Safe
Loading — Subpart C
Calculation of the Maximum Displacement
Example of Maximum Displacement Calculation
On the next two pages we present an example
showing the calculations explained above. The boat in question
may be described as:
| Boat
type |
Outboard
runabout |
| Length
over all (LOA) |
16.5 ft |
| Calculation
length (L) |
16.2 ft. (194.2 in.) |
| Beam |
6.75 ft. |
| Calculation
beam |
6.5
ft. (78.75 in.) |
| Horsepower
rating |
120. HP (maximum
by calculations) |
| Boat
weight (no engine) |
700
lb. |
| Displacement |
188 cubic feet
minus 1 cubic foot for the outboard well = 187 cubic feet
or 11,668.8 lb. |
The values on the forms have been taken from
measuring a boat or a hull mold as described in section 4.0
and entered on the blank form from Figure 4. Note that the
calculation length, as well as the calculation beam, are less
than the overall dimensions of the boat. The reasons for this
were previously explained; refer to the definition of calculation
length and calculation beam if you are unsure why.
Now look at Note 1 in Figure 4. It explains
that the volume of any feature aft of the transom and below
the float-plane contributing to the displacement of the boat
must be added to the formula, in cubic inches. At the same
time, if there is any volume not contributing to the displacement,
such as the engine-well volume below the float-plane, it must
be subtracted. Look at the boat drawing in Figure 4; you will
note that there is an area of the engine well that is below
the float-plane. Assume this volume to be one cubic foot,
or 1,728 cubic inches. It goes in the formula as shown in
Figure 5 below.
The purpose of these calculations is to ascertain
a measured cubic capacity of the boat, while the immersion
method measures the pounds of water displaced. In both instances,
the result is the same, namely: the boat’s displacement.
The former is expressed in cubic inches and translated to
weight; the latter is measured and expressed in pounds.
Look at Figure 5. All the values were established
and entered on the blank worksheet (Fig. 4), the cubic capacity
or maximum displacement of the boat when immersed to its static
float-plane having been calculated to 187 cubic feet. This
represents the volume. To calculate the displacement in pounds,
multiply by 62.4 lb, the weight of a cubic foot of fresh water.
Our boat displacement is: 11,668.8 lb. (See
example in Figure 5)
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