Mast Story
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Mast Story |
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Specification In June 2002, Aage lost his mast. According to the persons involved, it was a relatively non-dramatic event. But not an event you would actively push for to happen again. The reason for the dismasting was a deck hardware failure to which the running backstay was mounted. The deck clamp turned out never to have been beded in selants, and with no through bolts it was a disaster waiting to happen. The mast instantly snapped - and only remained airborn due to the upper shrouds being fixed to the lower spreaders. The mast that broke was not exactly original to Aage. Forgetting in the first place, that it was not a gaff-rig, the mast was too low (3-4 meters lower than the previous mast) and, worse, it was to weak to withstand a blow on a tack. In particular it was not sufficiently supported athwarthship and it was way too tapered. The mast top was never designed to withstand the forces from a 25 sqm flying jib. The story goes that the mast was intended as a very powerful Folkebåds mast - but that it turned out too powerful and since ended up on Aage. During the past four years we spent money and time to make the now broken mast stronger - notably by taking the runners aft and by making another set of spreaders to reach those crucial 11 degrees between wire and mast. By doing this we were actually able to reef later, and more importantly, to keep up a flying jib at all time in order to keep Aage balanced on the helm. See graphical illustration on the different masts. Painstakingly aware that the Summer cruise was in a shatter, we decided to take time to think up the mast the way we would like - and not necessarily just making a replicate of the old one. It would be costlier but a number of benefits would perhaps outweigh this. A number of things needed to be considered; 1) mast dimensions?, 2) runners or backstay (and 7/8 or mast-head), 3) new loads on Aage's chainplates, mast step and mast partners (if masthead), 4) wire dimension, 5) aesthetics , 6) cost, 7) weight aloft and sailing abilities, 8) put on jib forestay and discard the very non original balloner. All difficult things to decide on, especially since we didn't have any to ask on neither the soft issues (aesthetics) or the hard issues ( what's the rightening moment for Aage? (well we guess RM(30) is somewhere around 32,000 foot-pounds)). We decided to a) increase the mast length by a meter, b) make it oval and only moderately tapered to accommodate a... c) masthead design with backstay and jib stay. The hollow mast is made of Sitka Spruce, with roughly 45 mm walls and fully supported structure where fittings are placed (same wall thickness as that of Dorade - but we didn't learn that until after it was made (but note the much larger circumference of Dorade which is what adds to the weight)). This is a fairly heavy mast but should fit Aage. According to our calculations the mast will weigh some 40 kg more than the old one. This will have some impact on Aage's sailing capabilities but it remains to been seen if it is for the better or the worse. With the old mast Aage was excessively stiff and reefing was never done due to excessive heeling or water on the covering boards but only due the mast buckling under sheer column pressure. With the new mast we expect Aage to become less stiff and strong enough to safely fly three pieces of canvas to keep him balanced on the helm. We are definitely not going to put up more sail area but we expect that we will take reefs in a less of a hurry whenever there is a gust of wind. With the previous mast Aage did heel over in gusts but not alarmingly so. Rather the forces were put into bending and buckling the mast to a degree that by far exceeded the owners' "angst" thresshold.Spar specs (draft) and how spar specification and the tangs eventually turned out. Comparing Aage's mast with Dorade's (just a
nice theoretical exercise, really).
*Source: Uffa Fox
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