How the screw does NOT turn

(thou shalt not bolt and screw the same fastener…)

Today the belt driving the alternator and the fresh water pump broke. This, in it self, was a BUMMER. But shit happens even (more often?) in a boat. What followed was a needless day spent by Jedd in the locker. Thus this cautionary tail about trusting “professionals” to look after your boat. 

As I said, the belt broke. Jedd, being a responsible Cap’tn, descended into the tightness of the locker and did what was reasonable; put a spanner on the bolt head and tried to loosen the alternator and replace the belt. (Yes, we carry spares.) He tried, and then tied harder, and the head of the bolt sheared off. He consulted his land bound partner (me) and we both puzzled over this strange thing; why should a bolt shear off when at its other end the nut seem to (when recovered) come off so easily?

We made plans to drill the piece stuck in the alternator and extract it tomorrow, but it just did not make sense until I recalled:

A year before we called Stem to Stern to help us fix the RPM gauge. After spending 6 expensive hours (@ $110/hour) in fruitless labour, he decided that our alternator which supposed to send the signal to the tachometer was at fault.  Luckily (?) the boat came with a spare alternator, the mechanic installed it, but this did not work either. Folks at S & S suggested that we take the alternator to Michael Island to get it fixed. The alternator folks at Michael took a look at our gear and chuckled; the mechanic was trying to connect the wrong lead! But, they said, that the alternator was showing its age, and they sold me a guaranteed rebuilt item. (Who was I to argue and suggest an alternative motive on the part of these kind folks?) 

We took our purchase to the boat and S&S re- installed it “free of charge”. —Well, actually they did try to charge $400 for their time, but we talked them out of this. 

What I did not realize at the time was that the mechanic, for reasons only known to himself, put a nut at the end of the bolt that treaded into the belt tensioning mechanism on the alternator. So, to look at it, the tensioner comprised of a bolt passing through the alternator flange, then the slotted tensioning strut, and ended in a bolt thus pinching the alternator tightly to the tensioner. Who would suspect that the bolt was treaded into the alternator? As it was, of course you could not possibly unscrew the bolt -as soon as you tried the nut on the other hand locked the whole set up irrevocably!

So, back to the beginning: Unsuspecting, Jedd tries to unbolt and, since the bolt now cannot turn it shears off. There goes Jedd’s day with his friends. We are left with having to drill out the bolt stub; not a fun job considering the lack of room down in the locker, possibly having to tap the alternator flange (if we damage the thread whilst drilling) and at least another half day spent “not sailing” in a locker. 

And to think; all that was required in the first place was to attach a loose lead to the alternator. But we paid our tuition: in money (i’d put it app $500) and time. Wisdom costs!