Hi Roge
Unfortunately it's inherent in the design, with the jib set and the aft end of the boom raised with the outhaul tension on the jib, as soon as you furl the jib the boom drops to the deck and the jib luff tension reduces. When you say the boom is nailed to the deck, have you changed the jib to non-self-tacking. Either way the forestay should be initially tensioned by having the aft end of the boom on one side of the foredeck allowing it to drop a little further than mid position, tension the jib halyard and make it of on the cleat, lift and central the boom which will increase the forestay tension even more.
I did have a problem with the aft end of the boom catching the foredeck especially when beating
in a light wind, Matt reckons the mast was to far foreward and the stays needed shortening, i didn't find this to be the case so i raised the foot of the jib with an extra shackle and this gave me the clearance i needed.
Not sure if above is what you are looking for and i may be trying to tell you how to suck eggs but thought it worth replying with anyway.
Peter
