Hi Midget,As DickL is talking about f48/Mini 40 size,re cross beams and sizes,I will give you an idea of what I use on my testbed 1M Multi.Both fore and aft beams use 1/2metre 8mm carbon fibre tube with a 1metre 6mm tube running through it[or whatever your beam requires].The 8mm is secured to the centre hull the 6mm tube is just taped up to stop it from sliding through.This allows you to dismount the floats easily for transportation if needed.This arrangement will handle 3.75lbs of hull in any weather without any problems at all.One point about carbon fibre is the ends of the tube do require binding or in time they will crack.I use electricians tape[a couple of turns will do]To give you further info on strength,I can pick the multi up by the outrigger float no trouble nothing gets strained, so they have plenty of stiffness in them when you need to lift it out the water in awkward places. Regards Tricat