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

Let's see:
I guess the tube is fixed to the sledge with rivets or bolts? That would be very bad, because ud tubes don't like to take loads perpendicular to the surface, or twisting forces at a local point of the surface, no matter in what direction, wich means that everything that goes through the tube and is meant to transfer loads isn't good. The easiest solution should be to either fix it with a wide ring clamp, or to glue a aluminium or non-ud carbon tube piece either in or around the tube and use this reinforced section to bolt through. Or fix it on the endcap and bond it with the tube.
the ring also induces forces orthogonal to the surface, wich can damage the tube. It is difficult to find a good solution here, because of the sliding movement. Better would be a felt like ring surface, that sits tight and doesn't allow movement inside the ring and spreads the load better. Another option would be to reinforce the tube locally from the inside at the ring in work position. The reinforcement would be ideally a piece of non ud carbon tube.
The inox eyes are a bad solution for this kind of tube. Even the installation of them could damage the tube, as they are flattening the tube wall when you are tightening the screws, which produces the worst load for ud tubes: a radial
bending momentum. And drilling ud tubes is always a bad idea, because the holes can't take loads effectively in any direction. And the worst direction is the one your ropes are pulling, which tries to split the tube orthogonal to the fibres. The solution would be again a glued in endcap that takes the loads, or a local reinforcement, or a wide clamp.
That doesn't mean that your tube will fail, it simply means that it will take far less loads with that fastenings than with methods that take the special propertys of the carbon tube into account.
The fibres in that tube are highly orientated. The tube is incredible strong in one direction, but also incredible weak in every other aspect.

I forgot to add that the hardwood plugs must be thoroughly sealed every time a screw is used,  otherwise they will swell inside the tube and damage it.