Yet More Electrics; Bonding

[hriehl1]

1968 Hinterhoeller HR 28

In scrutinizing all the OEM and owner-installed wiring, there is a "network" of negative-side wires terminating at several thru-hulls. The prior owner kept the boat at a marina dock, had a crude 120V AC installation (must have been an 80-year-old screw-in fuse box) and complained his outboard lower-unit housing got eaten away by stray currents and he went through lots of zincs.

I have removed the AC system entirely and will keep the boat on a mooring but probably in a fairly well-populated mooring field. Is this bonding network still necessary? I have Casey's and Calder's books and will research it myself this evening, but if anyone has any quick answers or unique perspectives, I'm all ears.

[Ryan]

Isolated thru hulls do not need to be bonded to the boats negative buss for corrosion purposes. The key word is isolated. For corrosion to occur, the thru hull fittings need to be electrically connected to something else. Keep in mind that this connection can be facilitated by bilge water, water in hoses connected to the fittings, ect. as well as a hard wire connection. From your description of the previous owner's AC system, it is entirely possible that the corrosion he was seeing was due to a poor installation and/or maintenance of the electrical system as a whole. Most stray current corrosion problems are DC related, but the sloppy work you see in the AC system is most likely present somewhere in the DC system as things were modified over time.

FWIW, given what I know of your boat only from threads on this forum, I would be inclined to follow through with the complete rewire you are considering and then leave the thru hulls free of wires.

[mitiempo]

I agree. Bonding made sense in the past when shorepower and marinas were rare. In present times bonding the through hulls is an invitation for corrosion of an item that wasn't at risk before.

Here's a link to the best treatise I have come across relating to bonding.grounding by Stan Honey and reprinted from West Marine. It was also in Practical Sailor. http://www.sailmail.com/grounds.htm

[hriehl1]

Thanks.

I had an email exchange today with the prior owner who said the thru-hull bonding was in place when they bought the boat (2nd owners who bought in the early 70s). In the mid 90s they relaced all thru-hulls with nylon ones (still all nicely operative and in OK shape according to surveyor).

Prior Owner re-confirmed they lost more of their outboard's lower unit aluminum housing than they felt they should... they dangled zincs off the stern and outboard chassis while away from the boat... he felt it helped tho they went through 2 zincs a year (seems like a lot in New England's short season).

I've read Casey & Calder but sadly; the topic is not dumbed-down enough for me so I'll read each 3 more times.

Thanks for your thoughts. A 4-day weekend... re-wire the boat (early each day) then varnish the exterior wood (late each day)... Sweet.

[mitiempo]

Bonded nylon (probably Marelon) through hulls?

[hriehl1]

Yes... Marelon thru-hulls all well attached with an interior plate.

[mitiempo]

The bonding at the through is not needed with Marelon through hulls - would have no effect in any case. Remove it.