Hi Ross,

these are the only restrictions on masts,

11 MAST
11.1 The mast shall be made of an extruded aluminium alloy.
11.2 The maximum height of the top of the mast including all permanent fittings shall not be greater than 7360 mm above the top of the main beam.
11.3 The forestay attachment point shall be 5280 mm ± 100 mm from the top of the main beam. If more than one potential forestay

attachment point is provided then all such points shall fall within the measurement tolerance.
11.4 Section size: Width 59 mm min; 63 mm max. Depth 86 mm min; 91 mm max.
11.5 Tapered mast permitted, but when used tapering shall only be above the 5180 mm mark.
11.6 Mast rotation control must be fitted

So internal ribs are no problem, as long as external dimensions fit sizes above, which are easily checked.

Hi Gary I should have said "not legal at the time" the rules have been relaxed since.

Ross