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 What
You Should Really Know Aout Hulls
by
Cap'n Jack Perdue
A power
boating rig is made up mostly of a hull with an engine attached
that will push it across the water. How fast, and with how much
stability and comfort it will go will depend to a large extent on
the hull itself.
So forget for a moment how pretty it is to look
at and, instead, examine its functional features - how roomy and
safe, with how much living and storage space, and how the wetted
surface will make it behave at all speeds and in all kinds of weather.
The hull bottom determines the speed, stability
and manoeuvrability of your rig. And its specific shape will decide
just how soft and comfortable the ride will be. Your boat will most
likely have a flat, round or V-shaped bottom, or a little of all
three. Trawlers and other displacement hulls, for instance, are
a combination of round and flat designs on the bottom. The chines
are rounded, with a strong curvature that is carried almost to the
keel and have a narrow strip on either side of the keel that's flat.
This provides a gentle rolling motion in a beam sea and a softer
ride at slow speeds than you'll get from an off-plane deep-V hull.
But it's a displacement hull, and not designed for speed except
with a great deal of power.
A deep-V hull has a deadrise at the transom of 18
degrees or more while a modified deep-V deadrise falls between 10
and 18 degrees. Less than 10 degrees is considered a semi-V hull.
All deep-Vs have increasing deadrise forward, providing the soft
entry that's the hallmark of V-bottoms and a blessing for all aboard.
It's not famous for coming onto plane quickly, but it is fast and
frugal on fuel. (Top)
There are also specialized hull designs, such as
the gullwing and catamaran, that provide a remarkably stable ride.
Also, there is a great deal more to a hull that will affect its
suitability and, perhaps, the chief one is the material of which
it is made.
Up to about 50 years ago, boats were usually built
of wood. Some still are, and a well-maintained wooden hull will
provide a warmth, a flexibility and a softness of ride that is seldom
matched by other materials. However, wooden hulls require so much
maintenance that you really have to have a passion for wooden boats
if you plan to own one.
Aluminum boats have come a long way since they were
first introduced to the pleasure-craft boating market. If they get
shabby-looking, you can paint them and they'll look like new again.
But they are somewhat noisier than wood or fibreglass hulls, and
they lack the infinite compound shapes available in fibreglass boats.
That brings us to fibreglass, the material that
revolutionized pleasure craft less than half a century ago. You
can build fibreglass into just about any shape of boat hull or deck.
It won't leak, it will look spiffy, it will be of reasonable weight
and strength, require little maintenance and can be readily combined
with wood for decks, cabin work and finishing trim.
Here are a few things to remember about hulls that
may affect your choice. A boat that has a fairly flat bottom immediately
forward of the transom will get you onto plane faster with a load
than most other practical designs. A hull that has a well-defined
chine will give you a cleaner turn at high or medium speeds than
one that has little or no chine at all. (This is best illustrated
by racing hulls that rely on chine-hook turns.) (Top)
Here's something else to think about. An outboard-powered
hull designed for a transom bracket brings with it some definite
advantages. These include much more room in the open cockpit, a
better-performing outboard motor, operating in clean water behind
the hull. A transom bracket can also provide good, built-in boarding
platforms with direct access to the open rear cockpit.
If you are considering the extra delights of owning
a cruiser, there are some positive parameters to be considered when
choosing a hull spacious below decks, to accommodate bunks of an
acceptable size for comfortable sleep.
In our society, the accepted bed sizes are 39 by
75 inches for a single, 54 by 75 inches for a double. Not overly
generous, but most likely more roomy than you can expect on most
cruisers. But there are limits. Settle for nothing smaller in a
single berth than 27 inches of width at the shoulders which can,
if necessary, be tapered to as little as 18 inches at the foot.
Almost all hulls make use of the narrowing bow space for a pair
of bunks, which is an excellent use of this odd-shaped area. (These
are commonly known as toe-kickers, which can lead to interesting
distractions.)
You should also learn a little about the names of
what you are looking at, and here are a few examples.
A knuckle is the junction of two hull surfaces,
at an angle rather than a curve.
The garboard strake is the name given to the lowest
strake, next to the keel.
A hook is an inward curve in the keel, a rocker
is an outward curve. They are both to be avoided. (Top)
And the tumblehome is the inward curve of the sides
of the hull near the transom.
In the fibreglass hull, the woven roving is the
fibreglass matting which is used to build it. The gelcoat is the
hull's outer skin and is only 15,000th of an inch thick. The gelcoat
is spread into the mold and the fibreglass hull is built over it.
Fibreglass weighs about 130 pounds per cubic foot.
As compared with wood, white oak weighs 47 pounds per cubic foot.
But a much smaller amount of fibreglass goes into a hull.
When using wood, particularly for decks and trim,
it is good to know that a number of tropical woods are passed as
teak, but lack its qualities. These include so-called Iroko Teak
from Africa and Ipal from the Philippines. Authentic teak comes
almost exclusively from Burma and Thailand.
Finally, white pine, which is a very soft, light
wood and is useless for boat-building, is perfect for underwater
plugs to stop leaks in a wooden hull because it swells greatly when
wet. (Top)
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