A boat including a hydrofoil system, wherein the hydrofoil system comprises - a controller; - a hydrofoil for engagement with the boat, the hydrofoil comprising a plurality of adjustment members operable to vary the lift characteristics of the boat; - a propeller mounted on the hydrofoil; and characterized by - a gearbox system, the gearbox system comprising: a housing having an interior surface defining an interior space of defined dimension; a gearing system located within the interior space of the housing and comprising a propeller shaft engagement portion and a gearbox in mechanical communication with the propeller shaft engagement portion; and an engine located within the interior space of the housing and in mechanical communication with the gearbox; wherein the housing is water-tight, wherein the gearbox and engine are in thermal contact with the interior surface of the housing; and wherein the gearbox is an epicyclic gearbox; and wherein at least a portion of the housing is integral with the hydrofoil, or the housing is mounted on the hydrofoil; and wherein the propeller is mechanically engaged with the propeller shaft engagement portion and the gearbox system is in mechanical communication with the propeller. - a controller; - a hydrofoil for engagement with the boat, the hydrofoil comprising a plurality of adjustment members operable to vary the lift characteristics of the boat; - a propeller mounted on the hydrofoil; and characterized by - a gearbox system, the gearbox system comprising: a housing having an interior surface defining an interior space of defined dimension; a gearing system located within the interior space of the housing and comprising a propeller shaft engagement portion and a gearbox in mechanical communication with the propeller shaft engagement portion; and an engine located within the interior space of the housing and in mechanical communication with the gearbox; wherein the housing is water-tight, wherein the gearbox and engine are in thermal contact with the interior surface of the housing; and wherein the gearbox is an epicyclic gearbox; and wherein at least a portion of the housing is integral with the hydrofoil, or the housing is mounted on the hydrofoil; and wherein the propeller is mechanically engaged with the propeller shaft engagement portion and the gearbox system is in mechanical communication with the propeller. a housing having an interior surface defining an interior space of defined dimension; a gearing system located within the interior space of the housing and comprising a propeller shaft engagement portion and a gearbox in mechanical communication with the propeller shaft engagement portion; and an engine located within the interior space of the housing and in mechanical communication with the gearbox; wherein the housing is water-tight, wherein the gearbox and engine are in thermal contact with the interior surface of the housing; and wherein the gearbox is an epicyclic gearbox; and wherein at least a portion of the housing is integral with the hydrofoil, or the housing is mounted on the hydrofoil; and wherein the propeller is mechanically engaged with the propeller shaft engagement portion and the gearbox system is in mechanical communication with the propeller.