Safe Loading
Definitions of Terms Used in This Guideline
It is important to emphasize here that the definitions
included herein are strictly for the purpose of this Guideline
and regulation, and not necessarily the same as the technical
definition of a term that, in another application, may mean
something entirely different. For example, in naval architecture
the term displacement means: the weight of the water displaced
by a vessel. Consequently, maximum displacement will be considered
as the maximum load a ship may carry. However, for the purpose
of this regulation, maximum displacement means the total weight
of the water displaced by the vessel immersed to the point
just before it will sink. This is done so that we may calculate
the allowable load as a percentage of the boat’s total
capacity. Every definition contained herein shall be assumed
to be preceded by the following statement:
For the purpose of this regulation, we will
use the following definitions.
Monohull boat: A boat on which
the line of intersection of the water surface and the boat
at any operating draft forms a single closed curve. For example,
a catamaran, trimaran, or a pontoon boat is not a monohull
boat.
Some boats, e.g., power catamarans, may be considered
to be monohull boats for the purpose of this regulation if
the line of intersection of the surface of the water with
the hull forms a single closed curve, or “footprint”,
when the boat is carrying its maximum rated horsepower and
maximum weight capacity.
Maximum Displacement: The weight
of the volume of water displaced by the boat at its maximum
level of immersion in calm water without water coming aboard.
Static Float-Plane: The plane
below all points of major leakage, and the most forward point
of the boat below which the maximum displacement of the boat
exists (See Figure 1 below). It is important to understand
this term. Determination of the static float-plane is the
heart of the method for calculating capacity. The easiest
way to understand it is by visualizing the description called
“Boat Immersion” (see section 4.0), and considering
that all points of minor leaks have been sealed, while points
of major leaks remain above this plane.
Calculation Length: The horizontal
length from the most forward part of the boat below the static
float-plane to the vertical midpoint of the transom below
the static float-plane (See Figure 1.1 below and Figure 3
in section 4.0). The reason for figuring the length to the
vertical midpoint is that, since the transom is at an angle,
the mid-point intersection (as opposed to the intersection
at the top of the float plane) will eliminate the need to
add the volume of any space aft of that intersection, and
also to subtract the volume forward of the intersection. The
volumes of these two triangular spaces are equal, and they
will cancel each other out.
Calculation Beam: The broadest
part of the boat at each station measured below the static
float-plane. This distance is in inches between the outer
sides of the hull, excluding rub rails, fenders, or other
extensions. In the majority of cases, this beam will be the
widest when measured at the static float-plane, since most
hulls have a “flair” between the chine and the
sheer. However, in the case of a boat with a “tumblehome”
section aft, the broadest point, where the beam must be measured,
will be below the static float-plane. Figure 3-A in section
4.0 shows only half of a hull mold (for the sake of simplicity).
Do not make the mistake, when figuring the calculation beam,
of considering only half of the beam, as shown in the example.
The full width of the boat must be taken into consideration
when using the formula.
Level Boat: A boat is level when it is transversely
level and when either of the two following conditions is met:
- The forward point where the sheer intersects
the vertical centerline plane and the aft point where the
sheer intersects the upper boundary of the transom (stern)
are equidistant above the water surface, or are equidistant
below the water surface.
- The forward-most point of the boat is level
with or above the lowest point of water ingress.
Horizontal Boat: A boat is horizontal when it
is transversely level and when the lowest points at 40 % and
75% of the boat’s length behind the forward-most point
of the boat are level (See Figure 1 and Figure 2).
Figure
1 - Static Float Plane
Figure
1.1 - Static Float Plane — Alternate
Figure
2 - Intersection Determination and Horizontal Boat
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