Sizzling Summer Zincs

Stuart Goldman of Shelter Island, New York, asks:"For the last two years the zincs on the shaft and MaxProp on my Hinckley SW 42 have started to really dissolve in early July—after the boat has been in the water for about a month. The boat is on a mooring that’s at least 500 yards away from any other boat except a 50ft powerboat, which is also on a mooring about 50 yards
Author:
Publish date:
Updated on

Stuart Goldman of Shelter Island, New York, asks:

"For the last two years the zincs on the shaft and MaxProp on my Hinckley SW 42 have started to really dissolve in early July—after the boat has been in the water for about a month. The boat is on a mooring that’s at least 500 yards away from any other boat except a 50ft powerboat, which is also on a mooring about 50 yards away, and a 40 footer that is moored at about the same distance at a dock. I’ve asked both these owners whether they are having similar problems and they say that they are fine. This tells me, although I could be wrong, that stray electrical current in the water is not bombarding the boat.

When I leave the boat to go ashore I turn off both the house and starting batteries at the main breakers and the only device that remains activated is the emergency bilge pump, and it operates with a float switch. Am I missing anything?"

Nigel Calder replies:

Although your problem could be caused by either galvanic or stray current corrosion, because stray current corrosion will attack whatever metal is feeding the current into the water— and often that is not the zinc— I suspect that you have galvanic corrosion. Because you are not plugged into any shore power, the chances are that it is being generated on board.

The first question you need to answer is whether you have any substantial underwater metal masses that are tied into the bonding systems. These could include such things as bronze through–hulls, a bronze rudder, or an exposed metal keel.

But you should also test whether there is stray current in the water and to do this put two long leads into a millivolt meter and then hang both over the side in the water at different points around the boat. If you get any reading at all, in either an AC or DC mode, there is stray current in the water.

The best way to test for galvanic current is to put a silver/silver chloride half cell on a long lead and use it with your multi-meter (boatzincs.com/corrosion-reference-electrode-specs). There are some other tests that will help you determine whether you have galvanic corrosion and they are explained in more detail in my Boatowner’s Mechanical and Electrical Manual.

Related

Pestilence

Sailor-Punk and the State of Cruising

Back when I was a young man, sailing back and forth across the North Atlantic in an old fiberglass sailboat, it seemed fairly obvious to me how all that was wrong in the world might be set right. Everyone should be issued a boat at birth! Or so I declared to any who would listen ...read more

promoOnTheHorizon600x

Cats On The Horizon

Dragonfly 32 Evolution Denmark’s Quorning Boats has been systematically upgrading its line of folding, performance-cruiser trimarans in recent years as part of a long-term effort to incorporate the latest developments in yacht design, with the latest to receive this treatment ...read more

TOTW_PromoSite

SAIL's Tip of the Week

Presented by Vetus-Maxwell. Got a tip? Send it to sailmail@sailmagazine.com The double range  Every skipper knows about ranging two objects in line to keep the boat on track in a cross-current. What’s less obvious is monitoring both sides of a gap such as a harbor entrance. ...read more

FamilyCruise

Bareboating on Puget Sound

Depending on where you are, Puget Sound can look no bigger than a mountainous version of the Intracoastal Waterway. That’s what I thought when I first laid eyes on it from the lighthouse at Mukilteo Park on a sunny day last July. Then I went to the top of the iconic Space Needle ...read more

Bali4point1

Boat Review: Bali 4.1

Coming fast on the heels of its predecessor, the Bali 4.0, the Bali 4.1 adds a number of improvements, many of them inspired by feedback from owners and charterers. She’s an evolution of a concept that has already proven popular and very many benefits from its builder’s ...read more

Headsail

Ask Sail: Silencing A Rattling Headsail

Q: Our Pearson 26 has a 110-percent jib that tends to rattle very noisily at the top hank. We only bought the old boat recently, but it must have been happening for a long time, since there’s a deep groove worn inside that bronze hank. The jib has an unusually large and wide ...read more

Alerion2048x

Alerion Yachts 33, the 90 Minute Get Away

Easy to sail, luxurious, and swift; the Alerion 33 is the solution to your busy life. The intuitive, simple rig design, easy set-up, and put-away mean there’s no need to wait for crew to enjoy a weekend, a day, or an hour out sailing. Her beauty and comfort are evident in the ...read more