STEEL HULLS with Composite Superstructure / Topsides

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

  1. brian eiland
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    brian eiland Senior Member

    Hard to give you any exact figure as I have yet to determine the final shape of that bottom. Here is the first vessel I was thinking of using this construction 'style' on, a re-designing of a 40 coastal trawler known as a Pilgrim 40
    http://www.trawlerforum.com/forums/s3/redesigning-pilgrim-40-trawler-canal-boat-11212.html

    Per original, she is 40' length, 14' beam. Maybe increase the beam to 15' and the length to 42' ?
    Attached a few better pics of her bottom as it exist.
    Pilgrim 40 bottom, stern,800.jpg
    Pilgrim 40 bottom, star bow,800.jpg
    Pilgrim 40 bottom, port bow,800.jpg
    img47, 800.jpg

    Perhaps go to a harder chine shape, much as was done with the Great Harbor trawlers?
    Great Harbor hull form overlay.jpg

    I'm thinking 5-6 mm steel plate for the bottom?
    Built in a 'frameless manner' with 5 major bulkheads and as many stringers as it takes.

    I'm not totally opposed to alum, I just thought steel was more 'fool proof' for possible 'kit-boat' fabrication by a variety of other boat yards/fabricators wishing to move thru this hull-shell construction stage quickly with minimal errors and expense.
     
  2. brian eiland
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    brian eiland Senior Member

    Steel Deck?

    The steel deck is not totally off my considerations, BUT one of my thoughts about using the thick-cored PP sandwich deck is to limit condensation that might drip off the underside of that deck into the bilges.

    I was also considering how the underside edge of a steel deck might be properly attached to the hull considering the low freeboard of this Pilgrim design.

    I had hopes of keeping the full deck piece off of the vessel until all the innards (engine, generator, tanks, etc) were installed.
     
  3. brian eiland
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    brian eiland Senior Member

    Integral Tanks

    So you are pretty dead set against integral tanks??
     
  4. pdwiley
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    pdwiley Senior Member

    What I'm doing with mine is fitting cut sheets of 30mm thick foil backed polystyrene (as per Mike John's advice) between the stringers then lapping over them *over* the stringers but between the transverse frames. Deck head lining goes over this for a total of 70mm thickness.

    The polystyrene is used in house construction and won't support combustion.

    Very little chance of water vapour getting to the hull shell therefore minimal to no condensation on the metal. As I live in a cool climate I wouldn't consider a metal hull that wasn't insulated & lined. Lots of ways of doing it other than my choice, but IMO it must be done.

    I also applied 7 coats of paint over the weld-through primer on the steel before I did anything else.

    Labour intensive, sure, but you only get one chance to do a thorough job and I'm building for myself.

    My steel deck is fully welded from both sides, FWIW, as per designer specification. As my cabin top is ply, I am fitting it last so I have a big open space to drop in tanks, engine, bulkheads etc etc (now nearly all fitted). If you went with a bolted on superstructure on a steel deck/flange, you'd have big openings to fit stuff as well so I don't think a steel deck would be an access problem, really. I bolted some uni-strut to the deckhead in my engine bay so I could move the engine quite precisely and have it under control at all times. It's quite surprising what you can do single handed if you have sufficient rigging gear and patience.

    It also helps if you're *not* a machinist and make things to sub-millimeter tolerances going off of manufacturer supplied dimensions (access hatch to drop engine through comes to mind as Ray can attest, never mind that red paint on the coaming..... I allowed 5mm oversize after all, should have been enough).

    PDW
     
  5. ImaginaryNumber
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    ImaginaryNumber Imaginary Member

    You might be able to find some of what they had online here:

    http://web.archive.org/web/*/http://australiancompositepanels.com.au

    The January 7 archive has more than the April 29 archive. Didn't check out the 2011 archives.
     
