Erez,

Pretty much the minimal wallthickness you want on your beams is 1.6 mm. But this is very hard to get for 100 mm beams. At these large diameters 2 mm is almost an absolute min wallthickness that is carried by commerical suppliers. By far the easiest section to get commercially is 80x2 mm and hence its use in the Blade F16 homebuild plans. And added advantage is the fact that an alu 80x2 beam is pretty lightweight, they are 3.5 kg per beam. The only downside to this section is that its bending stiffness is sufficient but not excellent. Still, the end stiffness is similar to production Tiger F18's and Nacra F18's. The newer beams are stiffer though, but at a weight penalty.

A 90x1.6 mm round alu beam will be 12 % stiffer and 15 % lighter. This was considered too little to justify the extra effort in sourcing these sections and the larger frontal area. The last point is not unimportant. The frontal area needs to be smoothed into the deck or else it will not shed water properly. This can really be a drawback during a dive, it will impact negatively on dive recovery.

My advise therefor is to stick with the 80x2 mm beams.


>>also what alu tube (dia/wall) do you recomend for the boom and spi pole

Boom 50x1.6 mm ; this is really the BEST section there is for the F16's

Spi pole 40x1.6 or 40x2 mm ; I personally have the 40x2 mm and that has withstood all the abuse I put it through. It feels like 40x1.6 mm would also do the job but at less weight.


>>from the plans the spi pole is 3m, shuld i get longer? 3.5m?

I have a 3.5 mtr spi pole with my spi tack block fitted at 3.25 mtr. The 025 mtr sticking out I planned to use for holding a weathervane. This is actually a good place to have a weathervane, however I never did install it. I sail mostly be feel now. I think all the newer F16 spis are cut for 3.5 mtr poles now. For some reason the balance of the boat is not much affected by the longer poles. Personally I advice to start at 3.5 mtr and then find the best point for the spi tack. You can always make a pole shorter but never longer.


Wouter