the use of shape for added strength

Discussion in 'Boat Design' started by tunnels, Dec 3, 2012.

  1. tunnels

    tunnels Previous Member

    Simply adding shape to a flat panel can make it stronger and not having to add any more material .
    Almost like getting something for free so to speak .
    Transoms have been my thing and have made shaped transoms for some small boats that have very little plywood and just a small amount of foam core and the over all weight is possibly less than half of what a standard transom would be and you dont have the wet and heavy plywood ,then later the rot problem that most everyone gets some time or another !.

    Take a look at the family car can you find just one flat panel anywhere ?? even the frame of the car has shape !!.
    Over the years car designers have had the endless challenge of making car lighter and stronger better looking ,more fashionably acceptable and not forgetting there safety all these thing combined with smaller lighter stronger motors that are more powerful than could have been dreamed of 60 years ago! we have cars that go faster and with aerodynamics ,body styling and good looks and clever engineering from the race tracks they stay on the road better at speed and are much quieter and stable than the old cars , all of these things are directly or indirectly related to shape !! and yes they are made from better made stronger and resiliant metals and combined with other materials like plastics and adhesives .

    Shape is something very few boat designers if any take into consideration or try to use !! oh sure the topsides are wrapped round and meet at the bow so the bow is pretty strong but with creases and added shape it could be even stronger and the shape can be a should be carried on down to the transom corner ,round and eventually finish where the Motor is mounted .
    The hull bottom is the place where its more difficult to find a way to introduce shape to be beneficial . a concave is a shape thats been round for a long long time with flaired bows scolloped bottoms , has lots advantages but hasnt been used much in recent times . So shape !! what do you think ?? :eek::confused::(
  2. Ad Hoc
    Joined: Oct 2008
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    Location: Japan

    Ad Hoc Naval Architect

    Shape….depends whether one is viewing the question as an aesthetic point of view, as most seem to, or from a structural point of view, i.e. structural stiffness.

    I won’t delve into the aesthetic, as that is a subjective and an opinion based point of view and there shall be more opinions on this than there are stars in the sky.

    Structural stiffness, as all trained engineers and NA’s are taught is simple.

    The structural stiffness is related the E and I, “E” = Young’s modulus of the material and “I” = the second moment of inertia.

    If 2 materials are the same, i.e. the E is the same, then simply altering the I it affects the structural stiffness. This is not rocket science and it has not been forgotten. Only those that do not perform structural design calculations or exposed to structural design as their daily job or part of their job will see this is a “forgotten” or “whoa, that’s new”.

    To alter the I is child’s play.

    Take a flat bar, place it wide side down on a bench, push it down at the end…it bends. Rotate it 90 degrees, so the thin (thickness) part is now on the bench, press down the end….er…um…bit more difficult. The second moment of inertia, its shape, has changed. Nowt else.

    The I has increased from 0.30cm^3 when wide side facing down to 2.5cm^3, if say a 50x6mm FB, when on edge facing down. An increase of 833%, just by rotating the FB. See, simple :p
  3. tunnels

    tunnels Previous Member

    At last we have something to agree on !!
    Like i said shape can make things look nice and modern looking and stylish and its such a pity designers dont use it more .
    Means also we can use thinner cores and a little less glass and resin and theres a weight saving,every little helps !!. Couple all these things with a more user friendly shape with flowing lines its pleasing to the eye and add colour coordination and becomes a little sexy looking !!, colour and eye catching grahpics with modern up to date styling sells products !
  4. messabout
    Joined: Jan 2006
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    Location: Lakeland Fl USA

    messabout Senior Member

    Builders know intuitively that curvatures can increase the load bearing capacity of a structure. Think of a crowned deck as compared to a flat deck for example. SImply curving the material does not increase the strength of the material but it distributes the load in a different, more favorable way.

  5. tunnels

    tunnels Previous Member

    I know what you are saying ! designers are not taking these thing to heart and using it !! like i said my transom is created from pieces of a cylinder and joined plus i used parts of my old splash well and this helps even more . The old splashwell was quite big but the new one made from bits of the old is about 1/3rd of what it used to be .
    Have used this same principle on a inflatable ridged glass hull . stepped the motor back nearly 100mm so a slight increase in usable space plus added performance !!,the whole transom was 100% glass , its was really great because the duck billed drains were able to be made slightly bigger so inside drained even quicker !:)
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