  6. Titirangi

    Titirangi Previous Member

    I'm surprized your designer and ex Austral welder advised against alloy, although Astral have had their share of hull issues. The Austral Armidale PB hulls may have been better built in steel considering the range of patrols.
    I've built many alu hulls 10m to 47m over twenty years that have proved excellent value with no hull failure issues, min maintenance and low running cost compared to steel. Skills to build alloy are no more or less than skills required by steel workers, a good steel mig welder can with a few days practice mater alloy welding and plate for plate alu is much easier to work with, more malleable and much less surface prep required, nil edge prep if router cutting from cut files.
    Few years back I accepted a challenge to survey then R&M a fleet of aging extremely neglected alloy CAT ferries 30 to 50m operating in international waters. I know if any had been steel hulls with same degree of neglect including several with split seams (BW), multiple corrosion holes in ER plates, missing hull/jet annodes most would have been supporting reef fish long ago.
     
  7. MikeJohns
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    MikeJohns Senior Member

    Inexperienced alloy welders are often a big problem. The very welders we have had most problems with are steel welders with a one day conversion course. The problem is that a visually acceptable weld is often flawed. Xrays of the welds can be very revealing.

    In alloy shipbuilding it's taken that alloy welding proficiency takes many months or even years of welding experience, importantly with significant weld quality feedback such as xrays before a welder is really proficient.

    It's a fair observation that the more experience the welder has the better the weld, at least until they have a few years on the job. There have been some classic failures of plate edge joins in patrol boats and xray investigation has shown welds to be abysmal despite looking really good visually.

    Lloyds register has some publications (papers) on this I think are worth reading.

    Steel welding is much more forgiving in every regard. It's also much easier to get a good weld in awkward places.

    Another detriment of alloy we have not mentioned is that when it's left bare it gets very hot in sunlight, too hot to touch, so if the vessel is likely to operate in the tropics it should be painted.
     
  8. Ad Hoc
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    Ad Hoc Naval Architect

    In a way Mike you've touched on a problem I've seen many many times before.

    I always hear the same old tired arguments about aluminium being difficult to weld hard to get to grips with etc etc. The reason is myopia. Aluminium because it is a metal and because it can be welded, it is approached and treated in the same manner as steel, why, because it is a metal. :eek:

    Would one use a flame gun on a GRP deck to straighten an otherwise distorted/buckled/curved deck?...of course not, it’s obvious why not. Yet this “same” obvious difference in nature of steel v ally is not present. Aluminium is not steel and its only similarity is that it is isotropic and metal, beyond that it’s chalk and cheese.

    A crap steel weld is much more forgiving than a crap ally weld. Aluminium takes time to master, the learning curve is significantly longer. Yet when done correctly will last pretty much forever. Does anyone ever question the length of time to master high quality composite constriction…no…so why do so with aluminium, just because it’s a metal? Reason, the frame of reference is steel (again!!)...steel is easy to weld ergo why is ally so hard!!??

    Aluminium fabrication is a highly developed and fully mature process not new. Yet some practices used in aluminium still refer back to steel work….and incorrectly too. Which is why such problems persist. Aluminium must be treated totally separately. A steel welder that is retrained as an ally welder will always produce welds inferior to ‘a bloke’ picked up off the street with zero experience and trained totally and only in ally. The mentality of steel fabrication is incompatible with aluminium.

    Ally welders who say it is hard...is usually because they were poor ally welders to begin with!
     
  9. MikeJohns
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    MikeJohns Senior Member

    That was really about PDW's advice from the designer to build in steel. Not a yard with some good hands onsite already.

    The real problem with amatuer builders building in Alloy is that they don't have the benefit of working with experienced welders for a week or two to learn the ropes. And I agree I'd rather start with a freshman than try to convert an old seasoned steel hand.

    The speed of welding with Alloy is fantastic but that wire speed is a two edged sword that takes some skill to master well, and also alloy is less forgiving in the initial fit up.

    It's more sensible I think for a one off home amateur builder to hire an experienced welder to complete all the critical work. Most handyman types can weld steel quite proficiently but produce very poor fusion of alloy.

