Flotation - Modified Level Flotation

Boats requiring Modified Level Flotation shall be fitted with buoyant materials or acceptable flotation systems in at least the minimum quantities determined below.

Void compartments within the hull shall not be included as part of the flotation material. However, boats with outboard engines of 2 HP or less, as well as manually propelled boats, may use integral air chambers. For testing purposes, these need not be punctured or disabled, nor do the non-integral air chambers used in these same boats.

A special situation for Modified Level Flotation exists when there is a need to determine the flotation materials necessary for the boat shown in the following example, but only if it is rated solely for manual propulsion. Step 1 is the same; step 2 is omitted (no engine); and Step 3 is changed to reflect C = maximum weight capacity with no deductions. Therefore, Step 4 adds two factors instead of three. This Guideline presents the calculations for a boat rated for 2 HP or less, while the example will be different for a powered boat and for one manually propelled.

Example of Modified Level Flotation Calculations

Step 1. Determine the flotation needed to support the swamped boat (Fb)

Formula:

Fb = [(Wh x K) + Wd ] ÷ B

Where:

Wh = dry weight of hull (everything below swamped waterline)
Wd = dry weight of deck and superstructure
K = conversion factors for materials used
B = buoyancy of flotation materials used, in pounds per cubic foot

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.

This flotation material shall be distributed symmetrically about the balance point of the boat.

Step 2: Determine the flotation needed to support the swamped propulsion equipment (Fp)

NOTE:
If the boat is manually propelled only, proceed to Step 3.

Formula:

Fp = S ÷ B

Where:

S = swamped weight for 2.0 HP outboard, from Table 4 (Appendix A) = 20 lb.
B = buoyancy of flotation materials used, in pounds per cubic foot

Distribute the flotation material symmetrically within 30 inches of the outside of the transom top at the motor mounting area.

Step 3: Determine the flotation material needed to support the persons capacity (Fc)

Formula:

Fc = 0.25 (Cmod) ÷ B

Where:

Cmod = C (maximum weight capacity) minus dry weight of the engine
B = buoyancy of flotation materials used, in pounds per cubic foot

NOTE:
The maximum weight capacity includes the engine, the flotation of which was calculated in Step 2 above. The dry weight of the 2 HP engine (20 lb.) must then be deducted from the maximum weight capacity posted.

The regulations call for 2/15 (.133) of the persons capacity. This Guideline uses .25,
resulting in slightly more flotation material for the boat.

The flotation material should be distributed symmetrically, transversely and fore and aft of the midpoint of the passenger carrying area, and at the hull sides as close to the gunwales as possible. This will help the boat float in a level attitude when swamped.

Step 4. Determine the total flotation material needed (F)

Formula:

F = Fb + Fp + Fc

Where:

Fb = flotation for the boat (Step 1)
Fp = flotation for outboard motor, 2 HP or less (Step 2)
Fc = flotation for persons capacity and gear (Step 3)

Example 1: Boat rated for 2 horsepower.

Assume a boat with the following specifications:

Step 1: Determine flotation needed to support the swamped boat (Fb)

Formula: Fb = [(Wh x K) + Wd ] ÷ B

Substituting in the formula above:

Fb = [(80 x 0.33) + 5] ÷ 60.3

Fb = [(26.4) + 5] ÷ 60.3

Fb = 0.52 cu. ft.

Step 2: Determine flotation needed to support the propulsion equipment (Fp)

Formula: Fp = S ÷ B

Substituting in the formula above

Fp = 20 ÷ 60.3

Fp = 0.33 cu. ft.

Step 3: Determine the flotation needed to support the persons capacity (Fc)

Formula:

Fc = 0.25 (Cmod) ÷ B

Fc = 0. 25 (300 - 25) ÷ 60.3

Fc = 1. 14 cu. ft.

NOTE:
The regulations call for 2/15 (0.133) of the persons capacity; however, this Guideline’s calculations use .25, which results in slightly more flotation for the boat.

Step 4: Determine the total flotation material needed

Formula:

F = Fb + Fp + Fc

F = 0. 52 + 0.33 + 1.14

F = 1.99 cu. ft.

Example 2: Boat rated for manual propulsion only.

Assume the same boat as in example 1 above, but rated for manual propulsion only (no power).

Step 1. Determine flotation needed to support the swamped boat (Fb)

Formula:

Fb = [(Wh x K) + Wd ] ÷ B

Substituting in the formula above:

Fb = [(80 x 0.33) + 5] ÷ 60.3

Fb = [(26.4) + 5] ÷ 60.3

Fb = 0.52 cu. ft.

Step 2. Flotation for engine: OMIT.

Step 3. Determine the flotation needed to support the persons capacity (Fc)

Notice we omit the weight of the engine and leave maximum weight capacity at 300 lb.

Formula:

Fc = 0.25 (C) ÷ B

Fc = 0. 25 (300) ÷ 60.3

Fc = 1. 24 cu. ft.

Step 4. Determine the total flotation material needed

Formula:

F = Fb + Fc

F = 0.52 + 1.24

F = 1.76 cu. ft.

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