We are doing problems involving boats sailing from one shore to the other. Usually, in such problems we are told the velocity of the boat with respect to the water and the angle at which the boat sets out. We are then told the speed and direction of the stream (from ground).
My question is why do we assume that the flow of water effects all boat paths equally. For example, if one boat is much more massive than the other and both have the same velocity with respect to water and both set out at the same angle, how is it that the stream deviates the path of both by the same amount? Shouldn't the more massive one have deviated less? But we don't include mass in any of our calculations.
What am I missing?