The same size it is now.





Yes and yes.


Uhhmm, may I point out something here ?

I have a feeling that many of us here are evaluating the different design features with their gut rather the contents of their sculls. I mean that if the sheeting system can put the leech under 150 kg of tension and do so on a 2 mtr long boom then why does anyone think that a spinnaker luff tension or a trapeze wire are a problem for the same mast design ?

To give everybody an idea of what a commericially bought 250 Euro unstayed aluminium mast can handle I present the following example. On a class 5 landyacht (5.5 sq. mtr. sail on a 5.5 mtr mast), the lower mast section is 50 mm in outer diameter and it handles a 5:1 sheet system fitted to boom about 1 mtr away from the mast. When combined with the heeling loads this means the unstayed mast can handle about 250 kgm bending loads. The sleeved sail design handles in this case a max luff tension of 110 kg and a max leach tension of about 140 kg and is as flat as a board.

My F12, even with a 3:1 sheet system at the leech and a 75 kg skipper, will only put the mast under 294 kgm bending loads. An increase of only 18% and still well within the safety margin for the mast.


The luff tension on a 8.5 sq. mtr spi will not get anyway near 150 kg and neither will a man on the wire. But more importantly the spi luff tension and mainsail leech tension will largely cancel on another and the sideways loading that the spi+mainsail can put on the mast on the downwind is always less then the load the mainsail can generate when sailing close hauled. That is why we don't double trapeze downwind on normal cats. This means that a mast design that works upwind can always handle a spinnaker. The same cancellation principle applies to a trapeze (here the trapeze load and sail force load largely cancel one another)

One reason I opposed trapeze wires is that the proposed platform and rig don't really need it. It is already a wide boat for the rig. It compares to a 2.90 mtr wide F18 (which are now only 2.60 mtr wide). When taking the lower heeling moments of the smaller rig into account then 185 kgm (or a 67 kg skipper on a 50 kg F12) will already achieve parity with that design when hiking. A skipper of 45 kg would do so when on the trapeze, but I personally focus more an having such light crews team up for the F12 rather then solo sailing them. The other reason is that I want to avoid the cost of the trapeze gear (like harnasses that kids quickly grow out of) as well as the hassle associated with it, like puncturing the hulls with the hook. The reasons for not supporting a trapeze were however never technical in nature, the unstayed mast can take the loads associated with it. More of problem will be how the sail will respond under mast flexing. It may become hard to control properly, but only just giving it a try may give the answer there. The estimates however, suggest it may still be acceptable.

Personally, I like the unstayed mast setup idea with a spinnaker. Note that there are no side stays or forestay and the spi can gybe very easily in front of the mast. It can be a very clean set up altogether. The very small spi area may also allow using cheap non-ratcheting blocks. The spi pole is just the same section as the boom (same length etc) with three lines to support it. That leaves only the spi sail itself as the major cost, but with what a performance gain !

Wouter