Page 18 - WestlawnMasthead20_Dec11

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Steve D'Antonio Replies:
Thank you for taking the time to share your thoughts; the discourse is welcomed.
Regarding your first comment, if I gave the impression in the article that connecting a 12-volt pump to a 24-volt power
supply would enable it to operate properly (if at all) and do so using half the amperage, that most certainly was not my
intention. Indeed 24-volt gear must operate at that voltage and it’s only because of the specific design that its ampere
draw is half that of a 12-volt pump that does the same work.
As far as halogen and incandescent lamps are concerned, I was unaware of the details you pointed out. Albeit anecdot
in my experience as a boatbuilder and boatyard manager, 24-volt bulbs, when used on 24-volt systems whose voltage i
properly regulated, do last longer. However, this could simply have been a function of the quality of the of the products
had selected.
Again, thank you for sharing your thoughts.
Steve D'Antonio
Steve D'Antonio Marine Consulting, Inc.
PO Box 111
Wake, Virginia 23176-0111
Sign up for Steve's Marine Systems Excellence blog at
Regarding the Know It All question on corrosion, from the June 2011 issue . . .
Dear Dave,
I love the Know It All portion of
The Masthead
as I am always learning something. While I agree that the answer in the
latest issue is correct, I believe another plausible explanation and one that I have seen, whether the gasket is rubber, n
prene, plastic, or any other material used in this application, is poultice corrosion. (If moisture is trapped next to alumi-
num and there is an absence of a supply of air to keep the area dry, a chemical reaction takes place at the surface of t
metal. The aluminum is transformed into an aluminum hydroxide substance which appears as a thick, white, pasty sub
Poultice corrosion is the result of water, it doesn’t matter whether it is fresh, brackish, or salt in constant contact with t
aluminum. You often see this in aluminum fuel tanks, and painting and epoxy coating doesn’t seem to do anything but
prolong the inevitable. Fuel tanks that are bedded on strips of high density neoprene, Teflon or Starboard, and other hi
density plastics to prevent their contact with wooden supports will eventually fail from this corrosion; if not from other
causes of corrosion. It is the reason the ABYC standards now recommend that these barrier materials be permanently
bonded to the aluminum to preclude any moisture from coming between the tank and the bedding strips.
The poultice corrosion extending out beyond the insulating strips placed on the bottom of the tanks was easily explain-
able; bilge water repeatedly sloshed up and wetted the tank. But I have also seen it on the sides and the tops of tanks
that likely never experienced bilge slosh. Tanks with fuel in them in a damp bilge are subject to condensation and I mo
often than not find this in the mid morning when the air in the engine compartment or lazarette has started to warm, r
sulting in condensation on the tank surface. Condensation will occur on any cool surface exposed to the warmer air lad
with water molecules. Once it gets under the insulating strips and straps, poultice corrosion may begin.
Kim I MacCartney
Principal Marine Surveyor
ACE Recreational Marine Insurance
Marine Advisory Services
Telephone (757)234-4328
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