We have a B&G 213 wind instrument on our boat. This system has been B&G’s high end wind data input for many years. All the parts of the system as quite expensive to replace. The Mast Head Unit (MHU) is how the main navigation computer gets its information on wind speed and direction.
We recently were close-hauled into 25 knots of tradewind, and the accompanying seas. We were sailing fast, and the wind angle and strength combined with the boat speed was putting the “beat” into beating into the wind. We fell off one especially large wave, and thudded down into the bottom of the wave with a smack and a shudder. Suddenly all wind data disappeared from our instruments. It was dark, the boat was sailing fast, and ocean spray was everywhere, diagnosis had to wait until morning and our arrival at the next port.
It turns out, the problem was the MHU itself. It was GONE. Nothing broken, it had just unscrewed itself and gone walkabout.
The MHU plugs into the mast head fitting, and then the handnut screws down to secure it, and then a wire bail clips down to prevent the nut from backing off. It looks very secure, and it has been as long as we have owned the boat. The only scenario I can think of is the pounding we took when beating into the winds, knocked the wire bail loose, and then it was only a matter of time before the nut came loose and the wind instrument took a quick trip to Davy Jones’ Locker.
Fortunately, we had a spare, which plugged in and worked straight away. But these parts are well over $1000, and I’m not especially interested in littering the bottom of the ocean with them, so we added a belt to our suspenders…
I took a bit of monel wire and tied the wire bail down. Now there is no way I can think of for the nut to come loose.
And as an aside, when attaching the MHU to the mast fitting, always give the connection pins a good coating of silicon grease, or other good waterproof dielectric grease.