all good. Like so much in boat design you have to decide on your priorities and then see if steel offers you the best solution. We all sail compromises to some degree.

    So, where to start? Well the indesputable bits: Steel is tough. It's abrasion resistance and ability to take a beating is unquestionable. So are its fittings. I have lifted 35ft boats by their deck cleats. So 'roughty-toughty' comes out on top.

    Steel is also readily available and lots of welders can make a good enough effort putting one together. The welds are as strong as the material when first constructed and when repaired. 'Back yard built' can be more than adequate. I have yet to see any evidence of structural fatigue in boats built with angle or T section frames and plenty of flat bar longitudinal stringers.

    It's also quite cheap as a raw material and the tools and facilities needed to build one can often be sourced cheaply. However this does mean they are often built cheaply and some 'economies' in blasting, painting or ballast materials are a real problem.

    Now some of the things you have to consider. Size matters. There is a minimum thickness (and therefore weight) of hull plating that is stiff enough to build a 'durable' hull. (US 10 gauge) This generally means that it's increasingly difficult to build an all steel (hull, deck and cockpit and coach house) with good stability in sizes under 40 ft without massive displacement and deep draft. Sizes down to 32 ft are perfectly possible but in my experience are difficult to execute without using other materials for at least the cabin house and cockpit and they still need a draft of 5 ft, or so.

    Getting the ballast low also matters. It really needs to be lead and plenty of it. Whilst the weight of the bottom plating can contribute to stability, it's not very low down and I always feel a little wary when it's included in the quoted ballast ratio. You need weight low down, and external bulbs should be more common on steel boats as they have much to offer.

    Steel is indeed a stupid material for decks, cabin houses and cockpits. If you hit a container with your cockpit locker lid, things really aren't going too well. But it's not just the weight you don't need. These areas are covered in exposed edges and 'corners' and take a lot of wear and tear from dropped winch handles etc, and keeping up with the chipped pain and dings is necessary. Using wood is possible but I have seen loads of problems at the junction with the steel. GRP or aluminium work well, even when bolted, although the Dupont Detacouple with aluminium works better. But if a yard has the ability to build these parts in aluminium, why not the whole boat? In a stroke you do away with all the short comings of steel, and only sacrifice a very marginal amount of ruggedness.

    Steel rots and only paint and your constant vigilance can save it. The idea with a yacht that you can build in extra thickness to compensate for corrosion is palpable nonsense. It's a hangover from ships and inadequate paint regimes. You've just spent ages trying to shed weight without it returning to compensate for poor workmanship. However, the longevity of the boat starts at the design and build stage. Only a designer who has built in steel really appreciates how things must be arranged to ensure all parts can be adequately blasted, painted and maintained. How are you supposed to get the blast nozzle and spray gun or brush behind a T stringer or other tight corners? Have the angle-frames been put in 'open' or 'closed' ? The paint regime has to be done perfectly following the manufacturers scheme to to letter (expensive).

    Then, even if it has been designed and built perfectly, you have to constantly maintain it. Any damage must be made good and the coating kept in good condition. It's not really 'low maintenance'. People talk about how you can always have any rot cut out and a replacement area welded in for it to be as good as new, but this is major work with often quite some disruption to the interior. In my experience, most steel boats have to have a substantial yard visit at about 10 years old, where spot (or extensive) blasting and repainting is needed plus a full top coat re paint. At this stage any shortcomings in the build and design are obvious and many famous boats from well regarded builders have been a nightmare.

    Below is a photo of a 38 footer than in many ways represented the zenith of steel boat construction. Steel hull, lead bulb, aluminium decks, coach house, cockpit and light weight interior, that proved herself fast and able in the southern ocean. But another was never built. An all aluminium version was better in every way.

    In the eighties, I spent days at the Annapolis Boat show preaching steel to anyone who would listen. Now, I don't think all steel boats are bad, it's just there has to be some compelling reason to use steel as I think other options are more often the better 'compromise'.

    Attached Files:

  3. Finlander
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    Finlander Junior Member

    In the 80's, aluminum was super-exensive compared to steel. Now it might not be so. Generally, there are big differences in quality for aluminum. It's probably worth some careful research.

