The yachting world appreciates carbon fibre for strength to weight ratio. But this is only part of the story.
A carbon or glass fibre structure can be engineered much more preciselyy than a metal structure.

When engineering a structure with high loads such as a;mast, chainplate, bowsprit, rudder or keel fin, it is
most important to understand it's load patterns.The critical part is the dynamic loads which cannot be calculated.
When the yacht sails through big waves the dynamic loads can be up to 30% higher than the static loads.
We used load cells on many yachts in the 80's and 90's to understand exactly what happens. Once one has a good
idea where these loads are, and how high they are it is quite straightforward to engineer a laminate plan.
Before, however, the strength of a carbon laminate has to be known. The only way to be sure about the stength of a
part we build is the make sample parts, with different types of fibres and lay-ups, then have them analysed.

When you buy a certain type of aluminium or steel, you can find very precise data about compression, tensile and sheer strength
along with modulus of elasticity to decide which metal to buy. This is not the case with carbon laminates,
where strength data is known after epoxy is added to the carbon fibre.

The quality of carbon or glass laminate depends on many things:

  •  The quality of the fibres
  •  The quality or the resin
  •  The production team

 The production method:

  •   Prepreg with pressure bag
  •   Prepreg with autoclave
  •   Prepreg under vacuum
  •   Wet lay-up under vacuum
  •   Infusion

 

  •  The temperature and humidity of the laminating area
  •  The person who laminates
  •  The quality of the consumables

All the above have an influence on the final quality of a composite product. This is the reason why an engineer cannot calculate a composite structure without the data of each builder.

When building a “high-tec” aluminium mast, one of the best solutions is to extrude a relatively thick mast section and add reinforcing plates in the lower, highly loaded areas using aircraft rivets and epoxy glue, and mill the mast wall on the inside in the upper areas with lower loads.
With fibres this is much simpler, because the layers are only between 0.2 and 0.6mm thick, depending on which fibres are used. The reinforcing can be engineered much more precise than with aluminium. The thinnest reinforcing plate can be 2.5mm thick.

The difficulty designing a light structure is to eliminate material that is "not working", meaning material that is not loaded. This is a never ending development.

When designing composite parts it is important to completely change philosophy and forget about the metal knowledge, but think fibres and use the unidirectional fibres to carry high loads.

 

 

 

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