we had a spectecular pitchpole with our Nacra F20C last friday, runing with the spi in ~17knots wind and ~0.8m waves.
The helm was sitting near the back beam and the crew was out on the trapeze with the chiken line, behind the helm, but it was not enough to avoid losing control and capsizing.
What are the reasons for pitchpolling and what are the best ways to avoid it?

how far down were each of the boards?
how hard was the main sheeted?
how far out was the traveler?

boards about 40cm up. main fully sheeted in with traveller centered.

surprised about that..Done that many times with a lot bigger waves and never had a problem. What was your total crew weight?

It's going to be hard to comment on that because very few of us have experience with that boat and the curved boards. I think maybe it's possible that you had your weight too far back. Did the bows happen to leap up away from the water before it plunged back in?

I was going to ask the same question...

As I understand it, if the boat gets bow down the curved boards actually make the pitchpole more likely. The boards are now pulling down on the boat and exaggerating the typical pitchpole.

As long as you aren't jumping up as Jake notes above, weight farther back is better and boards up more can help as well in very steep chop I guess. Krantz or other folks who did the GT300 are experts in this now I think.

total crew weight about 165kg.
there was no bouncing of the bows. they just dived in.

Hi Segev,
i own a F20C and my observation is:
when you sail vertical to the waves which means ahead of the wind and you are quicker than the waves the boat tends to dive in because there is little volume in the front. Normally you can dive in up to the front beam and she will come up without capsizing because she's an extreme wavepiercer hull. That is complete different from some F18 !!! If you are getting nervous while she dives in an pull or push the rudder you will capsize, just depower the gennacker a bit.

Random BAMF gust? I've seen boats go from upright to pitchpole instantly , nothing you can do in certain situations. Otherwise, did the crew dump the shoot or was he/she holding onto the sheet for dear life, aggravating the situation? Also, did the helm drive down if the rudders weren't cavitated?

random gust? perhaps. The crew was not able to let the sheet off - it happened too fast. The helm drove down, the rudders did not seem to be cavitated.

If the crew was not able to let the sheet off because it happened to fast it definitly was a uninspected gust. I had this one time and can't even imagine what my fault was or what i could have done different to prevent the incident.
have fun sailing her hard....

Did you rake your mast foward at all or too much?

our mast was raked as in the NACRA guide for the F20C. at this position we have neutral helm. we consider taking it backwards, although there is not too much to take since the side stays are almost fully shortened.

Do you use elastics to keep the boards in place? How do you rig them (pulling in what direction)?
If you rig the elastics so they pull the top of the boards forward, you are reducing their angle of attack for vertical lift, making the boat more capsize prone.
Try rigging the elastics so they pull the top of the boards back, which increases that angle of attack and, consequently, the vertical component of lift.
The more you need vertical lift from the boards, the more you want the top of the board pulled back. Enlarge (sand) the cases in the fore and aft direction if you feel that more vertical lift is necessary.