    By the way, I recently saw a 40-foot sailboat made from stainless steel. Actually I think the bottom plating was stainless; then it was merged with something else above the waterline IIRC. The yardmaster told me it developed hundreds of tiny pinholes and leaked!

    He didn't know why, but I assume there was nickle in the bottom paint or something. Very strange.
  4. timgoz
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    timgoz Senior Member

    An all steel boat is basically one homogenous piece of steel. Cabin & decks of steel can be made watertight to a standard that other materials would have a hard time attaining.

    The ease of fitting instalations above decks is also in steels favor.

    Of course, I am tilted opinion wise, but some of the places I've been, and those I would like to return to or visit anew, require a no-nonsense strength.

    Take care.

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  5. MikeJohns
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    MikeJohns Senior Member

    Amanda, Crag and all

    Whoever wrote this confuses the issue a bit and tends to display a prejudiced against steel and for light boats.

    The real issue is the displacement to length ratio. A higher ratio makes steel excellent, a low ratio makes it less attractive. The motion will depend on the metacentric height and the stability is dependant on the overall design not just the hull material,
    Hull material mass is factored into the stability calcs and design aheavier material can make for a more comfortable boat. You cannot extrapolate stability comfort and safety from something as simple as the hull material without a large amount of wilful ignorance.

    With scantling thicknesses steel boat hulls over 40 feet can be equal in weight to well designed cruising hulls of other materials. Once you get to 50 feet they may be lighter.

    In a separate thread I have just been discussing fatigue, you should have a look through some of the material there. Steel has a very good fatigue response.

    Another good thread to peruse

    and a discussion of fibreglass

    Modern paint systems brought the surface maintenance level of steel to something pretty close to fibreglass in a marine environment, Internal access is important for repair ( as in any hull). For straight hull repair steel is the fastest cheapest strongest and easiest by far.

    Steel decks make very good sense for a number of reasons if your design allows, a simple painted steel deck is hard to beat for a very durable strong and watertight construction. If you are careless enough to chip the paint you need to patch it no different to any other material.

    Uncoated steel oxidises if the condition are right, it doesn’t rot as wood does and it corrodes slowly in a galvanic couple compared with Aluminium. It is the strongest of all common boat building materials.

    Plate thickness can make a big difference to longevity....for example bare steel in a dry marine environment (such as deck head) will corrode surprisingly slowly , wet corrosion is a bit different since it forms its own galvanic cells and pit corrodes, the rate is slow often around 1-2 mm per year. Typical pit corrosion in steel slows down with depth, steel thickness makes a very big difference to longevity if you do get corrosion the extra thickness allows substantial corrosion
    For example 2mm lost from a 6mm plate once stopped would not need replating while a 4mm hull would have to be replated in the corroded area.

    Commercial Plating minimum scantlings have a corrosion allowance. that makes them thicker than the stress levels would require.

    The design of the vessel is the only thing which determines whether any particular design feature should be adopted. You cannot generalise simply on the hull material. In my opinion external ballast bulbs are not a good idea since you are introducing complexity and dissimilar materials and steel boats are better with internal ballast and either integral or removable keel tanks, unless you are going lightweight.

    I don’t think lightweight boats make good voyagers as they lack stowage and comfort. But that’s another story.
  6. Gypsie
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    Gypsie Randall Future by Design

    Steel is the way to go for bluewater cruising, no reason why you cannot purchase a comfortable steel sailing yacht with reasonable sailing abilities. Many have been built in Australia in the last twenty years or so, I have a 40ft Bollard and she is a very strong and safe cruising yacht. Once you have had a steel cruising yacht and been on the bricks in a blow and run into other lumpy bits and survived, there is no going back.
    Happy cruising
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  7. Pericles
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    Pericles Senior Member

    Steel is 490lbs per cubic foot, alumunium is 168lbs, FRP is 95lbs and epoxy/marine ply composite with glass cloth laminated on both sides is about 43lbs per cubic foot. Cold moulding with epoxy and strips or sheets of marine ply to a hull thickness of 2 inches, as per Sam Devlin's methods, would give you a ship that could almost dual role an an icebreaker. Easy to repair as well with ply patches and 5200, in order to reach a repair yard. Steel? It rusts!

