STEEL HULLS with Composite Superstructure / Topsides

I believe I may have asked this question previously, but I don't recall if you gave an answer. Who was that 'draftsman' you spoke of?

 

Brian, I think the one single issue you need to consider and keep in front of all the options is boat survivability.

All sorts of options can be considered as construction material but bottom line is will it withstand heavy seas.

We got caught in a storm of Africa delivering a 47m steel Feadship to ZA for refit. Port bow quarter 10m steel plate got pounded in like tin foil, all the foredeck teak deck got pealed off - vessel had waist high steel plate bulwarks.

I'm currently refitting a 80m Tuna boat that got caught in a storm last week north of NZ. This boat is one of the strongest built steel boats for size I've worked on but she also suffered some damage.

GRP and other materials on yachts that can hove too works but experimenting with plastics on a motor vessel that has to run I think is taking to big a risk. Oceans don't care about looks or science they just kill foolish boats and people.

 

I don't know that I am following your reasoning here....not disputing your reporting, just not following your reasoning?

Isn't steel a much more ductile material than solid fiberglass? Sure it may suffer dents and bending, but isn't that better than fracture and holes?

Certainly steel is stronger than fiberglass in most cases, unless the glass boat is real hi-tech.

Then you seem to mix in some seamanship with the comment about hove-too?.... what difference does that make in the material selection?

OOPS! I'm sorry, I must have read your posting incorrectly the first time. I believe now what you are saying is that I need to be careful about the 'plastic' superstructure I am contemplating. You are very correct. Sorry

 

You seem somewhat fixated on ductility not sure why?

Steel, i.e. plate, for bending/forming, like any isotropic 'metal' ductility can be a feature. The more ductile the easier for bending in fabrication. But with composites they are inhomogeneous, anisotropic and generally do not behave in a linear manner. Thus crack propagation is not a 'simple' process as it is in metals. You also don't make a flat sheet of composite, then "bend it" to form your hull shape either, as one does with metals!

When designing with composites, it is deflection driven, not stress driven. Thus you ensure that any flexibility is accounted for, wanted or unwanted.

 

I see the biggest weakness in your hybrid idea is the composite deck. Sealing and attaching will become a major concern. There will also be potential rust traps. Why not go for a fully welded steel deck? This can have attachment lugs welded on for the composite superstructure. You can adhere insolation materials on the under side.

The hull-before-framing would lend itself to bonded composite framing with one big advantage: the hull could be thoroughly rust protected before the framing is adhered eliminating potential rust pockets. However this technique would be at the wave crest. Note that automotive brakes have composite linings adhered to steel. I am certain that the technology is out there.

As for the excellent CNC designer: He is brilliant at what he does but remains a diabolical businessman. I will try to track down an address which could be difficult. He keeps a low profile to hide form creditors.

Cheers

Michael

 

If I were out sailing the remote 'south sea islands' and encounter a reef that I just managed to scape across, what hull material would I prefer....steel.

I was impressed with the 'ductility' of this test, especially after I have seen results from impact test with balsa and foam sandwich constructions for years now:
http://www.portlandyacht.com/lionswhelp/construction/chrono/009NidaCoreTest.html

The ductility feature is not just an ease-of-building feature, but also a damage control feature as I see it.

BTW, doesn't both the Duflex kit panel constructions and Derek Kelsall's KSS construction involve 'bending flat sheets of composites'?

 

You could just ask him to contact me in the USA, obviously I'm not a creditor,...just looking for someone good at their work.

 

Apart from the obvious of not keeping watch or using ones charts, you are referring to a localised impact load. This has nothing to do with the ductility but more to do with mechanical strength and internal stiffening, coupled with correct load paths. Hull material is just one part of a complex sequence of events that cause damage when subjected to an externally applied load.

Damage control of….???

If you feel composites don’t offer the “safety factor” you seek, for whatever reason, then why remain with steel alone..what is wrong with Aluminium?

 

...from another forum I posted:

I'm proposing that the deck will be made up of a relatively thick piece of honeycomb panel with appropriate fiberglass skins on either side. This deck will sit down on top of those 5 metal bulkheads with their flat tops that stretch across the hull from gunnel to gunnel....like this pic...


Those athwartships metal frames should add a lot of stiffness to the hull structure, and tie the upper edges of the hull skins together, and check some of the thermal expansion/contraction differences. The one-piece PP honeycomb deck will sit on top of these bulkhead flat-tops and the deck shelf at hull interface.

Per a recommendation by MikeJohns

(Brian noted: I still want to question if I can bring the PP cored deck all the way over to the hull skin and bed it into a nice blog of advanced adhesive)

For a significant number of years now they have been gluing decks to hulls without any other fasteners. Plexus product comes to mind most immediately. These are methacrylate adhesives, and there are now a good number of these super adhesives on the market. So those products are prime candidates for joining our decks to hulls.

There are other good candidates for our adhesion problems,...what are known as 'toughened epoxies', or could be referred to as 'rubber toughened epoxies'. Here is what one builder said about one particular product he utilized.

ADHESIVE TECHNOLOGIES

One thing to keep in mind, these 'tough adhesives' get a lot of their toughness from being somewhat pliant (not brittle). Likewise the PP honeycomb material and panels are pliant (ductile). These characteristics work together to make a really TOUGH product.

 

Steel is much more repairable thruout the world than is alum.

Steel can be easily shrunk back into shape. Alum not so. Steel is much cheaper than alum.....etc

 

So why spend all this time debating/cogitating about the possible use of composite decks/deckhouses, if you feel steel is cheaper and more readily repairable anyway? :?::?:

BTW..you should never use heat on aluminium when fabricating for shape!

 

Do some investigation: Steel is not 'much cheaper' than aluminium and may well turn out more expensive in the long run. Alloy prices are at a real low right now. Alloy is faster to construct with and requires far less capacity in lifting gear. And it is clean! Much nicer to build with than dirty, heavy steel.

 

Because steel HULL makes sense, steel superstructure does not in this case.

PLEASE reread posting #49
http://www.boatdesign.net/forums/boat-building/steel-hulls-composite-superstructure-topsides-47349-4.html#post636961

 

Lifecycle maintenance of steel is expensive. Small steel boats are double trouble. Thin skin, heavy and most important because of the small size, impossible to keep corrosion free.
If you need a metal hull, go aluminum. Much lower maintenance.

 

Aluminium vs Steel Hull

I'm not so sure that alum is that much lower in maintenance,...unless of course you don't plan on painting the topsides, and you have to be real careful to isolate the prevalent copper-based antifoulants, and the other electrolysis problems. I lived on and maintained an alum 60' Chris Craft Roamer once long ago. It had it share of maintenance problems.

Of course there are endless arguments over this subject, and I just found this subject thread that in the first few pages I've read so far appears to be a very solid discussion of the issue:
http://www.boatdesign.net/forums/boat-design/aluminium-vs-steel-5785.html

I look forward to reading the whole thread.