Max Engine Size for My Boat


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    Lawrence Wise
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    Default Max Engine Size for My Boat

    The important thing is the freeboard you have on a boat. Freeboard is the distance from the water to the top of the side of the boat, at its lowest point. Your boat displaces water, and as long as the amount of water it displaces is less than the length, width and depth of your boat, it will float. The constants of your boat are the length and depth. The more weight you add, the less free board you will have. If it ever gets to the point that the water starts breaking over the side of you boat, your gonna get very, very wet. Therefore you have to look at everything you put into the boat so see how it is going to effect your freeboard. A jon boat does not have much free board at all, whereas a V bottom boat will come close to having twice as much as the jon boat. That in itself does not mean you can carry twice the load than what the jon will carry.

    I am sure you have seen the movies or tv news reports of the hydroplaning boat races. Invariably one flips clean over. That is what the horsepower can do to a fishing boat if you put too much on it. The larger the motor also, the more weight you have added - which means you must carry less gear. The transom of fishing boats are possibly their weakest link. You hang too much of a motor on there, your gonna damage the transom. I can almost guarantee you that it won't crack or pull apart until you are a long ways from shore. When it does, the boat will normally play submarine. You don't want that. Be patient, don't overload the boat, don't over power the boat.


    Here is info from the US Coast Guards web pages on motor size.

    * * * * *

    Can I use a bigger motor on my boat than what it's rated for?

    It is not a violation of Coast Guard regulations to install or use an engine larger than specified on the capacity label, but there may be state regulations prohibiting it, and restrictions from your own insurance company regarding this. There are no Coast Guard regulations against exceeding the safe loading capacity, however, there may be State regulations or restrictions from your insurance company which prohibit this. There is a Coast Guard regulation that gives Coast Guard Boarding Officers the power to terminate the use of a boat (send it back to shore) if, in the judgment of the Boarding Officer, the boat is overloaded. There is no fine for this, unless the operator refuses the Boarding Officer's order. We certainly hope that you will abide by the rating, as overloading may lead to capsizing or swamping of the boat.

    NOTE: The Coast Guard Capacity Information label is required only on monohull boats less
    than 20' in length. The label is not required on multi-hull boats, pontoon boats (catamarans), or
    on any sailboats, canoes, kayaks, or inflatable boats, regardless of length


    Info from US Coast Guard web pages regarding capacity on I/O boats.

    * * * * * * *

    Sec. 183.33——Maximum weight capacity: Inboard and inboard-outdrive boats
    (a) The maximum weight capacity (W) marked on a boat that has one or more inboard or
    inboard-outdrive units for propulsion must not exceed the greater value of W obtained from
    either of the following formulas:
    W = (maximum displacement) – boat weight - 4(machinery weight)
    5 5 5


    W = (maximum displacement –– boat weight)

    5

    (b) For the purposes of paragraph (a) of this section:
    (1) Maximum displacement is the weight of the volume of water displaced by the boat
    at its maximum level immersion in calm water without water coming aboard. For the
    purpose of this paragraph, a boat is level when it is transversely level and when either of
    the two following conditions are met:
    (i) 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.
    (ii) The most forward point of the boat is level with or above the lowest point of
    water ingress.
    (2) Boat weight is the combination of:
    (i) Hull weight;
    (ii) Deck and superstructure weight;
    (iii) Weight of permanent appurtenances; and
    (iv) Weight of full permanent fuel tanks.
    (3) Machinery weight is the combined weight of installed engines or motors, control
    equipment, drive units, and batteries.

    Info from US Coast Guard web page in ref: weight capacity of outboards.\

    * * * * *

    Sec. 183.35——Maximum weight capacity: Outboard boats
    (a) The maximum weight capacity marked on a boat that is designed or intended to use one or
    more outboard motors for propulsion must be a number that does not exceed one-fifth of the
    difference between its maximum displacement and boat weight.
    (b) For the purposes of paragraph (a) of this section:
    (1) Maximum displacement is the weight of the volume of water displaced by the boat
    at its maximum level immersion in calm water without water coming aboard except for
    water coming through one opening in the motor well with its greatest dimension not
    over 3 inches for outboard motor controls or fuel lines. For the purpose of this
    paragraph, a boat is level when it is transversely level and when either of the two
    following conditions are met:
    (i) 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.
    (ii) The most forward point of the boat is level with or above the lowest point of
    water ingress.
    (2) Boat weight is the combination of:
    (i) Hull weight;
    (ii) Deck and superstructure weight;
    (iii) Weight of permanent appurtenances; and
    (iv) Weight of full permanent fuel tanks.
    [CGD 72-61, 37 FR 15782, Aug. 4, 1972, as amended by CGD 73-250, 40 FR 43857, Sept. 23,
    1975; CGD 75-176, 42 FR 2681, Jan. 13, 1977; USCG-1999-5832, 64 FR 34716, June 29, 1999]
    Sec. 183.37——Maximum weight capacity: Boats rated for manual propulsion and boats rated
    for outboard motors of 2 horsepower or less
    (a) The maximum weight capacity marked on a boat that is rated for manual propulsion or for
    motors of 2 horsepower or less must not exceed 3/10 of the difference between the boat’’s
    maximum displacement and the boat’’s weight in pounds.
    (b) For the purposes of paragraph (a) of this section:
    (1) Maximum displacement is the weight of the volume of water displaced by the boat
    at its maximum level immersion in calm water without water coming aboard. For the
    purpose of this paragraph, a boat is level when it is transversely level and when either of
    the two following conditions are met:
    (i) 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.
    (ii) The most forward point of the boat is level with or above the lowest point of
    water ingress.
    (2) Boat weight is the combination of:
    (i) Hull weight;
    (ii) Deck and superstructure weight; and
    (iii) Weight of permanent appurtenances.

    Last edited by Whistler; 01-24-2007 at 03:45 PM.
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