    Home builds like PDW's don't have the benefit of a quality inspector giving constant feedback. For those reasons I recommend that the one offs either get their hull built or at least fit up very accurately and let an experienced hand weld it up.

    And beware of yards that have self taught welders who have swapped shielding gas and filler wire and produce visually passable welds. I've seen some shocking lack of fusion. We could start posting a few pics but it will derail Brian's thread.
     
  10. pdwiley
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    pdwiley Senior Member

    Yes and it was related to the likely difficulty in my determining what a good weld in ally was, and wasn't. Ditto the advice from my welder at work. The designer had both designed and built ally hulls so it wasn't lack of experience on his side, more experience in one-off builds by amateurs.

    I am egotistical to think I could have done it successfully because I'm fairly methodical and would have welded up a pile of coupons etc then broken them, as I had to do when doing my welding tickets all those years ago. Plus picked the brain of the experienced ally welder I knew. However, I decided to go with steel and am happy with that decision.

    The cost of steel certainly isn't all that cheap once one factors in sand blasting, priming and epoxy paints. However it is a lot more forgiving to work with for amateurs and easier to patch in the field if necessary. Plus the added abrasion resistance so vital for those indulging in Braille navigation......

    PDW
     
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  11. Ad Hoc
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    Ad Hoc Naval Architect

    Yup, that's the crux of it. An amateur with next to zero experience and zero assistance available, can storm on regardless and “get the job done”...but not so with ally. Even I was able to make passable welds in steel with just a few mins "training". Ally does require "support" and "back-up" to guide any amateur through the learning curve to become proficient, which not so readily available for many.
     
  12. MikeJohns
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    MikeJohns Senior Member

    Integral diesel tanks work well with a 10 year inspection schedule. Sullage tanks with salt water heads are particulalry problematic in steel unless inspected every two years and if in alloy I'd inspec 6 monthly. Potable Water tanks need painting inside with alloy and also inspecting regularly which is easy with a viewing port if the tank is accessible.

    Polythene sullage and potable water tanks make sense and will last the life of the boat with no maintenance.
     
  13. brian eiland
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    brian eiland Senior Member

    Tanks

    Thanks for that Mike. I'll look at that option a bit later. I did see this recommendation
    http://www.moellermarine.com/oem/fuel_tanks/

    I'm getting on a plane today for a long trip back to USA, then a meeting 3 hours from DC home base for several days. So I'll likely not be back to the forum for 5-6 days.
     
  14. brian eiland
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    brian eiland Senior Member

    Last edited: Sep 2, 2013

  15. michaeljc
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    michaeljc Senior Member

    There are a number of issues re welding of ally. Sections of over 7 mm thickness are not so difficult, especially if they are not to be visible. One can straight run this material as one does in steel. Providing there is enough penetration all is OK. When you get down to 4 mm visible welds the pressure really comes on. It is impossible to hide stop-starts. Top welders can one-run over 3 m of step-welding. Some people can never learn the coordination and consistency to do this. I have a steel mig ticket but would never try to do this. It requires daily repetition. Step welding (scallop pattern) is the recommended technique on light material as it combines penetration with sufficient bead thickness. Getting an even pattern over a long run is a real art.

    Another issue is the machines. They all have their own characteristics and are very dependent on exact adjustment. In a fully pro ally workshop there is one machine, one welder. No one else is permitted to touch it. I know of a workshop that brought in 4 new, high quality machines, of the same model. They all behaved slightly differently when on the same settings when welding ally. Then there is such settings as pulse. I know one ally superyacht builder in NZ who does not allow the staff to use pulse. I am not sure why.

    The last thing to be aware of is contamination. Ally workshops must not have any steel or wood fabrication taking place. Invisible steel grindings, or any other dust in the air from the likes of grinding disks is fatal - especially in Tig ally welding. Tig is even more difficult than Mig. Tig is used on highly visible light sections like bow rails.

    The only kind of operation in which to get an ally boat built is one that is doing nothing else. IMO
     
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