    His Sockeye 45 is beautiful.

  8. M&M Ovenden
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    M&M Ovenden Senior Member

    There are pros and cons for all materials. If there was a perfect answer about the best material the question would never be asked. As Mike pointed out, you can't judge a boat simply from the material it is built of. There are some very good boats made of all materials.

    If you are planning on buying a boat for extensive cruising you also have to plan you will have to maintain and maybe eventually do some repairs on that boat, no matter what it is built of.
    Being comfortable with the material with which your boat is built can also mean being comfortable with working with that material and the maintenance it involves. This is a personal preference that you have to assess from your own point of view.
    Personally, I am happier working with metals than composites and that weighs a lot in my choice for the boat I want to cruise on. I can carry extensive repairs on my metal boat anywhere in the world with the on board tools, or find welders and steel anywhere. Even if I contract the work done I'm more confident doing quality control on a metal hull. But that's me. I don't mind having to paint regularly, but some other people rather have to deal with gel coat and fiber glass or with sanding and varnishing. Knowing and accepting the potential work your boat can involve is important in your decision making if you want to enjoy it. There is no such thing as a no maintenance or never meet with bad luck cruising boat.

    Now to such a blunt comment as steel rust can I also bluntly point out that wood rots, fiberglass delaminates, aluminum does corrode. But of all those materials steel is the only one that screams red when it's due for a bit of care and that before it's too late.

  9. Pericles
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    Pericles Senior Member

    Airliners, other types of high performance aircraft and Spaceship One are rich in the use of composite laminates. So are high performance boats.

    Blue water cruising is more about the choice of vessel rather than of materials to build it. The Alaskan 52
    or the Tennant designed New Yorker 51 built by Avante
    would fit the bill, but are not built in steel. To quote from the Avante site:

    "A major advantage the “New Yorker” has over the traditional trawler is shown in the accompanying graph. (Cannot be displayed here.) With 160hp engines the displacement catamaran will be using less than 1/3 the fuel [just under 1.91 litres per nautical mile] of the monohulled vessel at the planned 15 knot cruising speed, assuming that the monohulled displacement vessel can actually reach that speed. These engines will take the “New Yorker” up to 20 knots. And if you should wish to go faster then around 270 hp per side will take you up to 28 knots. Of course the range will suffer at the higher speed because of the increased fuel useage. At the cruising speed of 15 knots[with either engine] we are looking at a range of just over 4000 nautical miles."-----

    Settling for steel at the start of the design process limits the options for innovation. Better to choose the style of vessel first and the rest follows. One style of vessel to which steel lends itself with merit would be a SWATH.

  10. MikeJohns
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    MikeJohns Senior Member


    Listing the mass of a material alone as design significant data is no more useful than stating its color. :)

    Steel rusts if you don't paint it……… What do we do with steel cars ?

    As for 2 inch cold moulded …..the scantling is meaningless unless you state the vessel dimensions frame spacing etc. Also to use it as an ice breaker you would need steel plates to protect the wood from abrasion.

    The thread was about a blue water cruising sailboat. That a space station aircraft or high-performance racing hull is built with light weight composites does not make them a better choice for a cruising yacht hull. Such arguments are a bit specious.

    My understanding of SWATH is that it is suitable for vessesl starting at a few hundred tonnes it is not very attractive for small vessels unless limited to sheltered waterways.

    Steel is a very good choice for blue water cruisers.
  11. yotphix
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    yotphix Junior Member

    Too true Mike, space craft, air craft and high performance racing hulls are very unlikely to encounter concrete piers, shipping containers and dead heads in their day to day use. They are all likely subject to a maintenance schedule a little beyond that of the average blue water cruiser as well!
    The materials used in these items are about as relevant to blue water cruising as saying that bricks and mortar make good houses so liveaboards should live in brick and mortar sailboats!
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  12. MikeJohns
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    MikeJohns Senior Member

    Alloy is an attractive material too. It does have some downsides like all materials. My biggest problem is that stress conentrations are often in weld zones and alloy is very poor in this regard. It is also still expensive. Very suitable for some types of vessel.

