Cruising World - February 2016

76

HANDS-ON SAILOR

FEBRUARY

2016

cruisingworld.com

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4 FRESH-WATER FLUSH

If you’re shutting down your boat for a spell, combat corrosion in

auxiliaries and other systems with an injection of clear, pure aqua.

STEVE D’ANTONIO

MONTHLY MAINTENANCE

A

client of mine recently

inquired about fresh-

water fl ushing for his engine,

generator and air- conditioning

systems. Dockmates had ad-

vised him that the practice

made good sense for a vessel

that would be left idle for an

extended period of time. His

questions were straightfor-

ward: “Is this a good idea that’s

worth the trouble? And if so,

how do I do it?”

Well, yes, in certain circum-

stances it is a good idea. And

it’s easily accomplished.

Any metallic component

that’s exposed to seawater is at

risk of corrosion, some more

so than others. Copper alloys

like bronze are exceptionally

corrosion -resistant. Other

metals, such as aluminum

and even stainless steel, are

signifi cantly more prone to

corrosion, particularly when

exposed to stagnant, oxygen-

depleted water, like that found

inside a cooling system that’s

been inactive for a while.

Both stainless steel and alu-

minum derive their corrosion

protection from an oxide fi lm

that forms on their surfaces as

long as they are exposed to air

or oxygen-rich water (which is

typically moving). Left stag-

nant, during the oxidation

process, the air in this wa-

ter is consumed by the metal;

once it’s depleted, the metal

becomes what’s referred to as

“active,” rather than passive.

Exposure to stagnant seawa-

ter, as opposed to fresh water,

exacerbates the likelihood of

corrosion. So if the seawater

is replaced with fresh water

during periods of disuse, the

corrosion potential for water

pumps, heat exchangers and

exhaust systems is diminished.

So what, exactly, consti-

tutes a “period of disuse”?

That’s open to interpretation,

and generally speaking, any

amount of time when salt can

be removed from the corrosion

equation is benefi cial. From a

practical point of view, howev-

er, I’d say that anything longer

than a month makes the fl ush-

ing process worthwhile. Let’s

examine how to do it.

Above all else, it’s import-

ant to remember that under

no circumstances should

water be force-fed into any

engine, either an auxiliary or a

genset, particularly if it’s not

running. Doing so can cause

water to fi ll the exhaust sys-

tem and then back up into the

engine’s cylinders through the

exhaust valves.

This risk can be entire-

STEVE’S TIP

Never use wire brushes to

clean zinc pencil anodes

exposed to fresh water,

as this leaves them inert.

Remove and clean with

a Scotch-Brite pad, or

replace altogether.