can you decrease plate thickness or use FC for a tug?

hmmm--- not a bad idea--ok you know i like fer-a-lite.
could this work too? in essence your talking about using the steel hull for a mold and keeping the mold in the hull?? there is that old rusted hull at the shipyard--5000.00 denarius! but need replating sandblasting and...well its a mess...

 

one thing people say often about FC is that its labour intensive--but l'd be willing to bet that a large steel boat would be nearly as labour intensive as a FC build...if not more...with all the welding grinding, fitting etc...of course a mold method for fc is not all that labour intensive if you use a staple gun...

Mike--one question I have for you is- back in the day-- and even now, is arc welding smaw, still the best way to go for a heavy displacement steel boat or is a flux core say 90 amp or even a 230 outfit flux core the way to go?

 

I prefer MIG, It's so easy . I wouldn't use flux cored, its expensive and it's not as clean. MIG is the cheapest too, here a spool 15kg of class approved wire is around $30 then add the gas. You can weld with straight CO2 which is sometimes even better for the amateur to achieve good depth to the weld. I know people who get CO2 for 1/4 the price of the argon mixes. It does spatter more. You can vary the ratios of Argon and CO2 for different weld characteristics too.

I'd suggest PM Murielle (M&M Ovenden) or Wynand (WynandN) They will give you better advice than I can.


[Edit added.......]

As for labor intensive. That depends on the design. A design incorporating simple surfaces and easily fabricated frames has a much faster build than a round rolled hullform.

The labor for FC is surprisingly crippling. The build time has more to with the number of bits you have to cut accurately and position accurately and fasten than the size of the boat. There are lots of things that get overlooked, on a FC hull they are a real pain to build.

A chined steel design (with well defined frames) from the designer would be much faster than FC but then it's much faster then a rolled plate hull built from offsets too.

 

No way is steel building as slow as FC. Even if it was close, it's still heaps stronger. Tom Colvin says building in FC is 2X as long as any other medium. You do not know more about building boats than Tom so please don't fantasise.

WRT welding methods, you have to consider your circumstances. If you are building outdoors then how are you going to provide shielding for a MIG welder using gas?

Cost wise, I'd say that MIG using solid wire and CO2/Argon shielding is cheapest & fastest. Flux cored MIG is very expensive. I paid $115 for a 5 kg spool of flux cored vs $32 for a 15kg spool of solid 0.9mm wire.

I used a stick welder for all the root runs because I wanted to know that they were sound. You can have problems with MIG much more easily than stick in getting good fusion.

The small MIG welders are IMO useless for serious work. The guns aren't up to continuous welding and the feed mechanisms are feeble. They're fine for light structural welds on RHS, angle and the like. This based on a very small sample I might add so there may be small MIG welders that are quality items but they still have small duty cycles.

I recently bought myself a new MIG welder. It has a 250A output with a 60% duty cycle at that output. It has geared drive rollers. I've put about 5 kg of solid wire through it so far and I'm happy with it. I could also show you one weld with incomplete fusion where I welded a lifting tab onto plate. When I later broke that tab free it was obvious that at the start of the weld I hadn't gotten full fusion with the plate. Sure, this is a reflection on my technique but the weld looked fine.

Lots more info on steel boat building in the steel boat area.

PDW - currently 'enjoying' travels and a break from boat building...

 

This is a fairly complete document of ferro construction including some discussion of man hours required......on the order of 50-60m/hrs per square metre of shell (non-professional crew). With training and experience that drops, but still not as fast as steel construction.

http://www.fao.org/docrep/003/v9468e/v9468e00.htm

If Tom figures steel is half the man/hours of FC, then NC steel will be 30% the man hours.....I assume chined rather than round bottom form.

 

hmmm --seems i was a bit off on that estimate for sure...

 

edit:
actually it is also totally about getting the exact boat you want too!