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Since we're dealing with forces, they must obey Newton's Laws. In this case, the third law tells us that,

Fnet=F[buoyancy] + F[boat weight]      Where m[boat]=p[avg of boat]V[amount submerged]
Fnet=p[salt water]V[displacement]g+p[avg of boat]V[amount submerged]g

Since V[displacement]=V[amount submerged] and both share gravity (g), Then...

Fnet=Vg(p[salt water]+p[amount submerged]).

When it comes to determining whether a sailboat will float, there exist three different situations. They are:

Fnet<0   (The sailboat experiences a force down, therefore "sinks")
Fnet>0   (The sailboat experiences a force up, therefore "floats")
Fnet=0   (The net force is zero, therefore achieves neutral buoyancy).

    In each case, the changing relationship originates from the density differences between water and the boat.  Note, by adding more mass inside the sailboat (gear, food, etc.) increases the density of the sailboat. Therefore, as long as the density of sailboat doesn't exceed the density of saltwater then the sailboat will stay afloat.    
    Even when buoyancy is established, strong winds can still cause a sailboat to capsize.
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