Most 40' cats have 60' masts, right? Again, that's what google says, I know nothing.

Maybe, but most of them weigh several tonnesand only have one mast.

How did you decide on the mast height on the 24m?

The same as on all the boats.  Started with the required Bruce Number (sq root of sail area in sq' divided by cube root of weight in lbs) and worked from there.  The 24m needed a BN at least 1.3 when fully loaded (10 tonnes, plus 3 tonnes of boat = 29,120 lbs.  Cube root is 30.1).  So SA is 30.1 x 1.3 squared = 1531 sq ' = 142 sq m. 2 sails of 71 sq m each.   Rectangular sail, boom length 4m, aspect ratio of 4:1 = 17.75m luff.  

If the free labour and overheads are still on offer after the lockdown, the most expensive part is the carbon, then the foam.  Using a truss structure, the beams can be made from glass rods which are easier to infuse than carbon, cost very little and although they have to be a little bigger to compensate for the lower stiffness, should still have less windage..  

Getting away from foam requires much smaller hull panels and maybe some form of corrugated core, which I am experimenting with this week.    Otherwise, the hull construction will be solid glass with easily built f'glass I section stringers.   Fairly thick glass (max 10 layers of 400 gsm uni in various directions) is required for toughness and to stop the small cross section hulls bending excessively, so we should get away with only one stringer per panel.  Building the hulls in half moulds, the join will act as the stringer on the deck and bottom.    10 layers of infused 400 gsm weighs 6 kgs per sq m.  20mm H100 (recyclable PET or similar) foam with 1200 glass each side also weighs 6 kgs per sqm, has better panel stiffness, is less tough, requires extra laminate at the beams and is a lot more costly.

hey, i was talking up reducing the foam costs before it was trendy!

;-)

If you are looking at protruded rods anyway, have you looked at half rods,square tubes ,or flat plates to corrugate your panels?

Yes, but all are heavy

Why not infuse the stringer in the mold?

no reason, and still high on the list.  

Didn't our friend in the northern European country have F700 for very cheap per m^2? have you decided against it? Apparently they are not locked down.

yes, but not as cheap as corrugated glass, if it works.  Picking up the mould today, might get the first piece laid up tonight