    Stainless makes a poor hull matrial.

  13. Pericles
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    Pericles Senior Member

    Hello Mike Johns,

    "My understanding of SWATH is that it is suitable for vessesl starting at a few hundred tonnes it is not very attractive for small vessels unless limited to sheltered waterways."

    Did you look at the Wikipedia link? The Asia Star is a 350 person all balcony luxury cruise ship with 20,295 gross tonnage.

    As you are in OZ you won't have seen running between Florida and Grand Bahama.

    Sea Shadow, built in 1985, is small, I grant you, but what use is a baby at first? The journey of a thousand miles starts with the first step.

    "Steel rusts if you don't paint it……… What do we do with steel cars ?" Scrap them if they become immersed in salt water. Roads in Northern Europe are salted in winter, which plays havoc with cars.

    "As for 2 inch cold moulded …..the scantling is meaningless unless you state the vessel dimensions frame spacing etc. Also to use it as an ice breaker you would need steel plates to protect the wood from abrasion."

    I guess you haven't looked at the construction photographs on Sam Devlin's website or read his book. There are precious few frames in a stitch and glue boat. The hull is monocoque and building layer upon layer to increase hull thickness is the construction method. The "ice breaker" dual role comment was a metaphor. Mind you, some of Sam's boats do cruise Alaskan waters all year round.

    Sorry guys, build in old fashioned heavy steel for all you want. It just won't do for me. I prefer voyaging to careening and chipping paint. I have about 3650 days and nights of reasonable life left to spend my sons' inheritances and wearing ear defenders and using a hammer isn't a productive use of my time. Steel is ok, but epoxy butter is better.

    As for blue water cruising, please do have a look at Sam's Oysta 42.

    It's stitch and glue, epoxy/ply composite construction and damn fine looking. ;)

  14. waikikin
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    waikikin Senior Member

    Is good, but limbers RULE!

    I beleive with steel that with quality, well applied coatings & significant emphasis on limbering & good drainage to sump & "fitout" access (all really applies to any constuction medium) it is an excellent & very meritous material. I will quote some relatively recent experience of mine in recreating a fine work boat that was in nearly daily use for some 40 years that did suffer from neglect in the years preceding our rebuilding of her for the sons of the original owner, in that it was a requirement of our work that if the owners "choose to bring along a bag of 101 marbles, & throw them about in every direction within the vessel, then be able to account for even the 101st marble at the lowest part of the bilge, that they would be very well satisfied in our endeavours & that the vessel would "be good" for at least as long as 40 more years"(roughly quoted). To me thats generational experience talking & a very high recomendation of a great construction material so far as longevity is concerned. Aside from this I also reckon other materials have great benefits, but that steel excells in the work boat world & that cruising vessels often fit that description in that the're in daily use & called upon to do some tough stuff(so long as the owner is committed to havin' some fun & adventure).Best regards from Jeff.

  15. MikeJohns
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    MikeJohns Senior Member

    I must confess to being a little confused by your posts. My comment on SWATH is that it does not fit the thread of cruising sailboat and is for large vessels, also SWATH is not performance but stability oriented .

    As for cars you paint them and unless you are particularly negligent you keep that coating in good order. As you do with a wooden structures.

    I am an engineer and I would have liked to have introduced a few facts re weight stength etc with regard to you rcomments on cold moulded timber 2” thick…we still don’t know the vital statistics of the vessel to which this is applied. If it is for a heavy displacement trawler yacht you may find that is even a bit on the thin side. Also when you start laminating other peoples laminates (building up layers of ply) you need to be darn sure of their quality.

    Anyway all that aside if you truly have 10 years left.....thats life.........get off the internet forget building and go and buy a boat ..........NOW! ……….hull material seems rather a trivial choice in your circumstances although if you want to crash into reefs rocks and wrecks with impunity steel is a very good material thing to consider, just get it well surveyed. :)

    Get to it your sons will be happy enough to inherit the boat.

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