Hello everyone,

I'm new in the forum, and already have my first question :-)

Who is able to do me a non-binding rough breaking-strength calculation for following sailing-boat-part made of carbon? Example pic at the end of this text.

It is about a so-called BOWSPRIT pipe (for the gennaker sails).

I'd like to change my old aluminum one for a carbon one.

My old aluminum tube has 8.5kg incl all fittings. The carbon tube only 2.5kg.
I haven't used it yet. I would like to ask forum experts first.

Conclusio should be: Is the carbon tube sufficiently dimensioned or at least as stable as the one made out of aluminium?

I have following info for you:

old aluminium tube:
- alloy: probably AlMgSi0,5
- Length: 2,300mm (approx. 1 meter boom, the rest is screwed on deck with 2 clamps)
- outer diameter: 80mm
- Inside diameter: 72mm
- Wall thickness thus: 4mm
- Weight of the pipe without fittings approx. 8 kg

Carbon tube:
pullwinded
- Length: 2,300mm (approx. 1 meter boom, the rest is screwed on deck with 2 clamps)
- outer diameter: 80mm
- Inside diameter: 76mm
- Wall thickness thus: 2mm

fiber alignment: Unidirectional inside + 75°/35° outside
fiber volume: aprox. 60 %
surface: smooth, shiny
temperature resistance: up to 110 °C
tensile-E-Modul: 240.000 MPa
tensile strength: 4.000 MPa
fracture strain: 1,50%
density: 1,8/cm³
thermal expansion coefficient: -0,1 * 10-6*K-1 along the fiber
radiolucent: 100%
specific elctrical resistance: 1,6*10-3Ohm*cm
heat conductivity: 17 [W/(m*K)]
specific heat capacity: 710 [J/kg*K)]
no vibrations
UV-resistent by using standard varnish
corrosion-resistent: e.g. petrol, oil, saltwater, hydrofluoric acid
handling: drill, mill, cutt, glue 

weight: approx. 1kg per meter

Would be super nice of you if you could help me

Many thanks in advance

The main problem here will be the fastening. As I showed, the pure strength of the part seem to leave quite a big safety margin, even if the safety factor of the original is just 1. But it is easily possible to crush that tube with an inappropriate fastening (method). This is due to it's orthopic material characteristics.
I think the shear forces induced by orthogonal forces shouldn't be the problem, although it isn't really possible by hand, as the winding is very loose and not continuous on a smaller scale. But shear forces are usually only a problem, when the beams are relatively short compared to their diameter. Your support and force induction are about a metre apart, wich is about a dozen times the diameter of the tube. But without an effort I am not willing to do here, I can't prove it mathematically. You could assume the tube as pure ud, but it is absolutely within the realm of possibilities, that the loose winding might produce a notch effect, wich makes the tube weaker than an pure ud tube. So I don't see much sense in calculating this.

Either way, you can't get any insurance from asking some guy at a forum, especially if you got no education in mechanical engineering to comprehend my approach. So further calculations, which will require some simplification of the problem will do you just as much as my feeling based on experience, that it seems like the tube will do the job, as long as you are using fibre reinforced plastic compatible fastening methods.
A picture of the tube mounting and the cable fastening method would be ideal.