I don't know who said that a capsize while folded can't happen, as that is not true, and the risk of this is clearly warned about, and fully covered in the F-31 Sailing Manual.
It is a rare occurrence, but stability while folded is limited, particularly with the larger F-boats with taller racing rigs, and usual cause is a fast tight turn while folded. It is also worth mentioning that since the original launching of my first folding trimaran in 1974, it was 16 years before anyone managed to roll one over while folded (during a fast sharp turn in 25 knots).
A folded capsize could also be possible with a strong sideways gust, but these have been extremely rare, and usually only in gale force conditions. Usual precaution in such conditions is to always leave one side extended until about to go on the trailer, and if to be left in a marina dock in gale force winds from the side, then the mast should be lowered or at least tied off to each side in some way.
The bigger boats such as the F-31 are more susceptible to a folded roll over than the smaller ones, as even though much bigger, they still only have the same folded beam of just over 8', with a much taller and heavier mast, so extra care has to be taken. In this regard the F-31 also has a secondary wider folded position of 9' 6", as described on Page 10 the Sailing Manual, which makes it more stable while folded, and this should always be used when motoring folded for any distance, or in very gusty conditions.
One can also fold in choppy conditions as stated - the main reason for this statement being to demonstrate the strength of the folding system, and no one has ever managed to damage it in this way. However, one still has to be careful of fast tight turns, gusty side winds, and obviously it would not be a good idea to be side on while folded in large waves. The stability while folded is limited, and there is just no need to take such risks, as folding is usually only necessary inside harbors etc.
Pleased to hear the 18 knots while sailing was enjoyed however!
Also, if you do not have a Sailing Manual then Farrier Marine's Sailing Manual (covers all models) can be downloaded from:
http://www.farriermarine.com/pdf/SailingManual2008.pdfThe daggerboard hum can be fixed by some work on the trailing edge - also covered in the Sailing Manual.
Ian Farrier
Farrier Marine
www.f-boat.com