A few Q&As about Aluminum

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A few Q&As about Aluminum

#1

Post by welder » Fri Jan 22, 2010 8:53 pm

Most people on first becoming aware of welded aluminum boats have questions. Lots of questions. Do these boats corrode in saltwater? Do they get hot? Do they attract lightning? Etc...

Below we will answer the most frequently asked questions and will continually answer more as they come up.



Q) Does aluminum corrode in saltwater?

A) "Aluminum owes its excellent corrosion resistance and its usage as one of the primary metals of commerce to the barrier oxide film that is bonded strongly to its surface and, that if damaged, re-forms immediately in most environments. On a surface freshly abraded and then exposed to air, the barrier oxide film is only 1 nm thick but is highly effective in protecting the aluminum from corrosion...."

Q) Do your boats get hot in the sun?

A) The answer is that our plate alloy boats do not get uncomfortably hot even in direct tropical sunlight. Seems a bit counterintuitive, doesn't it? A big piece of metal in the sun not getting hot?

What most of us think of when we think of a metal vehicle is a car. A car's body is made from sheet steel covered in paint and thus between the steel and paint acts like a heat sink building up heat and holding it. Cars can and do get quite hot in the sun (even here in Maine!).(On a side note - old Landrovers had aluminum alloy bodies - if you ever put your hand on a Landrover in the sun you would be surprised at the difference between them and a Jeep, for instance)

Aluminum in general and 5000 series alloy additionally are both tremendous conductors of heat rather than great accumulators of heat. The only metals better than aluminum for conducting heat are silver, gold and copper. For instance both very high-end cookware and stadium bleacher seats are made from aluminum alloys. For cookware the ability of the alloy to pass heat directly from the burner to the food is extremely important in cooking. More importantly when the chef turns down the heat the temperature in the pan goes down immediately as the alloy doesn't hold the heat. In a cast iron skillet you can turn down the heat but the darn thing will be very hot for a good long time afterwards! Lastly you can actually hold the handle of an alloy skillet when the pan is over the burner as the heat is mostly dissipated by the time it reaches your hand.

Same thing but in reverse for bleachers. If made from steel or even NON ALLOY you would have a lot of shrieking women at every Miami Dolphins game as the set their keisters on a heat sink.

With our boats the alloy sheds what heat it takes-on very quickly as the boat is residing in 90 degree air and 70 degree water thus the boat will equalize with its surroundings.

The only exception to this is our non-skid floor. The chemical composition of this does have some heat sink properties and the floor can become quite warm. As our non-skid is very, very aggressive to begin with you are probably not wearing bare feet anyhow but if you were in bare feet you would probably want to take a bucket of seawater now and again and cool it off.

Q) Are you more likely to get hit by lightning in a metal boat. Is it more dangerous in a thunderstorm?

A) I respectfully call this the Miami Boat Show question since the one time we did the Miami Show I spent about 50% of my time answering just this question!

First of all let me premise my answer by saying that you are never, ever safe in a lightning storm. You should do everything in your power to avoid being in a lightning storm - including not going out if storms are predicted and running in when the sky turns that ominous dark suggesting a storm is on its way.

Secondly, I know a lot about lightning - I was, as a young man, a meteorologist in the Marine Corps. I know the science behind lightning as well as the danger of it. Beyond my own knowledge I have checked with various experts on the subject including the National Weather Service and a professional yacht lightning consultant as the answer to this question is very important to be correct.

Finally, the answer is that you are safer in an alloy boat than in a glass boat. Why?

Assuming that you are talking apples to apples and that both boats are the same height above sea level there is nothing about aluminum that is more "attractive" than glass. Air is a great insulator and thus both glass and alloy provide the same easy shortcut that the lightning is seeking to ground.

Once lightning has found your boat the metal boat provides a very good conductor for the lightning's current to go to ground whereas the NON ALLOY boat does not. The strike on a glass boat may well run through the boats electrical system which, unfortunately, runs back towards the operator (you!)

