Chris (and others),




Up till now I'm happy with the data.

To support my earlier statements and my "How do you know ?"; I here provide you with some data. But indeed I feel both paths should be followed, stayed c.q. unstayed and see what works best.


Largest unstayed mast sailed in abundance (Standart Landyacht : http://www.char-a-voile.com/franc2/seagull.html) and measured by me was fitted to a 2.60 mtr wide landyacht of 75 kg car weight with a 90 kg skipper in it (me), carrying a 6.0 sq. mtr sail. The mast weights 8.15 kg overall and is 5.51 mtr long. It also uses a 8:1 tackle system (more then my own class 5 yacht).

Interestingly enough this landyacht righting moment is almost exactly the same as my 60 kg F12 with 1.85 mtr width with a 60 kg crew hiking of the side (not trapezing).

The 3:1 tackle system of my F12 at the end of the boom (2 mtr) results in less bending moment then the 7:1 tackle system at 1 mtr along the boom of the standart landyacht. Not much less but still less.

Interestingly enough both designs are quite close in there load pattern.

But also my current unstayed F12 mast design is 6.4 mtr long weights 9.5 kg and has a centre of mass of 2.400 mtr and it is (stepwise) tapered. The latter means that it is made up of plain prismatic tubing of decreasing diameters (3 or 4 sections). This makes it easy to homebuild and too collaps it into smaller section for transport.

Interestingly enough a plain conventional prismatic mast section must be no more then 7.125 kg in order to arrive at the same righting moment when horizntal. That is 1.12 kg/mtr and that is quite light for an alu mast. Note that the F16 alu masts are 1.65 kg/mtr. Actually 1.10 kg/mtr is only achieved on carbon F16 mast, but is used diamond wires as well as the F12 mast will not.

So this unstayed alu mast concept is not at all without attractive promises, especially when noting that real life version of this design has been in use for many years already and have proven to be reliable.

This is one reason why I'm continueing with this path. And indeed I have done math along that way.

So my mainpoint here is that we should not discard the unstayed mast to easily. The landyacht people have really progressed this idea into a dependable and high performance design.

Wouter