Boat sinking question

Discussion in 'Boats and Motors' started by reel, Jun 27, 2008.

  1. Did anyone ever do a calculation to determine if their boat will float if totally swamped.? I have added weight and an extra trolling motor and am a little worried.
  2. Don't know any calculations or method to figure it out - unless you want to do it the hard way!

    This may be pointing out the obvious, but make sure your bilge is in working order and is the capacity needed. Also have a bailing device on the boat - a hand pump or bucket of some sort.

    I like to err on the side of caution - if you think it's not right, it probably isn't!

  3. Basic Flotation


    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).


    F = Fb + Fp + Fc


    F = Total flotation
    Fb = Flotation for the submerged boat
    Fp = Flotation for the submerged propulsion machinery
    Fc = Flotation for the passengers (persons capacity)

    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).


    Fb =([Wh x K] + [Wd x K]+ .69We ) ÷ B


    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.

    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).


    Fp = G ÷ B


    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).


    Fc = .25 (C) ÷ B


    C = Maximum weight capacity.
    B = Buoyancy of 1 cu.ft. of flotation material used in pounds.

    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.


    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.

    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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  4. OSU_Fisherman

    OSU_Fisherman Bassin' Buckeye

  5. dude, i'm great at math, and that equation is already too much.... of course i have no clue what my boat weighs, and i'm not ready to admit i put on all the weight i lost last year, so that doesn't help....

    great question/info though!!!