Hi!

I'm planning to build a small rooftop boat.
Since it has to be able to be transported on the roof of a car and then carried by two people, it has to be very light.
The idea is to build it with infusion CF instead of plywood or glass, would that be possible?

Problems on the horizon: cost and the transom, how would I build the transom without cracking it when mounting the engine?

The boat in question is here:
http://bateau.com/studyplans/D15_study.htm?prod=D15

The boat will be used in rivers and on lakes with a small outboard.

The hull itself and it's materials.
The core: would a layer of Coremat 5mm or Soric 3mm be enough?

The shells: From inside and out = 200gr Blackstuff + 450gr Twill + core + 200gr Blackstuff + 300gr Aramid

Thoughts?

You have a chine design there so this type of hull may have been intended for construction using flat panels like ply wood.

For a sandwich or composite construction you can certainly save a bunch of weight but will need to consider the techniques involved and what you are prepared to do in time and $$.

To pursue infusion you would ideally need a mould to use. It could be a full female fibreglass mould that is a big job in itself or it could be a plywood/mdf mould? male or female as long as it is vacuum tight and sealed, probably with a layer of light fibreglass and paint etc. BTW you cannot use coremat with the infusion process as it will squash flat under vacuum. You can use soric but the 3mm you suggest is far too thin. I would consider a better infusion foam core like a grooved PVC, grooved acrylic or 3D PET core http://www.3d-core.eu/de/3d-core/produkte.html . Minimum 8mm thick.

Without going down the infusion path you could also consider flexing sheet foam over simple frame jig to hold the hull shape while the outside is hand laminated fibreglassed. Then when this is cured it can removed from the jig and held temporarily true while the inside is fibreglassed. The shape will then be locked in and you can continue to fit out with bulkheads and structure. The outside of the hull would then need fairing for paint.

Your transom will need some better material for the loads and durability. I would consider using a really high density 200kg PVC or Acrylic foam core.