Additionally, if you are in one of our boats with either a Hardtop, T-top or Walkaround cabin you are even safer. Lightning consultants encourage you to create a halo of metal or wires around the people on a boat as when the strike hits the current will follow the metal halo away from the operator and crew (You!) and towards the boats perimeter where it will continue along the hull and to ground. All of our superstructures are welded to the boat and thus provide excellent conductivity to ground.

Finally, let me reiterate - you are NOT safe on a metal boat in a lightning storm nor are you safe in a glass boat in a lightning storm. Relatively speaking, though, you are safer in a metal hull than a glass one.
Lester,
PacificV2325, Honda BF225
2386

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Re: A few Q&As about Aluminum

#2

Post by welder » Fri Jan 22, 2010 8:58 pm

More Info on Lightning and Boating...

Protect Yourself & Your Boat from Lightning with a Faraday Cage

This spring seems to have brought the most extreme weather in history.
With heavy thunderstorms you will often find lightning. Lightning on the
water can bring life-threatening circumstances. For your safety and the
safety of others boating with you we have updated and are republishing
this article on Lightning Protection.

Even though the odds are in your favor that your boat will never be hit by
lightning, if it happens it can have devastating effects. Don't take a
chance, protect yourself. If you are in a small boat and close to shore
when a thunderstorm approaches, get in and off the water immediately.
Better yet, don't go out if thunderstorms are predicted. But what if you
are miles offshore and a storm pops up? Hopefully, you have prepared in
advance.

The voltage of a lightning bolt is so high, materials that are normally
considered non-conductive, become conductors. The current is so high
that when it travels through a boat's structure - say through its mast,
then meets with some resistance, for example, the hull skin, the current,
in its attempt to reach ground, may simply blow a hole in the non-conductive
barrier. The safety conscious Captain should make sure that his vessel is
properly protected. Reference should be made in detail to the standards
for lightning protection as set forth by the American Boat and Yacht
Council (ABYC) and the job should be performed by a licensed marine
electrician.

In theory, a lightning protection system is used to create what is known as
a "Faraday cage," named after the late nineteenth-century scientist
Michael Faraday. The principle of a Faraday cage is to provide a
surrounding, well-grounded, metal structure, in which all of parts are
bonded together and carry the same electrical potential. Such a "cage"
carries the current from a lightning strike to ground much like lightning
rods on buildings. In other words, you need to provide an unobstructed way
for the lightning to dissipate its energy to ground (the water surrounding
you). Faraday himself risked his own life to prove this theory. An
additional benefit of a lightning protection system is that it tends to
bleed off any charge build-up in the general vicinity, possibly averting a
lightning strike in the first place.

So how does a lightning protection system work? On a boat, the "cage" is
formed by bonding together the vessel's mast and all other major metal
masses with heavy conductors. A marine electrician must tie in the
engines, stoves, air conditioning compressors, railings, arches etc. with
a low resistance wire which would ultimately provide a conductive path to
ground (the water) usually via the engine and propeller shaft, keel bolts,
or better yet, a separate external ground plate at least 1 foot square.
It is important to ensure your crew occupy the space inside the
"cage," something not always feasible when the vessel is not built of
steel or aluminum. On NON ALLOY or wooden boats it is desireable
to have a mast or other conductive metal protrusion extending
well above the vessel, creating what is known as a "cone" or zone of
protection.

It is generally accepted that this cone of protection extends 45 degrees,
all around, from the tip of the metal protrusion. This means that if the
aluminum mast of the average sailing vessel is properly bonded to the
vessel's other major metal masses, and is given a direct, low-resistance
path to ground, the entire boat should fall within the protective zone.
If the vessel has a wooden or composite mast, the same effect can be
achieved by installing a 6 to 12 inch metal spike at the top, and running
a heavy conductor down the mast as directly as possible to ground,
usually through the engine and propeller shaft.

Refer to the ABYC standards and have a professional marine electrician
install your lightning protection. This is not a do-it-yourself project.
Lester,
PacificV2325, Honda BF225
2386

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