Flotation
Basic Flotation
FEDERAL LAW
183.105 - Quantity of flotation required
(a) Each boat must have enough flotation
to keep any portion of the boat above the surface of
the water when the boat has been submerged in calm,
fresh water for at least 18 hours and loaded with:
(1) A weight that, when submerged, equals
two-fifteenths of the persons capacity marked on the
boat;
(2) A weight that, when submerged, equals
25 percent of the dead weight; and
(3) A weight in pounds that, when submerged,
equals 62.4 times the volume in cubic feet of the
two largest air chambers, if air chambers are used
for flotation.
(b) For the purpose of this section, “dead
weight” means the maximum weight capacity marked
on the boat minus the persons capacity marked on the
boat. |
In addition to the quantity of flotation required,
the regulation then deals with flotation material tests and
specifications. See Flotation
Materials. The regulation does not deal with the methods
to calculate how much foam is necessary, and where to install
it. That is the purpose of this Guideline.
Basically, our method is to calculate the flotation
material needed to support the following components when the
boat is submerged:
a. the submerged boat;
b. the submerged propulsion equipment;
c. a portion of the passenger load;
The total flotation material needed is the sum
of the three components above.
Boats requiring Basic Flotation are fitted with
buoyant materials or acceptable flotation systems in at least
the minimum quantity as determined below. Void compartments
or air chambers integral with the hull shall not be included
as part of the required flotation materials.
If non-integral air chambers are used for flotation,
the requirements for Basic Flotation shall be met excluding
the two largest air chambers.
Calculations: To determine
the total flotation material needed to support the boat, we
will separately determine the flotation needed to support
the boat (hull and deck), the propulsion machinery and the
passengers (persons capacity).
Formula:
F = Fb + Fp
+ Fc
Where:
F = Total flotation
Fb = Flotation for the submerged
boat
Fp = Flotation for the submerged
propulsion machinery
Fc = Flotation for the passengers
(persons capacity)
NOTE:
In Basic Flotation we are considering the submerged weights
since only a small portion of the boat will be out of the
water.
Step 1: Determine the flotation needed to support
the submerged boat (Fb).
Formula:
Fb =([Wh
x K] + [Wd x K]+ .69We
) ÷ B
Where:
Fb = flotation
needed
Wh = dry weight of hull
Wd = dry weight of deck and
superstructure
We = dry weight of factory installed
equipment, hardware and accessories
K = conversion factor for material used. See Table 4.1 below
B = buoyancy of one cubic foot of flotation material expressed
in pounds.
NOTE:
If air is used, B will simply be 62.4 pounds (the weight of
fresh water displaced by 1 cu ft). If foam is used, B will
equal the weight of 1 cu. ft. of fresh water, minus the weight
of one cu. ft. of the foam used, minus the amount of water
absorbed by this foam when submerged for 18 hours.
Of course the submerged weight of the hull is
the result of adding the weights of each component multiplied
by each component factor listed in Table 4.1 below e.g.: fiberglass
x 0.33, fir plywood x –0.81 , aluminum tanks x 0.63,
etc. There is no factor K as a whole; K is a value (multiplier)
used to derive the submerged weight of each component. See
example below.
Step 2: Determine the flotation material needed
to support the submerged propulsion equipment (Fp).
Formula:
Fp = G ÷
B
Where:
G = 75% of the installed weight of the engine,
drive and battery (inboard), or the engine, outdrive and
battery (sterndrive) - in pounds to the nearest whole number;
B = Buoyancy of 1 cu.ft. of flotation material
used in pounds.
Step 3: Determine the flotation material needed
to support the persons capacity (Fc).
Formula:
Fc = .25 (C) ÷
B
Where:
C = Maximum weight capacity.
B = Buoyancy of 1 cu.ft. of flotation material used in pounds.
NOTE:
The regulation calls for 2/15 (0.133) of the persons capacity.
This Guideline uses 0.25, resulting in slightly more flotation
in the boat. This safety factor will help ensure that the
boat meets the minimum requirement in the event of minor weight
changes during construction.
Step 4: Determine the total flotation material
needed (F) to support the boat. This is the sum of steps 1,
2, and 3 above.
Formula:
F = Fb + Fp
+ Fc
TABLE
4.1 - Factors (K) for Converting Various Boat Materials from
Dry to Submerged Weight
(In Table 4.1 - *1.5 pounds/square foot for
1/4 inch thick linoleum.)
The factors in Table 4.1 are calculated using
the following formula:
| Factor = |
Specific gravity – 1 |
| |
Specific gravity |
This formula may be used to obtain the factor
for materials not listed in Table 4.1.
NOTE:
The specific gravity is the ratio of the density of a substance
to the density of fresh water at 39º F.
Weight of water - fresh, at 39ºF = 62.4 pounds/cubic
foot
Specific gravity of water—fresh, at 39ºF
= 1.0
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