first impressions are it would be too heavy...but it would be stronger...

inital thought on the idea is that the contact faces of the aluminium on the foam would need to have a good bond, shear forces between the foam and aluminium would be high I imagine.

I believe the stiffness of the beam would be only marginally increased. If striker-less, you need to consider the stiffness of the beam because any deflection will reduce your rig tension, which generally affects pointing ability adversely.

70*1.6 tube - I = 201000 mm^4
70*1.6 tube + 50*1.6 tube - I = 272000 mm^4

Assuming material is 6061-T6 with yield stress of 240MPa, E=70GPa.

with a load of 220kg on the first beam (length = 2.5m) the maximum stress will be about 235MPa, and deflection = 50mm.
(With 2% deflection, buckling will probably be a concern!)

with the same load on the second beam the maximum stress will be about 174MPa, and deflection = 37mm (1.5%).

1% deflection is the limit allowed by Australian standards for aluminium boats (AS4132).

My "opinion" is that it is not suitable (I wouldn't do it). 220kg load on the beam is likely (crew weight on trapeze plus initial rig tension could amount to more than this then take into account increased accelerations when sailing in waves!).

Like all engineering, there are multiple solutions/opinions so please make comments.

well lunch is over, better get back to work.

Insert disclaimer here.

Having said all this, it is a racing machine and if you don't mind nursing it around the course in a blow! But it will be a heavy beam so the advantages in light conditions will be lost.

This is assuming the foam is rigid enough to force the internal beam to be parallel to the outer beam when flexing.