I can't say that I find my own F16 (A Taipan) to turtle easily. I have yet to do it and I've gone over quite a few times. My boat weights all up 121 kg as it is a homebuild and we didn't take much risk in the way of construction; quite close to the Viper I'd say.

I too find this claim regarding the Viper suspect. I too would check the mast for water tightness or something like that. Only a very small amount of water running in the mast would do the trick. I also serious dislike the t-terminal ends as the little holes do let water water in the mast and this is enough for trouble despite a sealant block above the hounds. The F16 mast should be completely water tight all the way up from the spreader arms. A partial sealing (above the hounds) is not enough in my experience and this is the reason why I specifically didn't use any T-terminals on my mast.

Regards,

Wouter