Fiberglass vs Aliminium

Discussion in 'Boat Design' started by BluSky, Mar 2, 2014.

  1. BluSky
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    BluSky Junior Member

    Hello, I am considering to design a watercraft (3m hull), and I have doubts about the material: glass fiber or aluminium.

    What do you recommend me? What are the main advantages and disadvantages of each material?

    Thank you in advance.
     
  2. PAR
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    PAR Yacht Designer/Builder

    Aluminum on a 3m boat would need to be very thin, meaning welding isn't likely (possible, but very tedious and difficult). This leaves riveting and a considerable internal structure, to hold up the unsupported panels. It's done with powerboats with some regularity, but typically not as a home built.

    'Glass construction, on the other hand, is much stiffer comparatively, so it needs considerably less internal support, though often at the cost of a weight penalty.

    Weight and cost wise, wood will be a better choice. A molded or glued lap build, will easily rival any substantial aluminum build, with far fewer parts, which cost a lot less too. Unless you employ exotic fabrics and cored construction, a 'glass one off build will be very hard pressed to compete in a weight battle, with these wooden structures.

    How is it that your are going to design a boat without the prerequisite understanding of the usual materials involved?
     
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  3. rwatson
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    rwatson Senior Member

    Par has summarised the situation very well.

    I can only add that to weld aluminium you need to buy $1000 + of Tig/ or Mig gear, while with fibreglass you just need some old ice-cream containers and paint brushes. Fibreglass by itself ( without some sort of 'padding' like wood or foam ) would be very heavy if you used it by itself to build a substantial hull.

    A lot of people would agree that sticking wood together with fiberglass and epoxy is the least painful way of getting a decent result on small boats.
     
  4. FAST FRED
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    FAST FRED Senior Member

    Perhaps riveting the aluminum , almost no ribs or frames as the Viking boats were done?

    Light and strong some sort of wood as done on canoes would be simple and has the advantage that a part that does not fit well can simply be created again.
     
  5. PAR
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    PAR Yacht Designer/Builder

    The stiffness of aluminum or lack there of, wouldn't allow a a build as you describe Fred. Home brew riveting isn't an easy thing, if you don't want leaks.
     
  6. rxcomposite
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    rxcomposite Senior Member

    Exactly what my former boss used to say. "You can practically build this (composite aircraft) with a brush, a scissor. and some empty cups."
     
  7. Fanie
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    Fanie Fanie

    If you consider the fiberglass vs wood, on only a 3m hull, how much more can the weight be (unless you fill the hull up ;)) ? In any case, weight can be an advantage since a very light hull gets pushed around a lot more than a heavier hull in a swell. Fiberglass should last longer and requires less maintenance (if any). Wood is easy to shape, for fiberglass you need a shape or former.
    Nothing with boats is straight forward and everything is a compromise. Probably why we like it ;)
     
  8. nimblemotors
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    nimblemotors Senior Member

    :rolleyes:
    If you have to ask the question, you must not know the answer.
    Please find out the answer first before coming here and asking.
     
  9. nimblemotors
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    nimblemotors Senior Member

    Aluminum has very good abrasion resistance, so it can be dragging it over rocks without damage, will dent on impacts, whereas Fiberglass will shred and crack.
    Aluminum is cold and noisy.

    Low-density polyethylene (LDPE plastic) looks like the best material for small boats in my opinion, but pretty hard to make one yourself.

    Wood is always a good choice if you want to spend the time taking care of it so it lasts.
     
  10. BluSky
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    BluSky Junior Member

    I am considering the design of a watercraft (3m) hull.

    Probably Aluminium is more suitable, but FiberGlass is more easy to handle it and cheapest.

    It is important an stabilizing system Probably the attached design is atractive.
    http://www.freepatentsonline.com/6912967.html

    On the other hand, do you recommend another stabilizing system for the watercraft?
     
  11. PAR
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    PAR Yacht Designer/Builder

    This is an incorrect assumption. It might be best if you studied the particular material parameters first before making grand conclusions. There are no aluminum PWC's in production and for obvious reasons. If you can't see why this is the case, you're frankly not yet ready to engineer or design a boat, particularly one that will go fast enough to kill its riders, in the event of a mishap.

    The link is to a potion of a patent application and it's of dubious value and questionable ability. Certainly nothing that could be considered reasonably "innovative". Winged tunnel jet boats currently exist and I'm not sure how they got the patent, (if they have), but it's value is as I mentioned dubious at best.

    As far as this being a "stabilizing system" , well this is the joke part of the equation, as a 15' boat, regardless of propulsion type, doesn't really need a stabilizing system, assuming it's a well design hull form with a reasonably matched drive.

    Simply put, you don't need a stabilizing system, though you do need some engineering and yacht design courses.

    Previously I asked:

    "How is it that your are going to design a boat without the prerequisite understanding of the usual materials involved?"

    I'll ask the same question again . . .
     
  12. Reefhunter
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    Reefhunter Junior Member

    Glas is heavy and needs multiple layers to become strong.

    Alum is lighter than any other materiel. Alum can be sound insulated. Alum welds are smoother, but not used on 5083 very often. Welding is preferred to riveting. Rivets are the weakest link.

    Wrong for a boat. LDPE is mainly used for zip baggies.

    Woodhulls in fw rot which is why you don't see too many of them. Wood covered with glas solves that problem, but it doesn't make any sense.
     
  13. discovery
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    discovery Junior Member

    To equate the 2 methods though, you will go through $1000 worth of paint brushes,containers,ect as well.
     
  14. daiquiri
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    daiquiri Engineering and Design

    Tell us something more about what you have in mind. What type of watercraft? Like the one shown in the patent? What speed? Where is it going to be used? You gave no useful info so far, which could let others help you in any way.
     

  15. rwatson
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    rwatson Senior Member

    Its a lot more complex than that. For aluminium you have cutting disks, polishing disks, wire for the welder, electricity, welder gas.

    Paintbrushes are a low level use, you will more likely be using some re-usable squeegees, acetone, wet and dry paper, peelply, paint - but the actual costs will vary a lot over the design of the boat.

    The BIG difference is the skill required to operate a MIG/TIG welder - as a bunch of threads in the Metal Boat Building forum will attest.
     
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